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Selection, by Alfred Russel Wallace
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Title: Contributions to the Theory of Natural Selection
A Series of Essays
Author: Alfred Russel Wallace
Release Date: August 29, 2007 [EBook #22428]
Language: English
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_CONTRIBUTIONS TO_ THE THEORY OF NATURAL SELECTION.
A Series of Essays.
BY
ALFRED RUSSEL WALLACE,
AUTHOR OF
"THE MALAY ARCHIPELAGO," ETC., ETC.
_SECOND EDITION, WITH CORRECTIONS AND ADDITIONS._
New York:
MACMILLAN AND CO.
1871.
[_The Right of Translation and Reproduction is reserved._]
LONDON:
PRINTED BY HEAD, HOLE & CO., FARRINGDON STREET,
AND IVY LANE, E.C.
PREFACE.
The present volume consists of essays which I have contributed to
various periodicals, or read before scientific societies during the last
fifteen years, with others now printed for the first time. The two first
of the series are printed without alteration, because, having gained me
the reputation of being an independent originator of the theory of
"natural selection," they may be considered to have some historical
value. I have added to them one or two very short explanatory notes, and
have given headings to subjects, to make them uniform with the rest of
the book. The other essays have been carefully corrected, often
considerably enlarged, and in some cases almost rewritten, so as to
express more fully and more clearly the views which I hold at the
present time; and as most of them originally appeared in publications
which have a very limited circulation, I believe that the larger portion
of this volume will be new to many of my friends and to most of my
readers.
I now wish to say a few words on the reasons which have led me to
publish this work. The second essay, especially when taken in connection
with the first, contains an outline sketch of the theory of the
origin of species (by means of what was afterwards termed by Mr.
Darwin--"natural selection,") as conceived by me before I had the least
notion of the scope and nature of Mr. Darwin's labours. They were
published in a way not likely to attract the attention of any but
working naturalists, and I feel sure that many who have heard of them,
have never had the opportunity of ascertaining how much or how little
they really contain. It therefore happens, that, while some writers give
me more credit than I deserve, others may very naturally class me with
Dr. Wells and Mr. Patrick Matthew, who, as Mr. Darwin has shown in the
historical sketch given in the 4th and 5th Editions of the "Origin of
Species," certainly propounded the fundamental principle of "natural
selection" before himself, but who made no further use of that
principle, and failed to see its wide and immensely important
applications.
The present work will, I venture to think, prove, that I both saw at the
time the value and scope of the law which I had discovered, and have
since been able to apply it to some purpose in a few original lines of
investigation. But here my claims cease. I have felt all my life, and I
still feel, the most sincere satisfaction that Mr. Darwin had been at
work long before me, and that it was not left for me to attempt to write
"The Origin of Species." I have long since measured my own strength, and
know well that it would be quite unequal to that task. Far abler men
than myself may confess, that they have not that untiring patience in
accumulating, and that wonderful skill in using, large masses of facts
of the most varied kind,--that wide and accurate physiological
knowledge,--that acuteness in devising and skill in carrying out
experiments,--and that admirable style of composition, at once clear,
persuasive and judicial,--qualities, which in their harmonious
combination mark out Mr. Darwin as the man, perhaps of all men now
living, best fitted for the great work he has undertaken and
accomplished.
My own more limited powers have, it is true, enabled me now and then to
seize on some conspicuous group of unappropriated facts, and to search
out some generalization which might bring them under the reign of known
law; but they are not suited to that more scientific and more laborious
process of elaborate induction, which in Mr. Darwin's hands has led to
such brilliant results.
Another reason which has led me to publish this volume at the present
time is, that there are some important points on which I differ from Mr.
Darwin, and I wish to put my opinions on record in an easily accessible
form, before the publication of his new work, (already announced,) in
which I believe most of these disputed questions will be fully
discussed.
I will now give the date and mode of publication of each of the essays
in this volume, as well as the amount of alteration they have undergone.
I.--ON THE LAW WHICH HAS REGULATED THE INTRODUCTION OF NEW SPECIES.
First published in the "Annals and Magazine of Natural History,"
September, 1855. Reprinted without alteration of the text.
II.--ON THE TENDENCY OF VARIETIES TO DEPART INDEFINITELY FROM THE
ORIGINAL TYPE.
First published in the "Journal of the Proceedings of the Linnæan
Society," August, 1858. Reprinted without alteration of the text, except
one or two grammatical emendations.
III.--MIMICRY AND OTHER PROTECTIVE RESEMBLANCES AMONG ANIMALS.
First published in the "Westminster Review," July, 1867. Reprinted with
a few corrections and some important additions, among which I may
especially mention Mr. Jenner Weir's observations and experiments on the
colours of the caterpillars eaten or rejected by birds.
IV.--THE MALAYAN PAPILIONIDÆ, OR SWALLOW-TAILED BUTTERFLIES, AS
ILLUSTRATIVE OF THE THEORY OF NATURAL SELECTION.
First published in the "Transactions of the Linnæan Society," Vol. XXV.
(read March, 1864), under the title, "On the Phenomena of Variation and
Geographical Distribution, as illustrated by the Papilionidæ of the
Malayan Region."
The introductory part of this essay is now reprinted, omitting tables,
references to plates, &c., with some additions, and several corrections.
Owing to the publication of Dr. Felder's "Voyage of the Novara"
(Lepidoptera) in the interval between the reading of my paper and its
publication, several of my new species must have their names changed for
those given to them by Dr. Felder, and this will explain the want of
agreement in some cases between the names used in this volume and those
of the original paper.
V.--ON INSTINCT IN MAN AND ANIMALS.
Not previously published.
VI.--THE PHILOSOPHY OF BIRDS' NESTS.
First published in the "Intellectual Observer," July, 1867. Reprinted
with considerable emendations and additions.
VII.--A THEORY OF BIRDS' NESTS; SHOWING THE RELATION OF CERTAIN
DIFFERENCES OF COLOUR IN BIRDS TO THEIR MODE OF NIDIFICATION.
First published in the "Journal of Travel and Natural History" (No. 2),
1868. Now reprinted with considerable emendations and additions, by
which I have endeavoured more clearly to express, and more fully to
illustrate, my meaning in those parts which have been misunderstood by
my critics.
VIII.--CREATION BY LAW.
First published in the "Quarterly Journal of Science," October, 1867.
Now reprinted with a few alterations and additions.
IX.--THE DEVELOPMENT OF HUMAN RACES UNDER THE LAW OF NATURAL SELECTION.
First published in the "Anthropological Review," May, 1864. Now
reprinted with a few important alterations and additions. I had intended
to have considerably extended this essay, but on attempting it I found
that I should probably weaken the effect without adding much to the
argument. I have therefore preferred to leave it as it was first
written, with the exception of a few ill-considered passages which never
fully expressed my meaning. As it now stands, I believe it contains the
enunciation of an important truth.
X.--THE LIMITS OF NATURAL SELECTION AS APPLIED TO MAN.
This is the further development of a few sentences at the end of an
article on "Geological Time and the Origin of Species," which appeared
in the "Quarterly Review," for April, 1869. I have here ventured to
touch on a class of problems which are usually considered to be beyond
the boundaries of science, but which, I believe, will one day be brought
within her domain.
* * * * *
For the convenience of those who are acquainted with any of my essays in
their original form, I subjoin references to the more important
additions and alterations now made to them.
_ADDITIONS AND CORRECTIONS TO THE ESSAYS AS ORIGINALLY PUBLISHED_.
Essays I. and II. are unaltered, but short notes are added at pp. 19,
24, 29, and 40.
III.--_Mimicry, and other Protective Resemblances among Animals._
PAGE
53 Additional illustration of protective colouring in the case of
the wood-dove and the robin.
63 On moths resembling bird's dung and mortar.
86 Correction of some names of African Papilios and a reference to
Mr. Trimen's observations.
89 Mr. Jenner Weir's observation on birds which refused to eat
_Spilosoma menthrasti_.
102 An additional case of snake mimicry in _Oxyrhopus trigeminus_.
107 Mr. Salvin's case of mimicry among hawks.
113 Name, _Diadema anomala_, added.
117 to 122. Use of gay colours in caterpillars, with an account of
Mr. Jenner Weir's and Mr. Butler's observations.
IV.--_The Malayan Papilionidæ or Swallow-tailed Butterflies, as
illustrative of the Theory of Natural Selection._
135 to 140. Additions to the discussion on the rank of the
Papilionidæ, and on the principles which determine the
comparative rank of groups in the animal kingdom.
164 Illustration of variability from Mr. Baker's revision of the
British Roses.
173 Additional facts, on local variations of colour.
196 Additional genus of birds (Ceycopsis) peculiar to Celebes.
199, 200. Concluding remarks.
VI.--_The Philosophy of Birds' Nests._
218 On nesting of Terns and Gulls, rewritten.
220 to 222. Daines Barrington, and others, on the song of birds.
223 On young birds learning to build, by memory and imitation.
224 Levaillant, on mode of nest-building.
229 On imperfect adaptation in birds' nests.
VII.--_A Theory of Birds' Nests._
231, 232. Introductory passages modified, with some omissions.
233 How modifications of organization would affect the form of the
nest.
235 Illustration from the habits of children and savages.
235, 236. Objection to term "hereditary habit" answered.
237 Passage rewritten, on more or less variable characters in
relation to nidification.
248 On males choosing or rejecting females, and on the various modes
in which colour may be acquired by female birds.
249 On probable ancestral colours of female birds.
255 Protective colouring of the Waxwing.
VIII.--_Creation by Law._
293 Amount of variation in dogs.
296, 297. The "Times" on Natural Selection.
298 to 300. On intermediate or generalized forms of extinct animals
as an indication of transmutation or development.
302 Tabular demonstration of the Origin of Species by Natural
Selection.
IX.--_The development of Human Races, under the law of Natural
Selection._
316 On colour as perhaps correlated with immunity from disease in
man.
326, 327. On the probable future development of man.
330 Concluding paragraph rewritten.
_London, March, 1870._
PREFACE TO THE SECOND EDITION.
The flattering reception of my Essays by the public and the press having
led to a second edition being called for within a year of its first
publication, I have taken the opportunity to make a few necessary
corrections. I have also added a few passages to the 6th and 7th Essays,
and have given two notes, explanatory of some portions of the last
chapter which appear to have been not always understood. These additions
are as follows:--
+-------------------------------------------------------------------+
| _To avoid altering the paging the additional pages now given have |
| been lettered._ |
+---------+---------+-----------------------------------------------+
| 1st Ed. | 2nd Ed. | |
+---------+---------+ |
| 221 | 221 | Additional facts as to birds acquiring |
| | | the song of other species. |
| | | |
| 223 | 223A } | Mr. Spruce's remarks on young birds |
| | 223B } | pairing with old. |
| | | |
| 228 | 228A } | Pouchet's observations on a change |
| | 228B } | in the nests of swallows. |
| | | |
| 229 | -- | Passage omitted about nest of Golden |
| | | Crested Warbler, which had been |
| | | inserted on Rennie's authority, but |
| | | has not been confirmed by any later |
| | | observers. |
| | | |
| 261 | 261 | Daines Barrington, on importance of |
| | | protection to the female bird. |
| | | |
| | 372 | Note A. |
| | | |
| | 372B | Note B. |
+---------+---------+-----------------------------------------------+
CONTENTS.
I.--_On the Law which has regulated the introduction of New
Species._ Pp. 1-25
Geographical distribution dependent on Geologic Changes
A Law deduced from well-known Geographical and Geological facts
The form of a true system of Classification determined by this Law
Geographical Distribution of Organisms
Geological Distribution of the forms of Life
High Organization of very ancient Animals consistent with this Law
Objections to Forbes' Theory of Polarity
Rudimentary Organs
Conclusion
II.--_On the Tendency of Varieties to depart indefinitely from the
Original Type._ Pp. 26-44
Instability of Varieties supposed to prove the permanent
distinctness of Species
The Struggle for Existence
The Law of Population of Species
The Abundance or Rarity of a Species dependent upon its more or less
perfect Adaptation to the Conditions of Existence
Useful Variations will tend to Increase, useless or hurtful
Variations to Diminish
Superior Varieties will ultimately extirpate the Original Species
The Partial Reversion of Domesticated Varieties explained
Lamarck's Hypothesis very different from that now advanced
Conclusion
III.--_Mimicry, and other Protective Resemblances among
Animals._ Pp. 45-129
Test of true and false Theories
Importance of the Principle of Utility
Popular Theories of Colour in Animals
Importance of Concealment as influencing Colour
Special modifications of Colour
Theory of Protective Colouring
Objection that Colour as being dangerous should not exist in Nature
Mimicry
Mimicry among Lepidoptera
Lepidoptera mimicking other Insects
Mimicry among Beetles
Beetles mimicking other Insects
Insects mimicking Species of other Orders
Cases of Mimicry among the Vertebrata
Mimicry among Snakes
Mimicry among Birds
Mimicry among Mammals
Objections to Mr. Bates' Theory of Mimicry
Mimicry by Female Insects only
Cause of the dull Colours of Female Birds
Use of the gaudy Colours of many Caterpillars
Summary
General deductions as to Colour in Nature
Conclusion
IV.--_The Malayan Papilionidæ, or Swallow-tailed Butterflies, as
illustrative of the Theory of Natural Selection._ Pp. 130-200
Special value of the Diurnal Lepidoptera for inquiries of this
Nature
Question of the rank of the Papilionidæ
Distribution of the Papilionidæ
Definition of the word Species
Laws and Modes of Variation
Simple Variability
Polymorphism or Dimorphism
Local form or variety
Co-existing Variety
Race or Subspecies
Species
Variation as specially influenced by Locality
Local Variation of Size
Local Variation of Form
Local Variations of Colour
Remarks on the facts of Local Variation
Mimicry
Concluding Remarks on Variation in Lepidoptera
Arrangement and Geographical Distribution of the Malayan Papilionidæ
Arrangement
Geographical Distribution
Range of the Groups of Malayan Papilionidæ
Remarkable peculiarities of the island of Celebes
Concluding Remarks
V.--_On Instinct in Man and Animals._ Pp. 201-210
How Instinct may be best Studied
Definition of Instinct
Does Man possess Instincts?
How Indians travel through unknown and trackless Forests
VI.--_The Philosophy of Birds' Nests._ Pp. 211-230
Instinct or Reason in the Construction of Birds' Nests
Do Men build by Reason or by Imitation?
Why does each Bird build a peculiar kind of Nest?
How do young Birds learn to build their first Nest?
Do Birds sing by Instinct or by Imitation?
Man's Works mainly Imitative
How young Birds may learn to build Nests.
Birds do Alter and Improve their Nests when altered conditions
require it
Conclusion
VII.--_A Theory of Birds' Nests; showing the relation of certain
differences of colour in female birds to their mode of
nidification._ Pp. 231-263
Changed Conditions and persistent Habits as influencing Nidification
Classification of Nests
Sexual differences of Colour in Birds
The Law which connects the Colours of Female Birds with the mode of
Nidification
What the Facts Teach us Colour more variable than Structure or
Habits, and therefore the Character which has generally been
modified
Exceptional cases confirmatory of the above Explanation
Real or apparent exceptions to the Law stated at p. 240
Various modes of Protection of Animals
Females of some groups require and obtain more Protection than the
Males
Conclusion
VIII.--_Creation by Law._ Pp. 264-301
Laws from which the Origin of Species may be deduced
Mr. Darwin's Metaphors liable to Misconception
A case of Orchis-structure explained by Natural Selection
Adaptation brought about by General Laws
Beauty in Nature
How new Forms are produced by Variation and Selection
The Objection that there are Limits to Variation
Objection to the argument from Classification
The _Times_ on Natural Selection
Intermediate or generalized forms of Extinct Animals an indication
of Transmutation or Development
Conclusion
A Demonstration of the Origin of Species
IX.--_The Development of Human Races under the Law of Natural
Selection_. Pp. 302-331
Wide difference of Opinion as to Man's Origin
Outline of the Theory of Natural Selection
Different effects of Natural Selection on Animals and on Man
Influence of External Nature in the development of the Human Mind
Extinction of Lower Races
The Origin of the Races of Man
The Bearing of these views on the Antiquity of Man
Their Bearing on the Dignity and Supremacy of Man
Their Bearing on the future Development of Man
Summary
Conclusion
X.--_The Limits of Natural Selection as applied to Man._ Pp. 333--371
What Natural Selection can Not do
The Brain of the Savage shown to be Larger than he Needs it to be
Size of Brain an important Element of Mental Power
Comparison of the Brains of Man and of Anthropoid Apes
Range of intellectual power in Man
Intellect of Savages and of Animals compared
The use of the Hairy Covering of Mammalia
The Constant absence of Hair from certain parts of Man's body a
remarkable Phenomenon
Savage Man feels the want of this Hairy Covering
Man's Naked Skin could not have been produced by Natural Selection
Feet and Hands of Man considered as Difficulties on the Theory of
Natural Selection
The Origin of Some of Man's Mental Faculties, by the preservation of
Useful Variations, not possible
Difficulty as to the Origin of the Moral Sense
Summary of the Argument as to the Insufficiency of Natural Selection
to account for the Development of Man
The Origin of Consciousness
The Nature of Matter
Matter is Force
All Force is probably Will-force
Conclusion
I.
ON THE LAW WHICH HAS REGULATED THE INTRODUCTION OF NEW SPECIES.[A]
+--------------------------------------------------------------+
| [A] Written at Sarawak in February, 1855, and published in |
| the "Annals and Magazine of Natural History," September, |
| 1855. |
+--------------------------------------------------------------+
_Geographical Distribution dependent on Geologic Changes._
Every naturalist who has directed his attention to the subject of the
geographical distribution of animals and plants, must have been
interested in the singular facts which it presents. Many of these facts
are quite different from what would have been anticipated, and have
hitherto been considered as highly curious, but quite inexplicable. None
of the explanations attempted from the time of Linnæus are now
considered at all satisfactory; none of them have given a cause
sufficient to account for the facts known at the time, or comprehensive
enough to include all the new facts which have since been, and are daily
being added. Of late years, however, a great light has been thrown upon
the subject by geological investigations, which have shown that the
present state of the earth and of the organisms now inhabiting it, is
but the last stage of a long and uninterrupted series of changes which
it has undergone, and consequently, that to endeavour to explain and
account for its present condition without any reference to those changes
(as has frequently been done) must lead to very imperfect and erroneous
conclusions.
The facts proved by geology are briefly these:--That during an immense,
but unknown period, the surface of the earth has undergone successive
changes; land has sunk beneath the ocean, while fresh land has risen up
from it; mountain chains have been elevated; islands have been formed
into continents, and continents submerged till they have become islands;
and these changes have taken place, not once merely, but perhaps
hundreds, perhaps thousands of times:--That all these operations have
been more or less continuous, but unequal in their progress, and during
the whole series the organic life of the earth has undergone a
corresponding alteration. This alteration also has been gradual, but
complete; after a certain interval not a single species existing which
had lived at the commencement of the period. This complete renewal of
the forms of life also appears to have occurred several times:--That
from the last of the geological epochs to the present or historical
epoch, the change of organic life has been gradual: the first appearance
of animals now existing can in many cases be traced, their numbers
gradually increasing in the more recent formations, while other species
continually die out and disappear, so that the present condition of the
organic world is clearly derived by a natural process of gradual
extinction and creation of species from that of the latest geological
periods. We may therefore safely infer a like gradation and natural
sequence from one geological epoch to another.
Now, taking this as a fair statement of the results of geological
inquiry, we see that the present geographical distribution of life upon
the earth must be the result of all the previous changes, both of the
surface of the earth itself and of its inhabitants. Many causes, no
doubt, have operated of which we must ever remain in ignorance, and we
may, therefore, expect to find many details very difficult of
explanation, and in attempting to give one, must allow ourselves to call
into our service geological changes which it is highly probable may have
occurred, though we have no direct evidence of their individual
operation.
The great increase of our knowledge within the last twenty years, both
of the present and past history of the organic world, has accumulated a
body of facts which should afford a sufficient foundation for a
comprehensive law embracing and explaining them all, and giving a
direction to new researches. It is about ten years since the idea of
such a law suggested itself to the writer of this essay, and he has
since taken every opportunity of testing it by all the newly-ascertained
facts with which he has become acquainted, or has been able to observe
himself. These have all served to convince him of the correctness of his
hypothesis. Fully to enter into such a subject would occupy much space,
and it is only in consequence of some views having been lately
promulgated, he believes, in a wrong direction, that he now ventures to
present his ideas to the public, with only such obvious illustrations of
the arguments and results as occur to him in a place far removed from
all means of reference and exact information.
_A Law deduced from well-known Geographical and Geological Facts._
The following propositions in Organic Geography and Geology give the
main facts on which the hypothesis is founded.
Geography.
1. Large groups, such as classes and orders, are generally spread over
the whole earth, while smaller ones, such as families and genera, are
frequently confined to one portion, often to a very limited district.
2. In widely distributed families the genera are often limited in range;
in widely distributed genera, well marked groups of species are peculiar
to each geographical district.
3. When a group is confined to one district, and is rich in species, it
is almost invariably the case that the most closely allied species are
found in the same locality or in closely adjoining localities, and that
therefore the natural sequence of the species by affinity is also
geographical.
4. In countries of a similar climate, but separated by a wide sea or
lofty mountains, the families, genera and species of the one are often
represented by closely allied families, genera and species peculiar to
the other.
Geology.
5. The distribution of the organic world in time is very similar to its
present distribution in space.
6. Most of the larger and some small groups extend through several
geological periods.
7. In each period, however, there are peculiar groups, found nowhere
else, and extending through one or several formations.
8. Species of one genus, or genera of one family occurring in the same
geological time are more closely allied than those separated in time.
9. As generally in geography no species or genus occurs in two very
distant localities without being also found in intermediate places, so
in geology the life of a species or genus has not been interrupted. In
other words, no group or species has come into existence twice.
10. The following law may be deduced from these facts:--_Every species
has come into existence coincident both in space and time with a
pre-existing closely allied species._
This law agrees with, explains and illustrates all the facts connected
with the following branches of the subject:--1st. The system of natural
affinities. 2nd. The distribution of animals and plants in space. 3rd.
The same in time, including all the phænomena of representative groups,
and those which Professor Forbes supposed to manifest polarity. 4th. The
phænomena of rudimentary organs. We will briefly endeavour to show its
bearing upon each of these.
_The Form of a true system of Classification determined by this Law._
If the law above enunciated be true, it follows that the natural series
of affinities will also represent the order in which the several species
came into existence, each one having had for its immediate antitype a
closely allied species existing at the time of its origin. It is
evidently possible that two or three distinct species may have had a
common antitype, and that each of these may again have become the
antitypes from which other closely allied species were created. The
effect of this would be, that so long as each species has had but one
new species formed on its model, the line of affinities will be simple,
and may be represented by placing the several species in direct
succession in a straight line. But if two or more species have been
independently formed on the plan of a common antitype, then the series
of affinities will be compound, and can only be represented by a forked
or many branched line. Now, all attempts at a Natural classification and
arrangement of organic beings show, that both these plans have obtained
in creation. Sometimes the series of affinities can be well represented
for a space by a direct progression from species to species or from
group to group, but it is generally found impossible so to continue.
There constantly occur two or more modifications of an organ or
modifications of two distinct organs, leading us on to two distinct
series of species, which at length differ so much from each other as to
form distinct genera or families. These are the parallel series or
representative groups of naturalists, and they often occur in different
countries, or are found fossil in different formations. They are said to
have an analogy to each other when they are so far removed from their
common antitype as to differ in many important points of structure,
while they still preserve a family resemblance. We thus see how
difficult it is to determine in every case whether a given relation is
an analogy or an affinity, for it is evident that as we go back along
the parallel or divergent series, towards the common antitype, the
analogy which existed between the two groups becomes an affinity. We are
also made aware of the difficulty of arriving at a true classification,
even in a small and perfect group;--in the actual state of nature it is
almost impossible, the species being so numerous and the modifications
of form and structure so varied, arising probably from the immense
number of species which have served as antitypes for the existing
species, and thus produced a complicated branching of the lines of
affinity, as intricate as the twigs of a gnarled oak or the vascular
system of the human body. Again, if we consider that we have only
fragments of this vast system, the stem and main branches being
represented by extinct species of which we have no knowledge, while a
vast mass of limbs and boughs and minute twigs and scattered leaves is
what we have to place in order, and determine the true position each
originally occupied with regard to the others, the whole difficulty of
the true Natural System of classification becomes apparent to us.
We shall thus find ourselves obliged to reject all these systems of
classification which arrange species or groups in circles, as well as
these which fix a definite number for the divisions of each group. The
latter class have been very generally rejected by naturalists, as
contrary to nature, notwithstanding the ability with which they have
been advocated; but the circular system of affinities seems to have
obtained a deeper hold, many eminent naturalists having to some extent
adopted it. We have, however, never been able to find a case in which
the circle has been closed by a direct and close affinity. In most cases
a palpable analogy has been substituted, in others the affinity is very
obscure or altogether doubtful. The complicated branching of the lines
of affinities in extensive groups must also afford great facilities for
giving a show of probability to any such purely artificial arrangements.
Their death-blow was given by the admirable paper of the lamented Mr.
Strickland, published in the "Annals of Natural History," in which he so
clearly showed the true synthetical method of discovering the Natural
System.
_Geographical Distribution of Organisms._
If we now consider the geographical distribution of animals and plants
upon the earth, we shall find all the facts beautifully in accordance
with, and readily explained by, the present hypothesis. A country having
species, genera, and whole families peculiar to it, will be the
necessary result of its having been isolated for a long period,
sufficient for many series of species to have been created on the type
of pre-existing ones, which, as well as many of the earlier-formed
species, have become extinct, and thus made the groups appear isolated.
If in any case the antitype had an extensive range, two or more groups
of species might have been formed, each varying from it in a different
manner, and thus producing several representative or analogous groups.
The Sylviadæ of Europe and the Sylvicolidæ of North America, the
Heliconidæ of South America and the Euploeas of the East, the group of
Trogons inhabiting Asia, and that peculiar to South America, are
examples that may be accounted for in this manner.
Such phænomena as are exhibited by the Galapagos Islands, which contain
little groups of plants and animals peculiar to themselves, but most
nearly allied to those of South America, have not hitherto received any,
even a conjectural explanation. The Galapagos are a volcanic group of
high antiquity, and have probably never been more closely connected with
the continent than they are at present. They must have been first
peopled, like other newly-formed islands, by the action of winds and
currents, and at a period sufficiently remote to have had the original
species die out, and the modified prototypes only remain. In the same
way we can account for the separate islands having each their peculiar
species, either on the supposition that the same original emigration
peopled the whole of the islands with the same species from which
differently modified prototypes were created, or that the islands were
successively peopled from each other, but that new species have been
created in each on the plan of the pre-existing ones. St. Helena is a
similar case of a very ancient island having obtained an entirely
peculiar, though limited, flora. On the other hand, no example is known
of an island which can be proved geologically to be of very recent
origin (late in the Tertiary, for instance), and yet possesses generic
or family groups, or even many species peculiar to itself.
When a range of mountains has attained a great elevation, and has so
remained during a long geological period, the species of the two sides
at and near their bases will be often very different, representative
species of some genera occurring, and even whole genera being peculiar
to one side only, as is remarkably seen in the case of the Andes and
Rocky Mountains. A similar phænomenon occurs when an island has been
separated from a continent at a very early period. The shallow sea
between the Peninsula of Malacca, Java, Sumatra and Borneo was probably
a continent or large island at an early epoch, and may have become
submerged as the volcanic ranges of Java and Sumatra were elevated. The
organic results we see in the very considerable number of species of
animals common to some or all of these countries, while at the same time
a number of closely allied representative species exist peculiar to
each, showing that a considerable period has elapsed since their
separation. The facts of geographical distribution and of geology may
thus mutually explain each other in doubtful cases, should the
principles here advocated be clearly established.
In all those cases in which an island has been separated from a
continent, or raised by volcanic or coralline action from the sea, or in
which a mountain-chain has been elevated in a recent geological epoch,
the phænomena of peculiar groups or even of single representative
species will not exist. Our own island is an example of this, its
separation from the continent being geologically very recent, and we
have consequently scarcely a species which is peculiar to it; while the
Alpine range, one of the most recent mountain elevations, separates
faunas and floras which scarcely differ more than may be due to climate
and latitude alone.
The series of facts alluded to in Proposition (3), of closely allied
species in rich groups being found geographically near each other, is
most striking and important. Mr. Lovell Reeve has well exemplified it in
his able and interesting paper on the Distribution of the Bulimi. It is
also seen in the Humming-birds and Toucans, little groups of two or
three closely allied species being often found in the same or closely
adjoining districts, as we have had the good fortune of personally
verifying. Fishes give evidence of a similar kind: each great river has
its peculiar genera, and in more extensive genera its groups of closely
allied species. But it is the same throughout Nature; every class and
order of animals will contribute similar facts. Hitherto no attempt has
been made to explain these singular phenomena, or to show how they have
arisen. Why are the genera of Palms and of Orchids in almost every case
confined to one hemisphere? Why are the closely allied species of
brown-backed Trogons all found in the East, and the green-backed in the
West? Why are the Macaws and the Cockatoos similarly restricted? Insects
furnish a countless number of analogous examples;--the Goliathi of
Africa, the Ornithopteræ of the Indian Islands, the Heliconidæ of South
America, the Danaidæ of the East, and in all, the most closely allied
species found in geographical proximity. The question forces itself
upon every thinking mind,--why are these things so? They could not be as
they are had no law regulated their creation and dispersion. The law
here enunciated not merely explains, but necessitates the facts we see
to exist, while the vast and long-continued geological changes of the
earth readily account for the exceptions and apparent discrepancies that
here and there occur. The writer's object in putting forward his views
in the present imperfect manner is to submit them to the test of other
minds, and to be made aware of all the facts supposed to be inconsistent
with them. As his hypothesis is one which claims acceptance solely as
explaining and connecting facts which exist in nature, he expects facts
alone to be brought to disprove it, not _à priori_ arguments against its
probability.
_Geological Distribution of the Forms of Life._
The phænomena of geological distribution are exactly analogous to those
of geography. Closely allied species are found associated in the same
beds, and the change from species to species appears to have been as
gradual in time as in space. Geology, however, furnishes us with
positive proof of the extinction and production of species, though it
does not inform us how either has taken place. The extinction of
species, however, offers but little difficulty, and the _modus operandi_
has been well illustrated by Sir C. Lyell in his admirable
"Principles." Geological changes, however gradual, must occasionally
have modified external conditions to such an extent as to have rendered
the existence of certain species impossible. The extinction would in
most cases be effected by a gradual dying-out, but in some instances
there might have been a sudden destruction of a species of limited
range. To discover how the extinct species have from time to time been
replaced by new ones down to the very latest geological period, is the
most difficult, and at the same time the most interesting problem in the
natural history of the earth. The present inquiry, which seeks to
eliminate from known facts a law which has determined, to a certain
degree, what species could and did appear at a given epoch, may, it is
hoped, be considered as one step in the right direction towards a
complete solution of it.
_High Organization of very ancient Animals consistent with this Law._
Much discussion has of late years taken place on the question, whether
the succession of life upon the globe has been from a lower to a higher
degree of organization. The admitted facts seem to show that there has
been a general, but not a detailed progression. Mollusca and Radiata
existed before Vertebrata, and the progression from Fishes to Reptiles
and Mammalia, and also from the lower mammals to the higher, is
indisputable. On the other hand, it is said that the Mollusca and
Radiata of the very earliest periods were more highly organized than the
great mass of those now existing, and that the very first fishes that
have been discovered are by no means the lowest organised of the class.
Now it is believed the present hypothesis will harmonize with all these
facts, and in a great measure serve to explain them; for though it may
appear to some readers essentially a theory of progression, it is in
reality only one of gradual change. It is, however, by no means
difficult to show that a real progression in the scale of organization
is perfectly consistent with all the appearances, and even with apparent
retrogression, should such occur.
Returning to the analogy of a branching tree, as the best mode of
representing the natural arrangement of species and their successive
creation, let us suppose that at an early geological epoch any group
(say a class of the Mollusca) has attained to a great richness of
species and a high organization. Now let this great branch of allied
species, by geological mutations, be completely or partially destroyed.
Subsequently a new branch springs from the same trunk, that is to say,
new species are successively created, having for their antitypes the
same lower organized species which had served as the antitypes for the
former group, but which have survived the modified conditions which
destroyed it. This new group being subject to these altered conditions,
has modifications of structure and organization given to it, and
becomes the representative group of the former one in another geological
formation. It may, however, happen, that though later in time, the new
series of species may never attain to so high a degree of organization
as those preceding it, but in its turn become extinct, and give place to
yet another modification from the same root, which may be of higher or
lower organization, more or less numerous in species, and more or less
varied in form and structure than either of those which preceded it.
Again, each of these groups may not have become totally extinct, but may
have left a few species, the modified prototypes of which have existed
in each succeeding period, a faint memorial of their former grandeur and
luxuriance. Thus every case of apparent retrogression may be in reality
a progress, though an interrupted one: when some monarch of the forest
loses a limb, it may be replaced by a feeble and sickly substitute. The
foregoing remarks appear to apply to the case of the Mollusca, which, at
a very early period, had reached a high organization and a great
development of forms and species in the testaceous Cephalopoda. In each
succeeding age modified species and genera replaced the former ones
which had become extinct, and as we approach the present æra, but few
and small representatives of the group remain, while the Gasteropods and
Bivalves have acquired an immense preponderance. In the long series of
changes the earth has undergone, the process of peopling it with organic
beings has been continually going on, and whenever any of the higher
groups have become nearly or quite extinct, the lower forms which have
better resisted the modified physical conditions have served as the
antitypes on which to found the new races. In this manner alone, it is
believed, can the representative groups at successive periods, and the
risings and fallings in the scale of organization, be in every case
explained.
_Objections to Forbes' Theory of Polarity._
The hypothesis of polarity, recently put forward by Professor Edward
Forbes to account for the abundance of generic forms at a very early
period and at present, while in the intermediate epochs there is a
gradual diminution and impoverishment, till the minimum occurred at the
confines of the Palæozoic and Secondary epochs, appears to us quite
unnecessary, as the facts may be readily accounted for on the principles
already laid down. Between the Palæozoic and Neozoic periods of
Professor Forbes, there is scarcely a species in common, and the greater
part of the genera and families also disappear to be replaced by new
ones. It is almost universally admitted that such a change in the
organic world must have occupied a vast period of time. Of this interval
we have no record; probably because the whole area of the early
formations now exposed to our researches was elevated at the end of the
Palæozoic period, and remained so through the interval required for the
organic changes which resulted in the fauna and flora of the Secondary
period. The records of this interval are buried beneath the ocean which
covers three-fourths of the globe. Now it appears highly probable that a
long period of quiescence or stability in the physical conditions of a
district would be most favourable to the existence of organic life in
the greatest abundance, both as regards individuals and also as to
variety of species and generic group, just as we now find that the
places best adapted to the rapid growth and increase of individuals also
contain the greatest profusion of species and the greatest variety of
forms,--the tropics in comparison with the temperate and arctic regions.
On the other hand, it seems no less probable that a change in the
physical conditions of a district, even small in amount if rapid, or
even gradual if to a great amount, would be highly unfavourable to the
existence of individuals, might cause the extinction of many species,
and would probably be equally unfavourable to the creation of new ones.
In this too we may find an analogy with the present state of our earth,
for it has been shown to be the violent extremes and rapid changes of
physical conditions, rather than the actual mean state in the temperate
and frigid zones, which renders them less prolific than the tropical
regions, as exemplified by the great distance beyond the tropics to
which tropical forms penetrate when the climate is equable, and also by
the richness in species and forms of tropical mountain regions which
principally differ from the temperate zone in the uniformity of their
climate. However this may be, it seems a fair assumption that during a
period of geological repose the new species which we know to have been
created would have appeared; that the creations would then exceed in
number the extinctions, and therefore the number of species would
increase. In a period of geological activity, on the other hand, it
seems probable that the extinctions might exceed the creations, and the
number of species consequently diminish. That such effects did take
place in connexion with the causes to which we have imputed them, is
shown in the case of the Coal formation, the faults and contortions of
which show a period of great activity and violent convulsions, and it is
in the formation immediately succeeding this that the poverty of forms
of life is most apparent. We have then only to suppose a long period of
somewhat similar action during the vast unknown interval at the
termination of the Palæozoic period, and then a decreasing violence or
rapidity through the Secondary period, to allow for the gradual
repopulation of the earth with varied forms, and the whole of the facts
are explained.[B] We thus have a clue to the increase of the forms of
life during certain periods, and their decrease during others, without
recourse to any causes but those we know to have existed, and to
effects fairly deducible from them. The precise manner in which the
geological changes of the early formations were effected is so extremely
obscure, that when we can explain important facts by a retardation at
one time and an acceleration at another of a process which we know from
its nature and from observation to have been unequal,--a cause so simple
may surely be preferred to one so obscure and hypothetical as polarity.
+--------------------------------------------------------------+
| [B] Professor Ramsay has since shown that a glacial epoch |
| probably occurred at the time of the Permian formation, |
| which will more satisfactorily account for the comparative |
| poverty of species. |
+--------------------------------------------------------------+
I would also venture to suggest some reasons against the very nature of
the theory of Professor Forbes. Our knowledge of the organic world
during any geological epoch is necessarily very imperfect. Looking at
the vast numbers of species and groups that have been discovered by
geologists, this may be doubted; but we should compare their numbers not
merely with those that now exist upon the earth, but with a far larger
amount. We have no reason for believing that the number of species on
the earth at any former period was much less than at present; at all
events the aquatic portion, with which geologists have most
acquaintance, was probably often as great or greater. Now we know that
there have been many complete changes of species; new sets of organisms
have many times been introduced in place of old ones which have become
extinct, so that the total amount which have existed on the earth from
the earliest geological period must have borne about the same proportion
to those now living, as the whole human race who have lived and died
upon the earth, to the population at the present time. Again, at each
epoch, the whole earth was no doubt, as now, more or less the theatre of
life, and as the successive generations of each species died, their
exuviæ and preservable parts would be deposited over every portion of
the then existing seas and oceans, which we have reason for supposing to
have been more, rather than less, extensive than at present. In order
then to understand our possible knowledge of the early world and its
inhabitants, we must compare, not the area of the whole field of our
geological researches with the earth's surface, but the area of the
examined portion of each formation separately with the whole earth. For
example, during the Silurian period all the earth was Silurian, and
animals were living and dying, and depositing their remains more or less
over the whole area of the globe, and they were probably (the species at
least) nearly as varied in different latitudes and longitudes as at
present. What proportion do the Silurian districts bear to the whole
surface of the globe, land and sea (for far more extensive Silurian
districts probably exist beneath the ocean than above it), and what
portion of the known Silurian districts has been actually examined for
fossils? Would the area of rock actually laid open to the eye be the
thousandth or the ten-thousandth part of the earth's surface? Ask the
same question with regard to the Oolite or the Chalk, or even to
particular beds of these when they differ considerably in their
fossils, and you may then get some notion of how small a portion of the
whole we know.
But yet more important is the probability, nay almost the certainty,
that whole formations containing the records of vast geological periods
are entirely buried beneath the ocean, and for ever beyond our reach.
Most of the gaps in the geological series may thus be filled up, and
vast numbers of unknown and unimaginable animals, which might help to
elucidate the affinities of the numerous isolated groups which are a
perpetual puzzle to the zoologist, may there be buried, till future
revolutions may raise them in their turn above the waters, to afford
materials for the study of whatever race of intelligent beings may then
have succeeded us. These considerations must lead us to the conclusion,
that our knowledge of the whole series of the former inhabitants of the
earth is necessarily most imperfect and fragmentary,--as much so as our
knowledge of the present organic world would be, were we forced to make
our collections and observations only in spots equally limited in area
and in number with those actually laid open for the collection of
fossils. Now, the hypothesis of Professor Forbes is essentially one that
assumes to a great extent the completeness of our knowledge of the whole
series of organic beings which have existed on the earth. This
appears to be a fatal objection to it, independently of all other
considerations. It may be said that the same objections exist against
every theory on such a subject, but this is not necessarily the case.
The hypothesis put forward in this paper depends in no degree upon the
completeness of our knowledge of the former condition of the organic
world, but takes what facts we have as fragments of a vast whole, and
deduces from them something of the nature and proportions of that whole
which we can never know in detail. It is founded upon isolated groups of
facts, recognizes their isolation, and endeavours to deduce from them
the nature of the intervening portions.
_Rudimentary Organs._
Another important series of facts, quite in accordance with, and even
necessary deductions from, the law now developed, are those of
rudimentary organs. That these really do exist, and in most cases have
no special function in the animal oeconomy, is admitted by the first
authorities in comparative anatomy. The minute limbs hidden beneath the
skin in many of the snake-like lizards, the anal hooks of the boa
constrictor, the complete series of jointed finger-bones in the paddle
of the Manatus and whale, are a few of the most familiar instances. In
botany a similar class of facts has been long recognised. Abortive
stamens, rudimentary floral envelopes and undeveloped carpels, are of
the most frequent occurrence. To every thoughtful naturalist the
question must arise, What are these for? What have they to do with the
great laws of creation? Do they not teach us something of the system of
Nature? If each species has been created independently, and without any
necessary relations with pre-existing species, what do these rudiments,
these apparent imperfections mean? There must be a cause for them; they
must be the necessary results of some great natural law. Now, if, as it
has been endeavoured to be shown, the great law which has regulated the
peopling of the earth with animal and vegetable life is, that every
change shall be gradual; that no new creature shall be formed widely
differing from anything before existing; that in this, as in everything
else in Nature, there shall be gradation and harmony,--then these
rudimentary organs are necessary, and are an essential part of the
system of Nature. Ere the higher Vertebrata were formed, for instance,
many steps were required, and many organs had to undergo modifications
from the rudimental condition in which only they had as yet existed. We
still see remaining an antitypal sketch of a wing adapted for flight in
the scaly flapper of the penguin, and limbs first concealed beneath the
skin, and then weakly protruding from it, were the necessary gradations
before others should be formed fully adapted for locomotion.[C] Many
more of these modifications should we behold, and more complete series
of them, had we a view of all the forms which have ceased to live. The
great gaps that exist between fishes, reptiles, birds, and mammals would
then, no doubt, be softened down by intermediate groups, and the whole
organic world would be seen to be an unbroken and harmonious system.
+--------------------------------------------------------------+
| [C] The theory of Natural Selection has now taught us that |
| these are not the steps by which limbs have been formed; and |
| that most rudimentary organs have been produced by abortion, |
| owing to disuse, as explained by Mr. Darwin. |
+--------------------------------------------------------------+
_Conclusion._
It has now been shown, though most briefly and imperfectly, how the law
that "_Every species has come into existence coincident both in time and
space with a pre-existing closely allied species_," connects together
and renders intelligible a vast number of independent and hitherto
unexplained facts. The natural system of arrangement of organic beings,
their geographical distribution, their geological sequence, the
phænomena of representative and substituted groups in all their
modifications, and the most singular peculiarities of anatomical
structure, are all explained and illustrated by it, in perfect
accordance with the vast mass of facts which the researches of modern
naturalists have brought together, and, it is believed, not materially
opposed to any of them. It also claims a superiority over previous
hypotheses, on the ground that it not merely explains, but necessitates
what exists. Granted the law, and many of the most important facts in
Nature could not have been otherwise, but are almost as necessary
deductions from it, as are the elliptic orbits of the planets from the
law of gravitation.
II.
ON THE TENDENCY OF VARIETIES TO DEPART INDEFINITELY FROM THE ORIGINAL
TYPE.[D]
+--------------------------------------------------------------+
| [D] Written at Ternate, February, 1858; and published in the |
| Journal of the Proceedings of the Linnæan Society for |
| August, 1858. |
+--------------------------------------------------------------+
_Instability of Varieties supposed to prove the permanent distinctness
of Species._
One of the strongest arguments which have been adduced to prove the
original and permanent distinctness of species is, that _varieties_
produced in a state of domesticity are more or less unstable, and often
have a tendency, if left to themselves, to return to the normal form of
the parent species; and this instability is considered to be a
distinctive peculiarity of all varieties, even of those occurring among
wild animals in a state of nature, and to constitute a provision for
preserving unchanged the originally created distinct species.
In the absence or scarcity of facts and observations as to _varieties_
occurring among wild animals, this argument has had great weight with
naturalists, and has led to a very general and somewhat prejudiced
belief in the stability of species. Equally general, however, is the
belief in what are called "permanent or true varieties,"--races of
animals which continually propagate their like, but which differ so
slightly (although constantly) from some other race, that the one is
considered to be a _variety_ of the other. Which is the _variety_ and
which the original _species_, there is generally no means of
determining, except in those rare cases in which the one race has been
known to produce an offspring unlike itself and resembling the other.
This, however, would seem quite incompatible with the "permanent
invariability of species," but the difficulty is overcome by assuming
that such varieties have strict limits, and can never again vary further
from the original type, although they may return to it, which, from the
analogy of the domesticated animals, is considered to be highly
probable, if not certainly proved.
It will be observed that this argument rests entirely on the assumption,
that _varieties_ occurring in a state of nature are in all respects
analogous to or even identical with those of domestic animals, and are
governed by the same laws as regards their permanence or further
variation. But it is the object of the present paper to show that this
assumption is altogether false, that there is a general principle in
nature which will cause many _varieties_ to survive the parent species,
and to give rise to successive variations departing further and further
from the original type; and which also produces, in domesticated
animals, the tendency of varieties to return to the parent form.
_The Struggle for Existence._
The life of wild animals is a struggle for existence. The full exertion
of all their faculties and all their energies is required to preserve
their own existence and provide for that of their infant offspring. The
possibility of procuring food during the least favourable seasons, and
of escaping the attacks of their most dangerous enemies, are the primary
conditions which determine the existence both of individuals and of
entire species. These conditions will also determine the population of a
species; and by a careful consideration of all the circumstances we may
be enabled to comprehend, and in some degree to explain, what at first
sight appears so inexplicable--the excessive abundance of some species,
while others closely allied to them are very rare.
_The Law of Population of Species._
The general proportion that must obtain between certain groups of
animals is readily seen. Large animals cannot be so abundant as small
ones; the carnivora must be less numerous than the herbivora; eagles and
lions can never be so plentiful as pigeons and antelopes; and the wild
asses of the Tartarian deserts cannot equal in numbers the horses of the
more luxuriant prairies and pampas of America. The greater or less
fecundity of an animal is often considered to be one of the chief causes
of its abundance or scarcity; but a consideration of the facts will show
us that it really has little or nothing to do with the matter. Even the
least prolific of animals would increase rapidly if unchecked, whereas
it is evident that the animal population of the globe must be
stationary, or perhaps, through the influence of man, decreasing.
Fluctuations there may be; but permanent increase, except in restricted
localities, is almost impossible. For example, our own observation must
convince us that birds do not go on increasing every year in a
geometrical ratio, as they would do, were there not some powerful check
to their natural increase. Very few birds produce less than two young
ones each year, while many have six, eight, or ten; four will certainly
be below the average; and if we suppose that each pair produce young
only four times in their life, that will also be below the average,
supposing them not to die either by violence or want of food. Yet at
this rate how tremendous would be the increase in a few years from a
single pair! A simple calculation will show that in fifteen years each
pair of birds would have increased to nearly ten millions![E] whereas we
have no reason to believe that the number of the birds of any country
increases at all in fifteen or in one hundred and fifty years. With such
powers of increase the population must have reached its limits, and
have become stationary, in a very few years after the origin of each
species. It is evident, therefore, that each year an immense number of
birds must perish--as many in fact as are born; and as on the lowest
calculation the progeny are each year twice as numerous as their
parents, it follows that, whatever be the average number of individuals
existing in any given country, _twice that number must perish
annually_,--a striking result, but one which seems at least highly
probable, and is perhaps under rather than over the truth. It would
therefore appear that, as far as the continuance of the species and the
keeping up the average number of individuals are concerned, large broods
are superfluous. On the average all above _one_ become food for hawks
and kites, wild cats or weasels, or perish of cold and hunger as winter
comes on. This is strikingly proved by the case of particular species;
for we find that their abundance in individuals bears no relation
whatever to their fertility in producing offspring.
+--------------------------------------------------------------+
| [E] This is under estimated. The number would really amount |
| to more than two thousand millions! |
+--------------------------------------------------------------+
Perhaps the most remarkable instance of an immense bird population is
that of the passenger pigeon of the United States, which lays only one,
or at most two eggs, and is said to rear generally but one young one.
Why is this bird so extraordinarily abundant, while others producing two
or three times as many young are much less plentiful? The explanation is
not difficult. The food most congenial to this species, and on which it
thrives best, is abundantly distributed over a very extensive region,
offering such differences of soil and climate, that in one part or
another of the area the supply never fails. The bird is capable of a
very rapid and long-continued flight, so that it can pass without
fatigue over the whole of the district it inhabits, and as soon as the
supply of food begins to fail in one place is able to discover a fresh
feeding-ground. This example strikingly shows us that the procuring a
constant supply of wholesome food is almost the sole condition requisite
for ensuring the rapid increase of a given species, since neither the
limited fecundity, nor the unrestrained attacks of birds of prey and of
man are here sufficient to check it. In no other birds are these
peculiar circumstances so strikingly combined. Either their food is more
liable to failure, or they have not sufficient power of wing to search
for it over an extensive area, or during some season of the year it
becomes very scarce, and less wholesome substitutes have to be found;
and thus, though more fertile in offspring, they can never increase
beyond the supply of food in the least favourable seasons.
Many birds can only exist by migrating, when their food becomes scarce,
to regions possessing a milder, or at least a different climate, though,
as these migrating birds are seldom excessively abundant, it is evident
that the countries they visit are still deficient in a constant and
abundant supply of wholesome food. Those whose organization does not
permit them to migrate when their food becomes periodically scarce, can
never attain a large population. This is probably the reasons why
woodpeckers are scarce with us, while in the tropics they are among the
most abundant of solitary birds. Thus the house sparrow is more
abundant than the redbreast, because its food is more constant and
plentiful,--seeds of grasses being preserved during the winter, and our
farm-yards and stubble-fields furnishing an almost inexhaustible supply.
Why, as a general rule, are aquatic, and especially sea birds, very
numerous in individuals? Not because they are more prolific than others,
generally the contrary; but because their food never fails, the
sea-shores and river-banks daily swarming with a fresh supply of small
mollusca and crustacea. Exactly the same laws will apply to mammals.
Wild cats are prolific and have few enemies; why then are they never as
abundant as rabbits? The only intelligible answer is, that their supply
of food is more precarious. It appears evident, therefore, that so long
as a country remains physically unchanged, the numbers of its animal
population cannot materially increase. If one species does so, some
others requiring the same kind of food must diminish in proportion. The
numbers that die annually must be immense; and as the individual
existence of each animal depends upon itself, those that die must be
the weakest--the very young, the aged, and the diseased--while those
that prolong their existence can only be the most perfect in health and
vigour--those who are best able to obtain food regularly, and avoid
their numerous enemies. It is, as we commenced by remarking, "a struggle
for existence," in which the weakest and least perfectly organized must
always succumb.
_The Abundance or Rarity of a Species dependent upon its more or less
perfect Adaptation to the Conditions of Existence._
It seems evident that what takes place among the individuals of a
species must also occur among the several allied species of a
group,--viz., that those which are best adapted to obtain a regular
supply of food, and to defend themselves against the attacks of their
enemies and the vicissitudes of the seasons, must necessarily obtain and
preserve a superiority in population; while those species which from
some defect of power or organization are the least capable of
counteracting the vicissitudes of food-supply, &c., must diminish in
numbers, and, in extreme cases, become altogether extinct. Between these
extremes the species will present various degrees of capacity for
ensuring the means of preserving life; and it is thus we account for the
abundance or rarity of species. Our ignorance will generally prevent us
from accurately tracing the effects to their causes; but could we become
perfectly acquainted with the organization and habits of the various
species of animals, and could we measure the capacity of each for
performing the different acts necessary to its safety and existence
under all the varying circumstances by which it is surrounded, we might
be able even to calculate the proportionate abundance of individuals
which is the necessary result.
If now we have succeeded in establishing these two points--1st, _that
the animal population of a country is generally stationary, being kept
down by a periodical deficiency of food, and other checks_; and, 2nd,
_that the comparative abundance or scarcity of the individuals of the
several species is entirely due to their organization and resulting
habits, which, rendering it more difficult to procure a regular supply
of food and to provide for their personal safety in some cases than in
others, can only be balanced by a difference in the population which
have to exist in a given area_--we shall be in a condition to proceed to
the consideration of _varieties_, to which the preceding remarks have a
direct and very important application.
_Useful Variations will tend to Increase; useless or hurtful Variations
to Diminish._
Most or perhaps all the variations from the typical form of a species
must have some definite effect, however slight, on the habits or
capacities of the individuals. Even a change of colour might, by
rendering them more or less distinguishable, affect their safety; a
greater or less development of hair might modify their habits. More
important changes, such as an increase in the power or dimensions of the
limbs or any of the external organs, would more or less affect their
mode of procuring food or the range of country which they could inhabit.
It is also evident that most changes would affect, either favourably or
adversely, the powers of prolonging existence. An antelope with shorter
or weaker legs must necessarily suffer more from the attacks of the
feline carnivora; the passenger pigeon with less powerful wings would
sooner or later be affected in its powers of procuring a regular supply
of food; and in both cases the result must necessarily be a diminution
of the population of the modified species. If, on the other hand, any
species should produce a variety having slightly increased powers of
preserving existence, that variety must inevitably in time acquire a
superiority in numbers. These results must follow as surely as old age,
intemperance, or scarcity of food produce an increased mortality. In
both cases there may be many individual exceptions; but on the average
the rule will invariably be found to hold good. All varieties will
therefore fall into two classes--those which under the same conditions
would never reach the population of the parent species, and those which
would in time obtain and keep a numerical superiority. Now, let some
alteration of physical conditions occur in the district--a long period
of drought, a destruction of vegetation by locusts, the irruption of
some new carnivorous animal seeking "pastures new"--any change in fact
tending to render existence more difficult to the species in question,
and tasking its utmost powers to avoid complete extermination; it is
evident that, of all the individuals composing the species, those
forming the least numerous and most feebly organized variety would
suffer first, and, were the pressure severe, must soon become extinct.
The same causes continuing in action, the parent species would next
suffer, would gradually diminish in numbers, and with a recurrence of
similar unfavourable conditions might also become extinct. Tho superior
variety would then alone remain, and on a return to favourable
circumstances would rapidly increase in numbers and occupy the place of
the extinct species and variety.
_Superior Varieties will ultimately Extirpate the original Species._
The _variety_ would now have replaced the _species_, of which it would
be a more perfectly developed and more highly organized form. It would
be in all respects better adapted to secure its safety, and to prolong
its individual existence and that of the race. Such a variety _could
not_ return to the original form; for that form is an inferior one, and
could never compete with it for existence. Granted, therefore, a
"tendency" to reproduce the original type of the species, still the
variety must ever remain preponderant in numbers, and under adverse
physical conditions _again alone survive_. But this new, improved, and
populous race might itself, in course of time, give rise to new
varieties, exhibiting several diverging modifications of form, any of
which, tending to increase the facilities for preserving existence,
must, by the same general law, in their turn become predominant. Here,
then, we have _progression and continued divergence_ deduced from the
general laws which regulate the existence of animals in a state of
nature, and from the undisputed fact that varieties do frequently occur.
It is not, however, contended that this result would be invariable; a
change of physical conditions in the district might at times materially
modify it, rendering the race which had been the most capable of
supporting existence under the former conditions now the least so, and
even causing the extinction of the newer and, for a time, superior race,
while the old or parent species and its first inferior varieties
continued to flourish. Variations in unimportant parts might also occur,
having no perceptible effect on the life-preserving powers; and the
varieties so furnished might run a course parallel with the parent
species, either giving rise to further variations or returning to the
former type. All we argue for is, that certain varieties have a tendency
to maintain their existence longer than the original species, and this
tendency must make itself felt; for though the doctrine of chances or
averages can never be trusted to on a limited scale, yet, if applied to
high numbers, the results come nearer to what theory demands, and, as we
approach to an infinity of examples, become strictly accurate. Now the
scale on which nature works is so vast--the numbers of individuals and
the periods of time with which she deals approach so near to infinity,
than any cause, however slight, and however liable to be veiled and
counteracted by accidental circumstances, must in the end produce its
full legitimate results.
_The Partial Reversion of Domesticated Varieties explained._
Let us now turn to domesticated animals, and inquire how varieties
produced among them are affected by the principles here enunciated. The
essential difference in the condition of wild and domestic animals is
this,--that among the former, their well-being and very existence depend
upon the full exercise and healthy condition of all their senses and
physical powers, whereas, among the latter, these are only partially
exercised, and in some cases are absolutely unused. A wild animal has to
search, and often to labour, for every mouthful of food--to exercise
sight, hearing, and smell in seeking it, and in avoiding dangers, in
procuring shelter from the inclemency of the seasons, and in providing
for the subsistence and safety of its offspring. There is no muscle of
its body that is not called into daily and hourly activity; there is no
sense or faculty that is not strengthened by continual exercise. The
domestic animal, on the other hand, has food provided for it, is
sheltered, and often confined, to guard it against the vicissitudes of
the seasons, is carefully secured from the attacks of its natural
enemies, and seldom even rears its young without human assistance. Half
of its senses and faculties become quite useless, and the other half are
but occasionally called into feeble exercise, while even its muscular
system is only irregularly brought into action.
Now when a variety of such an animal occurs, having increased power or
capacity in any organ or sense, such increase is totally useless, is
never called into action, and may even exist without the animal ever
becoming aware of it. In the wild animal, on the contrary, all its
faculties and powers being brought into full action for the necessities
of existence, any increase becomes immediately available, is
strengthened by exercise, and must even slightly modify the food, the
habits, and the whole economy of the race. It creates as it were a new
animal, one of superior powers, and which will necessarily increase in
numbers and outlive those which are inferior to it.
Again, in the domesticated animal all variations have an equal chance of
continuance; and those which would decidedly render a wild animal unable
to compete with its fellows and continue its existence are no
disadvantage whatever in a state of domesticity. Our quickly fattening
pigs, short-legged sheep pouter pigeons, and poodle dogs could never
have come into existence in a state of nature, because the very first
step towards such inferior forms would have led to the rapid extinction
of the race; still less could they now exist in competition with their
wild allies. The great speed but slight endurance of the race horse, the
unwieldy strength of the ploughman's team, would both be useless in a
state of nature. If turned wild on the pampas, such animals would
probably soon become extinct, or under favourable circumstances might
each gradually lose those extreme qualities which would never be called
into action, and in a few generations revert to a common type, which
must be that in which the various powers and faculties are so
proportioned to each other as to be best adapted to procure food and
secure safety,--that in which by the full exercise of every part of its
organisation the animal can alone continue to live. Domestic varieties,
when turned wild, _must_ return to something near the type of the
original wild stock, _or become altogether extinct_.[F]
+--------------------------------------------------------------+
| [F] That is, they will vary, and the variations which tend |
| to adapt them to the wild state, and therefore approximate |
| them to wild animals, will be preserved. Those individuals |
| which do not vary sufficiently will perish. |
+--------------------------------------------------------------+
We see, then, that no inferences as to the permanence of varieties in a
state of nature can be deduced from the observations of those occurring
among domestic animals. The two are so much opposed to each other in
every circumstance of their existence, that what applies to the one is
almost sure not to apply to the other. Domestic animals are abnormal,
irregular, artificial; they are subject to variations which never occur
and never can occur in a state of nature: their very existence depends
altogether on human care; so far are many of them removed from that just
proportion of faculties, that true balance of organisation, by means of
which alone an animal left to its own resources can preserve its
existence and continue its race.
_Lamarck's Hypothesis very different from that now advanced._
The hypothesis of Lamarck--that progressive changes in species have been
produced by the attempts of animals to increase the development of their
own organs, and thus modify their structure and habits--has been
repeatedly and easily refuted by all writers on the subject of varieties
and species, and it seems to have been considered that when this was
done the whole question has been finally settled; but the view here
developed renders such hypothesis quite unnecessary, by showing that
similar results must be produced by the action of principles constantly
at work in nature. The powerful retractile talons of the falcon-and the
cat-tribes have not been produced or increased by the volition of those
animals; but among the different varieties which occurred in the earlier
and less highly organized forms of these groups, _those always survived
longest which had the greatest facilities for seizing their prey_.
Neither did the giraffe acquire its long neck by desiring to reach the
foliage of the more lofty shrubs, and constantly stretching its neck for
the purpose, but because any varieties which occurred among its
antitypes with a longer neck than usual _at once secured a fresh range
of pasture over the same ground as their shorter-necked companions, and
on the first scarcity of food were thereby enabled to outlive them_.
Even the peculiar colours of many animals, more especially of insects,
so closely resembling the soil or leaves or bark on which they
habitually reside, are explained on the same principle; for though in
the course of ages varieties of many tints may have occurred, _yet those
races having colours best adapted to concealment from their enemies
would inevitably survive the longest_. We have also here an acting cause
to account for that balance so often observed in nature,--a deficiency
in one set of organs always being compensated by an increased
development of some others--powerful wings accompanying weak feet, or
great velocity making up for the absence of defensive weapons; for it
has been shown that all varieties in which an unbalanced deficiency
occurred could not long continue their existence. The action of this
principle is exactly like that of the centrifugal governor of the steam
engine, which checks and corrects any irregularities almost before they
become evident; and in like manner no unbalanced deficiency in the
animal kingdom can ever reach any conspicuous magnitude, because it
would make itself felt at the very first step, by rendering existence
difficult and extinction almost sure soon to follow. An origin such as
is here advocated will also agree with the peculiar character of the
modifications of form and structure which obtain in organized
beings--the many lines of divergence from a central type, the increasing
efficiency and power of a particular organ through a succession of
allied species, and the remarkable persistence of unimportant parts,
such as colour, texture of plumage and hair, form of horns or crests,
through a series of species differing considerably in more essential
characters. It also furnishes us with a reason for that "more
specialized structure" which Professor Owen states to be a
characteristic of recent compared with extinct forms, and which would
evidently be the result of the progressive modification of any organ
applied to a special purpose in the animal economy.
_Conclusion._
We believe we have now shown that there is a tendency in nature to the
continued progression of certain classes of _varieties_ further and
further from the original type--a progression to which there appears no
reason to assign any definite limits--and that the same principle which
produces this result in a state of nature will also explain why domestic
varieties have a tendency, when they become wild, to revert to the
original type. This progression, by minute steps, in various
directions, but always checked and balanced by the necessary conditions,
subject to which alone existence can be preserved, may, it is believed,
be followed out so as to agree with all the phænomena presented by
organized beings, their extinction and succession in past ages, and all
the extraordinary modifications of form, instinct and habits which they
exhibit.
III.
MIMICRY, AND OTHER PROTECTIVE RESEMBLANCES AMONG ANIMALS.
There is no more convincing proof of the truth of a comprehensive
theory, than its power of absorbing and finding a place for new facts,
and its capability of interpreting phænomena which had been previously
looked upon as unaccountable anomalies. It is thus that the law of
universal gravitation and the undulatory theory of light have become
established and universally accepted by men of science. Fact after fact
has been brought forward as being apparently inconsistent with them, and
one after another these very facts have been shown to be the
consequences of the laws they were at first supposed to disprove. A
false theory will never stand this test. Advancing knowledge brings to
light whole groups of facts which it cannot deal with, and its advocates
steadily decrease in numbers, notwithstanding the ability and scientific
skill with which it may have been supported. The great name of Edward
Forbes did not prevent his theory of "Polarity in the distribution of
Organic beings in Time" from dying a natural death; but the most
striking illustration of the behaviour of a false theory is to be found
in the "Circular and Quinarian System" of classification propounded by
MacLeay, and developed by Swainson, with an amount of knowledge and
ingenuity that have rarely been surpassed. This theory was eminently
attractive, both from its symmetry and completeness, and from the
interesting nature of the varied analogies and affinities which it
brought to light and made use of. The series of Natural History volumes
in "Lardner's Cabinet Cyclopædia," in which Mr. Swainson developed it in
most departments of the animal kingdom, made it widely known; and in
fact for a long time these were the best and almost the only popular
text-books for the rising generation of naturalists. It was favourably
received too by the older school, which was perhaps rather an indication
of its unsoundness. A considerable number of well-known naturalists
either spoke approvingly of it, or advocated similar principles, and for
a good many years it was decidedly in the ascendent. With such a
favourable introduction, and with such talented exponents, it must have
become established if it had had any germ of truth in it; yet it quite
died out in a few short years, its very existence is now a matter of
history; and so rapid was its fall that its talented creator, Swainson,
perhaps lived to be the last man who believed in it.
Such is the course of a false theory. That of a true one is very
different, as may be well seen by the progress of opinion on the subject
of Natural Selection. In less than eight years "The Origin of Species"
has produced conviction in the minds of a majority of the most eminent
living men of science. New facts, new problems, new difficulties as they
arise are accepted, solved or removed by this theory; and its principles
are illustrated by the progress and conclusions of every well
established branch of human knowledge. It is the object of the present
essay to show how it has recently been applied to connect together and
explain a variety of curious facts which had long been considered as
inexplicable anomalies.
_Importance of the Principle of Utility._
Perhaps no principle has ever been announced so fertile in results as
that which Mr. Darwin so earnestly impresses upon us, and which is
indeed a necessary deduction from the theory of Natural Selection,
namely--that none of the definite facts of organic nature, no special
organ, no characteristic form or marking, no peculiarities of instinct
or of habit, no relations between species or between groups of
species--can exist, but which must now be or once have been _useful_ to
the individuals or the races which possess them. This great principle
gives us a clue which we can follow out in the study of many recondite
phænomena, and leads us to seek a meaning and a purpose of some definite
character in minutiæ which we should be otherwise almost sure to pass
over as insignificant or unimportant.
_Popular Theories of Colour in Animals._
The adaptation of the external colouring of animals to their conditions
of life has long been recognised, and has been imputed either to an
originally created specific peculiarity, or to the direct action of
climate, soil, or food. Where the former explanation has been accepted,
it has completely checked inquiry, since we could never get any further
than the fact of the adaptation. There was nothing more to be known
about the matter. The second explanation was soon found to be quite
inadequate to deal with all the varied phases of the phænomena, and to
be contradicted by many well-known facts. For example, wild rabbits are
always of grey or brown tints well suited for concealment among grass
and fern. But when these rabbits are domesticated, without any change of
climate or food, they vary into white or black, and these varieties may
be multiplied to any extent, forming white or black races. Exactly the
same thing has occurred with pigeons; and in the case of rats and mice,
the white variety has not been shown to be at all dependent on
alteration of climate, food, or other external conditions. In many cases
the wings of an insect not only assume the exact tint of the bark or
leaf it is accustomed to rest on, but the form and veining of the leaf
or the exact rugosity of the bark is imitated; and these detailed
modifications cannot be reasonably imputed to climate or to food, since
in many cases the species does not feed on the substance it resembles,
and when it does, no reasonable connexion can be shown to exist between
the supposed cause and the effect produced. It was reserved for the
theory of Natural Selection to solve all these problems, and many others
which were not at first supposed to be directly connected with them. To
make these latter intelligible, it will be necessary to give a sketch of
the whole series of phænomena which may be classed under the head of
useful or protective resemblances.
_Importance of Concealment as Influencing Colour._
Concealment, more or less complete, is useful to many animals, and
absolutely essential to some. Those which have numerous enemies from
which they cannot escape by rapidity of motion, find safety in
concealment. Those which prey upon others must also be so constituted as
not to alarm them by their presence or their approach, or they would
soon die of hunger. Now it is remarkable in how many cases nature gives
this boon to the animal, by colouring it with such tints as may best
serve to enable it to escape from its enemies or to entrap its prey.
Desert animals as a rule are desert-coloured. The lion is a typical
example of this, and must be almost invisible when crouched upon the
sand or among desert rocks and stones. Antelopes are all more or less
sandy-coloured. The camel is pre-eminently so. The Egyptian cat and the
Pampas cat are sandy or earth-coloured. The Australian kangaroos are of
the same tints, and the original colour of the wild horse is supposed to
have been a sandy or clay-colour.
The desert birds are still more remarkably protected by their
assimilative hues. The stonechats, the larks, the quails, the
goatsuckers and the grouse, which abound in the North African and
Asiatic deserts, are all tinted and mottled so as to resemble with
wonderful accuracy the average colour and aspect of the soil in the
district they inhabit. The Rev. H. Tristram, in his account of the
ornithology of North Africa in the 1st volume of the "Ibis," says: "In
the desert, where neither trees, brush-wood, nor even undulation of the
surface afford the slightest protection to its foes, a modification of
colour which shall be assimilated to that of the surrounding country, is
absolutely necessary. Hence _without exception_ the upper plumage of
_every bird_, whether lark, chat, sylvain, or sand-grouse, and also the
fur of _all the smaller mammals_, and the skin of _all the snakes and
lizards_, is of one uniform isabelline or sand colour." After the
testimony of so able an observer it is unnecessary to adduce further
examples of the protective colours of desert animals.
Almost equally striking are the cases of arctic animals possessing the
white colour that best conceals them upon snowfields and icebergs. The
polar bear is the only bear that is white, and it lives constantly among
snow and ice. The arctic fox, the ermine and the alpine hare change to
white in winter only, because in summer white would be more conspicuous
than any other colour, and therefore a danger rather than a protection;
but the American polar hare, inhabiting regions of almost perpetual
snow, is white all the year round. Other animals inhabiting the same
Northern regions do not, however, change colour. The sable is a good
example, for throughout the severity of a Siberian winter it retains its
rich brown fur. But its habits are such that it does not need the
protection of colour, for it is said to be able to subsist on fruits and
berries in winter, and to be so active upon the trees as to catch small
birds among the branches. So also the woodchuck of Canada has a
dark-brown fur; but then it lives in burrows and frequents river banks,
catching fish and small animals that live in or near the water.
Among birds, the ptarmigan is a fine example of protective colouring.
Its summer plumage so exactly harmonizes with the lichen-coloured stones
among which it delights to sit, that a person may walk through a flock
of them without seeing a single bird; while in winter its white plumage
is an almost equal protection. The snow-bunting, the jer-falcon, and the
snowy owl are also white-coloured birds inhabiting the arctic regions,
and there can be little doubt but that their colouring is to some extent
protective.
Nocturnal animals supply us with equally good illustrations. Mice, rats,
bats, and moles possess the least conspicuous of hues, and must be quite
invisible at times when any light colour would be instantly seen. Owls
and goatsuckers are of those dark mottled tints that will assimilate
with bark and lichen, and thus protect them during the day, and at the
same time be inconspicuous in the dusk.
It is only in the tropics, among forests which never lose their foliage,
that we find whole groups of birds whose chief colour is green. The
parrots are the most striking example, but we have also a group of green
pigeons in the East; and the barbets, leaf-thrushes, bee-eaters,
white-eyes, turacos, and several smaller groups, have so much green in
their plumage as to tend greatly to conceal them among the foliage.
_Special Modifications of Colour._
The conformity of tint which has been so far shown to exist between
animals and their habitations is of a somewhat general character; we
will now consider the cases of more special adaptation. If the lion is
enabled by his sandy colour readily to conceal himself by merely
crouching down upon the desert, how, it may be asked, do the elegant
markings of the tiger, the jaguar, and the other large cats agree with
this theory? We reply that these are generally cases of more or less
special adaptation. The tiger is a jungle animal, and hides himself
among tufts of grass or of bamboos, and in these positions the vertical
stripes with which his body is adorned must so assimilate with the
vertical stems of the bamboo, as to assist greatly in concealing him
from his approaching prey. How remarkable it is that besides the lion
and tiger, almost all the other large cats are arboreal in their
habits, and almost all have ocellated or spotted skins, which must
certainly tend to blend them with the background of foliage; while the
one exception, the puma, has an ashy brown uniform fur, and has the
habit of clinging so closely to a limb of a tree while waiting for his
prey to pass beneath as to be hardly distinguishable from the bark.
Among birds, the ptarmigan, already mentioned, must be considered a
remarkable case of special adaptation. Another is a South-American
goatsucker (Caprimulgus rupestris) which rests in the bright sunshine on
little bare rocky islets in the Upper Rio Negro, where its unusually
light colours so closely resemble those of the rock and sand, that it
can scarcely be detected till trodden upon.
The Duke of Argyll, in his "Reign of Law," has pointed out the admirable
adaptation of the colours of the woodcock to its protection. The various
browns and yellows and pale ash-colour that occur in fallen leaves are
all reproduced in its plumage, so that when according to its habit it
rests upon the ground under trees, it is almost impossible to detect it.
In snipes the colours are modified so as to be equally in harmony with
the prevalent forms and colours of marshy vegetation. Mr. J. M. Lester,
in a paper read before the Rugby School Natural History Society,
observes:--"The wood-dove, when perched amongst the branches of its
favourite _fir_, is scarcely discernible; whereas, were it among some
lighter foliage, the blue and purple tints in its plumage would far
sooner betray it. The robin redbreast too, although it might be thought
that the red on its breast made it much easier to be seen, is in reality
not at all endangered by it, since it generally contrives to get among
some russet or yellow fading leaves, where the red matches very well
with the autumn tints, and the brown of the rest of the body with the
bare branches."
Reptiles offer us many similar examples. The most arboreal lizards, the
iguanas, are as green as the leaves they feed upon, and the slender
whip-snakes are rendered almost invisible as they glide among the
foliage by a similar colouration. How difficult it is sometimes to catch
sight of the little green tree-frogs sitting on the leaves of a small
plant enclosed in a glass case in the Zoological Gardens; yet how much
better concealed must they be among the fresh green damp foliage of a
marshy forest. There is a North-American frog found on lichen-covered
rocks and walls, which is so coloured as exactly to resemble them, and
as long as it remains quiet would certainly escape detection. Some of
the geckos which cling motionless on the trunks of trees in the tropics,
are of such curiously marbled colours as to match exactly with the bark
they rest upon.
In every part of the tropics there are tree-snakes that twist among
boughs and shrubs, or lie coiled up on the dense masses of foliage.
These are of many distinct groups, and comprise both venomous and
harmless genera; but almost all of them are of a beautiful green
colour, sometimes more or less adorned with white or dusky bands and
spots. There can be little doubt that this colour is doubly useful to
them, since it will tend to conceal them from their enemies, and will
lead their prey to approach them unconscious of danger. Dr. Gunther
informs me that there is only one genus of true arboreal snakes (Dipsas)
whose colours are rarely green, but are of various shades of black,
brown, and olive, and these are all nocturnal reptiles, and there can be
little doubt conceal themselves during the day in holes, so that the
green protective tint would be useless to them, and they accordingly
retain the more usual reptilian hues.
Fishes present similar instances. Many flat fish, as for example the
flounder and the skate, are exactly the colour of the gravel or sand on
which they habitually rest. Among the marine flower gardens of an
Eastern coral reef the fishes present every variety of gorgeous colour,
while the river fish even of the tropics rarely if ever have gay or
conspicuous markings. A very curious case of this kind of adaptation
occurs in the sea-horses (Hippocampus) of Australia, some of which bear
long foliaceous appendages resembling seaweed, and are of a brilliant
red colour; and they are known to live among seaweed of the same hue, so
that when at rest they must be quite invisible. There are now in the
aquarium of the Zoological Society some slender green pipe-fish which
fasten themselves to any object at the bottom by their prehensile
tails, and float about with the current, looking exactly like some
simple cylindrical algæ.
It is, however, in the insect world that this principle of the
adaptation of animals to their environment is most fully and strikingly
developed. In order to understand how general this is, it is necessary
to enter somewhat into details, as we shall thereby be better able to
appreciate the significance of the still more remarkable phenomena we
shall presently have to discuss. It seems to be in proportion to their
sluggish motions or the absence of other means of defence, that insects
possess the protective colouring. In the tropics there are thousands of
species of insects which rest during the day clinging to the bark of
dead or fallen trees; and the greater portion of these are delicately
mottled with gray and brown tints, which though symmetrically disposed
and infinitely varied, yet blend so completely with the usual colours of
the bark, that at two or three feet distance they are quite
undistinguishable. In some cases a species is known to frequent only one
species of tree. This is the case with the common South American
long-horned beetle (Onychocerus scorpio) which, Mr. Bates informed me,
is found only on a rough-barked tree, called Tapiribá, on the Amazon. It
is very abundant, but so exactly does it resemble the bark in colour and
rugosity, and so closely does it cling to the branches, that until it
moves it is absolutely invisible! An allied species (O. concentricus)
is found only at Pará, on a distinct species of tree, the bark of which
it resembles with equal accuracy. Both these insects are abundant, and
we may fairly conclude that the protection they derive from this strange
concealment is at least one of the causes that enable the race to
flourish.
Many of the species of Cicindela, or tiger beetle, will illustrate this
mode of protection. Our common Cicindela campestris frequents grassy
banks, and is of a beautiful green colour, while C. maritima, which is
found only on sandy sea-shores, is of a pale bronzy yellow, so as to be
almost invisible. A great number of the species found by myself in the
Malay islands are similarly protected. The beautiful Cicindela gloriosa,
of a very deep velvety green colour, was only taken upon wet mossy
stones in the bed of a mountain stream, where it was with the greatest
difficulty detected. A large brown species (C. heros) was found chiefly
on dead leaves in forest paths; and one which was never seen except on
the wet mud of salt marshes was of a glossy olive so exactly the colour
of the mud as only to be distinguished when the sun shone, by its
shadow! Where the sandy beach was coralline and nearly white, I found a
very pale Cicindela; wherever it was volcanic and black, a dark species
of the same genus was sure to be met with.
There are in the East small beetles of the family Buprestidæ which
generally rest on the midrib of a leaf, and the naturalist often
hesitates before picking them off, so closely do they resemble pieces of
bird's dung. Kirby and Spence mention the small beetle Onthophilus
sulcatus as being like the seed of an umbelliferous plant; and another
small weevil, which is much persecuted by predatory beetles of the genus
Harpalus, is of the exact colour of loamy soil, and was found to be
particularly abundant in loam pits. Mr. Bates mentions a small beetle
(Chlamys pilula) which was undistinguishable by the eye from the dung of
caterpillars, while some of the Cassidæ, from their hemispherical forms
and pearly gold colour, resemble glittering dew-drops upon the leaves.
A number of our small brown and speckled weevils at the approach of any
object roll off the leaf they are sitting on, at the same time drawing
in their legs and antennæ, which fit so perfectly into cavities for
their reception that the insect becomes a mere oval brownish lump, which
it is hopeless to look for among the similarly coloured little stones
and earth pellets among which it lies motionless.
The distribution of colour in butterflies and moths respectively is very
instructive from this point of view. The former have all their brilliant
colouring on the upper surface of all four wings, while the under
surface is almost always soberly coloured, and often very dark and
obscure. The moths on the contrary have generally their chief colour on
the hind wings only, the upper wings being of dull, sombre, and often
imitative tints, and these generally conceal the hind wings when the
insects are in repose. This arrangement of the colours is therefore
eminently protective, because the butterfly always rests with his wings
raised so as to conceal the dangerous brilliancy of his upper surface.
It is probable that if we watched their habits sufficiently we should
find the under surface of the wings of butterflies very frequently
imitative and protective. Mr. T. W. Wood has pointed out that the little
orange-tip butterfly often rests in the evening on the green and white
flower heads of an umbelliferous plant, and that when observed in this
position the beautiful green and white mottling of the under surface
completely assimilates with the flower heads and renders the creature
very difficult to be seen. It is probable that the rich dark colouring
of the under side of our peacock, tortoiseshell, and red-admiral
butterflies answers a similar purpose.
Two curious South American butterflies that always settle on the trunks
of trees (Gynecia dirce and Callizona acesta) have the under surface
curiously striped and mottled, and when viewed obliquely must closely
assimilate with the appearance of the furrowed bark of many kinds of
trees. But the most wonderful and undoubted case of protective
resemblance in a butterfly which I have ever seen, is that of the common
Indian Kallima inachis, and its Malayan ally, Kallima paralekta. The
upper surface of these insects is very striking and showy, as they are
of a large size, and are adorned with a broad band of rich orange on a
deep bluish ground. The under side is very variable in colour, so that
out of fifty specimens no two can be found exactly alike, but every one
of them will be of some shade of ash or brown or ochre, such as are
found among dead, dry, or decaying leaves. The apex of the upper wings
is produced into an acute point, a very common form in the leaves of
tropical shrubs and trees, and the lower wings are also produced into a
short narrow tail. Between these two points runs a dark curved line
exactly representing the midrib of a leaf, and from this radiate on each
side a few oblique lines, which serve to indicate the lateral veins of a
leaf. These marks are more clearly seen on the outer portion of the base
of the wings, and on the inner side towards the middle and apex, and it
is very curious to observe how the usual marginal and transverse striæ
of the group are here modified and strengthened so as to become adapted
for an imitation of the venation of a leaf. We come now to a still more
extraordinary part of the imitation, for we find representations of
leaves in every stage of decay, variously blotched and mildewed and
pierced with holes, and in many cases irregularly covered with powdery
black dots gathered into patches and spots, so closely resembling the
various kinds of minute fungi that grow on dead leaves that it is
impossible to avoid thinking at first sight that the butterflies
themselves have been attacked by real fungi.
But this resemblance, close as it is, would be of little use if the
habits of the insect did not accord with it. If the butterfly sat upon
leaves or upon flowers, or opened its wings so as to expose the upper
surface, or exposed and moved its head and antennæ as many other
butterflies do, its disguise would be of little avail. We might be sure,
however, from the analogy of many other cases, that the habits of the
insect are such as still further to aid its deceptive garb; but we are
not obliged to make any such supposition, since I myself had the good
fortune to observe scores of Kallima paralekta, in Sumatra, and to
capture many of them, and can vouch for the accuracy of the following
details. These butterflies frequent dry forests and fly very swiftly.
They were never seen to settle on a flower or a green leaf, but were
many times lost sight of in a bush or tree of dead leaves. On such
occasions they were generally searched for in vain, for while gazing
intently at the very spot where one had disappeared, it would often
suddenly dart out, and again vanish twenty or fifty yards further on. On
one or two occasions the insect was detected reposing, and it could then
be seen how completely it assimilates itself to the surrounding leaves.
It sits on a nearly upright twig, the wings fitting closely back to
back, concealing the antennæ and head, which are drawn up between their
bases. The little tails of the hind wing touch the branch, and form a
perfect stalk to the leaf, which is supported in its place by the claws
of the middle pair of feet, which are slender and inconspicuous. The
irregular outline of the wings gives exactly the perspective effect of a
shrivelled leaf. We thus have size, colour, form, markings, and habits,
all combining together to produce a disguise which may be said to be
absolutely perfect; and the protection which it affords is sufficiently
indicated by the abundance of the individuals that possess it.
The Rev. Joseph Greene has called attention to the striking harmony
between the colours of those British moths which are on the wing in
autumn and winter, and the prevailing tints of nature at those seasons.
In autumn various shades of yellow and brown prevail, and he shows that
out of fifty-two species that fly at this season, no less than forty-two
are of corresponding colours. Orgyia antiqua, O. gonostigma, the genera
Xanthia, Glæa, and Ennomos are examples. In winter, gray and silvery
tints prevail, and the genus Chematobia and several species of Hybernia
which fly during this season are of corresponding hues. No doubt if the
habits of moths in a state of nature were more closely observed, we
should find many cases of special protective resemblance. A few such
have already been noticed. Agriopis aprilina, Acronycta psi, and many
other moths which rest during the day on the north side of the trunks of
trees can with difficulty be distinguished from the grey and green
lichens that cover them. The lappet moth (Gastropacha querci) closely
resembles both in shape and colour a brown dry leaf; and the well-known
buff-tip moth, when at rest is like the broken end of a lichen-covered
branch. There are some of the small moths which exactly resemble the
dung of birds dropped on leaves, and on this point Mr. A. Sidgwick, in a
paper read before the Rugby School Natural History Society, gives the
following original observation:--"I myself have more than once mistaken
Cilix compressa, a little white and grey moth, for a piece of bird's
dung dropped upon a leaf, and _vice versâ_ the dung for the moth.
Bryophila Glandifera and Perla are the very image of the mortar walls on
which they rest; and only this summer, in Switzerland, I amused myself
for some time in watching a moth, probably Larentia tripunctaria,
fluttering about quite close to me, and then alighting on a wall of the
stone of the district which it so exactly matched as to be quite
invisible a couple of yards off." There are probably hosts of these
resemblances which have not been observed, owing to the difficulty of
finding many of the species in their stations of natural repose.
Caterpillars are also similarly protected. Many exactly resemble in tint
the leaves they feed upon; others are like little brown twigs, and many
are so strangely marked or humped, that when motionless they can hardly
be taken to be living creatures at all. Mr. Andrew Murray has remarked
how closely the larva of the peacock moth (Saturnia pavonia-minor)
harmonizes in its ground colour with that of the young buds of heather
on which it feeds, and that the pink spots with which it is decorated
correspond with the flowers and flower-buds of the same plant.
The whole order of Orthoptera, grasshoppers, locusts, crickets, &c., are
protected by their colours harmonizing with that of the vegetation or
the soil on which they live, and in no other group have we such striking
examples of special resemblance. Most of the tropical Mantidæ and
Locustidæ are of the exact tint of the leaves on which they habitually
repose, and many of them in addition have the veinings of their wings
modified so as exactly to imitate that of a leaf. This is carried to the
furthest possible extent in the wonderful genus, Phyllium, the "walking
leaf," in which not only are the wings perfect imitations of leaves in
every detail, but the thorax and legs are flat, dilated, and leaf-like;
so that when tho living insect is resting among the foliage on which it
feeds, the closest observation is often unable to distinguish between
the animal and the vegetable.
The whole family of the Phasmidæ, or spectres, to which this insect
belongs, is more or less imitative, and a great number of the species
are called "walking-stick insects," from their singular resemblance to
twigs and branches. Some of these are a foot long and as thick as one's
finger, and their whole colouring, form, rugosity, and the arrangement
of the head, legs, and antennæ, are such as to render them absolutely
identical in appearance with dead sticks. They hang loosely about shrubs
in the forest, and have the extraordinary habit of stretching out their
legs unsymmetrically, so as to render the deception more complete. One
of these creatures obtained by myself in Borneo (Ceroxylus laceratus)
was covered over with foliaceous excrescences of a clear olive green
colour, so as exactly to resemble a stick grown over by a creeping moss
or jungermannia. The Dyak who brought it me assured me it was grown over
with moss although alive, and it was only after a most minute
examination that I could convince myself it was not so.
We need not adduce any more examples to show how important are the
details of form and of colouring in animals, and that their very
existence may often depend upon their being by these means concealed
from their enemies. This kind of protection is found apparently in every
class and order, for it has been noticed wherever we can obtain
sufficient knowledge of the details of an animal's life-history. It
varies in degree, from the mere absence of conspicuous colour or a
general harmony with the prevailing tints of nature, up to such a minute
and detailed resemblance to inorganic or vegetable structures as to
realize the talisman of the fairy tale, and to give its possessor the
power of rendering itself invisible.
_Theory of Protective Colouring._
We will now endeavour to show how these wonderful resemblances have most
probably been brought about. Returning to the higher animals, let us
consider the remarkable fact of the rarity of white colouring in the
mammalia or birds of the temperate or tropical zones in a state of
nature. There is not a single white land-bird or quadruped in Europe,
except the few arctic or alpine species, to which white is a protective
colour. Yet in many of these creatures there seems to be no inherent
tendency to avoid white, for directly they are domesticated white
varieties arise, and appear to thrive as well as others. We have white
mice and rats, white cats, horses, dogs, and cattle, white poultry,
pigeons, turkeys, and ducks, and white rabbits. Some of these animals
have been domesticated for a long period, others only for a few
centuries; but in almost every case in which an animal has been
thoroughly domesticated, parti-coloured and white varieties are produced
and become permanent.
It is also well known that animals in a state of nature produce white
varieties occasionally. Blackbirds, starlings, and crows are
occasionally seen white, as well as elephants, deer, tigers, hares,
moles, and many other animals; but in no case is a permanent white race
produced. Now there are no statistics to show that the normal-coloured
parents produce white offspring oftener under domestication than in a
state of nature, and we have no right to make such an assumption if the
facts can be accounted for without it. But if the colours of animals do
really, in the various instances already adduced, serve for their
concealment and preservation, then white or any other conspicuous colour
must be hurtful, and must in most cases shorten an animal's life. A
white rabbit would be more surely the prey of hawk or buzzard, and the
white mole, or field mouse, could not long escape from the vigilant owl.
So, also, any deviation from those tints best adapted to conceal a
carnivorous animal would render the pursuit of its prey much more
difficult, would place it at a disadvantage among its fellows, and in a
time of scarcity would probably cause it to starve to death. On the
other hand, if an animal spreads from a temperate into an arctic
district, the conditions are changed. During a large portion of the
year, and just when the struggle for existence is most severe, white is
the prevailing tint of nature, and dark colours will be the most
conspicuous. The white varieties will now have an advantage; they will
escape from their enemies or will secure food, while their brown
companions will be devoured or will starve; and as "like produces like"
is the established rule in nature, the white race will become
permanently established, and dark varieties, when they occasionally
appear, will soon die out from their want of adaptation to their
environment. In each case the fittest will survive, and a race will be
eventually produced adapted to the conditions in which it lives.
We have here an illustration of the simple and effectual means by which
animals are brought into harmony with the rest of nature. That slight
amount of variability in every species, which we often look upon as
something accidental or abnormal, or so insignificant as to be hardly
worthy of notice, is yet the foundation of all those wonderful and
harmonious resemblances which play such an important part in the economy
of nature. Variation is generally very small in amount, but it is all
that is required, because the change in the external conditions to which
an animal is subject is generally very slow and intermittent. When these
changes have taken place too rapidly, the result has often been the
extinction of species; but the general rule is, that climatal and
geological changes go on slowly, and the slight but continual
variations in the colour, form, and structure of all animals, has
furnished individuals adapted to these changes, and who have become the
progenitors of modified races. Rapid multiplication, incessant slight
variation, and survival of the fittest--these are the laws which ever
keep the organic world in harmony with the inorganic, and with itself.
These are the laws which we believe have produced all the cases of
protective resemblance already adduced, as well as those still more
curious examples we have yet to bring before our readers.
It must always be borne in mind that the more wonderful examples, in
which there is not only a general but a special resemblance--as in the
walking leaf, the mossy phasma, and the leaf-winged butterfly--represent
those few instances in which the process of modification has been going
on during an immense series of generations. They all occur in the
tropics, where the conditions of existence are the most favourable, and
where climatic changes have for long periods been hardly perceptible. In
most of them favourable variations both of colour, form, structure, and
instinct or habit, must have occurred to produce the perfect adaptation
we now behold. All these are known to vary, and favourable variations
when not accompanied by others that were unfavourable, would certainly
survive. At one time a little step might be made in this direction, at
another time in that--a change of conditions might sometimes render
useless that which it had taken ages to produce--great and sudden
physical modifications might often produce the extinction of a race
just as it was approaching perfection, and a hundred checks of which we
can know nothing may have retarded the progress towards perfect
adaptation; so that we can hardly wonder at there being so few cases in
which a completely successful result has been attained as shown by the
abundance and wide diffusion of the creatures so protected.
_Objection that Colour, as being dangerous, should not exist in Nature._
It is as well here to reply to an objection that will no doubt occur to
many readers--that if protection is so useful to all animals, and so
easily brought about by variation and survival of the fittest, there
ought to be no conspicuously-coloured creatures; and they will perhaps
ask how we account for the brilliant birds, and painted snakes, and
gorgeous insects, that occur abundantly all over the world. It will be
advisable to answer this question rather fully, in order that we may be
prepared to understand the phenomena of "mimicry," which it is the
special object of this paper to illustrate and explain.
The slightest observation of the life of animals will show us, that they
escape from their enemies and obtain their food in an infinite number of
ways; and that their varied habits and instincts are in every case
adapted to the conditions of their existence. The porcupine and the
hedgehog have a defensive armour that saves them from the attacks of
most animals. The tortoise is not injured by the conspicuous colours of
his shell, because that shell is in most cases an effectual protection
to him. The skunks of North America find safety in their power of
emitting an unbearably offensive odour; the beaver in its aquatic habits
and solidly constructed abode. In some cases the chief danger to an
animal occurs at one particular period of its existence, and if that is
guarded against its numbers can easily be maintained. This is the case
with many birds, the eggs and young of which are especially obnoxious to
danger, and we find accordingly a variety of curious contrivances to
protect them. We have nests carefully concealed, hung from the slender
extremities of grass or boughs over water, or placed in the hollow of a
tree with a very small opening. When these precautions are successful,
so many more individuals will be reared than can possibly find food
during the least favourable seasons, that there will always be a number
of weakly and inexperienced young birds who will fall a prey to the
enemies of the race, and thus render necessary for the stronger and
healthier individuals no other safeguard than their strength and
activity. The instincts most favourable to the production and rearing of
offspring will in these cases be most important, and the survival of the
fittest will act so as to keep up and advance those instincts, while
other causes which tend to modify colour and marking may continue their
action almost unchecked.
It is perhaps in insects that we may best study the varied means by
which animals are defended or concealed. One of the uses of the
phosphorescence with which many insects are furnished, is probably to
frighten away their enemies; for Kirby and Spence state that a ground
beetle (Carabus) has been observed running round and round a luminous
centipede as if afraid to attack it. An immense number of insects have
stings, and some stingless ants of the genus Polyrachis are armed with
strong and sharp spines on the back, which must render them unpalatable
to many of the smaller insectivorous birds. Many beetles of the family
Curculionidæ have the wing cases and other external parts so excessively
hard, that they cannot be pinned without first drilling a hole to
receive the pin, and it is probable that all such find a protection in
this excessive hardness. Great numbers of insects hide themselves among
the petals of flowers, or in the cracks of bark and timber; and finally,
extensive groups and even whole orders have a more or less powerful and
disgusting smell and taste, which they either possess permanently, or
can emit at pleasure. The attitudes of some insects may also protect
them, as the habit of turning up the tail by the harmless rove-beetles
(Staphylindidæ) no doubt leads other animals besides children to the
belief that they can sting. The curious attitude assumed by sphinx
caterpillars is probably a safeguard, as well as the blood-red tentacles
which can suddenly be thrown out from the neck, by the caterpillars of
all the true swallow-tailed butterflies.
It is among the groups that possess some of these varied kinds of
protection in a high degree, that we find the greatest amount of
conspicuous colour, or at least the most complete absence of protective
imitation. The stinging Hymenoptera, wasps, bees, and hornets, are, as a
rule, very showy and brilliant insects, and there is not a single
instance recorded in which any one of them is coloured so as to resemble
a vegetable or inanimate substance. The Chrysididæ, or golden wasps,
which do not sting, possess as a substitute the power of rolling
themselves up into a ball, which is almost as hard and polished as if
really made of metal,--and they are all adorned with the most gorgeous
colours. The whole order Hemiptera (comprising the bugs) emit a powerful
odour, and they present a very large proportion of gay-coloured and
conspicuous insects. The lady-birds (Coccinellidæ) and their allies the
Eumorphidæ, are often brightly spotted, as if to attract attention; but
they can both emit fluids of a very disagreeable nature, they are
certainly rejected by some birds, and are probably never eaten by any.
The great family of ground beetles (Carabidæ) almost all possess a
disagreeable and some a very pungent smell, and a few, called bombardier
beetles, have the peculiar faculty of emitting a jet of very volatile
liquid, which appears like a puff of smoke, and is accompanied by a
distinct crepitating explosion. It is probably because these insects are
mostly nocturnal and predacious that they do not present more vivid
hues. They are chiefly remarkable for brilliant metallic tints or dull
red patches when they are not wholly black, and are therefore very
conspicuous by day, when insect-eaters are kept off by their bad odour
and taste, but are sufficiently invisible at night when it is of
importance that their prey should not become aware of their proximity.
It seems probable that in some cases that which would appear at first to
be a source of danger to its possessor may really be a means of
protection. Many showy and weak-flying butterflies have a very broad
expanse of wing, as in the brilliant blue Morphos of Brazilian forests,
and the large Eastern Papilios; yet these groups are tolerably
plentiful. Now, specimens of these butterflies are often captured with
pierced and broken wings, as if they had been seized by birds from whom
they had escaped; but if the wings had been much smaller in proportion
to the body, it seems probable that the insect would be more frequently
struck or pierced in a vital part, and thus the increased expanse of the
wings may have been indirectly beneficial.
In other cases the capacity of increase in a species is so great that
however many of the perfect insect may be destroyed, there is always
ample means for the continuance of the race. Many of the flesh flies,
gnats, ants, palm-tree weevils and locusts are in this category. The
whole family of Cetoniadæ or rose chafers, so full of gaily-coloured
species, are probably saved from attack by a combination of characters.
They fly very rapidly with a zigzag or waving course; they hide
themselves the moment they alight, either in the corolla of flowers, or
in rotten wood, or in cracks and hollows of trees, and they are
generally encased in a very hard and polished coat of mail which may
render them unsatisfactory food to such birds as would be able to
capture them. The causes which lead to the development of colour have
been here able to act unchecked, and we see the result in a large
variety of the most gorgeously-coloured insects.
Here, then, with our very imperfect knowledge of the life-history of
animals, we are able to see that there are widely varied modes by which
they may obtain protection from their enemies or concealment from their
prey. Some of those seem to be so complete and effectual as to answer
all the wants of the race, and lead to the maintenance of the largest
possible population. When this is the case, we can well understand that
no further protection derived from a modification of colour can be of
the slightest use, and the most brilliant hues may be developed without
any prejudicial effect upon the species. On some of the laws that
determine the development of colour something may be said presently. It
is now merely necessary to show that concealment by obscure or imitative
tints is only one out of very many ways by which animals maintain their
existence; and having done this we are prepared to consider the
phenomena of what has been termed "mimicry." It is to be particularly
observed, however, that the word is not here used in the sense of
voluntary imitation, but to imply a particular kind of resemblance--a
resemblance not in internal structure but in external appearance--a
resemblance in those parts only that catch the eye--a resemblance that
deceives. As this kind of resemblance has the same effect as voluntary
imitation or mimicry, and as we have no word that expresses the required
meaning, "mimicry" was adopted by Mr. Bates (who was the first to
explain the facts), and has led to some misunderstanding; but there need
be none, if it is remembered that both "mimicry" and "imitation" are
used in a metaphorical sense, as implying that close external likeness
which causes things unlike in structure to be mistaken for each other.
_Mimicry._
It has been long known to entomologists that certain insects bear a
strange external resemblance to others belonging to distinct genera,
families, or even orders, and with which they have no real affinity
whatever. The fact, however, appears to have been generally considered
as dependent upon some unknown law of "analogy"--some "system of
nature," or "general plan," which had guided the Creator in designing
the myriads of insect forms, and which we could never hope to
understand. In only one case does it appear that the resemblance was
thought to be useful, and to have been designed as a means to a definite
and intelligible purpose. The flies of the genus Volucella enter the
nests of bees to deposit their eggs, so that their larvæ may feed upon
the larvæ of the bees, and these flies are each wonderfully like the bee
on which it is parasitic. Kirby and Spence believed that this
resemblance or "mimicry" was for the express purpose of protecting the
flies from the attacks of the bees, and the connection is so evident
that it was hardly possible to avoid this conclusion. The resemblance,
however, of moths to butterflies or to bees, of beetles to wasps, and of
locusts to beetles, has been many times noticed by eminent writers; but
scarcely ever till within the last few years does it appear to have been
considered that these resemblances had any special purpose, or were of
any direct benefit to the insects themselves. In this respect they were
looked upon as accidental, as instances of the "curious analogies" in
nature which must be wondered at but which could not be explained.
Recently, however, these instances have been greatly multiplied; the
nature of the resemblances has been more carefully studied, and it has
been found that they are often carried out into such details as almost
to imply a purpose of deceiving the observer. The phenomena, moreover,
have been shown to follow certain definite laws, which again all
indicate their dependence on the more general law of the "survival of
the fittest," or "the preservation of favoured races in the struggle for
life." It will, perhaps, be as well here to state what these laws or
general conclusions are, and then to give some account of the facts
which support them.
The first law is, that in an overwhelming majority of cases of mimicry,
the animals (or the groups) which resemble each other inhabit the same
country, the same district, and in most cases are to be found together
on the very same spot.
The second law is, that these resemblances are not indiscriminate, but
are limited to certain groups, which in every case are abundant in
species and individuals, and can often be ascertained to have some
special protection.
The third law is, that the species which resemble or "mimic" these
dominant groups, are comparatively less abundant in individuals, and are
often very rare.
These laws will be found to hold good, in all the cases of true mimicry
among various classes of animals to which we have now to call the
attention of our readers.
_Mimicry among Lepidoptera._
As it is among butterflies that instances of mimicry are most numerous
and most striking, an account of some of the more prominent examples in
this group will first be given. There is in South America an extensive
family of these insects, the Heliconidæ, which are in many respects very
remarkable. They are so abundant and characteristic in all the woody
portions of the American tropics, that in almost every locality they
will be seen more frequently than any other butterflies. They are
distinguished by very elongate wings, body, and antennæ, and are
exceedingly beautiful and varied in their colours; spots and patches of
yellow, red, or pure white upon a black, blue, or brown ground, being
most general. They frequent the forests chiefly, and all fly slowly and
weakly; yet although they are so conspicuous, and could certainly be
caught by insectivorous birds more easily than almost any other
insects, their great abundance all over the wide region they inhabit
shows that they are not so persecuted. It is to be especially remarked
also, that they possess no adaptive colouring to protect them during
repose, for the under side of their wings presents the same, or at least
an equally conspicuous colouring as the upper side; and they may be
observed after sunset suspended at the end of twigs and leaves where
they have taken up their station for the night, fully exposed to the
attacks of enemies if they have any. These beautiful insects possess,
however, a strong pungent semi-aromatic or medicinal odour, which seems
to pervade all the juices of their system. When the entomologist
squeezes the breast of one of them between his fingers to kill it, a
yellow liquid exudes which stains the skin, and the smell of which can
only be got rid of by time and repeated washings. Here we have probably
the cause of their immunity from attack, since there is a great deal of
evidence to show that certain insects are so disgusting to birds that
they will under no circumstances touch them. Mr. Stainton has observed
that a brood of young turkeys greedily devoured all the worthless moths
he had amassed in a night's "sugaring," yet one after another seized and
rejected a single white moth which happened to be among them. Young
pheasants and partridges which eat many kinds of caterpillars seem to
have an absolute dread of that of the common currant moth, which they
will never touch, and tomtits as well as other small birds appear never
to eat the same species. In the case of the Heliconidæ, however, we
have some direct evidence to the same effect. In the Brazilian forests
there are great numbers of insectivorous birds--as jacamars, trogons,
and puffbirds--which catch insects on the wing, and that they destroy
many butterflies is indicated by the fact that the wings of these
insects are often found on the ground where their bodies have been
devoured. But among these there are no wings of Heliconidæ, while those
of the large showy Nymphalidæ, which have a much swifter flight, are
often met with. Again, a gentleman who had recently returned from Brazil
stated at a meeting of the Entomological Society that he once observed a
pair of puffbirds catching butterflies, which they brought to their nest
to feed their young; yet during half an hour they never brought one of
the Heliconidæ, which were flying lazily about in great numbers, and
which they could have captured more easily than any others. It was this
circumstance that led Mr. Belt to observe them so long, as he could not
understand why the most common insects should be altogether passed by.
Mr. Bates also tells us that he never saw them molested by lizards or
predacious flies, which often pounce on other butterflies.
If, therefore, we accept it as highly probable (if not proved) that the
Heliconidæ are very greatly protected from attack by their peculiar
odour and taste, we find it much more easy to understand their chief
characteristics--their great abundance, their slow flight, their gaudy
colours, and the entire absence of protective tints on their under
surfaces. This property places them somewhat in the position of those
curious wingless birds of oceanic islands, the dodo, the apteryx, and
the moas, which are with great reason supposed to have lost the power of
flight on account of the absence of carnivorous quadrupeds. Our
butterflies have been protected in a different way, but quite as
effectually; and the result has been that as there has been nothing to
escape from, there has been no weeding out of slow flyers, and as there
has been nothing to hide from, there has been no extermination of the
bright-coloured varieties, and no preservation of such as tended to
assimilate with surrounding objects.
Now let us consider how this kind of protection must act. Tropical
insectivorous birds very frequently sit on dead branches of a lofty
tree, or on those which overhang forest paths, gazing intently around,
and darting off at intervals to seize an insect at a considerable
distance, which they generally return to their station to devour. If a
bird began by capturing the slow-flying, conspicuous Heliconidæ, and
found them always so disagreeable that it could not eat them, it would
after a very few trials leave off catching them at all; and their whole
appearance, form, colouring, and mode of flight is so peculiar, that
there can be little doubt birds would soon learn to distinguish them at
a long distance, and never waste any time in pursuit of them. Under
these circumstances, it is evident that any other butterfly of a group
which birds were accustomed to devour, would be almost equally well
protected by closely resembling a Heliconia externally, as if it
acquired also the disagreeable odour; always supposing that there were
only a few of them among a great number of the Heliconias. If the birds
could not distinguish the two kinds externally, and there were on the
average only one eatable among fifty uneatable, they would soon give up
seeking for the eatable ones, even if they knew them to exist. If, on
the other hand, any particular butterfly of an eatable group acquired
the disagreeable taste of the Heliconias while it retained the
characteristic form and colouring of its own group, this would be really
of no use to it whatever; for the birds would go on catching it among
its eatable allies (compared with which it would rarely occur), it would
be wounded and disabled, even if rejected, and its increase would thus
be as effectually checked as if it were devoured. It is important,
therefore, to understand that if any one genus of an extensive family of
eatable butterflies were in danger of extermination from insect-eating
birds, and if two kinds of variation were going on among them, some
individuals possessing a slightly disagreeable taste, others a slight
resemblance to the Heliconidæ, this latter quality would be much more
valuable than the former. The change in flavour would not at all prevent
the variety from being captured as before, and it would almost certainly
be thoroughly disabled before being rejected. The approach in colour and
form to the Heliconidæ, however, would be at the very first a positive,
though perhaps a slight advantage; for although at short distances this
variety would be easily distinguished and devoured, yet at a longer
distance it might be mistaken for one of the uneatable group, and so be
passed by and gain another day's life, which might in many cases be
sufficient for it to lay a quantity of eggs and leave a numerous
progeny, many of which would inherit the peculiarity which had been the
safeguard of their parent.
Now, this hypothetical case is exactly realized in South America. Among
the white butterflies forming the family Pieridæ (many of which do not
greatly differ in appearance from our own cabbage butterflies) is a
genus of rather small size (Leptalis), some species of which are white
like their allies, while the larger number exactly resemble the
Heliconidæ in the form and colouring of the wings. It must always be
remembered that these two families are as absolutely distinguished from
each other by structural characters as are the carnivora and the
ruminants among quadrupeds, and that an entomologist can always
distinguish the one from the other by the structure of the feet, just as
certainly as a zoologist can tell a bear from a buffalo by the skull or
by a tooth. Yet the resemblance of a species of the one family to
another species in the other family was often so great, that both Mr.
Bates and myself were many times deceived at the time of capture, and
did not discover the distinctness of the two insects till a closer
examination detected their essential differences. During his residence
of eleven years in the Amazon valley, Mr. Bates found a number of
species or varieties of Leptalis, each of which was a more or less exact
copy of one of the Heliconidæ of the district it inhabited; and the
results of his observations are embodied in a paper published in the
Linnean Transactions, in which he first explained the phenomena of
"mimicry" as the result of natural selection, and showed its identity in
cause and purpose with protective resemblance to vegetable or inorganic
forms.
The imitation of the Heliconidæ by the Leptalides is carried out to a
wonderful degree in form as well as in colouring. The wings have become
elongated to the same extent, and the antennæ and abdomen have both
become lengthened, to correspond with the unusual condition in which
they exist in the former family. In colouration there are several types
in the different genera of Heliconidæ. The genus Mechanitis is generally
of a rich semi-transparent brown, banded with black and yellow; Methona
is of large size, the wings transparent like horn, and with black
transverse bands; while the delicate Ithomias are all more or less
transparent, with black veins and borders, and often with marginal and
transverse bands of orange red. These different forms are all copied by
the various species of Leptalis, every band and spot and tint of colour,
and the various degrees of transparency, being exactly reproduced. As if
to derive all the benefit possible from this protective mimicry, the
habits have become so modified that the Leptalides generally frequent
the very same spots as their models, and have the same mode of flight;
and as they are always very scarce (Mr. Bates estimating their numbers
at about one to a thousand of the group they resemble), there is hardly
a possibility of their being found out by their enemies. It is also
very remarkable that in almost every case the particular Ithomias and
other species of Heliconidæ which they resemble, are noted as being very
common species, swarming in individuals, and found over a wide range of
country. This indicates antiquity and permanence in the species, and is
exactly the condition most essential both to aid in the development of
the resemblance, and to increase its utility.
But the Leptalides are not the only insects who have prolonged their
existence by imitating the great protected group of Heliconidæ;--a genus
of quite another family of most lovely small American butterflies, the
Erycinidæ, and three genera of diurnal moths, also present species which
often mimic the same dominant forms, so that some, as Ithomia ilerdina
of St. Paulo, for instance, have flying with them a few individuals of
three widely different insects, which are yet disguised with exactly the
same form, colour, and markings, so as to be quite undistinguishable
when upon the wing. Again, the Heliconidæ are not the only group that
are imitated, although they are the most frequent models. The black and
red group of South American Papilios, and the handsome Erycinian genus
Stalachtis, have also a few who copy them; but this fact offers no
difficulty, since these two groups are almost as dominant as the
Heliconidæ. They both fly very slowly, they are both conspicuously
coloured, and they both abound in individuals; so that there is every
reason to believe that they possess a protection of a similar kind to
the Heliconidæ, and that it is therefore equally an advantage to other
insects to be mistaken for them. There is also another extraordinary
fact that we are not yet in a position clearly to comprehend: some
groups of the Heliconidæ themselves mimic other groups. Species of
Heliconia mimic Mechanitis, and every species of Napeogenes mimics some
other Heliconideous butterfly. This would seem to indicate that the
distasteful secretion is not produced alike by all members of the
family, and that where it is deficient protective imitation comes into
play. It is this, perhaps, that has caused such a general resemblance
among the Heliconidæ, such a uniformity of type with great diversity of
colouring, since any aberration causing an insect to cease to look like
one of the family would inevitably lead to its being attacked, wounded,
and exterminated, even although it was not eatable.
In other parts of the world an exactly parallel series of facts have
been observed. The Danaidæ and the Acræidæ of the Old World tropics form
in fact one great group with the Heliconidæ. They have the same general
form, structure, and habits: they possess the same protective odour, and
are equally abundant in individuals, although not so varied in colour,
blue and white spots on a black ground being the most general pattern.
The insects which mimic these are chiefly Papilios, and Diadema, a genus
allied to our peacock and tortoiseshell butterflies. In tropical Africa
there is a peculiar group of the genus Danais, characterized by
dark-brown and bluish-white colours, arranged in bands or stripes. One
of these, Danais niavius, is exactly imitated both by Papilio hippocoon
and by Diadema anthedon; another, Danais echeria, by Papilio cenea; and
in Natal a variety of the Danais is found having a white spot at the tip
of wings, accompanied by a variety of the Papilio bearing a
corresponding white spot. Acræa gea is copied in its very peculiar style
of colouration by the female of Papilio cynorta, by Panopæa hirce, and
by the female of Elymnias phegea. Acræa euryta of Calabar has a female
variety of Panopea hirce from the same place which exactly copies it;
and Mr. Trimen, in his paper on Mimetic Analogies among African
Butterflies, published in the Transactions of the Linnæan Society for
1868, gives a list of no less than sixteen species and varieties of
Diadema and its allies, and ten of Papilio, which in their colour and
markings are perfect mimics of species or varieties of Danais or Acræa
which inhabit the same districts.
Passing on to India, we have Danais tytia, a butterfly with
semi-transparent bluish wings and a border of rich reddish brown. This
remarkable style of colouring is exactly reproduced in Papilio agestor
and in Diadema nama, and all three insects not unfrequently come
together in collections made at Darjeeling. In the Philippine Islands
the large and curious Idea leuconöe with its semi-transparent white
wings, veined and spotted with black, is copied by the rare Papilio
idæoides from the same islands.
In the Malay archipelago the very common and beautiful Euploea midamus
is so exactly mimicked by two rare Papilios (P. paradoxa and P. ænigma)
that I generally caught them under the impression that they were the
more common species; and the equally common and even more beautiful
Euploea rhadamanthus, with its pure white bands and spots on a ground of
glossy blue and black, is reproduced in the Papilio caunus. Here also
there are species of Diadema imitating the same group in two or three
instances; but we shall have to adduce these further on in connexion
with another branch of the subject.
It has been already mentioned that in South America there is a group of
Papilios which have all the characteristics of a protected race, and
whose peculiar colours and markings are imitated by other butterflies
not so protected. There is just such a group also in the East, having
very similar colours and the same habits, and these also are mimicked by
other species in the same genus not closely allied to them, and also by
a few of other families. Papilio hector, a common Indian butterfly of a
rich black colour spotted with crimson, is so closely copied by Papilio
romulus, that the latter insect has been thought to be its female. A
close examination shows, however, that it is essentially different, and
belongs to another section of the genus. Papilio antiphus and P.
diphilus, black swallow-tailed butterflies with cream-coloured spots,
are so well imitated by varieties of P. theseus, that several writers
have classed them as the same species. Papilio liris, found only in the
island of Timor, is accompanied there by P. ænomaus, the female of
which so exactly resembles it that they can hardly be separated in the
cabinet, and on the wing are quite undistinguishable. But one of the
most curious cases is the fine yellow-spotted Papilio cöon, which is
unmistakeably imitated by the female tailed form of Papilio memnon.
These are both from Sumatra; but in North India P. cöon is replaced by
another species, which has been named P. doubledayi, having red spots
instead of yellow; and in the same district the corresponding female
tailed form of Papilio androgeus, sometimes considered a variety of P.
memnon, is similarly red-spotted. Mr. Westwood has described some
curious day-flying moths (Epicopeia) from North India, which have the
form and colour of Papilios of this section, and two of these are very
good imitations of Papilio polydorus and Papilio varuna, also from North
India.
Almost all these cases of mimicry are from the tropics, where the forms
of life are more abundant, and where insect development especially is of
unchecked luxuriance; but there are also one or two instances in
temperate regions. In North America, the large and handsome red and
black butterfly Danais erippus is very common; and the same country is
inhabited by Limenitis archippus, which closely resembles the Danais,
while it differs entirely from every species of its own genus.
The only case of probable mimicry in our own country is the
following:--A very common white moth (Spilosoma menthastri) was found by
Mr. Stainton to be rejected by young turkeys among hundreds of other
moths on which they greedily fed. Each bird in succession took hold of
this moth and threw it down again, as if too nasty to eat. Mr. Jenner
Weir also found that this moth was refused by the Bullfinch, Chaffinch,
Yellow Hammer, and Red Bunting, but eaten after much hesitation by the
Robin. We may therefore fairly conclude that this species would be
disagreeable to many other birds, and would thus have an immunity from
attack, which may be the cause of its great abundance and of its
conspicuous white colour. Now it is a curious thing that there is
another moth, Diaphora mendica, which appears about the same time, and
whose female only is white. It is about the same size as Spilosoma
menthastri, and sufficiently resembles it in the dusk, and this moth is
much less common. It seems very probable, therefore, that these species
stand in the same relation to each other as the mimicking butterflies of
various families do to the Heliconidæ and Danaidæ. It would be very
interesting to experiment on all white moths, to ascertain if those
which are most common are generally rejected by birds. It may be
anticipated that they would be so, because white is the most conspicuous
of all colours for nocturnal insects, and had they not some other
protection would certainly be very injurious to them.
_Lepidoptera mimicking other Insects._
In the preceding cases we have found Lepidoptera imitating other species
of the same order, and such species only as we have good reason to
believe were free from the attacks of many insectivorous creatures; but
there are other instances in which they altogether lose the external
appearance of the order to which they belong, and take on the dress of
bees or wasps--insects which have an undeniable protection in their
stings. The Sesiidæ and Ægeriidæ, two families of day-flying moths, are
particularly remarkable in this respect, and a mere inspection of the
names given to the various species shows how the resemblance has struck
everyone. We have apiformis, vespiforme, ichneumoniforme, scoliæforme,
sphegiforme (bee-like, wasp-like, ichneumon-like, &c.) and many others,
all indicating a resemblance to stinging Hymenoptera. In Britain we may
particularly notice Sesia bombiliformis, which very closely resembles
the male of the large and common humble bee, Bombus hortorum; Sphecia
craboniforme, which is coloured like a hornet, and is (on the authority
of Mr. Jenner Weir) much more like it when alive than when in the
cabinet, from the way in which it carries its wings; and the currant
clear-wing, Trochilium tipuliforme, which resembles a small black wasp
(Odynerus sinuatus) very abundant in gardens at the same season. It has
been so much the practice to look upon these resemblances as mere
curious analogies playing no part in the economy of nature, that we have
scarcely any observations of the habits and appearance when alive of the
hundreds of species of these groups in various parts of the world, or
how far they are accompanied by Hymenoptera, which they specifically
resemble. There are many species in India (like those figured by
Professor Westwood in his "Oriental Entomology") which have the hind
legs very broad and densely hairy, so as exactly to imitate the
brush-legged bees (Scopulipedes) which abound in the same country. In
this case we have more than mere resemblance of colour, for that which
is an important functional structure in the one group is imitated in
another whose habits render it perfectly useless.
_Mimicry among Beetles._
It may fairly be expected that if these imitations of one creature by
another really serve as a protection to weak and decaying species,
instances of the same kind will be found among other groups than the
Lepidoptera; and such is the case, although they are seldom so prominent
and so easily recognised as those already pointed out as occurring in
that order. A few very interesting examples may, however, be pointed out
in most of the other orders of insects. The Coleoptera or beetles that
imitate other Coleoptera of distinct groups are very numerous in
tropical countries, and they generally follow the laws already laid down
as regulating these phenomena. The insects which others imitate always
have a special protection, which leads them to be avoided as dangerous
or uneatable by small insectivorous animals; some have a disgusting
taste (analogous to that of the Heliconidæ); others have such a hard and
stony covering that they cannot be crushed or digested; while a third
set are very active, and armed with powerful jaws, as well as having
some disagreeable secretion. Some species of Eumorphidæ and Hispidæ,
small flat or hemispherical beetles which are exceedingly abundant, and
have a disagreeable secretion, are imitated by others of the very
distinct group of Longicornes (of which our common musk-beetle may be
taken as an example). The extraordinary little Cyclopeplus batesii,
belongs to the same sub-family of this group as the Onychocerus scorpio
and O. concentricus, which have already been adduced as imitating with
such wonderful accuracy the bark of the trees they habitually frequent;
but it differs totally in outward appearance from every one of its
allies, having taken upon itself the exact shape and colouring of a
globular Corynomalus, a little stinking beetle with clubbed antennæ. It
is curious to see how these clubbed antennæ are imitated by an insect
belonging to a group with long slender antennæ. The sub-family
Anisocerinæ, to which Cyclopeplus belongs, is characterised by all its
members possessing a little knob or dilatation about the middle of the
antennæ. This knob is considerably enlarged in C. batesii, and the
terminal portion of the antennæ beyond it is so small and slender as to
be scarcely visible, and thus an excellent substitute is obtained for
the short clubbed antennæ of the Corynomalus. Erythroplatis corallifer
is another curious broad flat beetle, that no one would take for a
Longicorn, since it almost exactly resembles Cephalodonta spinipes, one
of the commonest of the South American Hispidæ; and what is still more
remarkable, another Longicorn of a distinct group, Streptolabis
hispoides, was found by Mr. Bates, which resembles the same insect with
equal minuteness,--a case exactly parallel to that among butterflies,
where species of two or three distinct groups mimicked the same
Heliconia. Many of the soft-winged beetles (Malacoderms) are excessively
abundant in individuals, and it is probable that they have some similar
protection, more especially as other species often strikingly resemble
them. A Longicorn beetle, Pæciloderma terminale, found in Jamaica, is
coloured exactly in the same way as a Lycus (one of the Malacoderms)
from the same island. Eroschema poweri, a Longicorn from Australia,
might certainly be taken for one of the same group, and several species
from the Malay Islands are equally deceptive. In the Island of Celebes I
found one of this group, having the whole body and elytra of a rich deep
blue colour, with the head only orange; and in company with it an insect
of a totally different family (Eucnemidæ) with identically the same
colouration, and of so nearly the same size and form as to completely
puzzle the collector on every fresh occasion of capturing them. I have
been recently informed by Mr. Jenner Weir, who keeps a variety of small
birds, that none of them will touch our common "soldiers and sailors"
(species of Malacoderms), thus confirming my belief that they were a
protected group, founded on the fact of their being at once very
abundant, of conspicuous colours, and the objects of mimicry.
There are a number of the larger tropical weevils which have the
elytra and the whole covering of the body so hard as to be a great
annoyance to the entomologist, because in attempting to transfix them
the points of his pins are constantly turned. I have found it necessary
in these cases to drill a hole very carefully with the point of a
sharp penknife before attempting to insert a pin. Many of the fine
long-antennæd Anthribidæ (an allied group) have to be treated in the
same way. We can easily understand that after small birds have in vain
attempted to eat these insects, they should get to know them by sight,
and ever after leave them alone, and it will then be an advantage for
other insects which are comparatively soft and eatable, to be mistaken
for them. We need not be surprised, therefore, to find that there are
many Longicorns which strikingly resemble the "hard beetles" of their
own district. In South Brazil, Acanthotritus dorsalis is strikingly
like a Curculio of the hard genus Heiliplus, and Mr. Bates assures me
that he found Gymnocerus cratosomoides (a Longicorn) on the same tree
with a hard Cratosomus (a weevil), which it exactly mimics. Again, the
pretty Longicorn, Phacellocera batesii, mimics one of the hard
Anthribidæ of the genus Ptychoderes, having long slender antennæ. In the
Moluccas we find Cacia anthriboides, a small Longicorn which might be
easily mistaken for a very common species of Anthribidæ found in the
same districts; and the very rare Capnolymma stygium closely imitates
the common Mecocerus gazella, which abounded where it was taken. Doliops
curculionoides and other allied Longicorns from the Philippine Islands
most curiously resemble, both in form and colouring, the brilliant
Pachyrhynchi,--Curculionidæ, which are almost peculiar to that group of
islands. The remaining family of Coleoptera most frequently imitated is
the Cicindelidæ. The rare and curious Longicorn, Collyrodes lacordairei,
has exactly the form and colouring of the genus Collyris, while an
undescribed species of Heteromera is exactly like a Therates, and was
taken running on the trunks of trees, as is the habit of that group.
There is one curious example of a Longicorn mimicking a Longicorn, like
the Papilios and Heliconidæ which mimic their own allies. Agnia
fasciata, belonging to the sub-family Hypselominæ, and Nemophas grayi,
belonging to the Lamiinæ, were taken in Amboyna on the same fallen tree
at the same time, and were supposed to be the same species till they
were more carefully examined, and found to be structurally quite
different. The colouring of these insects is very remarkable, being rich
steel-blue black, crossed by broad hairy bands of orange buff, and out
of the many thousands of known species of Longicorns they are probably
the only two which are so coloured. The Nemophas grayi is the larger,
stronger, and better armed insect, and belongs to a more widely spread
and dominant group, very rich in species and individuals, and is
therefore most probably the subject of mimicry by the other species.
_Beetles mimicking other Insects._
We will now adduce a few cases in which beetles imitate other insects,
and insects of other orders imitate beetles.
Charis melipona, a South American Longicorn of the family Necydalidæ,
has been so named from its resemblance to a small bee of the genus
Melipona. It is one of the most remarkable cases of mimicry, since the
beetle has the thorax and body densely hairy like the bee, and the legs
are tufted in a manner most unusual in the order Coleoptera. Another
Longicorn, Odontocera odyneroides, has the abdomen banded with yellow,
and constricted at the base, and is altogether so exactly like a small
common wasp of the genus Odynerus, that Mr. Bates informs us he was
afraid to take it out of his net with his fingers for fear of being
stung. Had Mr. Bates's taste for insects been less omnivorous than it
was, the beetle's disguise might have saved it from his pin, as it had
no doubt often done from the beak of hungry birds. A larger insect,
Sphecomorpha chalybea, is exactly like one of the large metallic blue
wasps, and like them has the abdomen connected with the thorax by a
pedicel, rendering the deception most complete and striking. Many
Eastern species of Longicorns of the genus Oberea, when on the wing
exactly resemble Tenthredinidæ, and many of the small species of
Hesthesis run about on timber, and cannot be distinguished from ants.
There is one genus of South American Longicorns that appears to mimic
the shielded bugs of the genus Scutellera. The Gymnocerous capucinus is
one of these, and is very like Pachyotris fabricii, one of the
Scutelleridæ. The beautiful Gymnocerous dulcissimus is also very like
the same group of insects, though there is no known species that exactly
corresponds to it; but this is not to be wondered at, as the tropical
Hemiptera have been comparatively so little cared for by collectors.
_Insects mimicking Species of other Orders._
The most remarkable case of an insect of another order mimicking a
beetle is that of the Condylodera tricondyloides, one of the cricket
family from the Philippine Islands, which is so exactly like a
Tricondyla (one of the tiger beetles), that such an experienced
entomologist as Professor Westwood placed it among them in his cabinet,
and retained it there a long time before he discovered his mistake! Both
insects run along the trunks of trees, and whereas Tricondylas are very
plentiful, the insect that mimics it is, as in all other cases, very
rare. Mr. Bates also informs us that he found at Santarem on the Amazon,
a species of locust which mimicked one of the tiger beetles of the genus
Odontocheila, and was found on the same trees which they frequented.
There are a considerable number of Diptera, or two-winged flies, that
closely resemble wasps and bees, and no doubt derive much benefit from
the wholesome dread which those insects excite. The Midas dives, and
other species of large Brazilian flies, have dark wings and metallic
blue elongate bodies, resembling the large stinging Sphegidæ of the same
country; and a very large fly of the genus Asilus has black-banded
wings and the abdomen tipped with rich orange, so as exactly to resemble
the fine bee Euglossa dimidiata, and both are found in the same parts of
South America. We have also in our own country species of Bombylius
which are almost exactly like bees. In these cases the end gained by the
mimicry is no doubt freedom from attack, but it has sometimes an
altogether different purpose. There are a number of parasitic flies
whose larvæ feed upon the larvæ of bees, such as the British genus
Volucella and many of the tropical Bombylii, and most of these are
exactly like the particular species of bee they prey upon, so that they
can enter their nests unsuspected to deposit their eggs. There are also
bees that mimic bees. The cuckoo bees of the genus Nomada are parasitic
on the Andrenidæ, and they resemble either wasps or species of Andrena;
and the parasitic humble-bees of the genus Apathus almost exactly
resemble the species of humble-bees in whose nests they are reared. Mr.
Bates informs us that he found numbers of these "cuckoo" bees and flies
on the Amazon, which all wore the livery of working bees peculiar to the
same country.
There is a genus of small spiders in the tropics which feed on ants, and
they are exactly like ants themselves, which no doubt gives them more
opportunity of seizing their prey; and Mr. Bates found on the Amazon a
species of Mantis which exactly resembled the white ants which it fed
upon, as well as several species of crickets (Scaphura), which resembled
in a wonderful manner different sand-wasps of large size, which are
constantly on the search for crickets with which to provision their
nests.
Perhaps the most wonderful case of all is the large caterpillar
mentioned by Mr. Bates, which startled him by its close resemblance to a
small snake. The first three segments behind the head were dilatable at
the will of the insect, and had on each side a large black pupillated
spot, which resembled the eye of the reptile. Moreover, it resembled a
poisonous viper, not a harmless species of snake, as was proved by the
imitation of keeled scales on the crown produced by the recumbent feet,
as the caterpillar threw itself backward!
The attitudes of many of the tropical spiders are most extraordinary and
deceptive, but little attention has been paid to them. They often mimic
other insects, and some, Mr. Bates assures us, are exactly like flower
buds, and take their station in the axils of leaves, where they remain
motionless waiting for their prey.
_Cases of Mimicry among the Vertebrata._
Having thus shown how varied and extraordinary are the modes in which
mimicry occurs among insects, we have now to enquire if anything of the
same kind is to be observed among vertebrated animals. When we consider
all the conditions necessary to produce a good deceptive imitation, we
shall see at once that such can very rarely occur in the higher animals,
since they possess none of those facilities for the almost infinite
modifications of external form which exist in the very nature of insect
organization. The outer covering of insects being more or less solid
and horny, they are capable of almost any amount of change of form and
appearance without any essential modification internally. In many groups
the wings give much of the character, and these organs may be much
modified both in form and colour without interfering with their special
functions. Again, the number of species of insects is so great, and
there is such diversity of form and proportion in every group, that the
chances of an accidental approximation in size, form, and colour, of one
insect to another of a different group, are very considerable; and it is
these chance approximations that furnish the basis of mimicry, to be
continually advanced and perfected by the survival of those varieties
only which tend in the right direction.
In the Vertebrata, on the contrary, the skeleton being internal the
external form depends almost entirely on the proportions and arrangement
of that skeleton, which again is strictly adapted to the functions
necessary for the well-being of the animal. The form cannot therefore be
rapidly modified by variation, and the thin and flexible integument will
not admit of the development of such strange protuberances as occur
continually in insects. The number of species of each group in the same
country is also comparatively small, and thus the chances of that first
accidental resemblance which is necessary for natural selection to work
upon are much diminished. We can hardly see the possibility of a mimicry
by which the elk could escape from the wolf, or the buffalo from the
tiger. There is, however, in one group of Vertebrata such a general
similarity of form, that a very slight modification, if accompanied by
identity of colour, would produce the necessary amount of resemblance;
and at the same time there exist a number of species which it would be
advantageous for others to resemble, since they are armed with the most
fatal weapons of offence. We accordingly find that reptiles furnish us
with a very remarkable and instructive case of true mimicry.
_Mimicry among Snakes._
There are in tropical America a number of venomous snakes of the genus
Elaps, which are ornamented with brilliant colours disposed in a
peculiar manner. The ground colour is generally bright red, on which are
black bands of various widths and sometimes divided into two or three by
yellow rings. Now, in the same country are found several genera of
harmless snakes, having no affinity whatever with the above, but
coloured exactly the same. For example, the poisonous Elaps fulvius
often occurs in Guatemala with simple black bands on a coral-red ground;
and in the same country is found the harmless snake Pliocerus equalis,
coloured and banded in identically the same manner. A variety of Elaps
corallinus has the black bands narrowly bordered with yellow on the same
red ground colour, and a harmless snake, Homalocranium semicinctum, has
exactly the same markings, and both are found in Mexico. The deadly
Elaps lemniscatus has the black bands very broad, and each of them
divided into three by narrow yellow rings; and this again is exactly
copied by a harmless snake, Pliocerus elapoides, which is found along
with its model in Mexico.
But, more remarkable still, there is in South America a third group of
snakes, the genus Oxyrhopus, doubtfully venomous, and having no
immediate affinity with either of the preceding, which has also the same
curious distribution of colours, namely, variously disposed rings of
red, yellow, and black; and there are some cases in which species of all
three of these groups similarly marked inhabit the same district. For
example, Elaps mipartitus has single black rings very close together. It
inhabits the west side of the Andes, and in the same districts occur
Pliocerus euryzonus and Oxyrhopus petolarius, which exactly copy its
pattern. In Brazil Elaps lemniscatus is copied by Oxyrhopus trigeminus,
both having black rings disposed in threes. In Elaps hemiprichii the
ground colour appears to be black, with alternations of two narrow
yellow bands and a broader red one; and of this pattern again we have an
exact double in Oxyrhopus formosus, both being found in many localities
of tropical South America.
What adds much to the extraordinary character of these resemblances is
the fact, that nowhere in the world but in America are there any snakes
at all which have this style of colouring. Dr. Gunther, of the British
Museum, who has kindly furnished some of the details here referred to,
assures me that this is the case; and that red, black, and yellow rings
occur together on no other snakes in the world but on Elaps and the
species which so closely resemble it. In all these cases, the size and
form as well as the colouration, are so much alike, that none but a
naturalist would distinguish the harmless from the poisonous species.
Many of the small tree-frogs are no doubt also mimickers. When seen in
their natural attitudes, I have been often unable to distinguish them
from beetles or other insects sitting upon leaves, but regret to say I
neglected to observe what species or groups they most resembled, and the
subject does not yet seem to have attracted the attention of naturalists
abroad.
_Mimicry among Birds._
In the class of birds there are a number of cases that make some
approach to mimicry, such as the resemblance of the cuckoos, a weak and
defenceless group of birds, to hawks and Gallinaceæ. There is, however,
one example which goes much further than this, and seems to be of
exactly the same nature as the many cases of insect mimicry which have
been already given. In Australia and the Moluccas there is a genus of
honeysuckers called Tropidorhynchus, good sized birds, very strong and
active, having powerful grasping claws and long, curved, sharp beaks.
They assemble together in groups and small flocks, and they have a very
loud bawling note, which can be heard at a great distance, and serves to
collect a number together in time of danger. They are very plentiful
and very pugnacious, frequently driving away crows, and even hawks,
which perch on a tree where a few of them are assembled. They are all of
rather dull and obscure colours. Now in the same countries there is a
group of orioles, forming the genus Mimeta, much weaker birds, which
have lost the gay colouring of their allies the golden orioles, being
usually olive-green or brown; and in several cases these most curiously
resemble the Tropidorhynchus of the same island. For example, in the
island of Bouru is found the Tropidorhynchus bouruensis, of a dull
earthy colour, and the Mimeta bouruensis, which resembles it in the
following particulars:--The upper and under surfaces of the two birds
are exactly of the same tints of dark and light brown; the
Tropidorhynchus has a large bare black patch round the eyes; this is
copied in the Mimeta by a patch of black feathers. The top of the head
of the Tropidorhynchus has a scaly appearance from the narrow
scale-formed feathers, which are imitated by the broader feathers of the
Mimeta having a dusky line down each. The Tropidorhynchus has a pale
ruff formed of curious recurved feathers on the nape (which has given
the whole genus the name of Friar birds); this is represented in the
Mimeta by a pale band in the same position. Lastly, the bill of the
Tropidorhynchus is raised into a protuberant keel at the base, and the
Mimeta has the same character, although it is not a common one in the
genus. The result is, that on a superficial examination the birds are
identical, although they have important structural differences, and
cannot be placed near each other in any natural arrangement. As a proof
that the resemblance is really deceptive, it may be mentioned that the
Mimeta is figured and described as a honeysucker in the costly "Voyage
de l'Astrolabe," under the name of Philedon bouruensis!
Passing to the island of Ceram, we find allied species of both genera.
The Tropidorhynchus subcornutus is of an earthy brown colour washed with
yellow ochre, with bare orbits, dusky cheeks, and the usual pale
recurved nape-ruff. The Mimeta forsteni is absolutely identical in the
tints of every part of the body, the details of which are imitated in
the same manner as in the Bouru birds already described. In two other
islands there is an approximation towards mimicry, although it is not so
perfect as in the two preceding cases. In Timor the Tropidorhynchus
timoriensis is of the usual earthy brown above, with the nape-ruff very
prominent, the cheeks black, the throat nearly white, and the whole
under surface pale whitish brown. These various tints are all well
reproduced in Mimeta virescens, the chief want of exact imitation being
that the throat and breast of the Tropidorhynchus has a very scaly
appearance, being covered with rigid pointed feathers which are not
imitated in the Mimeta, although there are signs of faint dusky spots
which may easily furnish the groundwork of a more exact imitation by the
continued survival of favourable variations in the same direction. There
is also a large knob at the base of the bill of the Tropidorhynchus
which is not at all imitated by the Mimeta. In the island of Morty
(north of Gilolo) there exists the Tropidorhynchus fuscicapillus, of a
dark sooty brown colour, especially on the head, while the under parts
are rather lighter, and the characteristic ruff of the nape is wanting.
Now it is curious that in the adjacent island of Gilolo should be found
the Mimeta phæochromus, the upper surface of which is of exactly the
same dark sooty tint as the Tropidorhynchus, and is the only known
species that is of such a dark colour. The under side is not quite light
enough, but it is a good approximation. This Mimeta is a rare bird, and
may very probably exist in Morty, though not yet found there; or, on the
other hand, recent changes in physical geography may have led to the
restriction of the Tropidorhynchus to that island, where it is very
common.
Here, then, we have two cases of perfect mimicry and two others of good
approximation, occurring between species of the same two genera of
birds; and in three of these cases the pairs that resemble each other
are found together in the same island, and to which they are peculiar.
In all these cases the Tropidorhynchus is rather larger than the Mimeta,
but the difference is not beyond the limits of variation in species, and
the two genera are somewhat alike in form and proportion. There are, no
doubt, some special enemies by which many small birds are attacked, but
which are afraid of the Tropidorhynchus (probably some of the hawks),
and thus it becomes advantageous for the weak Mimeta to resemble the
strong, pugnacious, noisy, and very abundant Tropidorhynchus.
My friend, Mr. Osbert Salvin, has given me another interesting case of
bird mimicry. In the neighbourhood of Rio Janeiro is found an
insect-eating hawk (Harpagus diodon), and in the same district a
bird-eating hawk (Accipiter pileatus) which closely resembles it. Both
are of the same ashy tint beneath, with the thighs and under
wing-coverts reddish brown, so that when on the wing and seen from below
they are undistinguishable. The curious point, however, is that the
Accipiter has a much wider range than the Harpagus, and in the regions
where the insect-eating species is not found it no longer resembles it,
the under wing-coverts varying to white; thus indicating that the
red-brown colour is kept true by its being useful to the Accipiter to be
mistaken for the insect-eating species, which birds have learnt not to
be afraid of.
_Mimicry among Mammals._
Among the Mammalia the only case which may be true mimicry is that of
the insectivorous genus Cladobates, found in the Malay countries,
several species of which very closely resemble squirrels. The size is
about the same, the long bushy tail is carried in the same way, and the
colours are very similar. In this case the use of the resemblance must
be to enable the Cladobates to approach the insects or small birds on
which it feeds, under the disguise of the harmless fruit-eating
squirrel.
_Objections to Mr. Bates' Theory of Mimicry._
Having now completed our survey of the most prominent and remarkable
cases of mimicry that have yet been noticed, we must say something of
the objections that have been made to the theory of their production
given by Mr. Bates, and which we have endeavoured to illustrate and
enforce in the preceding pages. Three counter explanations have been
proposed. Professor Westwood admits the fact of the mimicry and its
probable use to the insect, but maintains that each species was created
a mimic for the purpose of the protection thus afforded it. Mr. Andrew
Murray, in his paper on the "Disguises of Nature," inclines to the
opinion that similar conditions of food and of surrounding circumstances
have acted in some unknown way to produce the resemblances; and when the
subject was discussed before the Entomological Society of London, a
third objection was added--that heredity or the reversion to ancestral
types of form and colouration, might have produced many of the cases of
mimicry.
Against the special creation of mimicking species there are all the
objections and difficulties in the way of special creation in other
cases, with the addition of a few that are peculiar to it. The most
obvious is, that we have gradations of mimicry and of protective
resemblance--a fact which is strongly suggestive of a natural process
having been at work. Another very serious objection is, that as mimicry
has been shown to be useful only to those species and groups which are
rare and probably dying out, and would cease to have any effect should
the proportionate abundance of the two species be reversed, it follows
that on the special-creation theory the one species must have been
created plentiful, the other rare; and, notwithstanding the many causes
that continually tend to alter the proportions of species, these two
species must have always been specially maintained at their respective
proportions, or the very purpose for which they each received their
peculiar characteristics would have completely failed. A third
difficulty is, that although it is very easy to understand how mimicry
may be brought about by variation and the survival of the fittest, it
seems a very strange thing for a Creator to protect an animal by making
it imitate another, when the very assumption of a Creator implies his
power to create it so as to require no such circuitous protection. These
appear to be fatal objections to the application of the special-creation
theory to this particular case.
The other two supposed explanations, which may be shortly expressed as
the theories of "similar conditions" and of "heredity," agree in making
mimicry, where it exists, an adventitious circumstance not necessarily
connected with the well-being of the mimicking species. But several of
the most striking and most constant facts which have been adduced,
directly contradict both those hypotheses. The law that mimicry is
confined to a few groups only is one of these, for "similar conditions"
must act more or less on all groups in a limited region, and "heredity"
must influence all groups related to each other in an equal degree.
Again, the general fact that those species which mimic others are rare,
while those which are imitated are abundant, is in no way explained by
either of these theories, any more than is the frequent occurrence of
some palpable mode of protection in the imitated species. "Reversion to
an ancestral type" no way explains why the imitator and the imitated
always inhabit the very same district, whereas allied forms of every
degree of nearness and remoteness generally inhabit different countries,
and often different quarters of the globe; and neither it, nor "similar
conditions," will account for the likeness between species of distinct
groups being superficial only--a disguise, not a true resemblance; for
the imitation of bark, of leaves, of sticks, of dung; for the
resemblance between species in different orders, and even different
classes and sub-kingdoms; and finally, for the graduated series of the
phenomena, beginning with a general harmony and adaptation of tint in
autumn and winter moths and in arctic and desert animals, and ending
with those complete cases of detailed mimicry which not only deceive
predacious animals, but puzzle the most experienced insect collectors
and the most learned entomologists.
_Mimicry by Female Insects only._
But there is yet another series of phenomena connected with this
subject, which considerably strengthens the view here adopted, while it
seems quite incompatible with either of the other hypotheses; namely,
the relation of protective colouring and mimicry to the sexual
differences of animals. It will be clear to every one that if two
animals, which as regards "external conditions" and "hereditary
descent," are exactly alike, yet differ remarkably in colouration, one
resembling a protected species and the other not, the resemblance that
exists in one only can hardly be imputed to the influence of external
conditions or as the effect of heredity. And if, further, it can be
proved that the one requires protection more than the other, and that in
several cases it is that one which mimics the protected species, while
the one that least requires protection never does so, it will afford
very strong corroborative evidence that there is a real connexion
between the necessity for protection and the phenomenon of mimicry. Now
the sexes of insects offer us a test of the nature here indicated, and
appear to furnish one of the most conclusive arguments in favour of the
theory that the phenomena termed "mimicry" are produced by natural
selection.
The comparative importance of the sexes varies much in different classes
of animals. In the higher vertebrates, where the number of young
produced at a birth is small and the same individuals breed many years
in succession, the preservation of both sexes is almost equally
important. In all the numerous cases in which the male protects the
female and her offspring, or helps to supply them with food, his
importance in the economy of nature is proportionately increased,
though it is never perhaps quite equal to that of the female. In
insects the case is very different; they pair but once in their lives,
and the prolonged existence of the male is in most cases quite
unnecessary for the continuance of the race. The female, however, must
continue to exist long enough to deposit her eggs in a place adapted for
the development and growth of the progeny. Hence there is a wide
difference in the need for protection in the two sexes; and we should,
therefore, expect to find that in some cases the special protection
given to the female was in the male less in amount or altogether
wanting. The facts entirely confirm this expectation. In the spectre
insects (Phasmidæ) it is often the females alone that so strikingly
resemble leaves, while the males show only a rude approximation. The
male Diadema misippus is a very handsome and conspicuous butterfly,
without a sign of protective or imitative colouring, while the female is
entirely unlike her partner, and is one of the most wonderful cases of
mimicry on record, resembling most accurately the common Danais
chrysippus, in whose company it is often found. So in several species of
South American Pieris, the males are white and black, of a similar type
of colouring to our own "cabbage" butterflies, while the females are
rich yellow and buff, spotted and marked so as exactly to resemble
species of Heliconidæ with which they associate in the forest. In the
Malay archipelago is found a Diadema which had always been considered a
male insect on account of its glossy metallic-blue tints, while its
companion of sober brown was looked upon as the female. I discovered,
however, that the reverse is the case, and that the rich and glossy
colours of the female are imitative and protective, since they cause her
exactly to resemble the common Euploea midamus of the same regions, a
species which has been already mentioned in this essay as mimicked by
another butterfly, Papilio paradoxa. I have since named this interesting
species Diadema anomala (see the Transactions of the Entomological
Society, 1869, p. 285). In this case, and in that of Diadema misippus,
there is no difference in the habits of the two sexes, which fly in
similar localities; so that the influence of "external conditions"
cannot be invoked here as it has been in the case of the South American
Pieris pyrrha and allies, where the white males frequent open sunny
places, while the Heliconia-like females haunt the shades of the forest.
We may impute to the same general cause (the greater need of protection
for the female, owing to her weaker flight, greater exposure to attack,
and supreme importance)--the fact of the colours of female insects being
so very generally duller and less conspicuous than those of the other
sex. And that it is chiefly due to this cause rather than to what Mr.
Darwin terms "sexual selection" appears to be shown by the otherwise
inexplicable fact, that in the groups which have a protection of any
kind independent of concealment, sexual differences of colour are either
quite wanting or slightly developed. The Heliconidæ and Danaidæ,
protected by a disagreeable flavour, have the females as bright and
conspicuous as the males, and very rarely differing at all from them.
The stinging Hymenoptera have the two sexes equally well coloured. The
Carabidæ, the Coccinellidæ, Chrysomelidæ, and the Telephori have both
sexes equally conspicuous, and seldom differing in colours. The
brilliant Curculios, which are protected by their hardness, are
brilliant in both sexes. Lastly, the glittering Cetoniadæ and
Buprestidæ, which seem to be protected by their hard and polished coats,
their rapid motions, and peculiar habits, present few sexual differences
of colour, while sexual selection has often manifested itself by
structural differences, such as horns, spines, or other processes.
_Cause of the dull Colours of Female Birds._
The same law manifests itself in Birds. The female while sitting on her
eggs requires protection by concealment to a much greater extent than
the male; and we accordingly find that in a large majority of the cases
in which the male birds are distinguished by unusual brilliancy of
plumage, the females are much more obscure, and often remarkably
plain-coloured. The exceptions are such as eminently to prove the rule,
for in most cases we can see a very good reason for them. In particular,
there are a few instances among wading and gallinaceous birds in which
the female has decidedly more brilliant colours than the male; but it is
a most curious and interesting fact that in most if not all these cases
the males sit upon the eggs; so that this exception to the usual rule
almost demonstrates that it is because the process of incubation is at
once very important and very dangerous, that the protection of obscure
colouring is developed. The most striking example is that of the gray
phalarope (Phalaropus fulicarius). When in winter plumage, the sexes of
this bird are alike in colouration, but in summer the female is much the
most conspicuous, having a black head, dark wings, and reddish-brown
back, while the male is nearly uniform brown, with dusky spots. Mr.
Gould in his "Birds of Great Britain" figures the two sexes in both
winter and summer plumage, and remarks on the strange peculiarity of the
usual colours of the two sexes being reversed, and also on the still
more curious fact that the "male alone sits on the eggs," which are
deposited on the bare ground. In another British bird, the dotterell,
the female is also larger and more brightly-coloured than the male; and
it seems to be proved that the males assist in incubation even if they
do not perform it entirely, for Mr. Gould tells us, "that they have been
shot with the breast bare of feathers, caused by sitting on the eggs."
The small quail-like birds forming the genus Turnix have also generally
large and bright-coloured females, and we are told by Mr. Jerdon in his
"Birds of India" that "the natives report that during the breeding
season the females desert their eggs and associate in flocks while the
males are employed in hatching the eggs." It is also an ascertained
fact, that the females are more bold and pugnacious than the males. A
further confirmation of this view is to be found in the fact (not
hitherto noticed) that in a large majority of the cases in which bright
colours exist in both sexes incubation takes place in a dark hole or in
a dome-shaped nest. Female kingfishers are often equally brilliant with
the male, and they build in holes in banks. Bee-eaters, trogons,
motmots, and toucans, all build in holes, and in none is there any
difference in the sexes, although they are, without exception, showy
birds. Parrots build in holes in trees, and in the majority of cases
they present no marked sexual difference tending to concealment of the
female. Woodpeckers are in the same category, since though the sexes
often differ in colour, the female is not generally less conspicuous
than the male. Wagtails and titmice build concealed nests, and the
females are nearly as gay as their mates. The female of the pretty
Australian bird Pardalotus punctatus, is very conspicuously spotted on
the upper surface, and it builds in a hole in the ground. The
gay-coloured hang-nests (Icterinæ) and the equally brilliant tanagers
may be well contrasted; for the former, concealed in their covered
nests, present little or no sexual difference of colour--while the
open-nested tanagers have the females dull-coloured and sometimes with
almost protective tints. No doubt there are many individual exceptions
to the rule here indicated, because many and various causes have
combined to determine both the colouration and the habits of birds.
These have no doubt acted and re-acted on each other; and when
conditions have changed one of these characters may often have become
modified, while the other, though useless, may continue by hereditary
descent an apparent exception to what otherwise seems a very general
rule. The facts presented by the sexual differences of colour in birds
and their mode of nesting, are on the whole in perfect harmony with that
law of protective adaptation of colour and form, which appears to have
checked to some extent the powerful action of sexual selection, and to
have materially influenced the colouring of female birds, as it has
undoubtedly done that of female insects.
_Use of the gaudy Colours of many Caterpillars._
Since this essay was first published a very curious difficulty has been
cleared up by the application of the general principle of protective
colouring. Great numbers of caterpillars are so brilliantly marked and
coloured as to be very conspicuous even at a considerable distance, and
it has been noticed that such caterpillars seldom hide themselves. Other
species, however, are green or brown, closely resembling the colours of
the substances on which they feed, while others again imitate sticks,
and stretch themselves out motionless from a twig so as to look like one
of its branches. Now, as caterpillars form so large a part of the food
of birds, it was not easy to understand why any of them should have such
bright colours and markings as to make them specially visible. Mr.
Darwin had put the case to me as a difficulty from another point of
view, for he had arrived at the conclusion that brilliant colouration in
the animal kingdom is mainly due to sexual selection, and this could not
have acted in the case of sexless larvæ. Applying here the analogy of
other insects, I reasoned, that since some caterpillars were evidently
protected by their imitative colouring, and others by their spiny or
hairy bodies, the bright colours of the rest must also be in some way
useful to them. I further thought that as some butterflies and moths
were greedily eaten by birds while others were distasteful to them, and
these latter were mostly of conspicuous colours, so probably these
brilliantly coloured caterpillars were distasteful, and therefore never
eaten by birds. Distastefulness alone would however be of little service
to caterpillars, because their soft and juicy bodies are so delicate,
that if seized and afterwards rejected by a bird they would almost
certainly be killed. Some constant and easily perceived signal was
therefore necessary to serve as a warning to birds never to touch these
uneatable kinds, and a very gaudy and conspicuous colouring with the
habit of fully exposing themselves to view becomes such a signal, being
in strong contrast with the green or brown tints and retiring habits of
the eatable kinds. The subject was brought by me before the
Entomological Society (see Proceedings, March 4th, 1867), in order that
those members having opportunities for making observations might do so
in the following summer; and I also wrote a letter to the _Field_
newspaper, begging that some of its readers would co-operate in making
observations on what insects were rejected by birds, at the same time
fully explaining the great interest and scientific importance of the
problem. It is a curious example of how few of the country readers of
that paper are at all interested in questions of simple natural history,
that I only obtained one answer from a gentleman in Cumberland, who gave
me some interesting observations on the general dislike and abhorrence
of all birds to the "Gooseberry Caterpillar," probably that of the
Magpie-moth (Abraxas grossulariata). Neither young pheasants,
partridges, nor wild-ducks could be induced to eat it, sparrows and
finches never touched it, and all birds to whom he offered it rejected
it with evident dread and abhorrence. It will be seen that these
observations are confirmed by those of two members of the Entomological
Society to whom we are indebted for more detailed information.
In March, 1869, Mr. J. Jenner Weir communicated a valuable series of
observations made during many years, but more especially in the two
preceding summers, in his aviary, containing the following birds of more
or less insectivorous habits:--Robin, Yellow-Hammer, Reed-bunting,
Bullfinch, Chaffinch, Crossbill, Thrush, Tree-Pipit, Siskin, and
Redpoll. He found that hairy caterpillars were uniformly rejected; five
distinct species were quite unnoticed by all his birds, and were allowed
to crawl about the aviary for days with impunity. The spiny caterpillars
of the Tortoiseshell and Peacock butterflies were equally rejected; but
in both these cases Mr. Weir thinks it is the taste, not the hairs or
spines, that are disagreeable, because some very young caterpillars of a
hairy species were rejected although no hairs were developed, and the
smooth pupæ of the above-named butterflies were refused as persistently
as the spined larvæ. In these cases, then, both hairs and spines would
seem to be mere signs of uneatableness.
His next experiments were with those smooth gaily-coloured caterpillars
which never conceal themselves, but on the contrary appear to court
observation. Such are those of the Magpie moth (Abraxas grossulariata),
whose caterpillar is conspicuously white and black spotted--the Diloba
coeruleocephala, whose larvæ is pale yellow with a broad blue or green
lateral band--the Cucullia verbasci, whose larvæ is greenish white with
yellow bands and black spots, and Anthrocera filipendulæ (the six spot
Burnet moth), whose caterpillar is yellow with black spots. These were
given to the birds at various times, sometimes mixed with other kinds of
larvæ which were greedily eaten, but they were in every case rejected
apparently unnoticed, and were left to crawl about till they died.
The next set of observations were on the dull-coloured and protected
larvæ, and the results of numerous experiments are thus summarised by
Mr. Weir. "All caterpillars whose habits are nocturnal, which are dull
coloured, with fleshy bodies and smooth skins, are eaten with the
greatest avidity. Every species of green caterpillar is also much
relished. All Geometræ, whose larvæ resemble twigs as they stand out
from the plant on their anal prolegs, are invariably eaten."
At the same meeting Mr. A. G. Butler, of the British Museum,
communicated the results of his observations with lizards, frogs, and
spiders, which strikingly corroborate those of Mr. Weir. Three green
lizards (Lacerta viridis) which he kept for several years, were very
voracious, eating all kinds of food, from a lemon cheesecake to a
spider, and devouring flies, caterpillars, and humble bees; yet there
were some caterpillars and moths which they would seize only to drop
immediately. Among these the principal were the caterpillar of the
Magpie moth (Abraxas grossulariata) and the perfect six spot Burnet moth
(Anthrocera filipendulæ). These would be first seized but invariably
dropped in disgust, and afterwards left unmolested. Subsequently frogs
were kept and fed with caterpillars from the garden, but two of
these--that of the before-mentioned Magpie moth, and that of the V. moth
(Halia wavaria), which is green with conspicuous white or yellow stripes
and black spots--were constantly rejected. When these species were first
offered, the frogs sprang at them eagerly and licked them into their
mouths; no sooner, however, had they done so than they seemed to be
aware of the mistake that they had made, and sat with gaping mouths,
rolling their tongues about until they had got quit of the nauseous
morsels.
With spiders the same thing occurred. These two caterpillars were
repeatedly put into the webs both of the geometrical and hunting spiders
(Epeira diadema and Lycosa sp.), but in the former case they were cut
out and allowed to drop; in the latter, after disappearing in the jaws
of their captor down his dark silken funnel, they invariably reappeared,
either from below or else taking long strides up the funnel again. Mr.
Butler has observed lizards fight with and finally devour humble bees,
and a frog sitting on a bed of stone-crop leap up and catch the bees
which flew over his head, and swallow them, in utter disregard of their
stings. It is evident, therefore, that the possession of a disagreeable
taste or odour is a more effectual protection to certain conspicuous
caterpillars and moths, than would be even the possession of a sting.
The observations of these two gentlemen supply a very remarkable
confirmation of the hypothetical solution of the difficulty which I had
given two years before. And as it is generally acknowledged that the
best test of the truth and completeness of a theory is the power which
it gives us of prevision, we may I think fairly claim this as a case in
which the power of prevision has been successfully exerted, and
therefore as furnishing a very powerful argument in favour of the truth
of the theory of Natural Selection.
_Summary._
I have now completed a brief, and necessarily very imperfect, survey of
the various ways in which the external form and colouring of animals is
adapted to be useful to them, either by concealing them from their
enemies or from the creatures they prey upon. It has, I hope, been shown
that the subject is one of much interest, both as regard a true
comprehension of the place each animal fills in the economy of nature,
and the means by which it is enabled to maintain that place; and also as
teaching us how important a part is played by the minutest details in
the structure of animals, and how complicated and delicate is the
equilibrium of the organic world.
My exposition of the subject having been necessarily somewhat lengthy
and full of details, it will be as well to recapitulate its main points.
There is a general harmony in nature between the colours of an animal
and those of its habitation. Arctic animals are white, desert animals
are sand-coloured; dwellers among leaves and grass are green; nocturnal
animals are dusky. These colours are not universal, but are very
general, and are seldom reversed. Going on a little further, we find
birds, reptiles, and insects, so tinted and mottled as exactly to match
the rock, or bark, or leaf, or flower, they are accustomed to rest
upon,--and thereby effectually concealed. Another step in advance, and
we have insects which are formed as well as coloured so as exactly to
resemble particular leaves, or sticks, or mossy twigs, or flowers; and
in these cases very peculiar habits and instincts come into play to aid
in the deception and render the concealment more complete. We now enter
upon a new phase of the phenomena, and come to creatures whose colours
neither conceal them nor make them like vegetable or mineral substances;
on the contrary, they are conspicuous enough, but they completely
resemble some other creature of a quite different group, while they
differ much in outward appearance from those with which all essential
parts of their organization show them to be really closely allied. They
appear like actors or masqueraders dressed up and painted for amusement,
or like swindlers endeavouring to pass themselves off for well-known and
respectable members of society. What is the meaning of this strange
travestie? Does Nature descend to imposture or masquerade? We answer,
she does not. Her principles are too severe. There is a use in every
detail of her handiwork. The resemblance of one animal to another is of
exactly the same essential nature as the resemblance to a leaf, or to
bark, or to desert sand, and answers exactly the same purpose. In the
one case the enemy will not attack the leaf or the bark, and so the
disguise is a safeguard; in the other case it is found that for various
reasons the creature resembled is passed over, and not attacked by the
usual enemies of its order, and thus the creature that resembles it has
an equally effectual safeguard. We are plainly shown that the disguise
is of the same nature in the two cases, by the occurrence in the same
group of one species resembling a vegetable substance, while another
resembles a living animal of another group; and we know that the
creatures resembled, possess an immunity from attack, by their being
always very abundant, by their being conspicuous and not concealing
themselves, and by their having generally no visible means of escape
from their enemies; while, at the same time, the particular quality that
makes them disliked is often very clear, such as a nasty taste or an
indigestible hardness. Further examination reveals the fact that, in
several cases of both kinds of disguise, it is the female only that is
thus disguised; and as it can be shown that the female needs protection
much more than the male, and that her preservation for a much longer
period is absolutely necessary for the continuance of the race, we have
an additional indication that the resemblance is in all cases
subservient to a great purpose--the preservation of the species.
In endeavouring to explain these phenomena as having been brought about
by variation and natural selection, we start with the fact that white
varieties frequently occur, and when protected from enemies show no
incapacity for continued existence and increase. We know, further, that
varieties of many other tints occasionally occur; and as "the survival
of the fittest" must inevitably weed out those whose colours are
prejudicial and preserve those whose colours are a safeguard, we require
no other mode of accounting for the protective tints of arctic and
desert animals. But this being granted, there is such a perfectly
continuous and graduated series of examples of every kind of protective
imitation, up to the most wonderful cases of what is termed "mimicry,"
that we can find no place at which to draw the line, and say,--so far
variation and natural selection will account for the phenomena, but for
all the rest we require a more potent cause. The counter theories that
have been proposed, that of the "special creation" of each imitative
form, that of the action of "similar conditions of existence" for some
of the cases, and of the laws of "hereditary descent and the reversion
to ancestral forms" for others,--have all been shown to be beset with
difficulties, and the two latter to be directly contradicted by some of
the most constant and most remarkable of the facts to be accounted for.
_General deductions as to Colour in Nature._
The important part that "protective resemblance" has played in
determining the colours and markings of many groups of animals, will
enable us to understand the meaning of one of the most striking facts in
nature, the uniformity in the colours of the vegetable as compared with
the wonderful diversity of the animal world. There appears no good
reason why trees and shrubs should not have been adorned with as many
varied hues and as strikingly designed patterns as birds and
butterflies, since the gay colours of flowers show that there is no
incapacity in vegetable tissues to exhibit them. But even flowers
themselves present us with none of those wonderful designs, those
complicated arrangements of stripes and dots and patches of colour,
that harmonious blending of hues in lines and bands and shaded spots,
which are so general a feature in insects. It is the opinion of Mr.
Darwin that we owe much of the beauty of flowers to the necessity of
attracting insects to aid in their fertilisation, and that much of the
development of colour in the animal world is due to "sexual selection,"
colour being universally attractive, and thus leading to its propagation
and increase; but while fully admitting this, it will be evident from
the facts and arguments here brought forward, that very much of the
_variety_ both of colour and markings among animals is due to the
supreme importance of concealment, and thus the various tints of
minerals and vegetables have been directly reproduced in the animal
kingdom, and again and again modified as more special protection became
necessary. We shall thus have two causes for the development of colour
in the animal world, and shall be better enabled to understand how, by
their combined and separate action, the immense variety we now behold
has been produced. Both causes, however, will come under the general law
of "Utility," the advocacy of which, in its broadest sense, we owe
almost entirely to Mr. Darwin. A more accurate knowledge of the varied
phenomena connected with this subject may not improbably give us some
information both as to the senses and the mental faculties of the lower
animals. For it is evident that if colours which please us also attract
them, and if the various disguises which have been here enumerated are
equally deceptive to them as to ourselves, then both their powers of
vision and their faculties of perception and emotion, must be
essentially of the same nature as our own--a fact of high philosophical
importance in the study of our own nature and our true relations to the
lower animals.
_Conclusion._
Although such a variety of interesting facts have been already
accumulated, the subject we have been discussing is one of which
comparatively little is really known. The natural history of the tropics
has never yet been studied on the spot with a full appreciation of "what
to observe" in this matter. The varied ways in which the colouring and
form of animals serve for their protection, their strange disguises as
vegetable or mineral substances, their wonderful mimicry of other
beings, offer an almost unworked and inexhaustible field of discovery
for the zoologist, and will assuredly throw much light on the laws and
conditions which have resulted in the wonderful variety of colour,
shade, and marking which constitutes one of the most pleasing
characteristics of the animal world, but the immediate causes of which
it has hitherto been most difficult to explain.
If I have succeeded in showing that in this wide and picturesque domain
of nature, results which have hitherto been supposed to depend either
upon those incalculable combinations of laws which we term chance or
upon the direct volition of the Creator, are really due to the action
of comparatively well-known and simple causes, I shall have attained my
present purpose, which has been to extend the interest so generally felt
in the more striking facts of natural history to a large class of
curious but much neglected details; and to further, in however slight a
degree, our knowledge of the subjection of the phenomena of life to the
"Reign of Law."
IV.
THE MALAYAN PAPILIONIDÆ OR SWALLOW-TAILED BUTTERFLIES, AS ILLUSTRATIVE
OF THE THEORY OF NATURAL SELECTION.
_Special Value of the Diurnal Lepidoptera for enquiries of this nature._
When the naturalist studies the habits, the structure, or the affinities
of animals, it matters little to which group he especially devotes
himself; all alike offer him endless materials for observation and
research. But, for the purpose of investigating the phenomena of
geographical distribution and of local, sexual, or general variation,
the several groups differ greatly in their value and importance. Some
have too limited a range, others are not sufficiently varied in specific
forms, while, what is of most importance, many groups have not received
that amount of attention over the whole region they inhabit, which could
furnish materials sufficiently approaching to completeness to enable us
to arrive at any accurate conclusions as to the phenomena they present
as a whole. It is in those groups which are, and have long been,
favourites with collectors, that the student of distribution and
variation will find his materials the most satisfactory, from their
comparative completeness.
Pre-eminent among such groups are the diurnal Lepidoptera or
Butterflies, whose extreme beauty and endless diversity have led to
their having been assiduously collected in all parts of the world, and
to the numerous species and varieties having been figured in a series of
magnificent works, from those of Cramer, the contemporary of Linnæus,
down to the inimitable productions of our own Hewitson.[G] But, besides
their abundance, their universal distribution, and the great attention
that has been paid to them, these insects have other qualities that
especially adapt them to elucidate the branches of inquiry already
alluded to. These are, the immense development and peculiar structure of
the wings, which not only vary in form more than those of any other
insects, but offer on both surfaces an endless variety of pattern,
colouring, and texture. The scales, with which they are more or less
completely covered, imitate the rich hues and delicate surfaces of satin
or of velvet, glitter with metallic lustre, or glow with the changeable
tints of the opal. This delicately painted surface acts as a register of
the minutest differences of organization--a shade of colour, an
additional streak or spot, a slight modification of outline continually
recurring with the greatest regularity and fixity, while the body and
all its other members exhibit no appreciable change. The wings of
Butterflies, as Mr. Bates has well put it, "serve as a tablet on which
Nature writes the story of the modifications of species;" they enable us
to perceive changes that would otherwise be uncertain and difficult of
observation, and exhibit to us on an enlarged scale the effects of the
climatal and other physical conditions which influence more or less
profoundly the organization of every living thing.
+--------------------------------------------------------------+
| [G] W. C. Hewitson, Esq., of Oatlands, Walton-on-Thames, |
| author of "Exotic Butterflies" and several other works, |
| illustrated by exquisite coloured figures drawn by himself; |
| and owner of the finest collection of Butterflies in the |
| world. |
+--------------------------------------------------------------+
A proof that this greater sensibility to modifying causes is not
imaginary may, I think, be drawn from the consideration, that while the
Lepidoptera as a whole are of all insects the least essentially varied
in form, structure, or habits, yet in the number of their specific forms
they are not much inferior to those orders which range over a much wider
field of nature, and exhibit more deeply seated structural
modifications. The Lepidoptera are all vegetable-feeders in their
larva-state, and suckers of juices or other liquids in their perfect
form. In their most widely separated groups they differ but little from
a common type, and offer comparatively unimportant modifications of
structure or of habits. The Coleoptera, the Diptera, or the Hymenoptera,
on the other hand, present far greater and more essential variations. In
either of these orders we have both vegetable and animal-feeders,
aquatic, and terrestrial, and parasitic groups. Whole families are
devoted to special departments in the economy of nature. Seeds, fruits,
bones, carcases, excrement, bark, have each their special and dependent
insect tribes from among them; whereas the Lepidoptera are, with but few
exceptions, confined to the one function of devouring the foliage of
living vegetation. We might therefore anticipate that their
species--population would be only equal to that of sections of the other
orders having a similar uniform mode of existence; and the fact that
their numbers are at all comparable with those of entire orders, so much
more varied in organization and habits, is, I think, a proof that they
are in general highly susceptible of specific modification.
_Question of the rank of the Papilionidæ._
The Papilionidæ are a family of diurnal Lepidoptera which have hitherto,
by almost universal consent, held the first rank in the order; and
though this position has recently been denied them, I cannot altogether
acquiesce in the reasoning by which it has been proposed to degrade them
to a lower rank. In Mr. Bates's most excellent paper on the Heliconidæ,
(published in the Transactions of the Linnæan Society, vol. xxiii., p.
495) he claims for that family the highest position, chiefly because of
the imperfect structure of the fore legs, which is there carried to an
extreme degree of abortion, and thus removes them further than any other
family from the Hesperidæ and Heterocera, which all have perfect legs.
Now it is a question whether any amount of difference which is exhibited
merely in the imperfection or abortion of certain organs, can establish
in the group exhibiting it a claim to a high grade of organization,
still less can this be allowed when another group along with perfection
of structure in the same organs, exhibits modifications peculiar to it,
together with the possession of an organ which in the remainder of the
order is altogether wanting. This is, however, the position of the
Papilionidæ. The perfect insects possess two characters quite peculiar
to them. Mr. Edward Doubleday, in his "Genera of Diurnal Lepidoptera,"
says, "The Papilionidæ may be known by the apparently four-branched
median nervule and the spur on the anterior tibiæ, characters found in
no other family." The four-branched median nervule is a character so
constant, so peculiar, and so well marked, as to enable a person to
tell, at a glance at the wings only of a butterfly, whether it does or
does not belong to this family; and I am not aware that any other group
of butterflies, at all comparable to this in extent and modifications of
form, possesses a character in its neuration to which the same degree of
certainty can be attached. The spur on the anterior tibiæ is also found
in some of the Hesperidæ, and is therefore supposed to show a direct
affinity between the two groups: but I do not imagine it can
counterbalance the differences in neuration and in every other part of
their organization. The most characteristic feature of the Papilionidæ,
however, and that on which I think insufficient stress has been laid, is
undoubtedly the peculiar structure of the larvæ. These all possess an
extraordinary organ situated on the neck, the well-known Y-shaped
tentacle, which is entirely concealed in a state of repose, but which is
capable of being suddenly thrown out by the insect when alarmed. When we
consider this singular apparatus, which in some species is nearly half
an inch long, the arrangement of muscles for its protrusion and
retraction, its perfect concealment during repose, its blood-red colour,
and the suddenness with which it can be thrown out, we must, I think, be
led to the conclusion that it serves as a protection to the larva, by
startling and frightening away some enemy when about to seize it, and is
thus one of the causes which has led to the wide extension and
maintained the permanence of this now dominant group. Those who believe
that such peculiar structures can only have arisen by very minute
successive variations, each one advantageous to its possessor, must see,
in the possession of such an organ by one group, and its complete
absence in every other, a proof of a very ancient origin and of very
long-continued modification. And such a positive structural addition to
the organization of the family, subserving an important function, seems
to me alone sufficient to warrant us in considering the Papilionidæ as
the most highly developed portion of the whole order, and thus in
retaining it in the position which the size, strength, beauty, and
general structure of the perfect insects have been generally thought to
deserve.
In Mr. Trimen's paper on "Mimetic Analogies among African Butterflies,"
in the Transactions of the Linnæan Society, for 1868, he has argued
strongly in favour of Mr. Bates' views as to the higher position of the
Danaidæ and the lower grade of the Papilionidæ, and has adduced, among
other facts, the undoubted resemblance of the pupa of Parnassius, a
genus of Papilionidæ, to that of some Hesperidæ and moths. I admit,
therefore, that he has proved the Papilionidæ to have retained several
characters of the nocturnal Lepidoptera which the Danaidæ have lost, but
I deny that they are therefore to be considered lower in the scale of
organization. Other characters may be pointed out which indicate that
they are farther removed from the moths even than the Danaidæ. The club
of the antennæ is the most prominent and most constant feature by which
butterflies may be distinguished from moths, and of all butterflies the
Papilionidæ have the most beautiful and most perfectly developed clubbed
antennæ. Again, butterflies and moths are broadly characterised by their
diurnal and nocturnal habits respectively, and the Papilionidæ, with
their close allies the Pieridæ, are the most pre-eminently diurnal of
butterflies, most of them lovers of sunshine, and not presenting a
single crepuscular species. The great group of the Nymphalidæ, on the
other hand (in which Mr. Bates includes the Danaidæ and Heliconidæ as
sub-families), contains an entire sub-family (Brassolidæ) and a number
of genera, such as Thaumantis, Zeuxidia, Pavonia, &c., of crepuscular
habits, while a large proportion of the Satyridæ and many of the
Danaidæ are shade-loving butterflies. This question, of what is to be
considered the highest type of any group of organisms, is one of such
general interest to naturalists that it will be well to consider it a
little further, by a comparison of the Lepidoptera with some groups of
the higher animals.
Mr. Trimen's argument, that the lepidopterous type, like that of birds,
being pre-eminently aërial, "therefore a diminution of the ambulatory
organs, instead of being a sign of inferiority, may very possibly
indicate a higher, because a more thoroughly aërial form," is certainly
unsound, for it would imply that the most aërial of birds (the swift and
the frigate-birds, for example) are the highest in the scale of
bird-organization, and the more so on account of their feet being very
ill adapted for walking. But no ornithologist has ever so classed them,
and the claim to the highest rank among birds is only disputed between
three groups, all very far removed from these. They are--1st. The
Falcons, on account of their general perfection, their rapid flight,
their piercing vision, their perfect feet armed with retractile claws,
the beauty of their forms, and the ease and rapidity of their motions;
2nd. The Parrots, whose feet, though ill-fitted for walking, are perfect
as prehensile organs, and which possess large brains with great
intelligence, though but moderate powers of flight; and, 3rd. The
Thrushes or Crows, as typical of the perching birds, on account of the
well-balanced development of their whole structure, in which no organ
or function has attained an undue prominence.
Turning now to the Mammalia, it might be argued that as they are
pre-eminently the terrestrial type of vertebrates, to walk and run well
is essential to the typical perfection of the group; but this would give
the superiority to the horse, the deer, or the hunting leopard, instead
of to the Quadrumana. We seem here to have quite a case in point, for
one group of Quadrumana, the Lemurs, is undoubtedly nearer to the low
Insectivora and Marsupials than the Carnivora or the Ungulata, as shown
among other characters by the Opossums possessing a hand with perfect
opposable thumb, closely resembling that of some of the Lemurs; and by
the curious Galeopithecus, which is sometimes classed as a Lemur, and
sometimes with the Insectivora. Again, the implacental mammals,
including the Ornithodelphia and the Marsupials, are admitted to be
lower than the placental series. But one of the distinguishing
characters of the Marsupials is that the young are born blind and
exceedingly imperfect, and it might therefore be argued that those
orders in which the young are born most perfect are the highest, because
farthest from the low Marsupial type. This would make the Ruminants and
Ungulata higher than the Quadrumana or the Carnivora. But the Mammalia
offer a still more remarkable illustration of the fallacy of this mode
of reasoning, for if there is one character more than another which is
essential and distinctive of the class, it is that from which it derives
its name, the possession of mammary glands and the power of suckling
the young. What more reasonable, apparently, than to argue that the
group in which this important function is most developed, that in which
the young are most dependent upon it, and for the longest period, must
be the highest in the Mammalian scale of organization? Yet this group is
the Marsupial, in which the young commence suckling in a foetal
condition, and continue to do so till they are fully developed, and are
therefore for a long time absolutely dependent on this mode of
nourishment.
These examples, I think, demonstrate that we cannot settle the rank of a
group by a consideration of the degree in which certain characters
resemble or differ from those in what is admitted to be a lower group;
and they also show that the highest group of a class may be more closely
connected to one of the lowest, than some other groups which have
developed laterally and diverged farther from the parent type, but which
yet, owing to want of balance or too great specialization in their
structure, have never reached a high grade of organization. The
Quadrumana afford a very valuable illustration, because, owing to their
undoubted affinity with man, we feel certain that they are really higher
than any other order of Mammalia, while at the same time they are more
distinctly allied to the lowest groups than many others. The case of the
Papilionidæ seems to me so exactly parallel to this, that, while I admit
all the proofs of affinity with the undoubtedly lower groups of
Hesperidæ and moths, I yet maintain that, owing to the complete and
even development of every part of their organization, these insects best
represent the highest perfection to which the butterfly type has
attained, and deserve to be placed at its head in every system of
classification.
_Distribution of the Papilionidæ._
The Papilionidæ are pretty widely distributed over the earth, but are
especially abundant in the tropics, where they attain their maximum of
size and beauty, and the greatest variety of form and colouring. South
America, North India, and the Malay Islands are the regions where these
fine insects occur in the greatest profusion, and where they actually
become a not unimportant feature in the scenery. In the Malay Islands in
particular, the giant Ornithopteræ may be frequently seen about the
borders of the cultivated and forest districts, their large size,
stately flight, and gorgeous colouring rendering them even more
conspicuous than the generality of birds. In the shady suburbs of the
town of Malacca two large and handsome Papilios (Memnon and Nephelus)
are not uncommon, flapping with irregular flight along the roadways, or,
in the early morning, expanding their wings to the invigorating rays of
the sun. In Amboyna and other towns of the Moluccas, the magnificent
Deiphobus and Severus, and occasionally even the azure-winged Ulysses,
frequent similar situations, fluttering about the orange-trees and
flower-beds, or sometimes even straying into the narrow bazaars or
covered markets of the city. In Java the golden-dusted Arjuna may often
be seen at damp places on the roadside in the mountain districts, in
company with Sarpedon, Bathycles, and Agamemnon, and less frequently the
beautiful swallow-tailed Antiphates. In the more luxuriant parts of
these islands one can hardly take a morning's walk in the neighbourhood
of a town or village without seeing three or four species of Papilio,
and often twice that number. No less than 130 species of the family are
now known to inhabit the Archipelago, and of these ninety-six were
collected by myself. Thirty species are found in Borneo, being the
largest number in any one island, twenty-three species having been
obtained by myself in the vicinity of Sarawak; Java has twenty-eight
species; Celebes twenty-four, and the Peninsula of Malacca, twenty-six
species. Further east the numbers decrease; Batchian producing
seventeen, and New Guinea only fifteen, though this number is certainly
too small, owing to our present imperfect knowledge of that great
island.
_Definition of the word Species._
In estimating these numbers I have had the usual difficulty to
encounter, of determining what to consider species and what varieties.
The Malayan region, consisting of a large number of islands of generally
great antiquity, possesses, compared to its actual area, a great number
of distinct forms, often indeed distinguished by very slight
characters, but in most cases so constant in large series of specimens,
and so easily separable from each other, that I know not on what
principle we can refuse to give them the name and rank of species. One
of the best and most orthodox definitions is that of Pritchard, the
great ethnologist, who says, that "_separate origin and distinctness of
race, evinced by a constant transmission of some characteristic
peculiarity of organization_," constitutes a species. Now leaving out
the question of "origin," which we cannot determine, and taking only the
proof of separate origin, "_the constant transmission of some
characteristic peculiarity of organization_," we have a definition which
will compel us to neglect altogether the _amount_ of difference between
any two forms, and to consider only whether the differences that present
themselves are _permanent_. The rule, therefore, I have endeavoured to
adopt is, that when the difference between two forms inhabiting separate
areas seems quite constant, when it can be defined in words, and when it
is not confined to a single peculiarity only, I have considered such
forms to be species. When, however, the individuals of each locality
vary among themselves, so as to cause the distinctions between the two
forms to become inconsiderable and indefinite, or where the differences,
though constant, are confined to one particular only, such as size,
tint, or a single point of difference in marking or in outline, I class
one of the forms as a variety of the other.
I find as a general rule that the constancy of species is in an inverse
ratio to their range. Those which are confined to one or two islands are
generally very constant. When they extend to many islands, considerable
variability appears; and when they have an extensive range over a large
part of the Archipelago, the amount of unstable variation is very large.
These facts are explicable on Mr. Darwin's principles. When a species
exists over a wide area, it must have had, and probably still possesses,
great powers of dispersion. Under the different conditions of existence
in various portions of its area, different variations from the type
would be selected, and, were they completely isolated, would soon become
distinctly modified forms; but this process is checked by the dispersive
powers of the whole species, which leads to the more or less frequent
intermixture of the incipient varieties, which thus become irregular and
unstable. Where, however, a species has a limited range, it indicates
less active powers of dispersion, and the process of modification under
changed conditions is less interfered with. The species will therefore
exist under one or more permanent forms according as portions of it have
been isolated at a more or less remote period.
_Laws and Modes of Variation._
What is commonly called variation consists of several distinct phenomena
which have been too often confounded. I shall proceed to consider these
under the heads of--1st, simple variability; 2nd, polymorphism; 3rd,
local forms; 4th, co-existing varieties; 5th, races or subspecies; and
6th, true species.
1. _Simple variability._--Under this head I include all those cases in
which the specific form is to some extent unstable. Throughout the whole
range of the species, and even in the progeny of individuals, there
occur continual and uncertain differences of form, analogous to that
variability which is so characteristic of domestic breeds. It is
impossible usefully to define any of these forms, because there are
indefinite gradations to each other form. Species which possess these
characteristics have always a wide range, and are more frequently the
inhabitants of continents than of islands, though such cases are always
exceptional, it being far more common for specific forms to be fixed
within very narrow limits of variation. The only good example of this
kind of variability which occurs among the Malayan Papilionidæ is in
Papilio Severus, a species inhabiting all the islands of the Moluccas
and New Guinea, and exhibiting in each of them a greater amount of
individual difference than often serves to distinguish well-marked
species. Almost equally remarkable are the variations exhibited in most
of the species of Ornithoptera, which I have found in some cases to
extend even to the form of the wing and the arrangement of the nervures.
Closely allied, however, to these variable species are others which,
though differing slightly from them, are constant and confined to
limited areas. After satisfying oneself, by the examination of numerous
specimens captured in their native countries, that the one set of
individuals are variable and the others are not, it becomes evident that
by classing all alike as varieties of one species we shall be obscuring
an important fact in nature; and that the only way to exhibit that fact
in its true light is to treat the invariable local form as a distinct
species, even though it does not offer better distinguishing characters
than do the extreme forms of the variable species. Cases of this kind
are the Ornithoptera Priamus, which is confined to the islands of Ceram
and Amboyna, and is very constant in both sexes, while the allied
species inhabiting New Guinea and the Papuan Islands is exceedingly
variable; and in the island of Celebes is a species closely allied to
the variable P. Severus, but which, being exceedingly constant, I have
described as a distinct species under the name of Papilio Pertinax.
2. _Polymorphism or dimorphism._--By this term I understand the
co-existence in the same locality of two or more distinct forms, not
connected by intermediate gradations, and all of which are occasionally
produced from common parents. These distinct forms generally occur in
the female sex only, and their offspring, instead of being hybrids, or
like the two parents, appear to reproduce all the distinct forms in
varying proportions. I believe it will be found that a considerable
number of what have been classed as _varieties_ are really cases of
polymorphism. Albinoism and melanism are of this character, as well as
most of those cases in which well-marked varieties occur in company with
the parent species, but without any intermediate forms. If these
distinct forms breed independently, and are never reproduced from a
common parent, they must be considered as separate species, contact
without intermixture being a good test of specific difference. On the
other hand, intercrossing without producing an intermediate race is a
test of dimorphism. I consider, therefore, that under any circumstances
the term "variety" is wrongly applied to such cases.
The Malayan Papilionidæ exhibit some very curious instances of
polymorphism, some of which have been recorded as varieties, others as
distinct species; and they all occur in the female sex. Papilio Memnon
is one of the most striking, as it exhibits the mixture of simple
variability, local and polymorphic forms, all hitherto classed under the
common title of varieties. The polymorphism is strikingly exhibited by
the females, one set of which resemble the males in form, with a
variable paler colouring; the others have a large spatulate tail to the
hinder wings and a distinct style of colouring, which causes them
closely to resemble P. Coon, a species having the two sexes alike and
inhabiting the same countries, but with which they have no direct
affinity. The tailless females exhibit simple variability, scarcely two
being found exactly alike even in the same locality. The males of the
island of Borneo exhibit constant differences of the under surface, and
may therefore be distinguished as a local form, while the continental
specimens, as a whole, offer such large and constant differences from
those of the islands, that I am inclined to separate them as a distinct
species, to which the name P. Androgeus (Cramer) may be applied. We
have here, therefore, distinct species, local forms, polymorphism, and
simple variability, which seem to me to be distinct phenomena, but which
have been hitherto all classed together as varieties. I may mention that
the fact of these distinct forms being one species is doubly proved. The
males, the tailed and tailless females, have all been bred from a single
group of the larvæ, by Messrs. Payen and Bocarmé, in Java, and I myself
captured, in Sumatra, a male P. Memnon, and a tailed female P. Achates,
under circumstances which led me to class them as the same species.
Papilio Pammon offers a somewhat similar case. The female was described
by Linnæus as P. Polytes, and was considered to be a distinct species
till Westermann bred the two from the same larvæ (see Boisduval,
"Species Général des Lépidoptères," p. 272). They were therefore classed
as sexes of one species by Mr. Edward Doubleday, in his "Genera of
Diurnal Lepidoptera," in 1846. Later, female specimens were received
from India closely resembling the male insect, and this was held to
overthrow the authority of M. Westermann's observation, and to
re-establish P. Polytes as a distinct species; and as such it
accordingly appears in the British Museum List of Papilionidæ in 1856,
and in the Catalogue of the East India Museum in 1857. This discrepancy
is explained by the fact of P. Pammon having two females, one closely
resembling the male, while the other is totally different from it. A
long familiarity with this insect (which replaced by local forms or by
closely allied species, occurs in every island of the Archipelago) has
convinced me of the correctness of this statement; for in every place
where a male allied to P. Pammon is found, a female resembling P.
Polytes also occurs, and sometimes, though less frequently than on the
continent, another female closely resembling the male: while not only
has no male specimen of P. Polytes yet been discovered, but the female
(Polytes) has never yet been found in localities to which the male
(Pammon) does not extend. In this case, as in the last, distinct
species, local forms, and dimorphic specimens, have been confounded
under the common appellation of varieties.
But, besides the true P. Polytes, there are several allied forms of
females to be considered, namely, P. Theseus (Cramer), P. Molanides (De
Haan), P. Elyros (G. R. Gray), and P. Romulus (Linnæus). The dark female
figured by Cramer as P. Theseus seems to be the common and perhaps the
only form in Sumatra, whereas in Java, Borneo, and Timor, along with
males quite identical with those of Sumatra, occur females of the
Polytes form, although a single specimen of the true P. Theseus taken at
Lombock would seem to show that the two forms do occur together. In the
allied species found in the Philippine Islands (P. Alphenor, Cramer = P.
Ledebouria, Eschscholtz, the female of which is P. Elyros, G. R. Gray,)
forms corresponding to these extremes occur, along with a number of
intermediate varieties, as shown by a fine series in the British Museum.
We have here an indication of how dimorphism may be produced; for let
the extreme Philippine forms be better suited to their conditions of
existence than the intermediate connecting links, and the latter will
gradually die out, leaving two distinct forms of the same insect, each
adapted to some special conditions. As these conditions are sure to vary
in different districts, it will often happen, as in Sumatra and Java,
that the one form will predominate in the one island, the other in the
adjacent one. In the island of Borneo there seems to be a third form;
for P. Melanides (De Haan) evidently belongs to this group, and has all
the chief characteristics of P. Theseus, with a modified colouration of
the hind wings. I now come to an insect which, if I am correct, offers
one of the most interesting cases of variation yet adduced. Papilio
Romulus, a butterfly found over a large part of India and Ceylon, and
not uncommon in collections, has always been considered a true and
independent species, and no suspicions have been expressed regarding it.
But a male of this form does not, I believe, exist. I have examined the
fine series in the British Museum, in the East India Company's Museum,
in the Hope Museum at Oxford, in Mr. Hewitson's and several other
private collections, and can find nothing but females; and for this
common butterfly no male partner can be found except the equally common
P. Pammon, a species already provided with two wives, and yet to whom we
shall be forced, I believe, to assign a third. On carefully examining P.
Romulus, I find that in all essential characters--the form and texture
of the wings, the length of the antennæ, the spotting of the head and
thorax, and even the peculiar tints and shades with which it is
ornamented--it corresponds exactly with the other females of the Pammon
group; and though, from the peculiar marking of the fore wings, it has
at first sight a very different aspect, yet a closer examination shows
that every one of its markings could be produced by slight and almost
imperceptible modifications of the various allied forms. I fully
believe, therefore, that I shall be correct in placing P. Romulus as a
third Indian form of the female P. Pammon, corresponding to P.
Melanides, the third form of the Malayan P. Theseus. I may mention here
that the females of this group have a superficial resemblance to the
Polydorus group of Papilios, as shown by P. Theseus having been
considered to be the female of P. Antiphus, and by P. Romulus being
arranged next to P. Hector. There is no close affinity between these two
groups of Papilio, and I am disposed to believe that we have here a case
of mimicry, brought about by the same causes which Mr. Bates has so well
explained in his account of the Heliconidæ, and which has led to the
singular exuberance of polymorphic forms in this and allied groups of
the genus Papilio. I shall have to devote a section of my essay to the
consideration of this subject.
The third example of polymorphism I have to bring forward is Papilio
Ormenus, which is closely allied to the well-known P. Erechtheus, of
Australia. The most common form of the female also resembles that of P.
Erechtheus; but a totally different-looking insect was found by myself
in the Aru Islands, and figured by Mr. Hewitson under the name of P.
Onesimus, which subsequent observation has convinced me is a second form
of the female of P. Ormenus. Comparison of this with Boisduval's
description of P. Amanga, a specimen of which from New Guinea is in the
Paris Museum, shows the latter to be a closely similar form; and two
other specimens were obtained by myself, one in the island of Goram and
the other in Waigiou, all evidently local modifications of the same
form. In each of these localities males and ordinary females of P.
Ormenus were also found. So far there is no evidence that these
light-coloured insects are not females of a distinct species, the males
of which have not been discovered. But two facts have convinced me this
is not the case. At Dorey, in New Guinea, where males and ordinary
females closely allied to P. Ormenus occur (but which seem to me worthy
of being separated as a distinct species), I found one of these
light-coloured females closely followed in her flight by three males,
exactly in the same manner as occurs (and, I believe, occurs only) with
the sexes of the same species. After watching them a considerable time,
I captured the whole of them, and became satisfied that I had discovered
the true relations of this anomalous form. The next year I had
corroborative proof of the correctness of this opinion by the discovery
in the island of Batchian of a new species allied to P. Ormenus, all the
females of which, either seen or captured by me, were of one form, and
much more closely resembling the abnormal light-coloured females of P.
Ormenus and P. Pandion than the ordinary specimens of that sex. Every
naturalist will, I think, agree that this is strongly confirmative of
the supposition that both forms of female are of one species; and when
we consider, further, that in four separate islands, in each of which I
resided for several months, the two forms of female were obtained and
only one form of male ever seen, and that about the same time, M.
Montrouzier in Woodlark Island, at the other extremity of New Guinea
(where he resided several years, and must have obtained all the large
Lepidoptera of the island), obtained females closely resembling mine,
which, in despair at finding no appropriate partners for them, he mates
with a widely different species--it becomes, I think, sufficiently
evident this is another case of polymorphism of the same nature as those
already pointed out in P. Pammon and P. Memnon. This species, however,
is not only dimorphic, but trimorphic; for, in the island of Waigiou, I
obtained a third female quite distinct from either of the others, and in
some degree intermediate between the ordinary female and the male. The
specimen is particularly interesting to those who believe, with Mr.
Darwin, that extreme difference of the sexes has been gradually produced
by what he terms sexual selection, since it may be supposed to exhibit
one of the intermediate steps in that process, which has been
accidentally preserved in company with its more favoured rivals, though
its extreme rarity (only one specimen having been seen to many hundreds
of the other form) would indicate that it may soon become extinct.
The only other case of polymorphism in the genus Papilio, at all equal
in interest to those I have now brought forward, occurs in America; and
we have, fortunately, accurate information about it. Papilio Turnus is
common over almost the whole of temperate North America; and the female
resembles the male very closely. A totally different-looking insect both
in form and colour, Papilio Glaucus, inhabits the same region; and
though, down to the time when Boisduval published his "Species Général,"
no connexion was supposed to exist between the two species, it is now
well ascertained that P. Glaucus is a second female form of P. Turnus.
In the "Proceedings of the Entomological Society of Philadelphia," Jan.,
1863, Mr. Walsh gives a very interesting account of the distribution of
this species. He tells us that in the New England States and in New York
all the females are yellow, while in Illinois and further south all are
black; in the intermediate region both black and yellow females occur in
varying proportions. Lat. 37° is approximately the southern limit of the
yellow form, and 42° the northern limit of the black form; and, to
render the proof complete, both black and yellow insects have been bred
from a single batch of eggs. He further states that, out of thousands
of specimens, he has never seen or heard of intermediate varieties
between these forms. In this interesting example we see the effects of
latitude in determining the proportions in which the individuals of each
form should exist. The conditions are _here_ favourable to the one form,
_there_ to the other; but we are by no means to suppose that these
conditions consist in climate alone. It is highly probable that the
existence of enemies, and of competing forms of life, may be the main
determining influences; and it is much to be wished that such a
competent observer as Mr. Walsh would endeavour to ascertain what are
the adverse causes which are most efficient in keeping down the numbers
of each of these contrasted forms.
Dimorphism of this kind in the animal kingdom does not seem to have any
direct relations to the reproductive powers, as Mr. Darwin has shown to
be the case in plants, nor does it appear to be very general. One other
case only is known to me in another family of my eastern Lepidoptera,
the Pieridæ; and but few occur in the Lepidoptera of other countries.
The spring and autumn broods of some European species differ very
remarkably; and this must be considered as a phenomenon of an analogous
though not of an identical nature, while the Araschnia prorsa, of
Central Europe, is a striking example of this alternate or seasonal
dimorphism. Among our nocturnal Lepidoptera, I am informed, many
analogous cases occur; and as the whole history of many of these has
been investigated by breeding successive generations from the egg, it is
to be hoped that some of our British Lepidopterists will give us a
connected account of all the abnormal phenomena which they present.
Among the Coleoptera Mr. Pascoe has pointed out the existence of two
forms of the male sex in seven species of the two genera Xenocerus and
Mecocerus belonging to the family Anthribidæ, (Proc. Ent. Soc. Lond.,
1862); and no less than six European Water-beetles, of the genus
Dytiscus, have females of two forms, the most common having the elytra
deeply sulcate, the rarer smooth as in the males. The three, and
sometimes four or more, forms under which many Hymenopterous insects
(especially Ants) occur, must be considered as a related phenomenon,
though here each form is specialized to a distinct function in the
economy of the species. Among the higher animals, albinoism and melanism
may, as I have already stated, be considered as analogous facts; and I
met with one case of a bird, a species of Lory (Eos fuscata), clearly
existing under two differently coloured forms, since I obtained both
sexes of each from a single flock, while no intermediate specimens have
yet been found.
The fact of the two sexes of one species differing very considerably is
so common, that it attracted but little attention till Mr. Darwin showed
how it could in many cases be explained by the principle of sexual
selection. For instance, in most polygamous animals the males fight for
the possession of the females, and the victors, always becoming the
progenitors of the succeeding generation, impress upon their male
offspring their own superior size, strength, or unusually developed
offensive weapons. It is thus that we can account for the spurs and the
superior strength and size of the males in Gallinaceous birds, and also
for the large canine tusks in the males of fruit-eating Apes. So the
superior beauty of plumage and special adornments of the males of so
many birds can be explained by supposing (what there are many facts to
prove) that the females prefer the most beautiful and perfect-plumaged
males, and that thus, slight accidental variations of form and colour
have been accumulated, till they have produced the wonderful train of
the Peacock and the gorgeous plumage of the Bird of Paradise. Both these
causes have no doubt acted partially in insects, so many species
possessing horns and powerful jaws in the male sex only, and still more
frequently the males alone rejoicing in rich colours or sparkling
lustre. But there is here another cause which has led to sexual
differences, viz., a special adaptation of the sexes to diverse habits
or modes of life. This is well seen in female Butterflies (which are
generally weaker and of slower flight), often having colours better
adapted to concealment; and in certain South American species (Papilio
torquatus) the females, which inhabit the forests, resemble the Æneas
group of Papilios which abound in similar localities, while the males,
which frequent the sunny open river-banks, have a totally different
colouration. In these cases, therefore, natural selection seems to have
acted independently of sexual selection; and all such cases may be
considered as examples of the simplest dimorphism, since the offspring
never offer intermediate varieties between the parent forms.
The phenomena of dimorphism and polymorphism may be well illustrated by
supposing that a blue-eyed, flaxen-haired Saxon man had two wives, one a
black-haired, red-skinned Indian squaw, the other a woolly-headed,
sooty-skinned negress--and that instead of the children being mulattoes
of brown or dusky tints, mingling the separate characteristics of their
parents in varying degrees, all the boys should be pure Saxon boys like
their father, while the girls should altogether resemble their mothers.
This would be thought a sufficiently wonderful fact; yet the phenomena
here brought forward as existing in the insect-world are still more
extraordinary; for each mother is capable not only of producing male
offspring like the father, and female like herself, but also of
producing other females exactly like her fellow-wife, and altogether
differing from herself. If an island could be stocked with a colony of
human beings having similar physiological idiosyncrasies with Papilio
Pammon or Papilio Ormenus, we should see white men living with yellow,
red, and black women, and their offspring always reproducing the same
types; so that at the end of many generations the men would remain pure
white, and the women of the same well-marked races as at the
commencement.
The distinctive character therefore of dimorphism is this, that the
union of these distinct forms does not produce intermediate varieties,
but reproduces the distinct forms unchanged. In simple varieties, on the
other hand, as well as when distinct local forms or distinct species are
crossed, the offspring never resembles either parent exactly, but is
more or less intermediate between them. Dimorphism is thus seen to be a
specialized result of variation, by which new physiological phenomena
have been developed; the two should therefore, whenever possible, be
kept separate.
3. _Local form, or variety._--This is the first step in the transition
from variety to species. It occurs in species of wide range, when groups
of individuals have become partially isolated in several points of its
area of distribution, in each of which a characteristic form has become
more or less completely segregated. Such forms are very common in all
parts of the world, and have often been classed by one author as
varieties, by another as species. I restrict the term to those cases
where the difference of the forms is very slight, or where the
segregation is more or less imperfect. The best example in the present
group is Papilio Agamemnon, a species which ranges over the greater part
of tropical Asia, the whole of the Malay archipelago, and a portion of
the Australian and Pacific regions. The modifications are principally of
size and form, and, though slight, are tolerably constant in each
locality. The steps, however, are so numerous and gradual that it would
be impossible to define many of them, though the extreme forms are
sufficiently distinct. Papilio Sarpedon presents somewhat similar but
less numerous variations.
4. _Co-existing Variety._--This is a somewhat doubtful case. It is when
a slight but permanent and hereditary modification of form exists in
company with the parent or typical form, without presenting those
intermediate gradations which would constitute it a case of simple
variability. It is evidently only by direct evidence of the two forms
breeding separately that this can be distinguished from dimorphism. The
difficulty occurs in Papilio Jason, and P. Evemon, which inhabit the
same localities, and are almost exactly alike in form, size, and
colouration, except that the latter always wants a very conspicuous red
spot on the under surface, which is found not only in P. Jason, but in
all the allied species. It is only by breeding the two insects that it
can be determined whether this is a case of a co-existing variety or of
dimorphism. In the former case, however, the difference being constant
and so very conspicuous and easily defined, I see not how we could
escape considering it as a distinct species. A true case of co-existing
forms would, I consider, be produced, if a slight variety had become
fixed as a local form, and afterwards been brought into contact with the
parent species, with little or no intermixture of the two; and such
instances do very probably occur.
5. _Race or subspecies._--These are local forms completely fixed and
isolated; and there is no possible test but individual opinion to
determine which of them shall be considered as species and which
varieties. If stability of form and "_the constant transmission of some
characteristic peculiarity of organization_" is the test of a species
(and I can find no other test that is more certain than individual
opinion) then every one of these fixed races, confined as they almost
always are to distinct and limited areas, must be regarded as a species;
and as such I have in most cases treated them. The various modifications
of Papilio Ulysses, P. Peranthus, P. Codrus, P. Eurypilus, P. Helenus,
&c., are excellent examples; for while some present great and
well-marked, others offer slight and inconspicuous differences, yet in
all cases these differences seem equally fixed and permanent. If,
therefore, we call some of these forms species, and others varieties, we
introduce a purely arbitrary distinction, and shall never be able to
decide where to draw the line. The races of Papilio Ulysses, for
example, vary in amount of modification from the scarcely differing New
Guinea form to those of Woodlark Island and New Caledonia, but all seem
equally constant; and as most of these had already been named and
described as species, I have added the New Guinea form under the name of
P. Autolycus. We thus get a little group of Ulyssine Papilios, the whole
comprised within a very limited area, each one confined to a separate
portion of that area, and, though differing in various amounts, each
apparently constant. Few naturalists will doubt that all these may and
probably have been derived from a common stock, and therefore it seems
desirable that there should be a unity in our method of treating them;
either call them all _varieties_ or all _species_. Varieties, however,
continually get overlooked; in lists of species they are often
altogether unrecorded; and thus we are in danger of neglecting the
interesting phenomena of variation and distribution which they present.
I think it advisable, therefore, to name all such forms; and those who
will not accept them as species may consider them as subspecies or
races.
6. _Species._--Species are merely those strongly marked races or local
forms which when in contact do not intermix, and when inhabiting
distinct areas are generally believed to have had a separate origin, and
to be incapable of producing a fertile hybrid offspring. But as the test
of hybridity cannot be applied in one case in ten thousand, and even if
it could be applied would prove nothing, since it is founded on an
assumption of the very question to be decided--and as the test of
separate origin is in every case inapplicable--and as, further, the test
of non-intermixture is useless, except in those rare cases where the
most closely allied species are found inhabiting the same area, it will
be evident that we have no means whatever of distinguishing so-called
"true species" from the several modes of variation here pointed out, and
into which they so often pass by an insensible gradation. It is quite
true that, in the great majority of cases, what we term "species" are
so well marked and definite that there is no difference of opinion about
them; but as the test of a true theory is, that it accounts for, or at
the very least is not inconsistent with, the whole of the phenomena and
apparent anomalies of the problem to be solved, it is reasonable to ask
that those who deny the origin of species by variation and selection
should grapple with the facts in detail, and show how the doctrine of
the distinct origin and permanence of species will explain and harmonize
them. It has been recently asserted by Dr. J. E. Gray (in the
Proceedings of the Zoological Society for 1863, page 134), that the
difficulty of limiting species is in proportion to our ignorance, and
that just as groups or countries are more accurately known and studied
in greater detail the limits of species become settled. This statement
has, like many other general assertions, its portion of both truth and
error. There is no doubt that many uncertain species, founded on few or
isolated specimens, have had their true nature determined by the study
of a good series of examples: they have been thereby established as
species or as varieties; and the number of times this has occurred is
doubtless very great. But there are other, and equally trustworthy
cases, in which, not single species, but whole groups have, by the study
of a vast accumulation of materials, been proved to have no definite
specific limits. A few of these must be adduced. In Dr. Carpenter's
"Introduction to the Study of the Foraminifera," he states that "_there
is not a single specimen of plant or animal of which the range of
variation has been studied by the collocation and comparison of so large
a number of specimens as have passed under the review of Messrs.
Williamson, Parker, Rupert Jones, and myself, in our studies of the
types of this group_;" and the result of this extended comparison of
specimens is stated to be, "_The range of variation is so great among
the Foraminifera as to include not merely those differential characters
which have been usually accounted_ SPECIFIC, _but also those upon which
the greater part of the_ GENERA _of this group have been founded, and
even in some instances those of its_ ORDERS" (Foraminifera, Preface, x).
Yet this same group had been divided by D'Orbigny and other authors into
a number of clearly defined _families_, _genera_, and _species_, which
these careful and conscientious researches have shown to have been
almost all founded on incomplete knowledge.
Professor DeCandolle has recently given the results of an extensive
review of the species of Cupuliferæ. He finds that the best-known
species of oaks are those which produce most varieties and subvarieties;
that they are often surrounded by provisional species; and, with the
fullest materials at his command, two-thirds of the species he considers
more or less doubtful. His general conclusion is, that "_in botany the
lowest series of groups,_ SUBVARIETIES, VARIETIES, _and_ RACES _are very
badly limited; these can be grouped into_ SPECIES _a little less vaguely
limited, which again can be formed into sufficiently precise_ GENERA."
This general conclusion is entirely objected to by the writer of the
article in the "Natural History Review," who, however, does not deny its
applicability to the particular order under discussion, while this very
difference of opinion is another proof that difficulties in the
determination of species do not, any more than in the higher groups,
vanish with increasing materials and more accurate research.
Another striking example of the same kind is seen in the genera Rubus
and Rosa, adduced by Mr. Darwin himself; for though the amplest
materials exist for a knowledge of these groups, and the most careful
research has been bestowed upon them, yet the various species have not
thereby been accurately limited and defined so as to satisfy the
majority of botanists. In Mr. Baker's revision of the British Roses,
just published by the Linnæan Society, the author includes under the
single species Rosa canina, no less than twenty-eight named _varieties_,
distinguished by more or less constant characters and often confined to
special localities; and to these are referred about seventy of the
_species_ of Continental and British botanists.
Dr. Hooker seems to have found the same thing in his study of the Arctic
flora. For though he has had much of the accumulated materials of his
predecessors to work upon, he continually expresses himself as unable to
do more than group the numerous and apparently fluctuating forms into
more or less imperfectly defined species. In his paper on the
"Distribution of Arctic Plants," (Trans. Linn. Soc. xxiii., p. 310) Dr.
Hooker says:--"The most able and experienced descriptive botanists vary
in their estimate of the value of the 'specific term' to a much greater
extent than is generally supposed." ... "I think I may safely affirm
that the 'specific term' has three different standard values, all
current in descriptive botany, but each more or less confined to one
class of observers." ... "This is no question of what is right or wrong
as to the real value of the specific term; I believe each is right
according to the standard he assumes as the specific."
Lastly, I will adduce Mr. Bates's researches on the Amazons. During
eleven years he accumulated vast materials, and carefully studied the
variation and distribution of insects. Yet he has shown that many
species of Lepidoptera, which before offered no special difficulties,
are in reality most intricately combined in a tangled web of affinities,
leading by such gradual steps from the slightest and least stable
variations to fixed races and well-marked species, that it is very often
impossible to draw those sharp dividing-lines which it is supposed that
a careful study and full materials will always enable us to do.
These few examples show, I think, that in every department of nature
there occur instances of the instability of specific form, which the
increase of materials aggravates rather than diminishes. And it must be
remembered that the naturalist is rarely likely to err on the side of
imputing greater indefiniteness to species than really exists. There is
a completeness and satisfaction to the mind in defining and limiting
and naming a species, which leads us all to do so whenever we
conscientiously can, and which we know has led many collectors to reject
vague intermediate forms as destroying the symmetry of their cabinets.
We must therefore consider these cases of excessive variation and
instability as being thoroughly well established; and to the objection
that, after all, these cases are but few compared with those in which
species can be limited and defined, and are therefore merely exceptions
to a general rule, I reply that a true law embraces all apparent
exceptions, and that to the great laws of nature there are no real
exceptions--that what appear to be such are equally results of law, and
are often (perhaps indeed always) those very results which are most
important as revealing the true nature and action of the law. It is for
such reasons that naturalists now look upon the study of _varieties_ as
more important than that of well-fixed species. It is in the former that
we see nature still at work, in the very act of producing those
wonderful modifications of form, that endless variety of colour, and
that complicated harmony of relations, which gratify every sense and
give occupation to every faculty of the true lover of nature.
_Variation as specially influenced by Locality._
The phenomena of variation as influenced by locality have not hitherto
received much attention. Botanists, it is true, are acquainted with the
influences of climate, altitude, and other physical conditions, in
modifying the forms and external characteristics of plants; but I am not
aware that any peculiar influence has been traced to locality,
independent of climate. Almost the only case I can find recorded is
mentioned in that repertory of natural-history facts, "The Origin of
Species," viz. that herbaceous groups have a tendency to become arboreal
in islands. In the animal world, I cannot find that any facts have been
pointed out as showing the special influence of locality in giving a
peculiar _facies_ to the several disconnected species that inhabit it.
What I have to adduce on this matter will therefore, I hope, possess
some interest and novelty.
On examining the closely allied species, local forms, and varieties
distributed over the Indian and Malayan regions, I find that larger or
smaller districts, or even single islands, give a special character to
the majority of their Papilionidæ. For instance: 1. The species of the
Indian region (Sumatra, Java, and Borneo) are almost invariably smaller
than the allied species inhabiting Celebes and the Moluccas; 2. The
species of New Guinea and Australia are also, though in a less degree,
smaller than the nearest species or varieties of the Moluccas; 3. In the
Moluccas themselves the species of Amboyna are the largest; 4. The
species of Celebes equal or even surpass in size those of Amboyna; 5.
The species and varieties of Celebes possess a striking character in the
form of the anterior wings, different from that of the allied species
and varieties of all the surrounding islands; 6. Tailed species in India
or the Indian region become tailless as they spread eastward through the
archipelago; 7. In Amboyna and Ceram the females of several species are
dull-coloured, while in the adjacent islands they are more brilliant.
_Local variation of Size._--Having preserved the finest and largest
specimens of Butterflies in my own collection, and having always taken
for comparison the largest specimens of the same sex, I believe that the
tables I now give are sufficiently exact. The differences of expanse of
wings are in most cases very great, and are much more conspicuous in the
specimens themselves than on paper. It will be seen that no less than
fourteen Papilionidæ inhabiting Celebes and the Moluccas are from
one-third to one-half greater in extent of wing than the allied species
representing them in Java, Sumatra, and Borneo. Six species inhabiting
Amboyna are larger than the closely allied forms of the northern
Moluccas and New Guinea by about one-sixth. These include almost every
case in which closely allied species can be compared.
Species of Papilionidæ of the Closely allied species of Java and
Moluccas and Celebes (large). the Indian region (small).
Expanse. Expanse.
Inches. Inches.
Ornithoptera (Helena { O. Pompeus 5·8
Amboyna) 7·6 { O. Amphrisius 6·0
Papilio Adamantius }
(Celebes) 5·8 }
P. Lorquinianus } P. Peranthus 3·8
(Moluccas) 4·8 }
P. Blumei (Celebes) 5·4 P. Brama 4·0
P. Alphenor (Celebes) 4·8 P. Theseus 3·6
P. Gigon (Celebes) 5·4 P. Demolion 4·0
P. Deucalion (Celebes) 4·6 P. Macareus 3·7
P. Agamemnon, var.
(Celebes) 4·4 P. Agamemnon, var. 3·8
P. Eurypilus (Moluccas) 4·0 } P. Jason 3·4
P. Telephus (Celebes) 4·3 }
P. Ægisthus (Moluccas) 4·4 P. Rama 3·2
P. Milon (Celebes) 4·4 P. Sarpedon 3·8
P. Androcles (Celebes) 4·8 P. Antiphates 3·7
P. Polyphontes (Celebes) 4·6 P. Diphilus 3·9
Leptocircus Ennius
(Celebes) 2·0 L. Meges 1·8
Species inhabiting Amboyna Allied species of New Guinea and
(large). the North Moluccas (smaller).
Papilio Ulysses 6·1 { P. Autolycus 5·2
{ P. Telegonus 4·0
P. Polydorus 4·9 P. Leodamas 4·0
P. Deiphobus 6·8 P. Deiphontes 5·8
P. Gambrisius 6·4 { P. Ormenus 5·6
{ P. Tydeus 6·0
P. Codrus 5·1 P. Codrus, var.
papuensis 4·3
Ornithoptera Priamus, Ornithoptera Poseidon,
(male) 8·3 (male) 7·0
_Local variation of Form._--The differences of form are equally clear.
Papilio Pammon everywhere on the continent is tailed in both sexes. In
Java, Sumatra, and Borneo, the closely allied P. Theseus has a very
short tail, or tooth only, in the male, while in the females the tail is
retained. Further east, in Celebes and the South Moluccas, the hardly
separable P. Alphenor has quite lost the tail in the male, while the
female retains it, but in a narrower and less spatulate form. A little
further, in Gilolo, P. Nicanor has completely lost the tail in both
sexes.
Papilio Agamemnon exhibits a somewhat similar series of changes. In
India it is always tailed; in the greater part of the archipelago it has
a very short tail; while far east, in New Guinea and the adjacent
islands, the tail has almost entirely disappeared.
In the Polydorus-group two species, P. Antiphus and P. Diphilus,
inhabiting India and the Indian region, are tailed, while the two which
take their place in the Moluccas, New Guinea, and Australia, P.
Polydorus and P. Leodamas, are destitute of tail, the species furthest
east having lost this ornament the most completely.
Western species, Tailed. Allied Eastern species not Tailed.
Papilio Pammon (India) P. Thesus (Islands) minute tail.
P. Agamemnon, var. (India) P. Agamemnon, var. (Islands).
P. Antiphus (India, Java) P. Polydorus (Moluccas).
P. Diphilus (India, Java) P. Leodamas (New Guinea).
The most conspicuous instance of local modification of form, however, is
exhibited in the island of Celebes, which in this respect, as in some
others, stands alone and isolated in the whole archipelago. Almost every
species of Papilio inhabiting Celebes has the wings of a peculiar shape,
which distinguishes them at a glance from the allied species of every
other island. This peculiarity consists, first, in the upper wings being
generally more elongate and falcate; and secondly, in the costa or
anterior margin being much more curved, and in most instances exhibiting
near the base an abrupt bend or elbow, which in some species is very
conspicuous. This peculiarity is visible, not only when the Celebesian
species are compared with their small-sized allies of Java and Borneo,
but also, and in an almost equal degree, when the large forms of Amboyna
and the Moluccas are the objects of comparison, showing that this is
quite a distinct phenomenon from the difference of size which has just
been pointed out.
In the following Table I have arranged the chief Papilios of Celebes in
the order in which they exhibit this characteristic form most
prominently.
Papilios of Celebes, having the Closely allied Papilios of the
wings falcate or with abruptly surrounding islands, with less
curved costa. wings and slightly falcate curved costa.
1. P. Gigon P. Demolion (Java).
2. P. Pamphylus P. Jason (Sumatra).
3. P. Milon P. Sarpedon (Moluccas, Java).
4. P. Agamemnon, var. P. Agamemnon, var. (Borneo).
5. P. Adamantius P. Peranthus (Java).
6. P. Ascalaphus P. Deiphontes (Gilolo).
7. P. Sataspes P. Helenus (Java).
8. P. Blumei P. Brama (Sumatra).
9. P. Androcles P. Antiphates (Borneo).
10. P. Rhesus P. Aristæus (Moluccas).
11. P. Theseus, var. (male) P. Thesus (male) (Java).
12. P. Codrus, var. P. Codrus (Moluccas).
13. P. Encelades P. Leucothoë (Malacca).
It thus appears that every species of Papilio exhibits this peculiar
form in a greater or less degree, except one, P. Polyphontes, allied to
P. Diphilus of India and P. Polydorus of the Moluccas. This fact I
shall recur to again, as I think it helps us to understand something of
the causes that may have brought about the phenomenon we are
considering. Neither do the genera Ornithoptera and Leptocircus exhibit
any traces of this peculiar form. In several other families of
Butterflies this characteristic form reappears in a few species. In the
Pieridæ the following species, all peculiar to Celebes, exhibit it
distinctly:--
1. Pieris Eperia compared with P. Coronis (Java).
2. Thyca Zebuda " " Thyca Descombesi
(India).
3. T. Rosenbergii " " T. Hyparete (Java).
4. Tachyris Hombronii " " T. Lyncida.
5. T. Lycaste " " T. Lyncida.
6. T. Zarinda " " T. Nero (Malacca).
7. T. Ithome " " T. Nephele.
8. Eronia tritæa " " Eronia Valeria
(Java).
9. Iphias Glaucippe, var. " " Iphias Glaucippe
(Java).
The species of Terias, one or two Pieris, and the genus Callidryas do
not exhibit any perceptible change of form.
In the other families there are but few similar examples. The following
are all that I can find in my collection:--
Cethosia Æole compared with Cethosia Biblis (Java).
Eurhinia megalonice " " Eurhinia Polynice
(Borneo).
Limenitis Limire " " Limenitis Procris
(Java).
Cynthia Arsinoë, var. " " Cynthia Arsinoë (Java,
Sumatra, Borneo)
All these belong to the family of the Nymphalidæ. Many other genera of
this family, as Diadema, Adolias, Charaxes, and Cyrestis, as well as the
entire families of the Danaidæ, Satyridæ, Lycænidæ, and Hesperidæ,
present no examples of this peculiar form of the upper wing in the
Celebesian species.
_Local variations of Colour._--In Amboyna and Ceram the female of the
large and handsome Ornithoptera Helena has the large patch on the hind
wings constantly of a pale dull ochre or buff colour, while in the
scarcely distinguishable varieties from the adjacent islands of Bouru
and New Guinea, it is of a golden yellow, hardly inferior in brilliancy
to its colour in the male sex. The female of Ornithoptera Priamus
(inhabiting Amboyna and Ceram exclusively) is of a pale dusky brown
tint, while in all the allied species the same sex is nearly black with
contrasted white markings. As a third example, the female of Papilio
Ulysses has the blue colour obscured by dull and dusky tints, while in
the closely allied species from the surrounding islands, the females are
of almost as brilliant an azure blue as the males. A parallel case to
this is the occurrence, in the small islands of Goram, Matabello, Ké,
and Aru, of several distinct species of Euploea and Diadema, having broad
bands or patches of white, which do not exist in any of the allied
species from the larger islands. These facts seem to indicate some local
influence in modifying colour, as unintelligible and almost as
remarkable as that which has resulted in the modifications of form
previously described.
_Remarks on the facts of Local variation._
The facts now brought forward seem to me of the highest interest. We see
that almost all the species in two important families of the Lepidoptera
(Papilionidæ and Pieridæ) acquire, in a single island, a characteristic
modification of form distinguishing them from the allied species and
varieties of all the surrounding islands. In other equally extensive
families no such change occurs, except in one or two isolated species.
However we may account for these phenomena, or whether we may be quite
unable to account for them, they furnish, in my opinion, a strong
corroborative testimony in favour of the doctrine of the origin of
species by successive small variations; for we have here slight
varieties, local races, and undoubted species, all modified in exactly
the same manner, indicating plainly a common cause producing identical
results. On the generally received theory of the original distinctness
and permanence of species, we are met by this difficulty: one portion of
these curiously modified forms are admitted to have been produced by
variation and some natural action of local conditions; whilst the other
portion, differing from the former only in degree, and connected with
them by insensible gradations, are said to have possessed this
peculiarity of form at their first creation, or to have derived it from
unknown causes of a totally distinct nature. Is not the _à priori_
evidence in favour of an identity of the causes that have produced such
similar results? and have we not a right to call upon our opponents for
some proofs of their own doctrine, and for an explanation of its
difficulties, instead of their assuming that they are right, and laying
upon us the burthen of disproof?
Let us now see if the facts in question do not themselves furnish some
clue to their explanation. Mr. Bates has shown that certain groups of
butterflies have a defence against insectivorous animals, independent of
swiftness of motion. These are generally very abundant, slow, and weak
fliers, and are more or less the objects of mimicry by other groups,
which thus gain an advantage in a freedom from persecution similar to
that enjoyed by those they resemble. Now the only Papilios which have
not in Celebes acquired the peculiar form of wing, belong to a group
which is imitated both by other species of Papilio and by Moths of the
genus Epicopeia. This group is of weak and slow flight; and we may
therefore fairly conclude that it possesses some means of defence
(probably in a peculiar odour or taste) which saves it from attack. Now
the arched costa and falcate form of wing is generally supposed to give
increased powers of flight, or, as seems to me more probable, greater
facility in making sudden turnings, and thus baffling a pursuer. But the
members of the Polydorus-group (to which belongs the only unchanged
Celebesian Papilio), being already guarded against attack, have no need
of this increased power of wing; and "natural selection" would therefore
have no tendency to produce it. The whole family of Danaidæ are in the
same position: they are slow and weak fliers; yet they abound in species
and individuals, and are the objects of mimicry. The Satyridæ have also
probably a means of protection--perhaps their keeping always near the
ground and their generally obscure colours; while the Lycænidæ and
Hesperidæ may find security in their small size and rapid motions. In
the extensive family of the Nymphalidæ, however, we find that several of
the larger species, of comparatively feeble structure, have their wings
modified (Cethosia, Limenitis, Junonia, Cynthia), while the large-bodied
powerful species, which have all an excessively rapid flight, have
exactly the same form of wing in Celebes as in the other islands. On the
whole, therefore, we may say that all the butterflies of rather large
size, conspicuous colours, and not very swift flight have been affected
in the manner described, while the smaller sized and obscure groups, as
well as those which are the objects of mimicry, and also those of
exceedingly swift flight have remained unaffected.
It would thus appear as if there must be (or once have been) in the
island of Celebes, some peculiar enemy to these larger-sized butterflies
which does not exist, or is less abundant, in the surrounding islands.
Increased powers of flight, or rapidity of turning, was advantageous in
baffling this enemy; and the peculiar form of wing necessary to give
this would be readily acquired by the action of "natural selection" on
the slight variations of form that are continually occurring.
Such an enemy one would naturally suppose to be an insectivorous bird;
but it is a remarkable fact that most of the genera of Fly-catchers
of Borneo and Java on the one side (Muscipeta, Philentoma,) and of
the Moluccas on the other (Monarcha, Rhipidura), are almost entirely
absent from Celebes. Their place seems to be supplied by the
Caterpillar-catchers (Graucalus, Campephaga, &c.), of which six or seven
species are known from Celebes and are very numerous in individuals. We
have no positive evidence that these birds pursue butterflies on the
wing, but it is highly probable that they do so when other food is
scarce. Mr. Bates has suggested to me that the larger Dragonflies
(Æshna, &c.) prey upon butterflies; but I did not notice that they were
more abundant in Celebes than elsewhere. However this may be, the fauna
of Celebes is undoubtedly highly peculiar in every department of which
we have any accurate knowledge; and though we may not be able
satisfactorily to trace how it has been effected, there can, I think, be
little doubt that the singular modification in the wings of so many of
the butterflies of that island is an effect of that complicated action
and reaction of all living things upon each other in the struggle for
existence, which continually tends to readjust disturbed relations, and
to bring every species into harmony with the varying conditions of the
surrounding universe.
But even the conjectural explanation now given fails us in the other
cases of local modification. Why the species of the Western islands
should be smaller than those further east,--why those of Amboyna should
exceed in size those of Gilolo and New Guinea--why the tailed species
of India should begin to lose that appendage in the islands, and retain
no trace of it on the borders of the Pacific,--and why, in three
separate cases, the females of Amboyna species should be less gaily
attired than the corresponding females of the surrounding islands,--are
questions which we cannot at present attempt to answer. That they
depend, however, on some general principle is certain, because analogous
facts have been observed in other parts of the world. Mr. Bates informs
me that, in three distinct groups, Papilios which on the Upper Amazon
and in most other parts of South America have spotless upper wings
obtain pale or white spots at Pará and on the Lower Amazon; and also
that the Æneas-group of Papilios never have tails in the equatorial
regions and the Amazons valley, but gradually acquire tails in many
cases as they range towards the northern or southern tropic. Even in
Europe we have somewhat similar facts; for the species and varieties of
butterflies peculiar to the island of Sardinia are generally smaller and
more deeply coloured than those of the mainland, and the same has
recently been shown to be the case with the common tortoiseshell
butterfly in the Isle of Man; while Papilio Hospiton, peculiar to the
former island, has lost the tail, which is a prominent feature of the
closely allied P. Machaon.
Facts of a similar nature to those now brought forward would no doubt be
found to occur in other groups of insects, were local faunas carefully
studied in relation to those of the surrounding countries; and they
seem to indicate that climate and other physical causes have, in some
cases, a very powerful effect in modifying specific form and colour, and
thus directly aid in producing the endless variety of nature.
_Mimicry._
Having fully discussed this subject in the preceding essay, I have only
to adduce such illustrations of it, as are furnished by the Eastern
Papilionidæ, and to show their bearing upon the phenomena of variation
already mentioned. As in America, so in the Old World, species of
Danaidæ are the objects which the other families most often imitate. But
besides these, some genera of Morphidæ and one section of the genus
Papilio are also less frequently copied. Many species of Papilio mimic
other species of these three groups so closely that they are
undistinguishable when on the wing; and in every case the pairs which
resemble each other inhabit the same locality.
The following list exhibits the most important and best marked cases of
mimicry which occur among the Papilionidæ of the Malayan region and
India:--
Mimickers. Species mimicked. Common habitat.
DANAIDÆ.
1. Papilio paradoxa Euploea Midamus } Sumatra, &c.
(male & female) (male & female) }
2. P. Caunus E. Rhadamanthus Borneo and
Sumatra.
3. P. Thule Danais sobrina New Guinea.
4. P. Macareus D. Aglaia Malacca, Java
5. Papilio Agestor Danais Tytia Northern India.
6. P. Idæoides Hestia Leuconoë Philippines.
7. P. Delessertii Ideopsis daos Penang.
MORPHIDÆ.
8. P. Pandion Drusilla bioculata New Guinea
(female)
PAPILIO (POLYDORUS- and COON-groups).
9. P. Pammon (Romulus, Papilio Hector India.
female)
10. P. Theseus, var. P. Antiphus Sumatra, Borneo.
(female)
11. P. Theseus, var. P. Diphilus Sumatra, Java.
(female)
12. P. Memnon, var. P. Coon Sumatra.
(Achates, female)
13. P. Androgeus, var. P. Doubledayi Northern India.
(Achates, female)
14. P. Oenomaus P. Liris Timor.
(female)
We have, therefore, fourteen species or marked varieties of Papilio,
which so closely resemble species of other groups in their respective
localities, that it is not possible to impute the resemblance to
accident. The first two in the list (Papilio paradoxa and P. Caunus) are
so exactly like Euploea Midamus and E. Rhadamanthus on the wing, that
although they fly very slowly, I was quite unable to distinguish them.
The first is a very interesting case, because the male and female differ
considerably, and each mimics the corresponding sex of the Euploea. A
new species of Papilio which I discovered in New Guinea resembles Danais
sobrina, from the same country, just as Papilio Marcareus resembles
Danais Aglaia in Malacca, and (according to Dr. Horsfield's figure)
still more closely in Java. The Indian Papilio Agestor closely imitates
Danais Tytia, which has quite a different style of colouring from the
preceding; and the extraordinary Papilio Idæoides from the Philippine
Islands, must, when on the wing, perfectly resemble the Hestia Leuconoë
of the same region, as also does the Papilio Delessertii imitate the
Ideopsis daos from Penang. Now in every one of these cases the Papilios
are very scarce, while the Danaidæ which they resemble are exceedingly
abundant--most of them swarming so as to be a positive nuisance to the
collecting entomologist by continually hovering before him when he is in
search of newer and more varied captures. Every garden, every roadside,
the suburbs of every village are full of them, indicating very clearly
that their life is an easy one, and that they are free from persecution
by the foes which keep down the population of less favoured races. This
superabundant population has been shown by Mr. Bates to be a general
characteristic of all American groups and species which are objects of
mimicry; and it is interesting to find his observations confirmed by
examples on the other side of the globe.
The remarkable genus Drusilla, a group of pale-coloured butterflies,
more or less adorned with ocellate spots, is also the object of mimicry
by three distinct genera (Melanitis, Hyantis, and Papilio). These
insects, like the Danaidæ, are abundant in individuals, have a very
weak and slow flight, and do not seek concealment, or appear to have any
means of protection from insectivorous creatures. It is natural to
conclude, therefore, that they have some hidden property which saves
them from attack; and it is easy to see that when any other insects, by
what we call accidental variation, come more or less remotely to
resemble them, the latter will share to some extent in their immunity.
An extraordinary dimorphic form of the female of Papilio Ormenus has
come to resemble the Drusillas sufficiently to be taken for one of that
group at a little distance; and it is curious that I captured one of
these Papilios in the Aru Islands hovering along the ground, and
settling on it occasionally, just as it is the habit of the Drusillas to
do. The resemblance in this case is only general; but this form of
Papilio varies much, and there is therefore material for natural
selection to act upon, so as ultimately to produce a copy as exact as in
the other cases.
The eastern Papilios allied to Polydorus, Coon, and Philoxenus, form a
natural section of the genus resembling, in many respects, the
Æneas-group of South America, which they may be said to represent in the
East. Like them, they are forest insects, have a low and weak flight,
and in their favourite localities are rather abundant in individuals;
and like them, too, they are the objects of mimicry. We may conclude,
therefore, that they possess some hidden means of protection, which
makes it useful to other insects to be mistaken for them.
The Papilios which resemble them belong to a very distinct section of
the genus, in which the sexes differ greatly; and it is those females
only which differ most from the males, and which have already been
alluded to as exhibiting instances of dimorphism, which resemble species
of the other group.
The resemblance of P. Romulus to P. Hector is, in some specimens, very
considerable, and has led to the two species being placed following each
other in the British Museum Catalogues and by Mr. E. Doubleday. I have
shown, however, that P. Romulus is probably a dimorphic form of the
female P. Pammon, and belongs to a distinct section of the genus.
The next pair, Papilio Theseus, and P. Antiphus, have been united as one
species both by De Haan and in the British Museum Catalogues. The
ordinary variety of P. Theseus found in Java almost as nearly resembles
P. Diphilus, inhabiting the same country. The most interesting case,
however, is the extreme female form of P. Memnon (figured by Cramer
under the name of P. Achates), which has acquired the general form and
markings of P. Coon, an insect which differs from the ordinary male P.
Memnon, as much as any two species which can be chosen in this extensive
and highly varied genus; and, as if to show that this resemblance is not
accidental, but is the result of law, when in India we find a species
closely allied to P. Coon, but with red instead of yellow spots (P.
Doubledayi), the corresponding variety of P. Androgeus (P. Achates,
Cramer, 182, A, B,) has acquired exactly the same peculiarity of having
red spots instead of yellow. Lastly, in the island of Timor, the female
of P. Oenomaus (a species allied to P. Memnon) resembles so closely P.
Liris (one of the Polydorus-group), that the two, which were often seen
flying together, could only be distinguished by a minute comparison
after being captured.
The last six cases of mimicry are especially instructive, because they
seem to indicate one of the processes by which dimorphic forms have been
produced. When, as in these cases, one sex differs much from the other,
and varies greatly itself, it may happen that occasionally individual
variations will occur having a distant resemblance to groups which are
the objects of mimicry, and which it is therefore advantageous to
resemble. Such a variety will have a better chance of preservation; the
individuals possessing it will be multiplied; and their accidental
likeness to the favoured group will be rendered permanent by hereditary
transmission, and, each successive variation which increases the
resemblance being preserved, and all variations departing from the
favoured type having less chance of preservation, there will in time
result those singular cases of two or more isolated and fixed forms,
bound together by that intimate relationship which constitutes them the
sexes of a single species. The reason why the females are more subject
to this kind of modification than the males is, probably, that their
slower flight, when laden with eggs, and their exposure to attack while
in the act of depositing their eggs upon leaves, render it especially
advantageous for them to have some additional protection. This they at
once obtain by acquiring a resemblance to other species which, from
whatever cause, enjoy a comparative immunity from persecution.
_Concluding remarks on Variation in Lepidoptera._
This summary of the more interesting phenomena of variation presented by
the eastern Papilionidæ is, I think, sufficient to substantiate my
position, that the Lepidoptera are a group that offer especial
facilities for such inquiries; and it will also show that they have
undergone an amount of special adaptive modification rarely equalled
among the more highly organized animals. And, among the Lepidoptera, the
great and pre-eminently tropical families of Papilionidæ and Danaidæ
seem to be those in which complicated adaptations to the surrounding
organic and inorganic universe have been most completely developed,
offering in this respect a striking analogy to the equally
extraordinary, though totally different, adaptations which present
themselves in the Orchideæ, the only family of plants in which mimicry
of other organisms appears to play any important part, and the only one
in which cases of conspicuous polymorphism occur; for as such we must
class the male, female, and hermaphrodite forms of Catasetum
tridentatum, which differ so greatly in form and structure that they
were long considered to belong to three distinct genera.
_Arrangement and Geographical Distribution of the Malayan Papilionidæ_.
_Arrangement._--Although the species of Papilionidæ inhabiting the
Malayan region are very numerous, they all belong to three out of the
nine genera into which the family is divided. One of the remaining
genera (Eurycus) is restricted to Australia, and another (Teinopalpus)
to the Himalayan Mountains, while no less than four (Parnassius,
Doritis, Thais, and Sericinus) are confined to Southern Europe and to
the mountain-ranges of the Palæarctic region.
The genera Ornithoptera and Leptocircus are highly characteristic of
Malayan entomology, but are uniform in character and of small extent.
The genus Papilio, on the other hand, presents a great variety of forms,
and is so richly represented in the Malay Islands, that more than
one-fourth of all the known species are found there. It becomes
necessary, therefore, to divide this genus into natural groups before we
can successfully study its geographical distribution.
Owing principally to Dr. Horsfield's observations in Java, we are
acquainted with a considerable number of the larvæ of Papilios; and
these furnish good characters for the primary division of the genus into
natural groups. The manner in which the hinder wings are plaited or
folded back at the abdominal margin, the size of the anal valves, the
structure of the antennæ, and the form of the wings are also of much
service, as well as the character of the flight and the style of
colouration. Using these characters, I divide the Malayan Papilios into
four sections, and seventeen groups, as follows:--
Genus ORNITHOPTERA.
a. Priamus-group. } Black and Green.
c. Brookeanus-group.}
b. Pompeus-group. Black and yellow.
Genus PAPILIO.
A. Larvæ short, thick, with numerous fleshy tubercles;
of a purplish colour.
a. Nox-group. Abdominal fold in male very large;
anal valves small, but swollen; antennæ moderate;
wings entire, or tailed; includes the Indian
Philoxenus-group.
b. Coon-group. Abdominal fold in male small; anal
valves small, but swollen; antennæ moderate;
wings tailed.
c. Polydorus-group. Abdominal fold in male small,
or none; anal valves small or obsolete, hairy;
wings tailed or entire.
B. Larvæ with third segment swollen, transversely or
obliquely banded; pupa much bent. Imago with
abdominal margin in male plaited, but not reflexed;
body weak; antennæ long; wings much
dilated, often tailed.
d. Ulysses-group.
{Protenor-group (Indian) is
e. Peranthus-group. {somewhat intermediate between
f. Memnon-group. {these, and is nearest
{to the Nox-group.
g. Helenus-group.
h. Erectheus-group.
i. Pammon-group.
k. Demolion-group.
C. Larvæ subcylindrical, variously coloured. Imago with
abdominal margin in male plaited, but not reflexed;
body weak; antennæ short, with a thick
curved club; wings entire.
l. Erithonius-group. Sexes alike, larva and pupa
something like those of P. Demolion.
m. Paradoxa-group. Sexes different.
n. Dissimilis-group. Sexes alike; larva bright-coloured;
pupa straight, cylindric.
D. Larvæ elongate, attenuate behind, and often bifid, with
lateral and oblique pale stripes, green. Imago
with the abdominal margin in male reflexed,
woolly or hairy within; anal valves small, hairy;
antennæ short, stout; body stout.
o. Macareus-group. Hind wings entire.
p. Antiphates-group. Hind wings much tailed (swallow-tails).
q. Eurypylus-group. Hind wings elongate or tailed.
Genus LEPTOCIRCUS.
Making, in all, twenty distinct groups of Malayan Papilionidæ.
The first section of the genus Papilio (A) comprises insects which,
though differing considerably in structure, having much general
resemblance. They all have a weak, low flight, frequent the most
luxuriant forest-districts, seem to love the shade, and are the objects
of mimicry by other Papilios.
Section B consists of weak-bodied, large-winged insects, with an
irregular wavering flight, and which, when resting on foliage, often
expand the wings, which the species of the other sections rarely or
never do. They are the most conspicuous and striking of eastern
Butterflies.
Section C consists of much weaker and slower-flying insects, often
resembling in their flight, as well as in their colours, species of
Danaidæ.
Section D contains the strongest-bodied and most swift-flying of the
genus. They love sunlight, and frequent the borders of streams and the
edges of puddles, where they gather together in swarms consisting of
several species, greedily sucking up the moisture, and, when disturbed,
circling round in the air, or flying high and with great strength and
rapidity.
_Geographical Distribution._--One hundred and thirty species of Malayan
Papilionidæ are now known within the district extending from the Malay
peninsula, on the north-west, to Woodlark Island, near New Guinea, on
the south-east.
The exceeding richness of the Malayan region in these fine insects is
seen by comparing the number of species found in the different tropical
regions of the earth. From all Africa only 33 species of Papilio are
known; but as several are still undescribed in collections, we may raise
their number to about 40. In all tropical Asia there are at present
described only 65 species, and I have seen in collections but two or
three which have not yet been named. In South America, south of Panama,
there are 150 species, or about one-seventh more than are yet known from
the Malayan region; but the area of the two countries is very different;
for while South America (even excluding Patagonia) contains 5,000,000
square miles, a line encircling the whole of the Malayan islands would
only include an area of 2,700,000 square miles, of which the land-area
would be about 1,000,000 square miles. This superior richness is partly
real and partly apparent. The breaking up of a district into small
isolated portions, as in an archipelago, seems highly favourable to the
segregation and perpetuation of local peculiarities in certain groups;
so that a species which on a continent might have a wide range, and
whose local forms, if any, would be so connected together that it would
be impossible to separate them, may become by isolation reduced to a
number of such clearly defined and constant forms that we are obliged to
count them as species. From this point of view, therefore, the greater
proportionate number of Malayan species may be considered as apparent
only. Its true superiority is shown, on the other hand, by the
possession of three genera and twenty groups of Papilionidæ against a
single genus and eight groups in South America, and also by the much
greater average size of the Malayan species. In most other families,
however, the reverse is the case, the South American Nymphalidæ,
Satyridæ, and Erycinidæ far surpassing those of the East in number,
variety, and beauty.
The following list, exhibiting the range and distribution of each group,
will enable us to study more easily their internal and external
relations.
_Range of the Groups of Malayan Papilionidæ._
Ornithoptera.
1. Priamus-group. Moluccas to Woodlark Island 5 species.
2. Pompeus-group. Himalayas to New Guinea,
(Celebes, maximum) 11"
3. Brookeana-group. Sumatra and Borneo 1"
Papilio.
4. Nox-group. North India, Java, and Philippines 5 species
5. Coon-group. North India to Java 2"
6. Polydorus-group. India to New Guinea
and Pacific 7"
7. Ulysses-group. Celebes to New Caledonia 4"
8. Peranthus-group. India to Timor and
Moluccas (India, maximum) 9"
9. Memnon-group. India to Timor and Moluccas
(Java, maximum) 10"
10. Helenus-group. Africa and India to New
Guinea 11"
11. Pammon-group. India to Pacific and Australia 9"
12. Erectheus-group. Celebes to Australia 2"
13. Demolion-group. India to Celebes 2"
14. Erithonius-group. Africa, India, Australia 1"
15. Paradoxa-group. India to Java (Borneo,
maximum) 5"
16. Dissimilis-group. India to Timor (India,
maximum) 2"
17. Macareus-group. India to New Guinea 10"
18. Antiphates-group. Widely distributed 8"
19. Eurypylus-group. India to Australia 15"
Leptocircus.
20. Leptocircus-group. India to Celebes 4"
This Table shows the great affinity of the Malayan with the Indian
Papilionidæ, only three out of the twenty groups ranging beyond, into
Africa, Europe, or America. The limitation of groups to the Indo-Malayan
or Austro-Malayan divisions of the archipelago, which is so well marked
in the higher animals, is much less conspicuous in insects, but is shown
in some degree by the Papilionidæ. The following groups are either
almost or entirely restricted to one portion of the archipelago:--
_Indo-Malayan Region._ _Austro-Malayan Region._
Nox-group. Priamus-group.
Coon-group. Ulysses-group.
Macareus-group (nearly). Erechtheus-group.
Paradoxa-group.
Dissimilis-group (nearly).
Brookeanus-group.
LEPTOCIRCUS (genus).
The remaining groups, which range over the whole archipelago, are, in
many cases, insects of very powerful flight, or they frequent open
places and the sea-beach, and are thus more likely to get blown from
island to island. The fact that three such characteristic groups as
those of Priamus, Ulysses, and Erechtheus are strictly limited to the
Australian region of the archipelago, while five other groups are with
equal strictness confined to the Indian region, is a strong
corroboration of that division which has been founded almost entirely on
the distribution of Mammalia and Birds.
If the various Malayan islands have undergone recent changes of level,
and if any of them have been more closely united within the period of
existing species than they are now, we may expect to find indications of
such changes in community of species between islands now widely
separated; while those islands which have long remained isolated would
have had time to acquire peculiar forms by a slow and natural process of
modification.
An examination of the relations of the species of the adjacent islands,
will thus enable us to correct opinions formed from a mere consideration
of their relative positions. For example, looking at a map of the
archipelago, it is almost impossible to avoid the idea that Java and
Sumatra have been recently united; their present proximity is so great,
and they have such an obvious resemblance in their volcanic structure.
Yet there can be little doubt that this opinion is erroneous, and that
Sumatra has had a more recent and more intimate connexion with Borneo
than it has had with Java. This is strikingly shown by the mammals of
these islands--very few of the species of Java and Sumatra being
identical, while a considerable number are common to Sumatra and Borneo.
The birds show a somewhat similar relationship; and we shall find that
the distribution of the Papilionidæ tells exactly the same tale. Thus:--
Sumatra has 21 species }
Borneo " 30 " } 20 sp. common to both islands;
Sumatra " 21 " }
Java " 28 " } 11 sp. common to both islands;
Borneo " 30 " }
Java " 28 " } 20 sp. common to both islands;
showing that both Sumatra and Java have a much closer relationship to
Borneo than they have to each other--a most singular and interesting
result, when we consider the wide separation of Borneo from them both,
and its very different structure. The evidence furnished by a single
group of insects would have had but little weight on a point of such
magnitude if standing alone; but coming as it does to confirm deductions
drawn from whole classes of the higher animals, it must be admitted to
have considerable value.
We may determine in a similar manner the relations of the different
Papuan Islands to New Guinea. Of thirteen species of Papilionidæ
obtained in the Aru Islands, six were also found in New Guinea, and
seven not. Of nine species obtained at Waigiou, six were New Guinea, and
three not. The five species found at Mysol were all New Guinea species.
Mysol, therefore, has closer relations to New Guinea than the other
islands; and this is corroborated by the distribution of the birds, of
which I will only now give one instance. The Paradise Bird found in
Mysol is the common New Guinea species, while the Aru Islands and
Waigiou have each a species peculiar to themselves.
The large island of Borneo, which contains more species of Papilionidæ
than any other in the archipelago, has nevertheless only three peculiar
to itself; and it is quite possible, and even probable, that one of
these may be found in Sumatra or Java. The last-named island has also
three species peculiar to it; Sumatra has not one, and the peninsula of
Malacca only two. The identity of species is even greater than in birds
or in most other groups of insects, and points very strongly to a recent
connexion of the whole with each other and the continent.
_Remarkable Peculiarities of the Island of Celebes._
If we now pass to the next island (Celebes), separated from those last
mentioned by a strait not wider than that which divides them from each
other, we have a striking contrast; for with a total number of species
less than either Borneo or Java, no fewer than eighteen are absolutely
restricted to it. Further east, the large islands of Ceram and New
Guinea have only three species peculiar to each, and Timor has five. We
shall have to look, not to single islands, but to whole groups, in order
to obtain an amount of individuality comparable with that of Celebes.
For example, the extensive group comprising the large islands of Java,
Borneo, and Sumatra, with the peninsula of Malacca, possessing
altogether 48 species, has about 24, or just half, peculiar to it; the
numerous group of the Philippines possess 22 species, of which 17 are
peculiar; the seven chief islands of the Moluccas have 27, of which 12
are peculiar; and the whole of the Papuan Islands, with an equal number
of species, have 17 peculiar. Comparable with the most isolated of these
groups is Celebes, with its 24 species, of which the large proportion of
18 are peculiar. We see, therefore, that the opinion I have elsewhere
expressed, of the high degree of isolation and the remarkable
distinctive features of this interesting island, is fully borne out by
the examination of this conspicuous family of insects. A single
straggling island with a few small satellites, it is zoologically of
equal importance with extensive groups of islands many times as large
as itself; and standing in the very centre of the archipelago,
surrounded on every side with islets connecting it with the larger
groups, and which seem to afford the greatest facilities for the
migration and intercommunication of their respective productions, it yet
stands out conspicuous with a character of its own in every department
of nature, and presents peculiarities which are, I believe, without a
parallel in any similar locality on the globe.
Briefly to summarize these peculiarities, Celebes possesses three genera
of mammals (out of the very small number which inhabit it) which are of
singular and isolated forms, viz., Cynopithecus, a tailless Ape allied
to the Baboons; Anoa, a straight-horned Antelope of obscure affinities,
but quite unlike anything else in the whole archipelago or in India: and
Babirusa, an altogether abnormal wild Pig. With a rather limited bird
population, Celebes has an immense preponderance of species confined to
it, and has also six remarkable genera (Meropogon, Ceycopsis,
Streptocitta, Enodes, Scissirostrum, and Megacephalon) entirely
restricted to its narrow limits, as well as two others (Prioniturus and
Basilornis) which only range to a single island beyond it.
Mr. Smith's elaborate tables of the distribution of Malayan Hymenoptera
(see "Proc. Linn. Soc." Zool. vol. vii.) show that out of the large
number of 301 species collected in Celebes, 190 (or nearly two-thirds)
are absolutely restricted to it, although Borneo on one side, and the
various islands of the Moluccas on the other, were equally well explored
by me; and no less than twelve of the genera are not found in any other
island of the archipelago. I have shown in the present essay that, in
the Papilionidæ, it has far more species of its own than any other
island, and a greater proportion of peculiar species than many of the
large groups of islands in the archipelago--and that it gives to a large
number of the species and varieties which inhabit it, 1st, an increase
of size, and, 2nd, a peculiar modification in the form of the wings,
which stamp upon the most dissimilar insects a mark distinctive of their
common birth-place.
What, I would ask, are we to do with phenomena such as these? Are we to
rest content with that very simple, but at the same time very
unsatisfying explanation, that all these insects and other animals were
created exactly _as_ they are, and originally placed exactly _where_
they are, by the inscrutable will of their Creator, and that we have
nothing to do but to register the facts and wonder? Was this single
island selected for a fantastic display of creative power, merely to
excite a childlike and unreasoning admiration? Is all this appearance of
gradual modification by the action of natural causes--a modification the
successive steps of which we can almost trace--all delusive? Is this
harmony between the most diverse groups, all presenting analogous
phenomena, and indicating a dependence upon physical changes of which we
have independent evidence, all false testimony? If I could think so, the
study of nature would have lost for me its greatest charm. I should
feel as would the geologist, if you could convince him that his
interpretation of the earth's past history was all a delusion--that
strata were never formed in the primeval ocean, and that the fossils he
so carefully collects and studies are no true record of a former living
world, but were all created just as they now are, and in the rocks where
he now finds them.
I must here express my own belief that none of these phenomena, however
apparently isolated or insignificant, can ever stand alone--that not the
wing of a butterfly can change in form or vary in colour, except in
harmony with, and as a part of the grand march of nature. I believe,
therefore, that all the curious phenomena I have just recapitulated, are
immediately dependent on the last series of changes, organic and
inorganic, in these regions; and as the phenomena presented by the
island of Celebes differ from those of all the surrounding islands, it
can, I conceive, only be because the past history of Celebes has been,
to some extent, unique and different from theirs. We must have much more
evidence to determine exactly in what that difference has consisted. At
present, I only see my way clear to one deduction, viz., that Celebes
represents one of the oldest parts of the archipelago; that it has been
formerly more completely isolated both from India and from Australia
than it is now, and that amid all the mutations it has undergone, a
relic or substratum of the fauna and flora of some more ancient land has
been here preserved to us.
It is only since my return home, and since I have been able to compare
the productions of Celebes side by side with those of the surrounding
islands, that I have been fully impressed with their peculiarity, and
the great interest that attaches to them. The plants and the reptiles
are still almost unknown; and it is to be hoped that some enterprising
naturalist may soon devote himself to their study. The geology of the
country would also be well worth exploring, and its newer fossils would
be of especial interest as elucidating the changes which have led to its
present anomalous condition. This island stands, as it were, upon the
boundary-line between two worlds. On one side is that ancient Australian
fauna, which preserves to the present day the facies of an early
geological epoch; on the other is the rich and varied fauna of Asia,
which seems to contain, in every class and order, the most perfect and
highly organised animals. Celebes has relations to both, yet strictly
belongs to neither: it possesses characteristics which are altogether
its own; and I am convinced that no single island upon the globe would
so well repay a careful and detailed research into its past and present
history.
_Concluding Remarks._
In writing this essay it has been my object to show how much may, under
favourable circumstances, be learnt by the study of what may be termed
the external physiology of a small group of animals, inhabiting a
limited district. This branch of natural history had received little
attention till Mr. Darwin showed how important an adjunct it may become
towards a true interpretation of the history of organized beings, and
attracted towards it some small share of that research which had before
been almost exclusively devoted to internal structure and physiology.
The nature of species, the laws of variation, the mysterious influence
of locality on both form and colour, the phenomena of dimorphism and of
mimicry, the modifying influence of sex, the general laws of
geographical distribution, and the interpretation of past changes of the
earth's surface, have all been more or less fully illustrated by the
very limited group of the Malayan Papilionidæ; while, at the same time,
the deductions drawn therefrom have been shown to be supported by
analogous facts, occurring in other and often widely-separated groups of
animals.
V.
ON INSTINCT IN MAN AND ANIMALS.
The most perfect and most striking examples of what is termed instinct,
those in which reason or observation appear to have the least influence,
and which seem to imply the possession of faculties farthest removed
from our own, are to be found among insects. The marvellous constructive
powers of bees and wasps, the social economy of ants, the careful
provision for the safety of a progeny they are never to see manifested
by many beetles and flies, and the curious preparations for the pupa
state by the larvæ of butterflies and moths, are typical examples of
this faculty, and are supposed to be conclusive as to the existence of
some power or intelligence, very different from that which we derive
from our senses or from our reason.
_How Instinct may be best Studied._
Whatever we may define instinct to be, it is evidently some form of
mental manifestation, and as we can only judge of mind by the analogy of
our own mental functions and by observation of the results of mental
action in other men and in animals, it is incumbent on us, first, to
study and endeavour to comprehend the minds of infants, of savage men,
and of animals not very far removed from ourselves, before we pronounce
positively as to the nature of the mental operations in creatures so
radically different from us as insects. We have not yet even been able
to ascertain what are the senses they possess, or what relation their
powers of seeing, hearing, and feeling have to ours. Their sight may far
exceed ours both in delicacy and in range, and may possibly give them
knowledge of the internal constitution of bodies analogous to that which
we obtain by the spectroscope; and that their visual organs do possess
some powers which ours do not, is indicated by the extraordinary
crystalline rods radiating from the optic ganglion to the facets of the
compound eye, which rods vary in form and thickness in different parts
of their length, and possess distinctive characters in each group of
insects. This complex apparatus, so different from anything in the eyes
of vertebrates, may subserve some function quite inconceivable by us, as
well as that which we know as vision. There is reason to believe that
insects appreciate sounds of extreme delicacy, and it is supposed that
certain minute organs, plentifully supplied with nerves, and situated in
the subcostal vein of the wing in most insects, are the organs of
hearing. But besides these, the Orthoptera (such as grasshoppers, &c.)
have what are supposed to be ears on their fore legs, and Mr. Lowne
believes that the little stalked balls, which are the sole remnants of
the hind wings in flies, are also organs of hearing or of some analogous
sense. In flies, too, the third joint of the antennæ contains thousands
of nerve-fibres, which terminate in small open cells, and this Mr. Lowne
believes to be the organ of smell, or of some other, perhaps new, sense.
It is quite evident, therefore, that insects may possess senses which
give them a knowledge of that which we can never perceive, and enable
them to perform acts which to us are incomprehensible. In the midst of
this complete ignorance of their faculties and inner nature, is it wise
for us to judge so boldly of their powers by a comparison with our own?
How can we pretend to fathom the profound mystery of their mental
nature, and decide what, and how much, they can perceive or remember,
reason or reflect! To leap at one bound from our own consciousness to
that of an insect's, is as unreasonable and absurd as if, with a pretty
good knowledge of the multiplication table, we were to go straight to
the study of the calculus of functions, or as if our comparative
anatomists should pass from the study of man's bony structure to that of
the fish, and, without any knowledge of the numerous intermediate forms,
were to attempt to determine the homologies between these distant types
of vertebrata. In such a case would not error be inevitable, and would
not continued study in the same direction only render the erroneous
conclusions more ingrained and more irremovable.
_Definition of Instinct._
Before going further into this subject, we must determine what we mean
by the term instinct. It has been variously defined as--"disposition
operating without the aid of instruction or experience," "a mental power
totally independent of organization," or "a power enabling an animal to
do that which, in those things man can do, results from a chain of
reasoning, and in things which man cannot do, is not to be explained by
any efforts of the intellectual faculties." We find, too, that the word
instinct is very frequently applied to acts which are evidently the
result either of organization or of habit. The colt or calf is said to
walk instinctively, almost as soon as it is born; but this is solely due
to its organization, which renders walking both possible and pleasurable
to it. So we are said instinctively to hold out our hands to save
ourselves from falling, but this is an acquired habit, which the infant
does not possess. It appears to me that instinct should be defined
as--"the performance by an animal of complex acts, absolutely without
instruction or previously-acquired knowledge." Thus, acts are said to be
performed by birds in building their nests, by bees in constructing
their cells, and by many insects in providing for the future wants of
themselves or their progeny, without ever having seen such acts
performed by others, and without any knowledge of why they perform them
themselves. This is expressed by the very common term "blind instinct."
But we have here a number of assertions of matters of fact, which,
strange to say, have never been proved to be facts at all. They are
thought to be so self-evident that they may be taken for granted. No
one has ever yet obtained the eggs of some bird which builds an
elaborate nest, hatched these eggs by steam or under a quite distinct
parent, placed them afterwards in an extensive aviary or covered garden,
where the situation and the materials of a nest similar to that of the
parent birds may be found, and then seen what kind of nest these birds
would build. If under these rigorous conditions they choose the same
materials, the same situation, and construct the nest in the same way
and as perfectly as their parents did, instinct would be proved in their
case; now it is only assumed, and assumed, as I shall show further on,
without any sufficient reason. So, no one has ever carefully taken the
pupæ of a hive of bees out of the comb, removed them from the presence
of other bees, and loosed them in a large conservatory with plenty of
flowers and food, and observed what kind of cells they would construct.
But till this is done, no one can say that bees build without
instruction, no one can say that with every new swarm there are no bees
older than those of the same year, who may be the teachers in forming
the new comb. Now, in a scientific inquiry, a point which can be proved
should not be assumed, and a totally unknown power should not be brought
in to explain facts, when known powers may be sufficient. For both these
reasons I decline to accept the theory of instinct in any case where all
other possible modes of explanation have not been exhausted.
_Does Man possess Instincts._
Many of the upholders of the instinctive theory maintain, that man has
instincts exactly of the same nature as those of animals, but more or
less liable to be obscured by his reasoning powers; and as this is a
case more open to our observation than any other, I will devote a few
pages to its consideration. Infants are said to suck by instinct, and
afterwards to walk by the same power, while in adult man the most
prominent case of instinct is supposed to be, the powers possessed by
savage races to find their way across a trackless and previously unknown
wilderness. Let us take first the case of the infant's sucking. It is
sometimes absurdly stated that the new-born infant "seeks the breast,"
and this is held to be a wonderful proof of instinct. No doubt it would
be if true, but unfortunately for the theory it is totally false, as
every nurse and medical man can testify. Still, the child undoubtedly
sucks without teaching, but this is one of those _simple_ acts dependent
upon organization, which cannot properly be termed instinct, any more
than breathing or muscular motion. Any object of suitable size in the
mouth of an infant excites the nerves and muscles so as to produce the
act of suction, and when at a little later period, the will comes into
play, the pleasurable sensations consequent on the act lead to its
continuance. So, walking is evidently dependent on the arrangement of
the bones and joints, and the pleasurable exertion of the muscles, which
lead to the vertical posture becoming gradually the most agreeable one;
and there can be little doubt that an infant would learn of itself to
walk, even if suckled by a wild beast.
_How Indians travel through unknown and trackless Forests._
Let us now consider the fact, of Indians finding their way through
forests they have never traversed before. This is much misunderstood,
for I believe it is only performed under such special conditions, as at
once to show that instinct has nothing to do with it. A savage, it is
true, can find his way through his native forests in a direction in
which he has never traversed them before; but this is because from
infancy he has been used to wander in them, and to find his way by
indications which he has observed himself or learnt from others. Savages
make long journeys in many directions, and, their whole faculties being
directed to the subject, they gain a wide and accurate knowledge of the
topography, not only of their own district, but of all the regions round
about. Every one who has travelled in a new direction communicates his
knowledge to those who have travelled less, and descriptions of routes
and localities, and minute incidents of travel, form one of the main
staples of conversation round the evening fire. Every wanderer or
captive from another tribe adds to the store of information, and as the
very existence of individuals and of whole families and tribes, depends
upon the completeness of this knowledge, all the acute perceptive
faculties of the adult savage are devoted to acquiring and perfecting
it. The good hunter or warrior thus comes to know the bearing of every
hill and mountain range, the directions and junctions of all the
streams, the situation of each tract characterized by peculiar
vegetation, not only within the area he has himself traversed, but for
perhaps a hundred miles around it. His acute observation enables him to
detect the slightest undulations of the surface, the various changes of
subsoil and alterations in the character of the vegetation, that would
be quite imperceptible to a stranger. His eye is always open to the
direction in which he is going; the mossy side of trees, the presence of
certain plants under the shade of rocks, the morning and evening flight
of birds, are to him indications of direction, almost as sure as the sun
in the heavens. Now, if such a savage is required to find his way across
this country in a direction in which he has never been before, he is
quite equal to the task. By however circuitous a route he has come to
the point he is to start from, he has observed all the bearings and
distances so well, that he knows pretty nearly where he is, the
direction of his own home and that of the place he is required to go to.
He starts towards it, and knows that by a certain time he must cross an
upland or a river, that the streams should flow in a certain direction,
and that he should cross some of them at a certain distance from their
sources. The nature of the soil throughout the whole region is known to
him, as well as all the great features of the vegetation. As he
approaches any tract of country he has been in or near before, many
minute indications guide him, but he observes them so cautiously that
his white companions cannot perceive by what he has directed his course.
Every now and then he slightly changes his direction, but he is never
confused, never loses himself, for he always feels at home; till at last
he arrives at a well-known country, and directs his course so as to
reach the exact spot desired. To the Europeans whom he guides, he seems
to have come without trouble, without any special observation, and in a
nearly straight unchanging course. They are astonished, and ask if he
has ever been the same route before, and when he answers "No," conclude
that some unerring instinct could alone have guided him. But take this
same man into another country very similar to his own, but with other
streams and hills, another kind of soil, with a somewhat different
vegetation and animal life; and after bringing him by a circuitous route
to a given point, ask him to return to his starting place, by a straight
line of fifty miles through the forest, and he will certainly decline to
attempt it, or, attempting it, will more or less completely fail. His
supposed instinct does not act out of his own country.
A savage, even in a new country, has, however, undoubted advantages,
from his familiarity with forest life, his entire fearlessness of being
lost, his accurate perception of direction and of distance, and he is
thus able very soon to acquire a knowledge of the district that seems
marvellous to a civilized man; but my own observation of savages in
forest countries has convinced me, that they find their way by the use
of no other faculties than those which we ourselves possess. It appears
to me, therefore, that to call in the aid of a new and mysterious power
to account for savages being able to do that which, under similar
conditions, we could almost all of us perform, although perhaps less
perfectly, is almost ludicrously unnecessary.
In the next essay I shall attempt to show, that much of what has been
attributed to instinct in birds, can be also very well explained by
crediting them with those faculties of observation, memory, and
imitation, and with that limited amount of reason, which they
undoubtedly exhibit.
VI.
THE PHILOSOPHY OF BIRDS' NESTS.
_Instinct or Reason in the Construction of Birds' Nests._
Birds, we are told, build their nests by _instinct_, while man
constructs his dwelling by the exercise of _reason_. Birds never change,
but continue to build for ever on the self-same plan; man alters and
improves his houses continually. Reason advances; instinct is
stationary.
This doctrine is so very general that it may almost be said to be
universally adopted. Men who agree on nothing else, accept this as a
good explanation of the facts. Philosophers and poets, metaphysicians
and divines, naturalists and the general public, not only agree in
believing this to be probable, but even adopt it as a sort of axiom that
is so self-evident as to need no proof, and use it as the very
foundation of their speculations on instinct and reason. A belief so
general, one would think, must rest on indisputable facts, and be a
logical deduction from them. Yet I have come to the conclusion that not
only is it very doubtful, but absolutely erroneous; that it not only
deviates widely from the truth, but is in almost every particular
exactly opposed to it. I believe, in short, that birds do _not_ build
their nests by instinct; that man does _not_ construct his dwelling by
reason; that birds do change and improve when affected by the same
causes that make men do so; and that mankind neither alter nor improve
when they exist under conditions similar to those which are almost
universal among birds.
_Do Men build by Reason or by Imitation?_
Let us first consider the theory of reason, as alone determining the
domestic architecture of the human race. Man, as a reasonable animal, it
is said, continually alters and improves his dwelling. This I entirely
deny. As a rule, he neither alters nor improves, any more than the birds
do. What have the houses of most savage tribes improved from, each as
invariable as the nest of a species of bird? The tents of the Arab are
the same now as they were two or three thousand years ago, and the mud
villages of Egypt can scarcely have improved since the time of the
Pharaohs. The palm-leaf huts and hovels of the various tribes of South
America and the Malay Archipelago, what have they improved from since
those regions were first inhabited? The Patagonian's rude shelter of
leaves, the hollowed bank of the South African Earthmen, we cannot even
conceive to have been ever inferior to what they now are. Even nearer
home, the Irish turf cabin and the Highland stone shelty can hardly have
advanced much during the last two thousand years. Now, no one imputes
this stationary condition of domestic architecture among these savage
tribes to instinct, but to simple imitation from one generation to
another, and the absence of any sufficiently powerful stimulus to
change or improvement. No one imagines that if an infant Arab could be
transferred to Patagonia, or to the Highlands, it would, when it grew
up, astonish its foster-parents by constructing a tent of skins. On the
other hand, it is quite clear that physical conditions, combined with
the degree of civilization arrived at, almost necessitate certain types
of structure. The turf, or stones, or snow--the palm-leaves, bamboo, or
branches, which are the materials of houses in various countries, are
used because nothing else is so readily to be obtained. The Egyptian
peasant has none of these, not even wood. What, then, can he use but
mud? In tropical forest-countries, the bamboo and the broad palm-leaves
are the natural material for houses, and the form and mode of structure
will be decided in part by the nature of the country, whether hot or
cool, whether swampy or dry, whether rocky or plain, whether frequented
by wild beasts, or whether subject to the attacks of enemies. When once
a particular mode of building has been adopted, and has become confirmed
by habit and by hereditary custom, it will be long retained, even when
its utility has been lost through changed conditions, or through
migration into a very different region. As a general rule, throughout
the whole continent of America, native houses are built directly upon
the ground--strength and security being given by thickening the low
walls and the roof. In almost the whole of the Malay Islands, on the
contrary, the houses are raised on posts, often to a great height, with
an open bamboo floor; and the whole structure is exceedingly slight and
thin. Now, what can be the reason of this remarkable difference between
countries, many parts of which are strikingly similar in physical
conditions, natural productions, and the state of civilization of their
inhabitants? We appear to have some clue to it in the supposed origin
and migrations of their respective populations. The indigenes of
tropical America are believed to have immigrated from the north--from a
country where the winters are severe, and raised houses with open floors
would be hardly habitable. They moved southwards by land along the
mountain ranges and uplands, and in an altered climate continued the
mode of construction of their forefathers, modified only by the new
materials they met with. By minute observations of the Indians of the
Amazon Valley, Mr. Bates arrived at the conclusion that they were
comparatively recent immigrants from a colder climate. He says:--"No one
could live long among the Indians of the Upper Amazon without being
struck with their constitutional dislike to the heat ... Their skin is
hot to the touch, and they perspire little ... They are restless and
discontented in hot, dry weather, but cheerful on cool days, when the
rain is pouring down their naked backs." And, after giving many other
details, he concludes, "How different all this is with the Negro, the
true child of tropical climes! The impression gradually forced itself on
my mind that the Red Indian lives as an immigrant or stranger in these
hot regions, and that his constitution was not originally adapted, and
has not since become perfectly adapted, to the climate."
The Malay races, on the other hand, are no doubt very ancient
inhabitants of the hottest regions, and are particularly addicted to
forming their first settlements at the mouths of rivers or creeks, or in
land-locked bays and inlets. They are a pre-eminently maritime or
semi-aquatic people, to whom a canoe is a necessary of life, and who
will never travel by land if they can do so by water. In accordance with
these tastes, they have built their houses on posts in the water, after
the manner of the lake-dwellers of ancient Europe; and this mode of
construction has become so confirmed, that even those tribes who have
spread far into the interior, on dry plains and rocky mountains,
continue to build in exactly the same manner, and find safety in the
height to which they elevate their dwellings above the ground.
_Why does each Bird build a peculiar kind of Nest?_
These general characteristics of the abode of savage man will be found
to be exactly paralleled by the nests of birds. Each species uses the
materials it can most readily obtain, and builds in situations most
congenial to its habits. The wren, for example, frequenting hedgerows
and low thickets, builds its nest generally of _moss_, a material always
found where it lives, and among which it probably obtains much of its
insect food; but it varies sometimes, using hay or feathers when these
are at hand. Rooks dig in pastures and ploughed fields for grubs, and
in doing so must continually encounter _roots_ and _fibres_. These are
used to line its nest. What more natural! The crow feeding on carrion,
dead rabbits, and lambs, and frequenting sheep-walks and warrens,
chooses _fur_ and _wool_ to line its nest. The lark frequents cultivated
fields, and makes its nest, on the ground, of grass lined with
_horsehair_--materials the most easy to meet with, and the best adapted
to its needs. The kingfisher makes its nest of the _bones_ of the fish
which it has eaten. Swallows use clay and mud from the margins of the
ponds and rivers over which they find their insect food. The materials
of birds' nests, like those used by savage man for his house, are, then,
those which come first to hand; and it certainly requires no more
special instinct to select them in one case than in the other.
But, it will be said, it is not so much the materials as the form and
structure of nests, that vary so much, and are so wonderfully adapted to
the wants and habits of each species; how are these to be accounted for
except by instinct? I reply, they may be in a great measure explained by
the general habits of the species, the nature of the tools they have to
work with, and the materials they can most easily obtain, with the very
simplest adaptations of means to an end, quite within the mental
capacities of birds. The delicacy and perfection of the nest will bear a
direct relation to the size of the bird, its structure and habits. That
of the wren or the humming-bird is perhaps not finer or more beautiful
in proportion than that of the blackbird, the magpie, or the crow. The
wren, having a slender beak, long legs, and great activity, is able with
great ease to form a well-woven nest of the finest materials, and places
it in thickets and hedgerows which it frequents in its search for food.
The titmouse, haunting fruit-trees and walls, and searching in cracks
and crannies for insects, is naturally led to build in holes where it
has shelter and security; while its great activity, and the perfection
of its tools (bill and feet), enable it readily to form a beautiful
receptacle for its eggs and young. Pigeons having heavy bodies and weak
feet and bills (imperfect tools for forming a delicate structure) build
rude, flat nests of sticks, laid across strong branches which will bear
their weight and that of their bulky young. They can do no better. The
Caprimulgidæ have the most imperfect tools of all, feet that will not
support them except on a flat surface (for they cannot truly perch) and
a bill excessively broad, short, and weak, and almost hidden by feathers
and bristles. They cannot build a nest of twigs or fibres, hair or moss,
like other birds, and they therefore generally dispense with one
altogether, laying their eggs on the bare ground, or on the stump or
flat limb of a tree. The clumsy hooked bills, short necks and feet, and
heavy bodies of Parrots, render them quite incapable of building a nest
like most other birds. They cannot climb up a branch without using both
bill and feet; they cannot even turn round on a perch without holding on
with their bill. How, then, could they inlay, or weave, or twist the
materials of a nest? Consequently, they all lay in holes of trees, the
tops of rotten stumps, or in deserted ants' nests, the soft materials of
which they can easily hollow out.
Many terns and sandpipers lay their eggs on the bare sand of the
sea-shore, and no doubt the Duke of Argyll is correct when he says, that
the cause of this habit is not that they are unable to form a nest, but
that, in such situations, any nest would be conspicuous and lead to the
discovery of the eggs. The choice of _place_ is, however, evidently
determined by the habits of the birds, who, in their daily search for
food, are continually roaming over extensive tide-washed flats. Gulls
vary considerably in their mode of nesting, but it is always in
accordance with their structure and habits. The situation is either on a
bare rock or on ledges of sea-cliffs, in marshes or on weedy shores. The
materials are sea-weed, tufts of grass or rushes, or the _débris_ of the
shore, heaped together with as little order and constructive art as
might be expected from the webbed feet and clumsy bill of these birds,
the latter better adapted for seizing fish than for forming a delicate
nest. The long-legged, broad-billed flamingo, who is continually
stalking over muddy flats in search of food, heaps up the mud into a
conical stool, on the top of which it lays its eggs. The bird can thus
sit upon them conveniently, and they are kept dry, out of reach of the
tides.
Now I believe that throughout the whole class of birds the same general
principles will be found to hold good, sometimes distinctly, sometimes
more obscurely apparent, according as the habits of the species are more
marked, or their structure more peculiar. It is true that, among birds
differing but little in structure or habits, we see considerable
diversity in the mode of nesting, but we are now so well assured that
important changes of climate and of surface have occurred within the
period of existing species, that it is by no means difficult to see how
such differences have arisen. Simple habits are known to be hereditary,
and as the area now occupied by each species is different from that of
every other, we may be sure that such changes would act differently upon
each, and would often bring together species which had acquired their
peculiar habits in distinct regions and under different conditions.
_How do Young Birds learn to Build their First Nest?_
But it is objected, birds do not _learn_ to make their nest as man does
to build, for all birds will make exactly the same nest as the rest of
their species, even if they have never seen one, and it is instinct
alone that can enable them to do this. No doubt this would be instinct
if it were true, and I simply ask for proof of the fact. This point,
although so important to the question at issue, is always assumed
without proof, and even against proof, for what facts there are, are
opposed to it. Birds brought up from the egg in cages do not make the
characteristic nest of their species, even though the proper materials
are supplied them, and often make no nest at all, but rudely heap
together a quantity of materials; and the experiment has never been
fairly tried, of turning out a pair of birds so brought up, into an
enclosure covered with netting, and watching the result of their
untaught attempts at nest-making. With regard to the songs of birds,
however, which is thought to be equally instinctive, the experiment has
been tried, and it is found that young birds never have the song
peculiar to their species if they have not heard it, whereas they
acquire very easily the song of almost any other bird with which they
are associated.
_Do Birds sing by Instinct or by Imitation?_
The Hon. Daines Barrington was of opinion that "notes in birds are no
more innate than language is in man, and depend entirely on the master
under which they are bred, _as far as their organs will enable them to
imitate_ the sounds which they have frequent opportunities of hearing."
He has given an account of his experiments in the "Philosophical
Transactions" for 1773 (Vol. 63); he says: "I have educated nestling
linnets under the three best singing larks--the skylark, woodlark, and
titlark, every one of which, instead of the linnet's song, adhered
entirely to that of their respective instructors. When the note of the
titlark linnet was thoroughly fixed, I hung the bird in a room with two
common linnets for a quarter of a year, which were full in song; the
titlark linnet, however, did not borrow any passage from the linnet's
song, but adhered stedfastly to that of the titlark." He then goes on
to say that birds taken from the nest at two or three weeks old have
already learnt the call-note of their species. To prevent this the birds
must be taken from the nest when a day or two old, and he gives an
account of a goldfinch which he saw at Knighton in Radnorshire, and
which sang exactly like a wren, without any portion of the proper note
of its species. This bird had been taken from the nest at two or three
days old, and had been hung at a window opposite a small garden, where
it had undoubtedly acquired the notes of the wren without having any
opportunity of learning even the call of the goldfinch.
He also saw a linnet, which had been taken from the nest when only two
or three days old, and which, not having any other sounds to imitate,
had learnt almost to articulate, and could repeat the words "Pretty
Boy," and some other short sentences.
Another linnet was educated by himself under a _vengolina_ (a small
African finch, which he says sings better than any foreign bird but the
American mocking bird), and it imitated its African master so exactly
that it was impossible to distinguish the one from the other.
Still more extraordinary was the case of a common house sparrow, which
only chirps in a wild state, but which learnt the song of the linnet and
goldfinch by being brought up near those birds.
The Rev. W. H. Herbert made similar observations, and states that the
young whinchat and wheatear, which have naturally little variety of
song, are ready in confinement to learn from other species, and become
much better songsters. The bullfinch, whose natural notes are weak,
harsh, and insignificant, has nevertheless a wonderful musical faculty,
since it can be taught to whistle complete tunes. The nightingale, on
the other hand, whose natural song is so beautiful, is exceedingly apt
in confinement to learn that of other birds instead. Bechstein gives an
account of a redstart which had built under the eaves of his house,
which imitated the song of a caged chaffinch in a window underneath,
while another in his neighbour's garden repeated some of the notes of a
blackcap, which had a nest close by.
These facts, and many others which might be quoted, render it certain
that the peculiar notes of birds are acquired by imitation, as surely as
a child learns English or French, not by instinct, but by hearing the
language spoken by its parents.
It is especially worthy of remark that, for young birds to acquire a new
song correctly, they must be taken out of hearing of their parents very
soon, for in the first three or four days they have already acquired
some knowledge of the parent notes, which they will afterwards imitate.
This shows that very young birds can both hear and remember, and it
would be very extraordinary if, after they could see, they could neither
observe nor recollect, and could live for days and weeks in a nest and
know nothing of its materials and the manner of its construction.
During the time they are learning to fly and return often to the nest,
they must be able to examine it inside and out in every detail, and as
we have seen that their daily search for food invariably leads them
among the materials of which it is constructed, and among places similar
to that in which it is placed, is it so very wonderful that when they
want one themselves they should make one like it? How else, in fact,
should they make it? Would it not be much more remarkable if they went
out of their way to get materials quite different from those used in the
parent nest, if they arranged them in a way they had seen no example of,
and formed the whole structure differently from that in which they
themselves were reared, and which we may fairly presume is that which
their whole organization is best adapted to put together with celerity
and ease? It has, however, been objected that observation, imitation, or
memory, can have nothing to do with a bird's architectural powers,
because the young birds, which in England are born in May or June, will
proceed in the following April or May to build a nest as perfect and as
beautiful as that in which it was hatched, although it could never have
seen one built. But surely the young birds _before_ they left the nest
had ample opportunities of observing its _form_, its _size_, its
_position_, the _materials_ of which it was constructed, and the manner
in which those materials were arranged. Memory would retain these
observations till the following spring, when the materials would come in
their way during their daily search for food, and it seems highly
probable that the older birds would begin building first, and that those
born the preceding summer would follow their example, learning from them
how the foundations of the nest are laid and the materials put
together.[H]
+--------------------------------------------------------------+
| [H] It has been very pertinently remarked by a friend, that, |
| if young birds did observe the nest they were reared in, |
| they would consider it to be a natural production like the |
| leaves and branches and matted twigs that surrounded it, and |
| could not possibly conclude that their parents had |
| constructed the one and not the other. This may be a valid |
| objection, and, if so, we shall have to depend on the mode |
| of instruction described in the succeeding paragraphs, but |
| the question can only be finally decided by a careful set of |
| experiments. |
+--------------------------------------------------------------+
Again, we have no right to assume that young birds generally pair
together. It seems probable that in each pair there is most frequently
only one bird born the preceding summer, who would be guided, to some
extent, by its partner.
My friend, Mr. Richard Spruce, the well-known traveller and botanist,
thinks this is the case, and has kindly allowed me to publish the
following observations, which he sent me after reading my book.
_How young Birds may learn to build Nests._
"Among the Indians of Peru and Ecuador, many of whose customs are relics
of the semi-civilisation that prevailed before the Spanish conquest, it
is usual for the young men to marry old women, and the young women old
men. A young man, they say, accustomed to be tended by his mother, would
fare ill if he had only an ignorant young girl to take care of him; and
the girl herself would be better off with a man of mature years, capable
of supplying the place of a father to her.
"Something like this custom prevails among many animals. A stout old
buck can generally fight his way to the doe of his choice, and indeed of
as many does as he can manage; but a young buck 'of his first horns,'
must either content himself with celibacy, or with some dame
well-stricken in years.
"Compare the nearly parallel case of the domestic cock and of many other
birds. Then consider the consequences amongst birds that pair, if an old
cock sorts with a young hen and an old hen with a young cock, as I think
is certainly the case with blackbirds and others that are known to fight
for the youngest and handsomest females. One of each pair being already
an 'old bird,' will be competent to instruct its younger partner (not
only in the futility of 'chaff,' but) in the selection of a site for a
nest and how to build it; then, how eggs are hatched and young birds
reared.
"Such, in brief, is my idea of how a bird on its first espousals may be
taught the Whole Duty of the married state."
On this difficult point I have sought for information from some of our
best field ornithologists, but without success, as it is in most cases
impossible to distinguish old from young birds after the first year. I
am informed, however, that the males of blackbirds, sparrows, and many
other kinds fight furiously, and the conqueror of course has the choice
of a mate. Mr. Spruce's view is at least as probable as the contrary one
(that young birds, _as a rule_, pair together), and it is to some extent
supported by the celebrated American observer, Wilson, who strongly
insists on the variety in the nests of birds of the same species, some
being so much better finished than others; and he believes _that the
less perfect nests are built by the younger, the more perfect by the
older, birds_.
At all events, till the crucial experiment is made, and a pair of birds
raised from the egg without ever seeing a nest are shown to be capable
of making one exactly of the parental type, I do not think we are
justified in calling in the aid of an unknown and mysterious faculty to
do that which is so strictly analogous to the house-building of savage
man.
Again, we always assume that because a nest appears to us delicately and
artfully built, that it therefore requires much special knowledge and
acquired skill (or their substitute, instinct) in the bird who builds
it. We forget that it is formed twig by twig and fibre by fibre, rudely
enough at first, but crevices and irregularities, which must seem huge
gaps and chasms in the eyes of the little builders, are filled up by
twigs and stalks pushed in by slender beak and active foot, and that the
wool, feathers, or horsehair are laid thread by thread, so that the
result seems a marvel of ingenuity to us, just as would the rudest
Iinand hut to a native of Brobdignag. Levaillant has given an account
of the process of nest-building by a little African warbler, which
sufficiently shows that a very beautiful structure may be produced with
very little art. The foundation was laid of moss and flax interwoven
with grass and tufts of cotton, and presented a rude mass, five or six
inches in diameter, and four inches thick. This was pressed and trampled
down repeatedly, so as at last to make it into a kind of felt. The birds
pressed it with their bodies, turning round upon them in every
direction, so as to get it quite firm and smooth before raising the
sides. These were added bit by bit, trimmed and beaten with the wings
and feet, so as to felt the whole together, projecting fibres being now
and then worked in with the bill. By these simple and apparently
inefficient means, the inner surface of the nest was rendered almost as
smooth and compact as a piece of cloth.
_Man's Works mainly Imitative._
But look at civilised man! it is said; look at Grecian, and Egyptian,
and Roman, and Gothic, and modern Architecture! What advance! what
improvement! what refinements! This is what reason leads to, whereas
birds remain for ever stationary. If, however, such advances as these
are required, to prove the effects of reason as contrasted with
instinct, then all savage and many half-civilized tribes have no reason,
but build instinctively quite as much as birds do.
Man ranges over the whole earth, and exists under the most varied
conditions, leading necessarily to equally varied habits. He
migrates--he makes wars and conquests--one race mingles with
another--different customs are brought into contact--the habits of a
migrating or conquering race are modified by the different circumstances
of a new country. The civilized race which conquered Egypt must have
developed its mode of building in a forest country where timber was
abundant, for it is not probable, that the idea of cylindrical columns
originated in a country destitute of trees. The pyramids might have been
built by an indigenous race, but not the temples of El Uksor and Karnak.
In Grecian architecture, almost every characteristic feature can be
traced to an origin in wooden buildings. The columns, the architrave,
the frieze, the fillets, the cantelevers, the form of the roof, all
point to an origin in some southern forest-clad country, and strikingly
corroborate the view derived from philology, that Greece was colonised
from north-western India. But to erect columns and span them with huge
blocks of stone, or marble, is not an act of reason, but one of pure
unreasoning imitation. The arch is the only true and reasonable mode of
covering over wide spaces with stone, and therefore, Grecian
architecture, however exquisitely beautiful, is false in principle, and
is by no means a good example of the application of reason to the art of
building. And what do most of us do at the present day but imitate the
buildings of those that have gone before us? We have not even been able
to discover or develope any definite style of building best suited for
us. We have no characteristic national style of architecture, and to
that extent are even below the birds, who have each their characteristic
form of nest, exactly adapted to their wants and habits.
_Birds do Alter and Improve their Nests when altered Conditions require
it._
The great uniformity in the architecture of each species of bird which
has been supposed to prove a nest-building instinct, we may, therefore,
fairly impute to the uniformity of the conditions under which each
species lives. Their range is often very limited, and they very seldom
permanently change their country, so as to be placed in new conditions.
When, however, new conditions do occur, they take advantage of them just
as freely and wisely as man could do. The chimney and house-swallows are
a standing proof of a change of habit since chimneys and houses were
built, and in America this change has taken place within about three
hundred years. Thread and worsted are now used in many nests instead of
wool and horsehair, and the jackdaw shows an affection for the church
steeple which can hardly be explained by instinct. In the more thickly
populated parts of the United States, the Baltimore oriole uses all
sorts of pieces of string, skeins of silk, or the gardener's bass, to
weave into its fine pensile nest, instead of the single hairs and
vegetable fibres it has painfully to seek in wilder regions; and Wilson,
a most careful observer, believes that it improves in nest-building by
practice--the older birds making the best nests. The purple martin takes
possession of empty gourds or small boxes, stuck up for its reception in
almost every village and farm in America; and several of the American
wrens will also build in cigar boxes, with a small hole cut in them, if
placed in a suitable situation. The orchard oriole of the United States
offers us an excellent example of a bird which modifies its nest
according to circumstances. When built among firm and stiff branches the
nest is very shallow, but if, as is often the case, it is suspended from
the slender twigs of the weeping willow, it is made much deeper, so that
when swayed about violently by the wind the young may not tumble out. It
has been observed also, that the nests built in the warm Southern States
are much slighter and more porous in texture than those in the colder
regions of the north. Our own house-sparrow equally well adapts himself
to circumstances. When he builds in trees, as he, no doubt, always did
originally, he constructs a well-made domed nest, perfectly fitted to
protect his young ones; but when he can find a convenient hole in a
building or among thatch, or in any well-sheltered place, he takes much
less trouble, and forms a very loosely-built nest.
A curious example of a recent change of habits has occurred in Jamaica.
Previous to 1854, the palm swift (Tachornis phænicobea) inhabited
exclusively the palm trees in a few districts in the island. A colony
then established themselves in two cocoa-nut palms in Spanish Town, and
remained there till 1857, when one tree was blown down, and the other
stripped of its foliage. Instead of now seeking out other palm trees,
the swifts drove out the swallows who built in the Piazza of the House
of Assembly, and took possession of it, building their nests on the tops
of the end walls and at the angles formed by the beams and joists, a
place which they continue to occupy in considerable numbers. It is
remarked that here they form their nest with much less elaboration than
when built in the palms, probably from being less exposed.
A still more curious example of change and improvement in nest building
was published by Mr. F. A. Pouchet, in the tenth number of the _Comptes
Rendus_ for 1870, just as the first edition of this work appeared. Forty
years ago M. Pouchet had himself collected nests of the House-Martin or
Window-Swallow (_Hirundo urbica_) from old buildings at Rouen, and
deposited them in the museum of that city. On recently obtaining some
more nests he was surprised, on comparing them with the old ones, to
find that they exhibited a decided change of form and structure. This
led him to investigate the matter more closely. The changed nests had
been obtained from houses in a newly erected quarter of the city, and he
found that all the nests in the newly-built streets were of the new
form. But on visiting the churches and older buildings, and some rocks
where these birds build, he found many nests of the old type along with
some of the new pattern. He then examined all the figures and
descriptions of the older naturalists, and found that they invariably
represented the older form only.
The difference between the two forms he states to be as follows. In the
old form the nest is a portion of a globe--when situated in the upper
angle of a window one-fourth of a hemisphere--and the opening is very
small and circular, being of a size just sufficient to allow the body of
the bird to pass. In the new form the nest is much wider in proportion
to its height, being a segment of a depressed spheroid, and the aperture
is very wide and shallow, and close to the horizontal surface to which
the nest is attached above.
M. Pouchet thinks that the new form is an undoubted improvement on the
old. The nest has a wider bottom and must allow the young ones to have
more freedom of motion than in the old narrower, and deeper nests, and
its wide aperture allows the young birds to peep out and breathe the
fresh air. This is so wide as to serve as a sort of balcony for them,
and two young ones can often be seen on it without interfering with the
passage in and out of the old birds. At the same time, by being so close
to the roof, it is a better protection against rain, against cold, and
against enemies, than the small round hole of the old nests. Here, then,
we have an improvement in nest building, as well marked as any
improvement that takes place in human dwellings in so short a time.
But perfection of structure and adaptation to purpose, are not universal
characteristics of birds' nests, since there are decided imperfections
in the nesting of many birds which are quite compatible with our present
theory, but are hardly so with that of instinct, which is supposed to be
infallible. The Passenger pigeon of America often crowds the branches
with its nests till they break, and the ground is strewn with shattered
nests, eggs, and young birds. Rooks' nests are often so imperfect that
during high winds the eggs fall out; but the Window-Swallow is the most
unfortunate in this respect, for White, of Selborne, informs us that he
has seen them build, year after year, in places where their nests are
liable to be washed away by a heavy rain and their young ones destroyed.
_Conclusion._
A fair consideration of all these facts will, I think, fully support the
statement with which I commenced, and show, that the mental faculties
exhibited by birds in the construction of their nests, are the same in
kind as those manifested by mankind in the formation of their dwellings.
These are, essentially, imitation, and a slow and partial adaptation to
new conditions. To compare the work of birds with the highest
manifestations of human art and science, is totally beside the question.
I do not maintain that birds are gifted with reasoning faculties at all
approaching in variety and extent to those of man. I simply hold that
the phenomena presented by their mode of building their nests, when
fairly compared with those exhibited by the great mass of mankind in
building their houses, indicate no essential difference in the kind or
nature of the mental faculties employed. If instinct means anything, it
means the capacity to perform some complex act without teaching or
experience. It implies innate ideas of a very definite kind, and, if
established, would overthrow Mr. Mill's sensationalism and all the
modern philosophy of experience. That the existence of true instinct may
be established in other cases is not impossible, but in the particular
instance of birds' nests, which is usually considered one of its
strongholds, I cannot find a particle of evidence to show the existence
of anything beyond those lower reasoning and imitative powers, which
animals are universally admitted to possess.
VII.
A THEORY OF BIRDS' NESTS;
SHOWING THE RELATION OF CERTAIN DIFFERENCES OF COLOUR IN FEMALE
BIRDS, TO THEIR MODE OF NIDIFICATION.
The habit of forming a more or less elaborate structure for the
reception of their eggs and young, must undoubtedly be looked upon as
one of the most remarkable and interesting characteristics of the class
of birds. In other classes of vertebrate animals, such structures are
few and exceptional, and never attain to the same degree of completeness
and beauty. Birds' nests have, accordingly, attracted much attention,
and have furnished one of the stock arguments to prove the existence of
a blind but unerring instinct in the lower animals. The very general
belief that every bird is enabled to build its nest, not by the ordinary
faculties of observation, memory, and imitation, but by means of some
innate and mysterious impulse, has had the bad effect of withdrawing
attention from the very evident relation that exists between the
structure, habits, and intelligence of birds, and the kind of nests they
construct.
In the preceding essay I have detailed several of these relations, and
they teach us, that a consideration of the structure, the food, and
other specialities of a bird's existence, will give a clue, and
sometimes a very complete one, to the reason why it builds its nest of
certain materials, in a definite situation, and in a more or less
elaborate manner.
I now propose to consider the question from a more general point of
view, and to discuss its application to some important problems in the
natural history of birds.
_Changed Conditions and persistent Habits as influencing Nidification._
Besides the causes above alluded to, there are two other factors whose
effect in any particular case we can only vaguely guess at, but which
must have had an important influence in determining the existing details
of nidification. These are--changed conditions of existence, whether
internal or external, and the influence of hereditary or imitative
habit; the first inducing alterations in accordance with changes of
organic structure, of climate, or of the surrounding fauna and flora;
the other preserving the peculiarities so produced, even when changed
conditions render them no longer necessary. Many facts have been already
given which show that birds do adapt their nests to the situations in
which they place them, and the adoption of eaves, chimneys, and boxes,
by swallows, wrens, and many other birds, shows that they are always
ready to take advantage of changed conditions. It is probable,
therefore, that a permanent change of climate would cause many birds to
modify the form or materials of their abodes, so as better to protect
their young. The introduction of new enemies to eggs or young birds,
might introduce many alterations tending to their better concealment. A
change in the vegetation of a country, would often necessitate the use
of new materials. So, also, we may be sure, that as a species slowly
became modified in any external or internal characters, it would
necessarily change in some degree its mode of building. This effect
would be produced by modifications of the most varied nature; such as
the power and rapidity of flight, which must often determine the
distance to which a bird will go to obtain materials for its nest; the
capacity of sustaining itself almost motionless in the air, which must
sometimes determine the position in which a nest can be built; the
strength and grasping power of the foot in relation to the weight of the
bird, a power absolutely essential to the constructor of a
delicately-woven and well-finished nest; the length and fineness of the
beak, which has to be used like a needle in building the best textile
nests; the length and mobility of the neck, which is needful for the
same purpose; the possession of a salivary secretion like that used in
the nests of many of the swifts and swallows, as well as that of the
song-thrush--peculiarities of habits, which ultimately depend on
structure, and which often determine the material most frequently met
with or most easily to be obtained. Modifications in any of these
characters would necessarily lead, either to a change in the materials
of the nest, or in the mode of combining them in the finished
structure, or in the form or position of that structure.
During all these changes, however, certain specialities of nest-building
would continue, for a shorter or a longer time after the causes which
had necessitated them had passed away. Such records of a vanished past
meet us everywhere, even in man's works, notwithstanding his boasted
reason. Not only are the main features of Greek architecture, mere
reproductions in stone of what were originally parts of a wooden
building, but our modern copyists of Gothic architecture often build
solid buttresses capped with weighty pinnacles, to support a wooden roof
which has no outward thrust to render them necessary; and even think
they ornament their buildings by adding sham spouts of carved stone,
while modern waterpipes, stuck on without any attempt at harmony, do the
real duty. So, when railways superseded coaches, it was thought
necessary to build the first-class carriages to imitate a number of
coach-bodies joined together; and the arm-loops for each passenger to
hold on by, which were useful when bad roads made every journey a
succession of jolts and lurches, were continued on our smooth
macadamised mail-routes, and, still more absurdly, remain to this day in
our railway carriages, the relic of a kind of locomotion we can now
hardly realize. Another good example is to be seen in our boots. When
elastic sides came into fashion we had been so long used to fasten them
with buttons or laces, that a boot without either looked bare and
unfinished, and accordingly the makers often put on a row of useless
buttons or imitation laces, because habit rendered the appearance of
them necessary to us. It is universally admitted that the habits of
children and of savages give us the best clue to the habits and mode of
thought of animals; and every one must have observed how children at
first imitate the actions of their elders, without any regard to the use
or applicability of the particular acts. So, in savages, many customs
peculiar to each tribe are handed down from father to son merely by the
force of habit, and are continued long after the purpose which they
originally served has ceased to exist. With these and a hundred similar
facts everywhere around us, we may fairly impute much of what we cannot
understand in the details of Bird-Architecture to an analogous cause. If
we do not do so, we must assume, either that birds are guided in every
action by pure reason to a far greater extent than men are, or that an
infallible instinct leads them to the same result by a different road.
The first theory has never, that I am aware of, been maintained by any
author, and I have already shown that the second, although constantly
assumed, has never been proved, and that a large body of facts is
entirely opposed to it. One of my critics has, indeed, maintained that I
admit "instinct" under the term "hereditary habit;" but the whole course
of my argument shows that I do not do so. Hereditary habit is, indeed,
the same as instinct when the term is applied to some simple action
dependent upon a peculiarity of structure which is hereditary; as when
the descendants of tumbler pigeons tumble, and the descendants of pouter
pigeons pout. In the present case, however, I compare it strictly to the
hereditary, or more properly, persistent or imitative, habits of
savages, in building their houses as their fathers did. Imitation is a
lower faculty than invention. Children and savages imitate before they
originate; birds, as well as all other animals, do the same.
The preceding observations are intended to show, that the exact mode of
nidification of each species of bird is probably the result of a variety
of causes, which have been continually inducing changes in accordance
with changed organic or physical conditions. The most important of these
causes seem to be, in the first place, the structure of the species,
and, in the second, its environment or conditions of existence. Now we
know, that every one of the characters or conditions included under
these two heads is variable. We have seen that, on the large scale, the
main features of the nest built by each group of birds, bears a relation
to the organic structure of that group, and we have, therefore, a right
to infer, that as structure varies, the nest will vary also in some
particular corresponding to the changes of structure. We have seen also,
that birds change the position, the form, and the construction of their
nest, whenever the available materials or the available situations, vary
naturally or have been altered by man; and we have, therefore, a right
to infer that similar changes have taken place, when, by a natural
process, external conditions have become in any way permanently altered.
We must remember, however, that all these factors are very stable during
many generations, and only change at a rate commensurate with those of
the great physical features of the earth as revealed to us by geology;
and we may, therefore, infer that the form and construction of nests,
which we have shown to be dependent on them, are equally stable. If,
therefore, we find less important and more easily modified characters
than these, so correlated with peculiarities of nidification as to
indicate that one is probably the cause of the other, we shall be
justified in concluding that these variable characters are dependent on
the mode of nidification, and not that the form of the nest has been
determined by these variable characters. Such a correlation I am now
about to point out.
_Classification of Nests._
For the purpose of this inquiry it is necessary to group nests into two
great classes, without any regard to their most obvious differences or
resemblances, but solely looking to the fact of whether the contents
(eggs, young, or sitting bird) are hidden or exposed to view. In the
first class we place all those in which the eggs and young are
completely hidden, no matter whether this is effected by an elaborate
covered structure, or by depositing the eggs in some hollow tree or
burrow underground. In the second, we group all in which the eggs,
young, and sitting bird are exposed to view, no matter whether there is
the most beautifully formed nest, or none at all. Kingfishers, which
build almost invariably in holes in banks; Woodpeckers and Parrots,
which build in hollow trees; the Icteridæ of America, which all make
beautiful covered and suspended nests; and our own Wren, which builds a
domed nest, are examples of the former; while our Thrushes, Warblers,
and Finches, as well as the Crowshrikes, Chatterers, and Tanagers of the
tropics, together with all Raptorial birds and Pigeons, and a vast
number of others in every part of the world, all adopt the latter mode
of building.
It will be seen that this division of birds according to their
nidification, bears little relation to the character of the nest itself.
It is a functional not a structural classification. The most rude and
the most perfect specimens of bird-architecture are to be found in both
sections. It has, however, a certain relation to natural affinities, for
large groups of birds, undoubtedly allied, fall into one or the other
division exclusively. The species of a genus or of a family are rarely
divided between the two primary classes, although they are frequently
divided between the two very distinct modes of nidification that exist
in the first of them.
All the Scansorial or climbing, and most of the Fissirostral or
wide-gaped birds, for example, build concealed nests; and, in the latter
group, the two families which build open nests, the Swifts and the
Goat-suckers, are undoubtedly very widely separated from the other
families with which they are associated in our classifications. The
Tits vary much in their mode of nesting, some making open nests
concealed in a hole, while others build domed or even pendulous covered
nests, but they all come under the same class. Starlings vary in a
similar way. The talking Mynahs, like our own starlings, build in holes,
the glossy starlings of the East (of the genus Calornis) form a hanging
covered nest, while the genus Sturnopastor builds in a hollow tree. One
of the most striking cases in which one family of birds is divided
between the two classes, is that of the Finches; for while most of the
European species build exposed nests, many of the Australian finches
make them dome-shaped.
_Sexual differences of Colour in Birds._
Turning now from the nests to the creatures who make them, let us
consider birds themselves from a somewhat unusual point of view, and
form them into separate groups, according as both sexes, or the males
only, are adorned with conspicuous colours.
The sexual differences of colour and plumage in birds are very
remarkable, and have attracted much attention; and, in the case of
polygamous birds, have been well explained by Mr. Darwin's principle of
sexual selection. We can, to a great extent, understand how male
Pheasants and Grouse have acquired their more brilliant plumage and
greater size, by the continual rivalry of the males both in strength and
beauty; but this theory does not throw any light on the causes which
have made the female Toucan, Bee-eater, Parroquet, Macaw and Tit, in
almost every case as gay and brilliant as the male, while the gorgeous
Chatterers, Manakins, Tanagers, and Birds of Paradise, as well as our
own Blackbird, have mates so dull and inconspicuous that they can hardly
be recognised as belonging to the same species.
_The Law which connects the Colours of Female Birds with the mode of
Nidification._
The above-stated anomaly can, however, now be explained by the influence
of the mode of nidification, since I find that, with but very few
exceptions, it is the rule--_that when both sexes are of strikingly gay
and conspicuous colours, the nest is of the first class, or such as to
conceal the sitting bird; while, whenever there is a striking contrast
of colours, the male being gay and conspicuous, the female dull and
obscure, the nest is open and the sitting bird exposed to view_. I will
now proceed to indicate the chief facts that support this statement, and
will afterwards explain the manner in which I conceive the relation has
been brought about.
We will first consider those groups of birds in which the female is
gaily or at least conspicuously coloured, and is in most cases exactly
like the male.
1. Kingfishers (Alcedinidæ). In some of the most brilliant species of
this family the female exactly resembles the male; in others there is a
sexual difference, but it rarely tends to make the female less
conspicuous. In some, the female has a band across the breast, which is
wanting in the male, as in the beautiful Halcyon diops of Ternate. In
others the band is rufous in the female, as in several of the American
species; while in Dacelo gaudichaudii, and others of the same genus, the
tail of the female is rufous, while that of the male is blue. In most
kingfishers the nest is in a deep hole in the ground; in Tanysiptera it
is said to be in a hole in the nests of termites, or sometimes in
crevices under overhanging rocks.
2. Motmots (Momotidæ). In these showy birds the sexes are exactly alike,
and the nest in a hole under ground.
3. Puff-birds (Bucconidæ). These birds are often gaily coloured; some
have coral-red bills; the sexes are exactly alike, and the nest is in a
hole in sloping ground.
4. Trogons (Trogonidæ). In these magnificent birds the females are
generally less brightly coloured than the males, but are yet often gay
and conspicuous. The nest is in a hole of a tree.
5. Hoopoes (Upupidæ). The barred plumage and long crests of these birds
render them conspicuous. The sexes are exactly alike, and the nest is in
a hollow tree.
6. Hornbills (Bucerotidæ). These large birds have enormous coloured
bills, which are generally quite as well coloured and conspicuous in the
females. Their nests are always in hollow trees, where the female is
entirely concealed.
7. Barbets (Capitonidæ). These birds are all very gaily-coloured, and,
what is remarkable, the most brilliant patches of colour are disposed
about the head and neck, and are very conspicuous. The sexes are
exactly alike, and the nest is in a hole of a tree.
8. Toucans (Rhamphastidæ). These fine birds are coloured in the most
conspicuous parts of their body, especially on the large bill, and on
the upper and lower tail coverts, which are crimson, white, or yellow.
The sexes are exactly alike, and they always build in a hollow tree.
9. Plaintain-eaters (Musophagidæ). Here again the head and bill are most
brilliantly coloured in both sexes, and the nest is in a hole of a tree.
10. Ground cuckoos (Centropus). These birds are often of conspicuous
colours, and are alike in both sexes. They build a domed nest.
11. Woodpeckers (Picidæ). In this family the females often differ from
the males, in having a yellow or white, instead of a crimson crest, but
are almost as conspicuous. They all nest in holes in trees.
12. Parrots (Psittaci). In this great tribe, adorned with the most
brilliant and varied colours, the rule is, that the sexes are precisely
alike, and this is the case in the most gorgeous families, the lories,
the cockatoos, and the macaws; but in some there is a sexual difference
of colour to a slight extent. All build in holes, mostly in trees, but
sometimes in the ground, or in white ants' nests. In the single case in
which the nest is exposed, that of the Australian ground parrot,
Pezoporus formosus, the bird has lost the gay colouring of its allies,
and is clothed in sombre and completely protective tints of dusky green
and black.
13. Gapers (Eurylæmidæ). In these beautiful Eastern birds, somewhat
allied to the American chatterers, the sexes are exactly alike, and are
adorned with the most gay and conspicuous markings. The nest is a woven
structure, _covered over_, and suspended from the extremities of
branches over water.
14. Pardalotus (Ampelidæ). In these Australian birds the females differ
from the males, but are often very conspicuous, having brightly-spotted
heads. Their nests are sometimes dome-shaped, sometimes in holes of
trees, or in burrows in the ground.
15. Tits (Paridæ). These little birds are always pretty, and many
(especially among the Indian species) are very conspicuous. They always
have the sexes alike, a circumstance very unusual among the smaller
gaily-coloured birds of our own country. The nest is always covered over
or concealed in a hole.
16. Nuthatches (Sitta). Often very pretty birds, the sexes alike, and
the nest in a hole.
17.---- (Sittella). The female of these Australian nuthatches is often
the most conspicuous, being white-and black-marked. The nest is,
according to Gould, "completely concealed among upright twigs connected
together."
18. Creepers (Climacteris). In these Australian creepers the sexes are
alike, or the female most conspicuous, and the nest is in a hole of a
tree.
19. Estrelda, Amadina. In these genera of Eastern and Australian finches
the females, although more or less different from the males, are still
very conspicuous having a red rump, or being white spotted. They differ
from most others of the family in building domed nests.
20. Certhiola. In these pretty little American creepers the sexes are
alike, and they build a domed nest.
21. Mynahs (Sturnidæ). These showy Eastern starlings have the sexes
exactly alike. They build in holes of trees.
22. Calornis (Sturnidæ). These brilliant metallic starlings have no
sexual differences. They build a pensile covered nest.
23. Hangnests (Icteridæ). The red or yellow and black plumage of most of
these birds is very conspicuous, and is exactly alike in both sexes.
They are celebrated for their fine purse-shaped pensile nests.
It will be seen that this list comprehends six important families of
Fissirostres, four of Scansores, the Psittaci, and several genera, with
three entire families of Passeres, comprising about twelve hundred
species, or about one-seventh of all known birds.
* * * * *
The cases in which, whenever the male is gaily coloured, the female is
much less gay or quite inconspicuous, are exceedingly numerous,
comprising, in fact, almost all the bright-coloured Passeres, except
those enumerated in the preceding class. The following are the most
remarkable:--
1. Chatterers (Cotingidæ). These comprise some of the most gorgeous
birds in the world, vivid blues, rich purples, and bright reds, being
the most characteristic colours. The females are always obscurely
tinted, and are often of a greenish hue, not easily visible among the
foliage.
2. Manakins (Pipridæ). These elegant birds, whose caps or crests are of
the most brilliant colours, are usually of a sombre green in the female
sex.
3. Tanagers (Tanagridæ). These rival the chatterers in the brilliancy of
their colours, and are even more varied. The females are generally of
plain and sombre hues, and always less conspicuous than the males.
In the extensive families of the warblers (Sylviadæ), thrushes
(Turdidæ), flycatchers (Muscicapidæ), and shrikes (Laniadæ), a
considerable proportion of the species are beautifully marked with gay
and conspicuous tints, as is also the case in the Pheasants and Grouse;
but in every case the females are less gay, and are most frequently of
the very plainest and least conspicuous hues. Now, throughout _the whole
of these families the nest is open_, and I am not aware of a single
instance in which any one of these birds builds a _domed nest_, or
places it in a _hole of a tree_, or _underground_, or in any place where
it is effectually concealed.
In considering the question we are now investigating, it is not
necessary to take into account the larger and more powerful birds,
because these seldom depend much on concealment to secure their safety.
In the raptorial birds bright colours are as a rule absent; and their
structure and habits are such as not to require any special protection
for the female. The larger waders are sometimes very brightly coloured
in both sexes; but they are probably little subject to the attacks of
enemies, since the scarlet ibis, the most conspicuous of birds, exists
in immense quantities in South America. In game birds and water-fowl,
however, the females are often very plainly coloured, when the males are
adorned with brilliant hues; and the abnormal family of the Megapodidæ
offers us the interesting fact of an identity in the colours of the
sexes (which in Megacephalon and Talegalla are somewhat conspicuous), in
conjunction with the habit of not sitting on the eggs at all.
_What the Facts Teach us._
Taking the whole body of evidence here brought forward, embracing as it
does almost every group of bright-coloured birds, it will, I think, be
admitted that the relation between the two series of facts in the
colouring and nidification of birds has been sufficiently established.
There are, it is true, a few apparent and some real exceptions, which I
shall consider presently; but they are too few and unimportant to weigh
much against the mass of evidence on the other side, and may for the
present be neglected. Let us then consider what we are to do with this
unexpected set of correspondences between groups of phenomena which, at
first sight, appear so disconnected. Do they fall in with any other
groups of natural phenomena? Do they teach us anything of the way in
which nature works, and give us any insight into the causes which have
brought about the marvellous variety, and beauty, and harmony of living
things? I believe we can answer these questions in the affirmative; and
I may mention, as a sufficient proof that these are not isolated facts,
that I was first led to see their relation to each other by the study of
an analogous though distinct set of phenomena among insects, that of
protective resemblance and "mimicry."
On considering this remarkable series of corresponding facts, the first
thing we are taught by them seems to be, that there is no incapacity in
the female sex among birds, to receive the same bright hues and strongly
contrasted tints with which their partners are so often decorated, since
whenever they are _protected and concealed_ during the period of
incubation _they are similarly adorned_. The fair inference is, that it
is chiefly due to the absence of protection or concealment during this
important epoch, that gay and conspicuous tints are withheld or left
undeveloped. The mode in which this has been effected is very
intelligible, if we admit the action of natural and sexual selection. It
would appear from the numerous cases in which both sexes are adorned
with equally brilliant colours (while both sexes are rarely armed with
equally developed offensive and defensive weapons when not required for
individual safety), that the normal action of "sexual selection" is to
develop colour and beauty in both sexes, by the preservation and
multiplication of all varieties of colour in either sex which are
pleasing to the other. Several very close observers of the habits of
animals have assured me, that male birds and quadrupeds do often take
very strong likes and dislikes to individual females, and we can hardly
believe that the one sex (the female) can have a general taste for
colour while the other has no such taste. However this may be, the fact
remains, that in a vast number of cases the female acquires as brilliant
and as varied colours as the male, and therefore most probably acquires
them in the same way as the male does; that is, either because the
colour is useful to it, or is correlated with some useful variation, or
is pleasing to the other sex. The only remaining supposition is that it
is transmitted from the other sex, without being of any use. From the
number of examples above adduced of bright colours in the female, this
would imply that colour-characters acquired by one sex are generally
(but not necessarily) transmitted to the other. If this be the case it
will, I think, enable us to explain the phenomena, even if we do not
admit that the male bird is ever influenced in the choice of a mate by
her more gay or perfect plumage.
The female bird, while sitting on her eggs in an uncovered nest, is much
exposed to the attacks of enemies, and any modification of colour which
rendered her more conspicuous would often lead to her destruction and
that of her offspring. All variations of colour in this direction in the
female, would therefore sooner or later be eliminated, while such
modifications as rendered her inconspicuous, by assimilating her to
surrounding objects, as the earth or the foliage, would, on the whole,
survive the longest, and thus lead to the attainment of those brown or
green and inconspicuous tints, which form the colouring (of the upper
surface at least), of the vast majority of female birds which sit upon
open nests.
This does not imply, as some have thought, that all female birds were
once as brilliant as the males. The change has been a very gradual one,
generally dating from the origin of genera or of larger groups, but
there can be no doubt that the remote ancestry of birds having great
sexual differences of colour, were nearly or quite alike, sometimes
(perhaps in most cases) more nearly resembling the female, but
occasionally perhaps being nearer what the male is now. The young birds
(which usually resemble the females) will probably give some idea of
this ancestral type, and it is well known that the young of allied
species and of different sexes are often undistinguishable.
_Colour more variable than Structure or Habits, and therefore the
Character which has generally been Modified._
At the commencement of this essay, I have endeavoured to prove, that the
characteristic differences and the essential features of birds' nests,
are dependent on the structure of the species and upon the present and
past conditions of their existence. Both these factors are more
important and less variable than colour; and we must therefore conclude
that in most cases the mode of nidification (dependent on structure and
environment) has been the cause, and not the effect, of the similarity
or differences of the sexes as regards colour. When the confirmed habit
of a group of birds, was to build their nests in holes of trees like the
toucans, or in holes in the ground like the kingfishers, the protection
the female thus obtained, during the important and dangerous time of
incubation, placed the two sexes on an equality as regards exposure to
attack, and allowed "sexual selection," or any other cause, to act
unchecked in the development of gay colours and conspicuous markings in
both sexes.
When, on the other hand (as in the Tanagers and Flycatchers), the habit
of the whole group was to build open cup-shaped nests in more or less
exposed situations, the production of colour and marking in the female,
by whatever cause, was continually checked by its rendering her too
conspicuous, while in the male it had free play, and developed in him
the most gorgeous hues. This, however, was not perhaps universally the
case; for where there was more than usual intelligence and capacity for
change of habits, the danger the female was exposed to by a partial
brightness of colour or marking might lead to the construction of a
concealed or covered nest, as in the case of the Tits and Hangnests.
When this occurred, a special protection to the female would be no
longer necessary; so that the acquisition of colour and the modification
of the nest, might in some cases act and react on each other and attain
their full development together.
_Exceptional Cases confirmatory of the above Explanation._
There exist a few very curious and anomalous facts in the natural
history of birds, which fortunately serve as crucial tests of the truth
of this mode of explaining the inequalities of sexual colouration. It
has been long known, that in some species the males either assisted in,
or wholly performed, the act of incubation. It has also been often
noticed, that in certain birds the usual sexual differences were
reversed, the male being the more plainly coloured, the female more gay
and often larger. I am not, however, aware that these two anomalies had
ever been supposed to stand to each other in the relation of cause and
effect, till I adduced them in support of my views of the general theory
of protective adaptation. Yet it is undoubtedly the fact, that in the
best known cases in which the female bird is more conspicuously coloured
than the male, it is either positively ascertained that the latter
performs the duties of incubation, or there are good reasons for
believing such to be the case. The most satisfactory example is that of
the Gray Phalarope (Phalaropus fulicarius), the sexes of which are alike
in winter, while in summer the female instead of the male takes on a gay
and conspicuous nuptial plumage; but the male performs the duties of
incubation, sitting upon the eggs, which are laid upon the bare ground.
In the Dotterell (Eudromias morinellus) the female is larger and more
brightly coloured than the male; and here, also, it is almost certain
that the latter sits upon the eggs. The Turnices of India also, have the
female larger and often more brightly coloured; and Mr. Jerdon states,
in his "Birds of India," that the natives report, that, during the
breeding season, the females desert their eggs and associate in flocks,
while the males are employed in hatching the eggs. In the few other
cases in which the females are more brightly coloured, the habits are
not accurately known. The case of the Ostriches and Emeus will occur to
many as a difficulty, for here the male incubates, but is not less
conspicuous than the female; but there are two reasons why the case does
not apply;--the birds are too large to derive any safety from
concealment, from enemies which would devour the eggs they can defend
themselves by force, while to escape from their personal foes they trust
to speed.
We find, therefore, that a very large mass of facts relating to the
sexual colouration and the mode of nidification of birds, including some
of the most extraordinary anomalies to be found in their natural
history, can be shown to have an interdependent relation to each other,
on the simple principle of the need of greater protection to that parent
which performs the duties of incubation. Considering the very imperfect
knowledge we possess of the habits of most extra-European birds, the
exceptions to the prevalent rule are few, and generally occur in
isolated species or in small groups; while several apparent exceptions
can be shown to be really confirmations of the law.
_Real or apparent Exceptions to the Law stated at page 240._
The only marked exceptions I have been able to discover are the
following:--
1. King crows (Dicrourus). These birds are of a glossy black colour with
long forked tails. The sexes present no difference, and they build open
nests. This apparent exception may probably be accounted for by the fact
that these birds do not need the protection of a less conspicuous
colour. They are very pugnacious, and often attack and drive away crows,
hawks, and kites; and as they are semi-gregarious in their habits, the
females are not likely to be attacked while incubating.
2. Orioles (Oriolidæ). The true orioles are very gay birds; the sexes
are, in many Eastern species, either nearly or quite alike, and the
nests are open. This is one of the most serious exceptions, but it is
one that to some extent proves the rule; for in this case it has been
noticed, that the parent birds display excessive care and solicitude in
concealing the nest among thick foliage, and in protecting their
offspring by incessant and anxious watching. This indicates that the
want of protection consequent on the bright colour of the female makes
itself felt, and is obviated by an increased development of the mental
faculties.
3. Ground thrushes (Pittidæ). These elegant and brilliantly-coloured
birds are generally alike in both sexes, and build an open nest. It is
curious, however, that this is only an apparent exception, for almost
all the bright colours are on the under surface, the back being usually
olive green or brown, and the head black, with brown or whitish stripes,
all which colours would harmonize with the foliage, sticks, and roots
which surround the nest, built on or near the ground, and thus serve as
a protection to the female bird.
4. Grallina Australis. This Australian bird is of strongly contrasted
black and white colours. The sexes are exactly alike, and it builds an
open clay nest in an exposed situation on a tree. This appears to be a
most striking exception, but I am by no means sure that it is so. We
require to know what tree it usually builds on, the colour of the bark
or of the lichens that grow upon it, the tints of the ground, or of
other surrounding objects, before we can say that the bird, when sitting
on its nest, is really conspicuous. It has been remarked that small
patches of white and black blend at a short distance to form grey, one
of the commonest tints of natural objects.
5. Sunbirds (Nectarineidæ). In these beautiful little birds the males
only are adorned with brilliant colours, the females being quite plain,
yet they build covered nests in all the cases in which the nidification
is known. This is a negative rather than a positive exception to the
rule, since there may be other causes besides the need for protection,
which prevent the female acquiring the gay colours of her mate, and
there is one curious circumstance which tends to elucidate it. The male
of Leptocoma zeylanica is said to assist in incubation. It is possible,
therefore, that the group may originally have used open nests, and some
change of conditions, leading the male bird to sit, may have been
followed by the adoption of a domed nest. This is, however, the most
serious exception I have yet found to the general rule.
6. Superb warblers (Maluridæ). The males of these little birds are
adorned with the most gorgeous colours, while the females are very
plain, yet they make domed nests. It is to be observed, however, that
the male plumage is nuptial merely, and is retained for a very short
time; the rest of the year both sexes are plain alike. It is probable,
therefore, that the domed nest is for the protection of these delicate
little birds against the rain, and that there is some unknown cause
which has led to the development of colour in the males only.
There is one other case which at first sight looks like an exception,
but which is far from being one in reality, and deserves to be
mentioned. In the beautiful Waxwing, (Bombycilla garrula,) the sexes are
very nearly alike, and the elegant red wax tips to the wing-feathers are
nearly, and sometimes quite, as conspicuous in the female as in the
male. Yet it builds an open nest, and a person looking at the bird would
say it ought according to my theory to cover its nest. But it is, in
reality, as completely protected by its colouration as the most plainly
coloured bird that flies. It breeds only in very high latitudes, and the
nest, placed in fir-trees, is formed chiefly of lichens. Now the
delicate gray and ashy and purplish hues of the head and back, together
with the yellow of the wings and tail, are tints that exactly harmonize
with the colours of various species of lichens, while the brilliant red
wax tips exactly represent the crimson fructification of the common
lichen, Cladonia coccifera. When sitting on its nest, therefore, the
female bird will exhibit no colours that are not common to the materials
of which it is constructed; and the several tints are distributed in
about the same proportions as they occur in nature. At a short distance
the bird would be indistinguishable from the nest it is sitting on, or
from a natural clump of lichens, and will thus be completely protected.
I think I have now noticed all exceptions of any importance to the law
of dependence of sexual colour on nidification. It will be seen that
they are very few in number, compared with those which support the
generalization; and in several cases there are circumstances in the
habits or structure of the species that sufficiently explain them. It is
remarkable also that I have found scarcely any _positive_ exceptions,
that is, cases of very brilliant or conspicuous female birds in which
the nest was not concealed. Much less can there be shown any group of
birds, in which the females are all of decidedly conspicuous colours on
the upper surface, and yet sit in open nests. The many cases in which
birds of dull colours in both sexes make domed or concealed nests, do
not, of course, affect this theory one way or the other; since its
purpose is only to account for the fact, that brilliant females of
brilliant males are _always_ found to have covered or hidden nests,
while obscure females of brilliant males _almost always_ have open and
exposed nests. The fact that all classes of nests occur with dull
coloured birds in both sexes merely shows, as I have strongly
maintained, that in most cases the character of the nest determines the
colouration of the female, and not _vice versâ_.
If the views here advocated are correct, as to the various influences
that have determined the specialities of every bird's nest, and the
general colouration of female birds, with their action and reaction on
each other, we can hardly expect to find evidence more complete than
that here set forth. Nature is such a tangled web of complex relations,
that a series of correspondences running through hundreds of species,
genera, and families, in every part of the system, can hardly fail to
indicate a true casual connexion; and when, of the two factors in the
problem, one can be shown to be dependent on the most deeply seated and
the most stable facts of structure and conditions of life, while the
other is a character universally admitted to be superficial and easily
modified, there can be little doubt as to which is cause and which
effect.
_Various modes of Protection of Animals._
But the explanation of the phenomenon here attempted does not rest alone
on the facts I have been able now to adduce. In the essay on "Mimicry,"
it is shown how important a part the necessity for protection has
played, in determining the external form and colouration, and sometimes
even the internal structure of animals.
As illustrating this latter point, I may refer to the remarkable hooked,
branched, or star-like spiculæ in many sponges, which are believed to
have the function chiefly, of rendering them unpalatable to other
creatures. The Holothuridæ or sea-cucumbers possess a similar
protection, many of them having anchor-shaped spicules embedded in their
skin, as the Synapta; while others (Cuviera squamata) are covered with a
hard calcareous pavement. Many of these are of a bright red or purple
colour, and are very conspicuous, while the allied Trepang, or
Beche-de-mer (Holothuria edulis), which is not armed with any such
defensive weapons, is of a dull sand-or mud-colour, so as hardly to be
distinguished from the sea bed on which it reposes. Many of the smaller
marine animals are protected by their almost invisible transparency,
while those that are most brightly coloured will be often found to have
a special protection, either in stinging tentacles like Physalia, or in
a hard calcareous crust, as in the star fishes.
_Females of some Groups require and obtain more Protection than the
Males._
In the struggle for existence incessantly going on, protection or
concealment is one of the most general and most effectual means of
maintaining life; and it is by modifications of colour that this
protection can be most readily obtained, since no other character is
subject to such numerous and rapid variations. The case I have now
endeavoured to illustrate is exactly analogous to what occurs among
butterflies. As a general rule, the female butterfly is of dull and
inconspicuous colours, even when the male is most gorgeously arrayed;
but when the species is protected from attack by a disagreeable odour,
as in the Heliconidæ, Danaidæ and Acroeidæ, both sexes display the same
or equally brilliant hues. Among the species which gain a protection by
imitating these, the very weak and slow-flying Leptalides resemble them
in both sexes, because both sexes alike require protection, while in the
more active and strong-winged genera--Papilio, Pieris, and Diadema--it
is generally the females only that mimic the protected groups, and in
doing so often become actually more gay and more conspicuous than the
males, thus reversing the usual and in fact almost universal characters
of the sexes. So, in the wonderful Eastern leaf-insects of the genus
Phyllium, it is the female only that so marvellously imitates a green
leaf; and in all these cases the difference can be traced to the greater
need of protection for the female, on whose continued existence, while
depositing her eggs, the safety of the race depends. In Mammalia and in
reptiles, however brilliant the colours may be, there is rarely any
difference between that of the sexes, because the female is not
necessarily more exposed to attack than the male. It may, I think, be
looked upon as a confirmation of this view, that no single case is known
either in the above-named genera--Papilio, Pieris, and Diadema--or in
any other butterfly, of a male _alone_, mimicking one of the Danaidæ or
Heliconidæ. Yet the necessary colour is far more abundant in the males,
and variations always seem ready for any useful purpose. This seems to
depend on the general law, that each species and each sex can only be
modified just as far as is absolutely necessary for it to maintain
itself in the struggle for existence, not a step further. A male insect
by its structure and habits is less exposed to danger, and also requires
less protection than the female. It cannot, therefore, alone acquire any
further protection through the agency of natural selection. But the
female requires some extra protection, to balance the greater danger to
which she is exposed, and her greater importance to the existence of the
species; and this she always acquires, in one way or another, through
the action of natural selection.
In his "Origin of Species," fourth edition, p. 241, Mr. Darwin
recognises the necessity for protection as sometimes being a cause of
the obscure colours of female birds; but he does not seem to consider it
so very important an agent in modifying colour as I am disposed to do.
In the same paragraph (p. 240), he alludes to the fact of female birds
and butterflies being sometimes very plain, sometimes as gay as the
males; but, apparently, considers this mainly due to peculiar laws of
inheritance, which sometimes continue acquired colour in the line of one
sex only, sometimes in both. Without denying the action of such a law
(which Mr. Darwin informs me he has facts to support), I impute the
difference, in the great majority of cases, to the greater or less need
of protection in the female sex in these groups of animals.
This need was seen to exist a century ago by the Hon. Daines Barrington,
who, in the article already quoted (see p. 220), after alluding to the
fact that singing birds are all small, and suggesting (but I think
erroneously) that this may have arisen from the difficulty larger birds
would have in concealing themselves if they called the attention of
their enemies by loud notes, goes on thus:--"I should rather conceive it
is for the same reason no hen bird sings, because this talent would be
still more dangerous during incubation, which _may possibly also account
for the inferiority in point of plumage_." This is a curious
anticipation of the main idea on which this essay is founded. It has
been unnoticed for near a century, and my attention was only recently
called to it by Mr. Darwin himself.
_Conclusion._
To some persons it will perhaps appear, that the causes to which I
impute so much of the external aspect of nature are too simple, too
insignificant, and too unimportant for such a mighty work. But I would
ask them to consider, that the great object of all the peculiarities of
animal structure is to preserve the life of the individual, and to
maintain the existence of the species. Colour has hitherto been too
often looked upon as something adventitious and superficial, something
given to an animal not to be useful to itself, but solely to gratify man
or even superior beings--to add to the beauty and ideal harmony of
nature. If this were the case, then, it is evident that the colours of
organised beings would be an exception to most other natural phenomena.
They would not be the product of general laws, or determined by
ever-changing external conditions; and we must give up all enquiry into
their origin and causes, since (by the hypothesis) they are dependent on
a Will whose motives must ever be unknown to us. But, strange to say, no
sooner do we begin to examine and classify the colours of natural
objects, than we find that they are intimately related to a variety of
other phenomena, and are, like them, strictly subordinated to general
laws. I have here attempted to elucidate some of these laws in the case
of birds, and have shown how the mode of nidification has affected the
colouring of the female sex in this group. I have before shown to how
great an extent, and in how many ways, the need of protection has
determined the colours of insects, and of some groups of reptiles and
mammalia, and I would now call particular attention to the fact that the
gay tints of flowers, so long supposed to be a convincing proof that
colour has been bestowed for other purposes than the good of its
possessor, have been shown by Mr. Darwin to follow the same great law of
utility. Flowers do not often need protection, but very often require
the aid of insects to fertilize them, and maintain their reproductive
powers in the greatest vigour. Their gay colours attract insects, as do
also their sweet odours and honeyed secretions; and that this is the
main function of colour in flowers is shown by the striking fact, that
those flowers which can be perfectly fertilized by the wind, and do not
need the aid of insects, _rarely or never have gaily-coloured flowers_.
This wide extension of the general principle of utility to the colours
of such varied groups, both in the animal and vegetable kingdoms,
compels us to acknowledge that the "reign of law" has been fairly traced
into this stronghold of the advocates of special creation. And to those
who oppose the explanation I have given of the facts adduced in this
essay, I would again respectfully urge that they must grapple with the
whole of the facts, not one or two of them only. It will be admitted
that, on the theory of evolution and natural selection, a wide range of
facts with regard to colour in nature have been co-ordinated and
explained. Until at least an equally wide range of facts can be shown to
be in harmony with any other theory, we can hardly be expected to
abandon that which has already done such good service, and which has led
to the discovery of so many interesting and unexpected harmonies among
the most common (but hitherto most neglected and least understood), of
the phenomena presented by organised beings.
VIII.
CREATION BY LAW.
Among the various criticisms that have appeared on Mr. Darwin's
celebrated "Origin of Species," there is, perhaps, none that will appeal
to so large a number of well educated and intelligent persons, as that
contained in the Duke of Argyll's "Reign of Law." The noble author
represents the feelings and expresses the ideas of that large class, who
take a keen interest in the progress of Science in general, and
especially that of Natural History, but have never themselves studied
nature in detail, or acquired that personal knowledge of the structure
of closely allied forms,--the wonderful gradations from species to
species and from group to group, and the infinite variety of the
phenomena of "variation" in organic beings,--which are absolutely
necessary for a full appreciation of the facts and reasonings contained
in Mr. Darwin's great work.
Nearly half of the Duke's book is devoted to an exposition of his idea
of "Creation by Law," and he expresses so clearly what are his
difficulties and objections as regards the theory of "Natural
Selection," that I think it advisable that they should be fairly
answered, and that his own views should be shown to lead to conclusions,
as hard to accept as any which he imputes to Mr. Darwin.
The point on which the Duke of Argyll lays most stress, is, that proofs
of Mind everywhere meet us in Nature, and are more especially manifest
wherever we find "contrivance" or "beauty." He maintains that this
indicates the constant supervision and direct interference of the
Creator, and cannot possibly be explained by the unassisted action of
any combination of laws. Now, Mr. Darwin's work has for its main object,
to show, that all the phenomena of living things,--all their wonderful
organs and complicated structures, their infinite variety of form, size,
and colour, their intricate and involved relations to each other,--may
have been produced by the action of a few general laws of the simplest
kind, laws which are in most cases mere statements of admitted facts.
The chief of these laws or facts are the following:--
1. _The Law of Multiplication in Geometrical Progression._--All
organized beings have enormous powers of multiplication. Even man, who
increases slower than all other animals, could under the most favourable
circumstances double his numbers every fifteen years, or a hundred-fold
in a century. Many animals and plants could increase their numbers from
ten to a thousand-fold every year.
2. _The Law of Limited Populations._--The number of living individuals
of each species in any country, or in the whole globe, is practically
stationary; whence it follows that the whole of this enormous increase
must die off almost as fast as produced, except only those individuals
for whom room is made by the death of parents. As a simple but striking
example, take an oak forest. Every oak will drop annually thousands or
millions of acorns, but till an old tree falls, not one of these
millions can grow up into an oak. They must die at various stages of
growth.
3. _The Law of Heredity, or Likeness of Offspring to their
Parents._--This is a universal, but not an absolute law. All creatures
resemble their parents in a high degree, and in the majority of cases
very accurately; so that even individual peculiarities, of whatever
kind, in the parents, are almost always transmitted to some of the
offspring.
4. _The Law of Variation._--This is fully expressed by the lines:--
"No being on this earthly ball,
Is like another, all in all."
Offspring resemble their parents very much, but not wholly--each being
possesses its individuality. This "variation" itself varies in amount,
but it is always present, not only in the whole being, but in every part
of every being. Every organ, every character, every feeling is
individual; that is to say, _varies_ from the same organ, character, or
feeling in every other individual.
5. _The Law of unceasing Change of Physical Conditions upon the Surface
of the Earth._--Geology shows us that this change has always gone on in
times past, and we also know that it is now everywhere going on.
6. _The Equilibrium or Harmony of Nature._--When a species is well
adapted to the conditions which environ it, it flourishes; when
imperfectly adapted it decays; when ill-adapted it becomes extinct. If
_all_ the conditions which determine an organism's well-being are taken
into consideration, this statement can hardly be disputed.
* * * * *
This series of facts or laws, are mere statements of what is the
condition of nature. They are facts or inferences which are generally
known, generally admitted--but in discussing the subject of the "Origin
of Species"--as generally forgotten. It is from these universally
admitted facts, that the origin of all the varied forms of nature may be
deduced by a logical chain of reasoning, which, however, is at every
step verified and shown to be in strict accord with facts; and, at the
same time, many curious phenomena which can by no other means be
understood, are explained and accounted for. It is probable, that these
primary facts or laws are but results of the very nature of life, and of
the essential properties of organized and unorganized matter. Mr.
Herbert Spencer, in his "First Principles" and his "Biology" has, I
think, made us able to understand how this may be; but at present we may
accept these simple laws without going further back, and the question
then is--whether the variety, the harmony, the contrivance, and the
beauty we perceive in organic beings, can have been produced by the
action of these laws alone, or whether we are required to believe in the
incessant interference and direct action of the mind and will of the
Creator. It is simply a question of how the Creator has worked. The
Duke (and I quote him as having well expressed the views of the more
intelligent of Mr. Darwin's opponents) maintains, that He has personally
applied general laws to produce effects, which those laws are not in
themselves capable of producing; that the universe alone, with all its
laws intact, would be a sort of chaos, without variety, without harmony,
without design, without beauty; that there is not (and therefore we may
presume that there could not be) any self-developing power in the
universe. I believe, on the contrary, that the universe is so
constituted as to be self-regulating; that as long as it contains Life,
the forms under which that life is manifested have an inherent power of
adjustment to each other and to surrounding nature; and that this
adjustment necessarily leads to the greatest amount of variety and
beauty and enjoyment, because it does depend on general laws, and not on
a continual supervision and re-arrangement of details. As a matter of
feeling and religion, I hold this to be a far higher conception of the
Creator and of the Universe than that which may be called the "continual
interference" hypothesis; but it is not a question to be decided by our
feelings or convictions, it is a question of facts and of reason. Could
the change, which Geology shows us has ever taken place in the forms of
life, have been produced by general laws, or does it imperatively
require the incessant supervision of a creative mind? This is the
question for us to consider, and our opponents have the difficult task
of proving a negative, if we show that there are both facts and
analogies in our favour.
_Mr. Darwin's Metaphors liable to Misconception._
Mr. Darwin has laid himself open to much misconception, and has given to
his opponents a powerful weapon against himself, by his continual use of
metaphor in describing the wonderful co-adaptations of organic beings.
"It is curious," says the Duke of Argyll, "to observe the language
which this most advanced disciple of pure naturalism instinctively
uses, when he has to describe the complicated structure of this curious
order of plants (the Orchids). 'Caution in ascribing intentions to
nature,' does not seem to occur to him as possible. Intention is the one
thing which he does see, and which, when he does not see, he seeks for
diligently until he finds it. He exhausts every form of words and of
illustration, by which intention or mental purpose can be described.
'Contrivance'--'curious contrivance,'--'beautiful contrivance,'--these
are expressions which occur over and over again. Here is one sentence
describing the parts of a particular species: 'the Labellum is developed
into a long nectary, _in order_ to attract Lepidoptera, and we shall
presently give reason for suspecting that the nectar is _purposely_ so
lodged, that it can be sucked only slowly _in order_ to give time for
the curious chemical quality of the viscid matter setting hard and
dry.'" Many other examples of similar expressions are quoted by the
Duke, who maintains that no explanation of these "contrivances" has
been or can be given, except on the supposition of a personal contriver,
specially arranging the details of each case, although causing them to
be produced by the ordinary processes of growth and reproduction.
Now there is a difficulty in this view of the origin of the structure of
Orchids which the Duke does not allude to. The majority of flowering
plants are fertilized, either without the agency of insects or, when
insects are required, without any very important modification of the
structure of the flower. It is evident, therefore, that flowers might
have been formed as varied, fantastic, and beautiful as the Orchids, and
yet have been fertilized without more complexity of structure than is
found in Violets, or Clover, or Primroses, or a thousand other flowers.
The strange springs and traps and pitfalls found in the flowers of
Orchids cannot be necessary _per se_, since exactly the same end is
gained in ten thousand other flowers which do not possess them. Is it
not then an extraordinary idea, to imagine the Creator of the Universe
_contriving_ the various complicated parts of these flowers, as a
mechanic might contrive an ingenious toy or a difficult puzzle? Is it
not a more worthy conception that they are some of the results of those
general laws which were so co-ordinated at the first introduction of
life upon the earth as to result necessarily in the utmost possible
development of varied forms?
But let us take one of the simpler cases adduced and see if our general
laws are unable to account for it.
_A Case of Orchis-structure explained by Natural Selection._
There is a Madagascar Orchis--the Angræcum sesquipedale--with an
immensely long and deep nectary. How did such an extraordinary organ
come to be developed? Mr. Darwin's explanation is this. The pollen of
this flower can only be removed by the base of the proboscis of some
very large moths, when trying to get at the nectar at the bottom of the
vessel. The moths with the longest probosces would do this most
effectually; they would be rewarded for their long tongues by getting
the most nectar; whilst on the other hand, the flowers with the deepest
nectaries would be the best fertilized by the largest moths preferring
them. Consequently, the deepest nectaried Orchids and the longest
tongued moths would each confer on the other an advantage in the battle
of life. This would tend to their respective perpetuation, and to the
constant lengthening of nectaries and probosces. Now let it be
remembered, that what we have to account for, is only the unusual length
of this organ. A nectary is found in many orders of plants and is
especially common in the Orchids, but in this one case only is it more
than a foot long. How did this arise? We begin with the fact, proved
experimentally by Mr. Darwin, that moths do visit Orchids, do thrust
their spiral trunks into the nectaries, and do fertilize them by
carrying the pollinia of one flower to the stigma of another. He has
further explained the exact mechanism by which this is effected, and
the Duke of Argyll admits the accuracy of his observations. In our
British species, such as Orchis pyramidalis, it is not necessary that
there should be any exact adjustment between the length of the nectary
and that of the proboscis of the insect; and thus a number of insects of
various sizes are found to carry away the pollinia and aid in the
fertilization. In the Angræcum sesquipedale, however, it is necessary
that the proboscis should be forced into a particular part of the
flower, and this would only be done by a large moth burying its
proboscis to the very base, and straining to drain the nectar from the
bottom of the long tube, in which it occupies a depth of one or two
inches only. Now let us start from the time when the nectary was only
half its present length or about six inches, and was chiefly fertilized
by a species of moth which appeared at the time of the plant's
flowering, and whose proboscis was of the same length. Among the
millions of flowers of the Angræcum produced every year, some would
always be shorter than the average, some longer. The former, owing to
the structure of the flower, would not get fertilized, because the moths
could get all the nectar without forcing their trunks down to the very
base. The latter would be well fertilized, and the longest would on the
average be the best fertilized of all. By this process alone the average
length of the nectary would annually increase, because, the
short-nectaried flowers being sterile and the long ones having abundant
offspring, exactly the same effect would be produced as if a gardener
destroyed the short ones and sowed the seed of the long ones only; and
this we know by experience would produce a regular increase of length,
since it is this very process which has increased the size and changed
the form of our cultivated fruits and flowers.
But this would lead in time to such an increased length of the nectary
that many of the moths could only just reach the surface of the nectar,
and only the few with exceptionally long trunks be able to suck up a
considerable portion.
This would cause many moths to neglect these flowers because they could
not get a satisfying supply of nectar, and if these were the only moths
in the country the flowers would undoubtedly suffer, and the further
growth of the nectary be checked by exactly the same process which had
led to its increase. But there are an immense variety of moths, of
various lengths of proboscis, and as the nectary became longer, other
and larger species would become the fertilizers, and would carry on the
process till the largest moths became the sole agents. Now, if not
before, the moth would also be affected, for those with the longest
probosces would get most food, would be the strongest and most vigorous,
would visit and fertilize the greatest number of flowers, and would
leave the largest number of descendants. The flowers most completely
fertilized by these moths being those which had the longest nectaries,
there would in each generation be on the average an increase in the
length of the nectaries, and also an average increase in the length of
the probosces of the moths; and this would be a _necessary result_ from
the fact that nature ever fluctuates about a mean, or that in every
generation there would be flowers with longer and shorter nectaries, and
moths with longer and shorter probosces than the average. No doubt there
are a hundred causes that might have checked this process before it had
reached the point of development at which we find it. If, for instance,
the variation in the quantity of nectar had been at any stage greater
than the variation in the length of the nectary, then smaller moths
could have reached it and have effected the fertilization. Or if the
growth of the probosces of the moths had from other causes increased
quicker than that of the nectary, or if the increased length of
proboscis had been injurious to them in any way, or if the species of
moth with the longest proboscis had become much diminished by some enemy
or other unfavourable conditions, then, in any of these cases, the
shorter nectaried flowers, which would have attracted and could have
been fertilized by the smaller kinds of moths, would have had the
advantage. And checks of a similar nature to these no doubt have acted
in other parts of the world, and have prevented such an extraordinary
development of nectary as has been produced by favourable conditions in
Madagascar only, and in one single species of Orchid. I may here mention
that some of the large Sphinx moths of the tropics have probosces nearly
as long as the nectary of Angræcum sesquipedale. I have carefully
measured the proboscis of a specimen of Macrosila cluentius from South
America, in the collection of the British Museum, and find it to be nine
inches and a quarter long! One from tropical Africa (Macrosila morganii)
is seven inches and a half. A species having a proboscis two or three
inches longer could reach the nectar in the largest flowers of Angræcum
sesquipedale, whose nectaries vary in length from ten to fourteen
inches. That such a moth exists in Madagascar may be safely predicted;
and naturalists who visit that island should search for it with as much
confidence as Astronomers searched for the planet Neptune,--and I
venture to predict they will be equally successful!
Now, instead of this beautiful self-acting adjustment, the opposing
theory is, that the Creator of the Universe, by a direct act of his
Will, so disposed the natural forces influencing the growth of this one
species of plant as to cause its nectary to increase to this enormous
length; and at the same time, by an equally special act, determined the
flow of nourishment in the organization of the moth, so as to cause its
proboscis to increase in exactly the same proportion, having previously
so constructed the Angræcum that it could only be maintained in
existence by the agency of this moth. But what proof is given or
suggested that this was the mode by which the adjustment took place?
None whatever, except a feeling that there is an adjustment of a
delicate kind, and an inability to see how known causes could have
produced such an adjustment. I believe I have shown, however, that such
an adjustment is not only possible but inevitable, unless at some point
or other we deny the action of those simple laws which we have already
admitted to be but the expressions of existing facts.
_Adaptation brought about by General Laws._
It is difficult to find anything like parallel cases in inorganic
nature, but that of a river may perhaps illustrate the subject in some
degree. Let us suppose a person totally ignorant of Modern Geology to
study carefully a great River System. He finds in its lower part, a deep
broad channel filled to the brim, flowing slowly through a flat country
and carrying out to the sea a quantity of fine sediment. Higher up it
branches into a number of smaller channels, flowing alternately through
flat valleys and between high banks; sometimes he finds a deep rocky bed
with perpendicular walls, carrying the water through a chain of hills;
where the stream is narrow he finds it deep, where wide shallow. Further
up still, he comes to a mountainous region, with hundreds of streams and
rivulets, each with its tributary rills and gullies, collecting the
water from every square mile of surface, and every channel adapted to
the water that it has to carry. He finds that the bed of every branch,
and stream, and rivulet, has a steeper and steeper slope as it
approaches its sources, and is thus enabled to carry off the water from
heavy rains, and to bear away the stones and pebbles and gravel, that
would otherwise block up its course. In every part of this system he
would see exact adaptation of means to an end. He would say, that this
system of channels must have been designed, it answers its purpose so
effectually. Nothing but a mind could have so exactly adapted the slopes
of the channels, their capacity, and frequency, to the nature of the
soil and the quantity of the rainfall. Again, he would see special
adaptation to the wants of man, in broad quiet navigable rivers flowing
through fertile plains that support a large population, while the rocky
streams and mountain torrents, were confined to those sterile regions
suitable only for a small population of shepherds and herdsmen. He would
listen with incredulity to the Geologist, who assured him, that the
adaptation and adjustment he so admired was an inevitable result of the
action of general laws. That the rains and rivers, aided by subterranean
forces, had modelled the country, had formed the hills and valleys, had
scooped out the river beds, and levelled the plains;--and it would only
be after much patient observation and study, after having watched the
minute changes produced year by year, and multiplying them by thousands
and ten thousands, after visiting the various regions of the earth and
seeing the changes everywhere going on, and the unmistakable signs of
greater changes in past times,--that he could be made to understand that
the surface of the earth, however beautiful and harmonious it may
appear, is strictly due in every detail to the action of forces which
are demonstrably self-adjusting.
Moreover, when he had sufficiently extended his inquiries, he would
find, that every evil effect which he would imagine must be the result
of non-adjustment does somewhere or other occur, only it is not always
evil. Looking on a fertile valley, he would perhaps say--"If the channel
of this river were not well adjusted, if for a few miles it sloped the
wrong way, the water could not escape, and all this luxuriant valley,
full of human beings, would become a waste of waters." Well, there are
hundreds of such cases. Every lake is a valley "wasted by water," and in
some cases (as the Dead Sea) it is a positive evil, a blot upon the
harmony and adaptation of the surface of the earth. Again, he might
say--"If rain did not fall here, but the clouds passed over us to some
other regions, this verdant and highly cultivated plain would become a
desert." And there are such deserts over a large part of the earth,
which abundant rains would convert into pleasant dwelling-places for
man. Or he might observe some great navigable river, and reflect how
easily rocks, or a steeper channel in places, might render it useless to
man;--and a little inquiry would show him hundreds of rivers in every
part of the world, which are thus rendered useless for navigation.
Exactly the same thing occurs in organic nature. We see some one
wonderful case of adjustment, some unusual development of an organ, but
we pass over the hundreds of cases in which that adjustment and
development do not occur. No doubt when one adjustment is absent another
takes its place, because no organism can continue to exist that is not
adjusted to its environment; and unceasing variation with unlimited
powers of multiplication, in most cases, furnish the means of
self-adjustment. The world is so constituted, that by the action of
general laws there is produced the greatest possible variety of surface
and of climate; and by the action of laws equally general, the greatest
possible variety of organisms have been produced, adapted to the varied
conditions of every part of the earth. Tho objector would probably
himself admit, that the varied surface of the earth--the plains and
valleys, the hills and mountains, the deserts and volcanoes, the winds
and currents, the seas and lakes and rivers, and the various climates of
the earth--are all the results of general laws acting and re-acting
during countless ages; and that the Creator does not appear to guide and
control the action of these laws--here determining the height of a
mountain, there altering the channel of a river--here making the rains
more abundant, there changing the direction of a current. He would
probably admit that the forces of inorganic nature are self-adjusting,
and that the result necessarily fluctuates about a given mean condition
(which is itself slowly changing), while within certain limits the
greatest possible amount of variety is produced. If then a "contriving
mind" is not necessary at every step of the process of change eternally
going on in the inorganic world, why are we required to believe in the
continual action of such a mind in the region of organic nature? True,
the laws at work are more complex, the adjustments more delicate, the
appearance of special adaptation more remarkable; but why should we
measure the creative mind by our own? Why should we suppose the machine
too complicated, to have been designed by the Creator so complete that
it would necessarily work out harmonious results? The theory of
"continual interference" is a limitation of the Creator's power. It
assumes that he could not work by pure law in the organic, as he has
done in the inorganic world; it assumes that he could not foresee the
consequences of the laws of matter and mind combined--that results would
continually arise which are contrary to what is best, and that he has to
change what would otherwise be the course of nature, in order to produce
that beauty, and variety, and harmony, which even we, with our limited
intellects, can conceive to be the result of self-adjustment in a
universe governed by unvarying law. If we could not conceive the world
of nature to be self-adjusting and capable of endless development, it
would even then be an unworthy idea of a Creator, to impute the
incapacity of our minds to him; but when many human minds can conceive,
and can even trace out in detail some of the adaptations in nature as
the necessary results of unvarying law, it seems strange that, in the
interests of religion, any one should seek to prove that the System of
Nature, instead of being above, is far below our highest conceptions of
it. I, for one, cannot believe that the world would come to chaos if
left to Law alone. I cannot believe that there is in it no inherent
power of developing beauty or variety, and that the direct action of the
Deity is required to produce each spot or streak on every insect, each
detail of structure in every one of the millions of organisms that live
or have lived upon the earth. For it is impossible to draw a line. If
any modifications of structure could be the result of law, why not all?
If some self-adaptations could arise, why not others? If any varieties
of colour, why not all the varieties we see? No attempt is made to
explain this, except by reference to the fact that "purpose" and
"contrivance" are everywhere visible, and by the illogical deduction
that they could only have arisen from the direct action of some mind,
because the direct action of our minds produces similar "contrivances";
but it is forgotten that adaptation, however produced, must have the
appearance of design. The channel of a river looks as if made _for_ the
river, although it is made _by_ it; the fine layers and beds in a
deposit of sand, often look as if they had been sorted, and sifted, and
levelled, designedly; the sides and angles of a crystal exactly resemble
similar forms designed by man; but we do not therefore conclude that
these effects have, in each individual case, required the directing
action of a creative mind, or see any difficulty in their being produced
by natural Law.
_Beauty in Nature._
Let us, however, leave this general argument for a while, and turn to
another special case, which has been appealed to as conclusive against
Mr. Darwin's views. "Beauty" is, to some persons, as great a
stumbling-block as "contrivance." They cannot conceive a system of the
Universe, so perfect, as necessarily to develop every form of Beauty,
but suppose that when anything specially beautiful occurs, it is a step
beyond what that system could have produced, something which the Creator
has added for his own delectation.
Speaking of the Humming Birds, the Duke of Argyll says: "In the first
place, it is to be observed of the whole group, that there is no
connection which can be traced or conceived, between the splendour of
the humming birds and any function essential to their life. If there
were any such connection, that splendour could not be confined, as it
almost exclusively is, to only one sex. The female birds are, of course,
not placed at any disadvantage in the struggle for existence by their
more sombre colouring." And after describing the various ornaments of
these birds, he says: "Mere ornament and variety of form, and these for
their own sake, is the only principle or rule with reference to which
Creative Power seems to have worked in these wonderful and beautiful
birds.... A crest of topaz is no better in the struggle for existence
than a crest of sapphire. A frill ending in spangles of the emerald is
no better in the battle of life than a frill ending in spangles of the
ruby. A tail is not affected for the purposes of flight, whether its
marginal or its central feathers are decorated with white.... Mere
beauty and mere variety, for their own sake, are objects which we
ourselves seek when we can make the Forces of Nature subordinate to the
attainment of them. There seems to be no conceivable reason why we
should doubt or question, that these are ends and aims also in the forms
given to living organisms" ("Reign of Law," p. 248).
Here the statement that "no connection can be conceived between the
splendour of the humming birds and any function essential to their
life," is met by the fact, that Mr. Darwin has not only conceived but
has shown, both by observation and reasoning, how beauty of colour and
form may have a direct influence on the most important of all the
functions of life, that of reproduction. In the variations to which
birds are subject, any more brilliant colour than usual would be
attractive to the females, and would lead to the individuals so adorned
leaving more than the average number of offspring. Experiment and
observation have shown, that this kind of sexual selection does actually
take place; and the laws of inheritance would necessarily lead to the
further development of any individual peculiarity that was attractive,
and thus the splendour of the humming birds is directly connected with
their very existence. It is true that "a crest of topaz may be no better
than a crest of sapphire," but either of these may be much better than
no crest at all; and the different conditions under which the parent
form must have existed in different parts of its range, will have
determined different variations of tint, either of which were
advantageous. The reason why female birds are not adorned with equally
brilliant plumes is sufficiently clear; they would be injurious, by
rendering their possessors too conspicuous during incubation. Survival
of the fittest, has therefore favoured the development of those dark
green tints on the upper surface of so many female humming birds, which
are most conducive to their protection while the important functions of
hatching and rearing the young are being carried on. Keeping in mind the
laws of multiplication, variation, and survival of the fittest, which
are for ever in action, these varied developments of beauty and
harmonious adjustments to conditions, are not only conceivable but
demonstrable results.
The objection I am now combating is solely founded on the supposed
analogy of the Creator's mind to ours, as regards the love of Beauty for
its own sake; but if this analogy is to be trusted, then there ought to
be no natural objects which are disagreeable or ungraceful in our eyes.
And yet it is undoubtedly the fact that there are many such. Just as
surely as the Horse and Deer are beautiful and graceful, the Elephant,
Rhinoceros, Hippopotamus, and Camel are the reverse. The majority of
Monkeys and Apes are not beautiful; the majority of Birds have no beauty
of colour; a vast number of Insects and Reptiles are positively ugly.
Now, if the Creator's mind is like ours, whence this ugliness? It is
useless to say "that is a mystery we cannot explain," because we have
attempted to explain one-half of creation by a method that will not
apply to the other half. We know that a man with the highest taste and
with unlimited wealth, practically does abolish all ungraceful and
disagreeable forms and colours from his own domains. If the beauty of
creation is to be explained by the Creator's love of beauty, we are
bound to ask why he has not banished deformity from the earth, as the
wealthy and enlightened man does from his estate and from his dwelling;
and if we can get no satisfactory answer, we shall do well to reject the
explanation offered. Again, in the case of flowers, which are always
especially referred to, as the surest evidence of beauty being an end of
itself in creation, the whole of the facts are never fairly met. At
least half the plants in the world have not bright-coloured or beautiful
flowers; and Mr. Darwin has lately arrived at the wonderful
generalization, that flowers have become beautiful solely to attract
insects to assist in their fertilization. He adds, "I have come to this
conclusion from finding it an invariable rule, that when a flower is
fertilized by the wind it never has a gaily-coloured corolla." Here is a
most wonderful case of beauty being _useful_, when it might be least
expected. But much more is proved; for when beauty is of no use to the
plant it is not given. It cannot be imagined to do any harm. It is
simply not necessary, and is therefore withheld! We ought surely to have
been told how this fact is consistent with beauty being "an end in
itself," and with the statement of its being given to natural objects
"for its own sake."
_How new Forms are produced by Variation and Selection._
Let us now consider another of the popular objections which the Duke of
Argyll thus sets forth:--
"Mr. Darwin does not pretend to have discovered any law or rule,
according to which new Forms have been born from old Forms. He does not
hold that outward conditions, however changed, are sufficient to account
for them.... His theory seems to be far better than a mere theory--to be
an established scientific truth--in so far as it accounts, in part at
least, for the success and establishment and spread of new Forms _when
they have arisen_. But it does not even suggest the law under which, or
by or according to which, such new Forms are introduced. Natural
Selection can do nothing, except with the materials presented to its
hands. It cannot select except among the things open to selection....
Strictly speaking, therefore, Mr. Darwin's theory is not a theory on the
Origin of Species at all, but only a theory on the causes which lead to
the relative success or failure of such new forms as may be born into
the world." ("Reign of Law," p. 230.)
In this, and many other passages in his work, the Duke of Argyll sets
forth his idea of Creation as a "Creation by birth," but maintains that
each birth of a new form from parents differing from itself, has been
produced by a special interference of the Creator, in order to direct
the process of development into certain channels; that each new species
is in fact a "special creation," although brought into existence through
the ordinary laws of reproduction. He maintains therefore, that the laws
of multiplication and variation cannot furnish the right kinds of
materials at the right times for natural selection to work on. I
believe, on the contrary, that it can be logically _proved_ from the six
axiomatic laws before laid down, that such materials would be furnished;
but I prefer to show there are abundance of _facts_ which demonstrate
that they are furnished.
The experience of all cultivators of plants and breeders of animals
shows, that when a sufficient number of individuals are examined,
variations of any required kind can always be met with. On this depends
the possibility of obtaining breeds, races, and fixed varieties of
animals and plants; and it is found, that any one form of variation may
be accumulated by selection, without materially affecting the other
characters of the species; each _seems_ to vary in the one required
direction only. For example, in turnips, radishes, potatoes, and
carrots, the root or tuber varies in size, colour, form, and flavour,
while the foliage and flowers seem to remain almost stationary; in the
cabbage and lettuce, on the contrary, the foliage can be modified into
various forms and modes of growth, the root, flower, and fruit remaining
little altered; in the cauliflower and brocoli the flower heads vary; in
the garden pea the pod only changes. We get innumerable forms of fruit
in the apple and pear, while the leaves and flowers remain
undistinguishable; the same occurs in the gooseberry and garden currant.
Directly however, (in the very same genus) we want the flower to vary in
the Ribes sanguineum, it does so, although mere cultivation for hundreds
of years has not produced marked differences in the flowers of Ribes
grossularia. When fashion demands any particular change in the form or
size, or colour of a flower, sufficient variation always occurs in the
right direction, as is shown by our roses, auriculas, and geraniums;
when, as recently, ornamental leaves come into fashion sufficient
variation is found to meet the demand, and we have zoned pelargoniums,
and variegated ivy, and it is discovered that a host of our commonest
shrubs and herbaceous plants have taken to vary in this direction just
when we want them to do so! This rapid variation is not confined to old
and well-known plants subjected for a long series of generations to
cultivation, but the Sikim Rhododendrons, the Fuchsias, and Calceolarias
from the Andes, and the Pelargoniums from the Cape are equally
accommodating, and vary just when and where and how we require them.
Turning to animals we find equally striking examples. If we want any
special quality in any animal we have only to breed it in sufficient
quantities and watch carefully, and the required variety is _always_
found, and can be increased to almost any desired extent. In Sheep, we
get flesh, fat, and wool; in Cows, milk; in Horses, colour, strength,
size, and speed; in Poultry, we have got almost any variety of colour,
curious modifications of plumage, and the capacity of perpetual
egg-laying. In Pigeons we have a still more remarkable proof of the
universality of variation, for it has been at one time or another the
fancy of breeders to change the form of every part of these birds, and
they have never found the required variations absent. The form, size,
and shape of bill and feet, have been changed to such a degree as is
found only in distinct genera of wild birds; the number of tail feathers
has been increased, a character which is generally one of the most
permanent nature, and is of high importance in the classification of
birds; and the size, the colour, and the habits, have been also changed
to a marvellous extent. In Dogs, the degree of modification and the
facility with which it is effected, is almost equally apparent. Look at
the constant amount of variation in opposite directions that must have
been going on, to develop the poodle and the greyhound from the same
original stock! Instincts, habits, intelligence, size, speed, form, and
colour, have always varied, so as to produce the very races which the
wants or fancies or passions of men may have led them to desire. Whether
they wanted a bull-dog to torture another animal, a greyhound to catch
a hare, or a bloodhound to hunt down their oppressed fellow-creatures,
the required variations have always appeared.
Now this great mass of facts, of which a mere sketch has been here
given, are fully accounted for by the "Law of Variation" as laid down at
the commencement of this paper. Universal variability--small in amount
but in every direction, ever fluctuating about a mean condition until
made to advance in a given direction by "election," natural or
artificial,--is the simple basis for the indefinite modification of the
forms of life;--partial, unbalanced, and consequently unstable
modifications being produced by man, while those developed under the
unrestrained action of natural laws, are at every step self-adjusted to
external conditions by the dying out of all unadjusted forms, and are
therefore stable and comparatively permanent. To be consistent in their
views, our opponents must maintain that every one of the variations that
have rendered possible the changes produced by man, have been determined
at the right time and place by the will of the Creator. Every race
produced by the florist or the breeder, the dog or the pigeon fancier,
the ratcatcher, the sporting man, or the slave-hunter, must have been
provided for by varieties occurring when wanted; and as these variations
were never withheld, it would prove, that the sanction of an all-wise
and all-powerful Being, has been given to that which the highest human
minds consider to be trivial, mean, or debasing.
This appears to be a complete answer to the theory, that variation
sufficient in amount to be accumulated in a given direction must be the
direct act of the Creative Mind, but it is also sufficiently condemned
by being so entirely unnecessary. The facility with which man obtains
new races, depends chiefly upon the number of individuals he can procure
to select from. When hundreds of florists or breeders are all aiming at
the same object, the work of change goes on rapidly. But a common
species in nature contains a thousand-or a million-fold more individuals
than any domestic race; and survival of the fittest must unerringly
preserve all that vary in the right direction, not only in obvious
characters but in minute details, not only in external but in internal
organs; so that if the materials are sufficient for the needs of man,
there can be no want of them to fulfil the grand purpose of keeping up a
supply of modified organisms, exactly adapted to the changed conditions
that are always occurring in the inorganic world.
_The Objection that there are Limits to Variation._
Having now, I believe, fairly answered the chief objections of the Duke
of Argyll, I proceed to notice one or two of those adduced in an able
and argumentative essay on the "Origin of Species" in the _North British
Review_ for July, 1867. The writer first attempts to prove that there
are strict limits to variation. When we begin to select variations in
any one direction, the process is comparatively rapid, but after a
considerable amount of change has been effected it becomes slower and
slower, till at length its limits are reached and no care in breeding
and selection can produce any further advance. The race-horse is chosen
as an example. It is admitted that, with any ordinary lot of horses to
begin with, careful selection would in a few years make a great
improvement, and in a comparatively short time the standard of our best
racers might be reached. But that standard has not for many years been
materially raised, although unlimited wealth and energy are expended in
the attempt. This is held to prove that there are definite limits to
variation in any special direction, and that we have no reason to
suppose that mere time, and the selective process being carried on by
natural law, could make any material difference. But the writer does not
perceive that this argument fails to meet the real question, which is,
not whether indefinite and unlimited change in any or all directions is
possible, but whether such differences as do occur in nature could have
been produced by the accumulation of variations by selection. In the
matter of speed, a limit of a definite kind as regards land animals does
exist in nature. All the swiftest animals--deer, antelopes, hares,
foxes, lions, leopards, horses, zebras, and many others, have reached
very nearly the same degree of speed. Although the swiftest of each must
have been for ages preserved, and the slowest must have perished, we
have no reason to believe there is any advance of speed. The possible
limit under existing conditions, and perhaps under possible terrestrial
conditions, has been long ago reached. In cases, however, where this
limit had not been so nearly reached as in the horse, we have been
enabled to make a more marked advance and to produce a greater
difference of form. The wild dog is an animal that hunts much in
company, and trusts more to endurance than to speed. Man has produced
the greyhound, which differs much more from the wolf or the dingo than
the racer does from the wild Arabian. Domestic dogs, again, have varied
more in size and in form than the whole family of Canidæ in a state of
nature. No wild dog, fox, or wolf, is either so small as some of the
smallest terriers and spaniels, or so large as the largest varieties of
hound or Newfoundland dog. And, certainly, no two wild animals of the
family differ so widely in form and proportions as the Chinese pug and
the Italian greyhound, or the bulldog and the common greyhound. The
known range of variation is, therefore, more than enough for the
derivation of all the forms of Dogs, Wolves, and Foxes from a common
ancestor.
Again, it is objected that the Pouter or the Fan-tail pigeon cannot be
further developed in the same direction. Variation seems to have reached
its limits in these birds. But so it has in nature. The Fan-tail has not
only more tail feathers than any of the three hundred and forty existing
species of pigeons, but more than any of the eight thousand known
species of birds. There is, of course, some limit to the number of
feathers of which a tail useful for flight can consist, and in the
Fan-tail we have probably reached that limit. Many birds have the
oesophagus or the skin of the neck more or less dilatable, but in no
known bird is it so dilatable as in the Pouter pigeon. Here again the
possible limit, compatible with a healthy existence, has probably been
reached. In like manner the differences in the size and form of the beak
in the various breeds of the domestic Pigeon, is greater than that
between the extreme forms of beak in the various genera and sub-families
of the whole Pigeon tribe. From these facts, and many others of the same
nature, we may fairly infer, that if rigid selection were applied to any
organ, we could in a comparatively short time produce a much greater
amount of change than that which occurs between species and species in a
state of nature, since the differences which we do produce are often
comparable with those which exist between distinct genera or distinct
families. The facts adduced by the writer of the article referred to, of
the definite limits to variability in certain directions in domesticated
animals, are, therefore, no objection whatever to the view, that all the
modifications which exist in nature have been produced by the
accumulation, by natural selection, of small and useful variations,
since those very modifications have equally definite and very similar
limits.
_Objection to the Argument from Classification._
To another of this writer's objections--that by Professor Thomson's
calculations the sun can only have existed in a solid state 500,000,000
of years, and that therefore _time_ would not suffice for the slow
process of development of all living organisms--it is hardly necessary
to reply, as it cannot be seriously contended, even if this calculation
has claims to approximate accuracy, that the process of change and
development may not have been sufficiently rapid to have occurred within
that period. His objection to the Classification argument is, however,
more plausible. The uncertainty of opinion among Naturalists as to which
are species and which varieties, is one of Mr. Darwin's very strong
arguments that these two names cannot belong to things quite distinct in
nature and origin. The Reviewer says that this argument is of no weight,
because the works of man present exactly the same phenomena; and he
instances patent inventions, and the excessive difficulty of determining
whether they are new or old. I accept the analogy though it is a very
imperfect one, and maintain that such as it is, it is all in favour of
Mr. Darwin's views. For are not all inventions of the same kind directly
affiliated to a common ancestor? Are not improved Steam Engines or
Clocks the lineal descendants of some existing Steam Engine or Clock? Is
there ever a new Creation in Art or Science any more than in Nature? Did
ever patentee absolutely originate any complete and entire invention, no
portion of which was derived from anything that had been made or
described before? It is therefore clear that the difficulty of
distinguishing the various classes of inventions which claim to be new,
is of the same nature as the difficulty of distinguishing varieties and
species, because neither are absolute new creations, but both are alike
descendants of pre-existing forms, from which and from each other they
differ by varying and often imperceptible degrees. It appears, then,
that however plausible this writer's objections may seem, whenever he
descends from generalities to any specific statement, his supposed
difficulties turn out to be in reality strongly confirmatory of Mr.
Darwin's view.
_The "Times," on Natural Selection._
The extraordinary misconception of the whole subject by popular writers
and reviewers, is well shown by an article which appeared in the _Times_
newspaper on "The Reign of Law." Alluding to the supposed economy of
nature, in the adaptation of each species to its own place and its
special use, the reviewer remarks: "To this universal law of the
greatest economy, the law of natural selection stands in direct
antagonism as the law of 'greatest possible waste' of time and of
creative power. To conceive a duck with webbed feet and a spoon-shaped
bill, living by suction, to pass naturally into a gull with webbed feet
and a knife-like bill, living on flesh, in the longest possible time and
in the most laborious possible way, we may conceive it to pass from the
one to the other state by natural selection. The battle of life the
ducks will have to fight will increase in peril continually as they
cease (with the change of their bill) to be ducks, and attain a
_maximum_ of danger in the condition in which they begin to be gulls;
and ages must elapse and whole generations must perish, and countless
generations of the one species be created and sacrificed, to arrive at
one single pair of the other."
In this passage the theory of natural selection is so absurdly
misrepresented that it would be amusing, did we not consider the
misleading effect likely to be produced by this kind of teaching in so
popular a journal. It is assumed that the duck and the gull are
essential parts of nature, each well fitted for its place, and that if
one had been produced from the other by a gradual metamorphosis, the
intermediate forms would have been useless, unmeaning, and unfitted for
any place, in the system of the universe. Now, this idea can only exist
in a mind ignorant of the very foundation and essence of the theory of
natural selection, which is, the preservation of _useful_ variations
only, or, as has been well expressed, in other words, the "survival of
the fittest." Every intermediate form which could possibly have arisen
during the transition from the duck to the gull, so far from having an
unusually severe battle to fight for existence, or incurring any
"_maximum_ of danger," would necessarily have been as accurately
adjusted to the rest of nature, and as well fitted to maintain and to
enjoy its existence, as the duck or the gull actually are. If it were
not so, it never could have been produced under the law of natural
selection.
_Intermediate or generalized Forms of extinct Animals, an indication of
Transmutation or Development._
The misconception of this writer illustrates another point very
frequently overlooked. It is an essential part of Mr. Darwin's theory,
that one existing animal has not been derived from any other existing
animal, but that both are the descendants of a common ancestor, which
was at once different from either, but, in essential characters,
intermediate between them both. The illustration of the duck and the
gull is therefore misleading; one of these birds has not been derived
from the other, but both from a common ancestor. This is not a mere
supposition invented to support the theory of natural selection, but is
founded on a variety of indisputable facts. As we go back into past
time, and meet with the fossil remains of more and more ancient races of
extinct animals, we find that many of them actually are intermediate
between distinct groups of existing animals. Professor Owen continually
dwells on this fact: he says in his "Palæontology," p. 284: "A more
generalized vertebrate structure is illustrated, in the extinct
reptiles, by the affinities to ganoid fishes, shown by Ganocephala,
Labyrinthodontia, and Icthyopterygia; by the affinities of the
Pterosauria to Birds, and by the approximation of the Dinosauria to
Mammals. (These have been recently shown by Professor Huxley to have
more affinity to Birds.) It is manifested by the combination of modern
crocodilian, chelonian, and lacertian characters in the Cryptodontia
and the Dicnyodontia, and by the combined lacertian and crocodilian
characters in the Thecodontia and Sauropterygia." In the same work he
tells us that, "the Anoplotherium, in several important characters
resembled the embryo Ruminant, but retained throughout life those marks
of adhesion to a generalized mammalian type;"--and assures us that he
has "never omitted a proper opportunity for impressing the results of
observations showing the more generalized structures of extinct as
compared with the more specialized forms of recent animals." Modern
palæontologists have discovered hundreds of examples of these more
generalized or ancestral types. In the time of Cuvier, the Ruminants and
the Pachyderms were looked upon as two of the most distinct orders of
animals; but it is now demonstrated that there once existed a variety of
genera and species, connecting by almost imperceptible grades such
widely different animals as the pig and the camel. Among living
quadrupeds we can scarcely find a more isolated group than the genus
Equus, comprising the horses, asses, and Zebras; but through many
species of Paloplotherium, Hippotherium, and Hipparion, and numbers of
extinct forms of Equus found in Europe, India, and America, an almost
complete transition is established with the Eocene Anoplothorium and
Paleotherium, which are also generalized or ancestral types of the Tapir
and Rhinoceros. The recent researches of M. Gaudry in Greece have
furnished much new evidence of the same character. In the Miocene beds
of Pikermi he has discovered the group of the Simocyonidæ intermediate
between bears and wolves; the genus Hyænictis which connects the hyænas
with the civets; the Ancylotherium, which is allied both to the extinct
mastodon and to the living pangolin or scaly ant-eater; and the
Helladotherium, which connects the now isolated giraffe with the deer
and antelopes.
Between reptiles and fishes an intermediate type has been found in the
Archegosaurus of the Coal formation; while the Labyrinthodon of the
Trias combined characters of the Batrachia with those of crocodiles,
lizards, and ganoid fishes. Even birds, the most apparently isolated of
all living forms, and the most rarely preserved in a fossil state, have
been shown to possess undoubted affinities with reptiles; and in the
Oolitic Archæopteryx, with its lengthened tail, feathered on each side,
we have one of the connecting links from the side of birds; while
Professor Huxley has recently shown that the entire order of
Dinosaurians have remarkable affinities to birds, and that one of them,
the Compsognathus, makes a nearer approach to bird organisation than
does Archæopteryx to that of reptiles.
Analogous facts to those occur in other classes of animals, as
an example of which we have the authority of a distinguished
paleontologist, M. Barande, quoted by Mr. Darwin, for the statement,
that although the Palæozoic Invertebrata can certainly be classed under
existing groups, yet at this ancient period the groups were not so
distinctly separated from each other as they are now; while Mr. Scudder
tells us, that some of the fossil insects discovered in the Coal
formation of America offer characters intermediate between those of
existing orders. Agassiz, again, insists strongly that the more ancient
animals resemble the embryonic forms of existing species; but as the
embryos of distinct groups are known to resemble each other more than
the adult animals (and in fact to be undistinguishable at a very early
age), this is the same as saying that the ancient animals are exactly
what, on Darwin's theory, the ancestors of existing animals ought to be;
and this, it must be remembered, is the evidence of one of the strongest
opponents of the theory of natural selection.
_Conclusion._
I have thus endeavoured to meet fairly, and to answer plainly, a few of
the most common objections to the theory of natural selection, and I
have done so in every case by referring to admitted facts and to logical
deductions from those facts.
As an indication and general summary of the line of argument I have
adopted, I here give a brief demonstration in a tabular form of the
Origin of Species by means of Natural Selection, referring for the
_facts_ to Mr. Darwin's works, and to the pages in this volume, where
they are more or less fully treated.
_A Demonstration of the Origin of Species by Natural Selection_.
___________________________________________________________________
| | |
|_PROVED FACTS_. |_NECESSARY CONSEQUENCES_ |
| |(_afterwards taken as Proved |
| |Facts_). |
|_________________________________|_________________________________|
| | |
|RAPID INCREASE OF ORGANISMS, | |
|pp. 29, 265; ("Origin |STRUGGLE FOR EXISTENCE, |
|of Species," p. 75, 5th Ed.) |the deaths equalling the |
| |births on the average, p. 30; |
|TOTAL NUMBER OF INDIVIDUALS |("Origin of Species," chap. |
|STATIONARY, pp. 30, |III.) |
|266. | |
|_________________________________|_________________________________|
| | |
|STRUGGLE FOR EXISTENCE. |SURVIVAL OF THE FITTEST, |
| |or Natural Selection; meaning |
|HEREDITY WITH VARIATION, |simply, that on the |
|or general likeness with |whole those die who are |
|individual differences of parents|least fitted to maintain their |
|and offspring, pp. |existence; ("Origin of Species," |
|266, 287-291, 308; ("Origin |chap. IV.) |
|of Species," chap. I., II., V.) | |
|_________________________________|_________________________________|
| | |
|SURVIVAL OF THE FITTEST. |CHANGES OF ORGANIC FORMS, |
| |to keep them in harmony |
|CHANGE OF EXTERNAL CONDITIONS, |with the Changed Conditions; |
|universal and unceasing.--See |and as the changes |
|"Lyell's |of conditions are permanent |
|Principles of Geology." |changes, in the sense |
| |of not reverting back to |
| |identical previous conditions, |
| |the changes of organic |
| |forms must be in the |
| |same sense permanent, and |
| |thus originate SPECIES. |
|_________________________________|_________________________________|
IX.
THE DEVELOPMENT OF HUMAN RACES UNDER THE LAW OF NATURAL SELECTION.
Among the most advanced students of man, there exists a wide difference
of opinion on some of the most vital questions respecting his nature and
origin. Anthropologists are now, indeed, pretty well agreed that man is
not a recent introduction into the earth. All who have studied the
question, now admit that his antiquity is very great; and that, though
we have to some extent ascertained the minimum of time during which he
_must_ have existed, we have made no approximation towards determining
that far greater period during which he _may_ have, and probably _has_
existed. We can with tolerable certainty affirm that man must have
inhabited the earth a thousand centuries ago, but we cannot assert that
he positively did not exist, or that there is any good evidence against
his having existed, for a period of ten thousand centuries. We know
positively, that he was contemporaneous with many now extinct animals,
and has survived changes of the earth's surface fifty or a hundred times
greater than any that have occurred during the historical period; but we
cannot place any definite limit to the number of species he may have
outlived, or to the amount of terrestrial change he may have witnessed.
_Wide differences of opinion as to Man's Origin._
But while on this question of man's antiquity there is a very general
agreement,--and all are waiting eagerly for fresh evidence to clear up
those points which all admit to be full of doubt,--on other, and not
less obscure and difficult questions, a considerable amount of dogmatism
is exhibited; doctrines are put forward as established truths, no doubt
or hesitation is admitted, and it seems to be supposed that no further
evidence is required, or that any new facts can modify our convictions.
This is especially the case when we inquire,--Are the various forms
under which man now exists primitive, or derived from pre-existing
forms; in other words, is man of one or many species? To this question
we immediately obtain distinct answers diametrically opposed to each
other: the one party positively maintaining, that man is a _species_ and
is essentially _one_--that all differences are but local and temporary
variations, produced by the different physical and moral conditions by
which he is surrounded; the other party maintaining with equal
confidence, that man is a genus of _many species_, each of which is
practically unchangeable, and has ever been as distinct, or even more
distinct, than we now behold them. This difference of opinion is
somewhat remarkable, when we consider that both parties are well
acquainted with the subject; both use the same vast accumulation of
facts; both reject those early traditions of mankind which profess to
give an account of his origin; and both declare that they are seeking
fearlessly after truth alone; yet each will persist in looking only at
the portion of truth on his own side of the question, and at the error
which is mingled with his opponent's doctrine. It is my wish to show how
the two opposing views can be combined, so as to eliminate the error and
retain the truth in each, and it is by means of Mr. Darwin's celebrated
theory of "Natural Selection" that I hope to do this, and thus to
harmonise the conflicting theories of modern anthropologists.
Let us first see what each party has to say for itself. In favour of the
unity of mankind it is argued, that there are no races without
transitions to others; that every race exhibits within itself variations
of colour, of hair, of feature, and of form, to such a degree as to
bridge over, to a large extent, the gap that separates it from other
races. It is asserted that no race is homogeneous; that there is a
tendency to vary; that climate, food, and habits produce, and render
permanent, physical peculiarities, which, though slight in the limited
periods allowed to our observation, would, in the long ages during which
the human race has existed, have sufficed to produce all the differences
that now appear. It is further asserted that the advocates of the
opposite theory do not agree among themselves; that some would make
three, some five, some fifty or a hundred and fifty species of man; some
would have had each species created in pairs, while others require
nations to have at once sprung into existence, and that there is no
stability or consistency in any doctrine but that of one primitive
stock.
The advocates of the original diversity of man, on the other hand, have
much to say for themselves. They argue that proofs of change in man have
never been brought forward except to the most trifling amount, while
evidence of his permanence meets us everywhere. The Portuguese and
Spaniards, settled for two or three centuries in South America, retain
their chief physical, mental, and moral characteristics; the Dutch boers
at the Cape, and the descendants of the early Dutch settlers in the
Moluccas, have not lost the features or the colour of the Germanic
races; the Jews, scattered over the world in the most diverse climates,
retain the same characteristic lineaments everywhere; the Egyptian
sculptures and paintings show us that, for at least 4000 or 5000 years,
the strongly contrasted features of the Negro and the Semitic races have
remained altogether unchanged; while more recent discoveries prove, that
the mound-builders of the Mississippi valley, and the dwellers on
Brazilian mountains, had, even in the very infancy of the human race,
some traces of the same peculiar and characteristic type of cranial
formation that now distinguishes them.
If we endeavour to decide impartially on the merits of this difficult
controversy, judging solely by the evidence that each party has brought
forward, it certainly seems that the best of the argument is on the
side of those who maintain the primitive diversity of man. Their
opponents have not been able to refute the permanence of existing races
as far back as we can trace them, and have failed to show, in a single
case, that at any former epoch the well marked varieties of mankind
approximated more closely than they do at the present day. At the same
time this is but negative evidence. A condition of immobility for four
or five thousand years, does not preclude an advance at an earlier
epoch, and--if we can show that there are causes in nature which would
check any further physical change when certain conditions were
fulfilled--does not even render such an advance improbable, if there are
any general arguments to be adduced in its favour. Such a cause, I
believe, does exist; and I shall now endeavour to point out its nature
and its mode of operation.
_Outline of the Theory of Natural Selection._
In order to make my argument intelligible, it is necessary for me to
explain very briefly the theory of "Natural Selection" promulgated by
Mr. Darwin, and the power which it possesses of modifying the forms of
animals and plants. The grand feature in the multiplication of organic
life is, that close general resemblance is combined with more or less
individual variation. The child resembles its parents or ancestors more
or less closely in all its peculiarities, deformities, or beauties; it
resembles them in general more than it does any other individuals; yet
children of the same parents are not all alike, and it often happens
that they differ very considerably from their parents and from each
other. This is equally true, of man, of all animals, and of all plants.
Moreover, it is found that individuals do not differ from their parents
in certain particulars only, while in all others they are exact
duplicates of them. They differ from them and from each other, in every
particular: in form, in size, in colour; in the structure of internal as
well as of external organs; in those subtle peculiarities which produce
differences of constitution, as well as in those still more subtle ones
which lead to modifications of mind and character. In other words, in
every possible way, in every organ and in every function, individuals of
the same stock vary.
Now, health, strength, and long life, are the results of a harmony
between the individual and the universe that surrounds it. Let us
suppose that at any given moment this harmony is perfect. A certain
animal is exactly fitted to secure its prey, to escape from its enemies,
to resist the inclemencies of the seasons, and to rear a numerous and
healthy offspring. But a change now takes place. A series of cold
winters, for instance, come on, making food scarce, and bringing an
immigration of some other animals to compete with the former inhabitants
of the district. The new immigrant is swift of foot, and surpasses its
rivals in the pursuit of game; the winter nights are colder, and require
a thicker fur as a protection, and more nourishing food to keep up the
heat of the system. Our supposed perfect animal is no longer in harmony
with its universe; it is in danger of dying of cold or of starvation.
But the animal varies in its offspring. Some of these are swifter than
others--they still manage to catch food enough; some are hardier and
more thickly furred--they manage in the cold nights to keep warm enough;
the slow, the weak, and the thinly clad soon die off. Again and again,
in each succeeding generation, the same thing takes place. By this
natural process, which is so inevitable that it cannot be conceived not
to act, those best adapted to live, live; those least adapted, die. It
is sometimes said that we have no direct evidence of the action of this
selecting power in nature. But it seems to me we have better evidence
than even direct observation would be, because it is more universal,
viz., the evidence of necessity. It must be so; for, as all wild animals
increase in a geometrical ratio, while their actual numbers remain on
the average stationary, it follows, that as many die annually as are
born. If, therefore, we deny natural selection, it can only be by
asserting that, in such a case as I have supposed, the strong, the
healthy, the swift, the well clad, the well organised animals in every
respect, have no advantage over,--do not on the average live longer
than, the weak, the unhealthy, the slow, the ill-clad, and the
imperfectly organised individuals; and this no sane man has yet been
found hardy enough to assert. But this is not all; for the offspring on
the average resemble their parents, and the selected portion of each
succeeding generation will therefore be stronger, swifter, and more
thickly furred than the last; and if this process goes on for thousands
of generations, our animal will have again become thoroughly in harmony
with the new conditions in which it is placed. But it will now be a
different creature. It will be not only swifter and stronger, and more
furry, it will also probably have changed in colour, in form, perhaps
have acquired a longer tail, or differently shaped ears; for it is an
ascertained fact, that when one part of an animal is modified, some
other parts almost always change, as it were in sympathy with it. Mr.
Darwin calls this "correlation of growth," and gives as instances, that
hairless dogs have imperfect teeth; white cats, when blue-eyed, are
deaf; small feet accompany short beaks in pigeons; and other equally
interesting cases.
Grant, therefore, the premises: 1st. That peculiarities of every kind
are more or less hereditary. 2nd. That the offspring of every animal
vary more or less in all parts of their organization. 3rd. That
the universe in which these animals live, is not absolutely
invariable;--none of which propositions can be denied; and then
consider, that the animals in any country (those at least which are not
dying out) must at each successive period be brought into harmony with
the surrounding conditions; and we have all the elements for a change of
form and structure in the animals, keeping exact pace with changes of
whatever nature in the surrounding universe. Such changes must be slow,
for the changes in the universe are very slow; but just as these slow
changes become important, when we look at results after long periods of
action, as we do when we perceive the alterations of the earth's surface
during geological epochs; so the parallel changes in animal form become
more and more striking, in proportion as the time they have been going
on is great; as we see when we compare our living animals with those
which we disentomb from each successively older geological formation.
This is, briefly, the theory of "natural selection," which explains the
changes in the organic world as being parallel with, and in part
dependent on, those in the inorganic. What we now have to inquire
is,--Can this theory be applied in any way to the question of the origin
of the races of man? or is there anything in human nature that takes him
out of the category of those organic existences, over whose successive
mutations it has had such powerful sway?
_Different effects of Natural Selection on Animals and on Man._
In order to answer these questions, we must consider why it is that
"natural selection" acts so powerfully upon animals; and we shall, I
believe, find, that its effect depends mainly upon their self-dependence
and individual isolation. A slight injury, a temporary illness, will
often end in death, because it leaves the individual powerless against
its enemies. If an herbivorous animal is a little sick and has not fed
well for a day or two, and the herd is then pursued by a beast of prey,
our poor invalid inevitably falls a victim. So, in a carnivorous animal,
the least deficiency of vigour prevents its capturing food, and it soon
dies of starvation. There is, as a general rule, no mutual assistance
between adults, which enables them to tide over a period of sickness.
Neither is there any division of labour; each must fulfil _all_ the
conditions of its existence, and, therefore, "natural selection" keeps
all up to a pretty uniform standard.
But in man, as we now behold him, this is different. He is social and
sympathetic. In the rudest tribes the sick are assisted, at least with
food; less robust health and vigour than the average does not entail
death. Neither does the want of perfect limbs, or other organs, produce
the same effects as among animals. Some division of labour takes place;
the swiftest hunt, the less active fish, or gather fruits; food is, to
some extent, exchanged or divided. The action of natural selection is
therefore checked; the weaker, the dwarfish, those of less active limbs,
or less piercing eyesight, do not suffer the extreme penalty which falls
upon animals so defective.
In proportion as these physical characteristics become of less
importance, mental and moral qualities will have increasing influence on
the well-being of the race. Capacity for acting in concert for
protection, and for the acquisition of food and shelter; sympathy, which
leads all in turn to assist each other; the sense of right, which checks
depredations upon our fellows; the smaller development of the combative
and destructive propensities; self-restraint in present appetites; and
that intelligent foresight which prepares for the future, are all
qualities, that from their earliest appearance must have been for the
benefit of each community, and would, therefore, have become the
subjects of "natural selection." For it is evident that such qualities
would be for the well-being of man; would guard him against external
enemies, against internal dissensions, and against the effects of
inclement seasons and impending famine, more surely than could any
merely physical modification. Tribes in which such mental and moral
qualities were predominant, would therefore have an advantage in the
struggle for existence over other tribes in which they were less
developed, would live and maintain their numbers, while the others would
decrease and finally succumb.
Again, when any slow changes of physical geography, or of climate, make
it necessary for an animal to alter its food, its clothing, or its
weapons, it can only do so by the occurrence of a corresponding change
in its own bodily structure and internal organization. If a larger or
more powerful beast is to be captured and devoured, as when a
carnivorous animal which has hitherto preyed on antelopes is obliged
from their decreasing numbers to attack buffaloes, it is only the
strongest who can hold,--those with most powerful claws, and formidable
canine teeth, that can struggle with and overcome such an animal.
Natural selection immediately comes into play, and by its action these
organs gradually become adapted to their new requirements. But man,
under similar circumstances, does not require longer nails or teeth,
greater bodily strength or swiftness. He makes sharper spears, or a
better bow, or he constructs a cunning pitfall, or combines in a hunting
party to circumvent his new prey. The capacities which enable him to do
this are what he requires to be strengthened, and these will, therefore,
be gradually modified by "natural selection," while the form and
structure of his body will remain unchanged. So, when a glacial epoch
comes on, some animals must acquire warmer fur, or a covering of fat, or
else die of cold. Those best clothed by nature are, therefore, preserved
by natural selection. Man, under the same circumstances, will make
himself warmer clothing, and build better houses; and the necessity of
doing this will react upon his mental organization and social
condition--will advance them while his natural body remains naked as
before.
When the accustomed food of some animal becomes scarce or totally fails,
it can only exist by becoming adapted to a new kind of food, a food
perhaps less nourishing and less digestible. "Natural selection" will
now act upon the stomach and intestines, and all their individual
variations will be taken advantage of, to modify the race into harmony
with its new food. In many cases, however, it is probable that this
cannot be done. The internal organs may not vary quick enough, and then
the animal will decrease in numbers, and finally become extinct. But
man guards himself from such accidents by superintending and guiding the
operations of nature. He plants the seed of his most agreeable food, and
thus procures a supply, independent of the accidents of varying seasons
or natural extinction. He domesticates animals, which serve him either
to capture food or for food itself, and thus, changes of any great
extent in his teeth or digestive organs are rendered unnecessary. Man,
too, has everywhere the use of fire, and by its means can render
palatable a variety of animal and vegetable substances, which he could
hardly otherwise make use of; and thus obtains for himself a supply of
food far more varied and abundant than that which any animal can
command.
Thus man, by the mere capacity of clothing himself, and making weapons
and tools, has taken away from nature that power of slowly but
permanently changing the external form and structure, in accordance with
changes in the external world, which she exercises over all other
animals. As the competing races by which they are surrounded, the
climate, the vegetation, or the animals which serve them for food, are
slowly changing, they must undergo a corresponding change in their
structure, habits, and constitution, to keep them in harmony with the
new conditions--to enable them to live and maintain their numbers. But
man does this by means of his intellect alone, the variations of which
enable him, with an unchanged body, still to keep in harmony with the
changing universe.
There is one point, however, in which nature will still act upon him as
it does on animals, and, to some extent, modify his external characters.
Mr. Darwin has shown, that the colour of the skin is correlated with
constitutional peculiarities both in vegetables and animals, so that
liability to certain diseases or freedom from them is often accompanied
by marked external characters. Now, there is every reason to believe
that this has acted, and, to some extent, may still continue to act, on
man. In localities where certain diseases are prevalent, those
individuals of savage races which were subject to them would rapidly die
off; while those who were constitutionally free from the disease would
survive, and form the progenitors of a new race. These favoured
individuals would probably be distinguished by peculiarities of
_colour_, with which again peculiarities in the texture or the abundance
of _hair_ seem to be correlated, and thus may have been brought about
those racial differences of colour, which seem to have no relation to
mere temperature or other obvious peculiarities of climate.
From the time, therefore, when the social and sympathetic feelings came
into active operation, and the intellectual and moral faculties became
fairly developed, man would cease to be influenced by "natural
selection" in his physical form and structure. As an animal he would
remain almost stationary, the changes of the surrounding universe
ceasing to produce in him that powerful modifying effect which they
exercise over other parts of the organic world. But from the moment
that the form of his body became stationary, his mind would become
subject to those very influences from which his body had escaped; every
slight variation in his mental and moral nature which should enable him
better to guard against adverse circumstances, and combine for mutual
comfort and protection, would be preserved and accumulated; the better
and higher specimens of our race would therefore increase and spread,
the lower and more brutal would give way and successively die out, and
that rapid advancement of mental organization would occur, which has
raised the very lowest races of man so far above the brutes (although
differing so little from some of them in physical structure), and, in
conjunction with scarcely perceptible modifications of form, has
developed the wonderful intellect of the European races.
_Influence of external Nature in the development of the Human Mind._
But from the time when this mental and moral advance commenced, and
man's physical character became fixed and almost immutable, a new series
of causes would come into action, and take part in his mental growth.
The diverse aspects of nature would now make themselves felt, and
profoundly influence the character of the primitive man.
When the power that had hitherto modified the body had its action
transferred to the mind, then races would advance and become improved,
merely by the harsh discipline of a sterile soil and inclement seasons.
Under their influence, a hardier, a more provident, and a more social
race would be developed, than in those regions where the earth produces
a perennial supply of vegetable food, and where neither foresight nor
ingenuity are required to prepare for the rigours of winter. And is it
not the fact that in all ages, and in every quarter of the globe, the
inhabitants of temperate have been superior to those of hotter
countries? All the great invasions and displacements of races have been
from North to South, rather than the reverse; and we have no record of
there ever having existed, any more than there exists to-day, a solitary
instance of an indigenous inter-tropical civilization. The Mexican
civilization and government came from the North, and, as well as the
Peruvian, was established, not in the rich tropical plains, but on the
lofty and sterile plateaux of the Andes. The religion and civilization
of Ceylon were introduced from North India; the successive conquerors of
the Indian peninsula came from the North-west; the northern Mongols
conquered the more Southern Chinese; and it was the bold and adventurous
tribes of the North that overran and infused new life into Southern
Europe.
_Extinction of Lower Races._
It is the same great law of "the preservation of favoured races in the
struggle for life," which leads to the inevitable extinction of all
those low and mentally undeveloped populations with which Europeans come
in contact. The red Indian in North America, and in Brazil; the
Tasmanian, Australian, and New Zealander in the southern hemisphere, die
out, not from any one special cause, but from the inevitable effects of
an unequal mental and physical struggle. The intellectual and moral, as
well as the physical, qualities of the European are superior; the same
powers and capacities which have made him rise in a few centuries from
the condition of the wandering savage with a scanty and stationary
population, to his present state of culture and advancement, with a
greater average longevity, a greater average strength, and a capacity of
more rapid increase,--enable him when in contact with the savage man, to
conquer in the struggle for existence, and to increase at his expense,
just as the better adapted, increase at the expense of the less adapted
varieties in the animal and vegetable kingdoms,--just as the weeds of
Europe overrun North America and Australia, extinguishing native
productions by the inherent vigour of their organization, and by their
greater capacity for existence and multiplication.
_The Origin of the Races of Man._
If these views are correct; if in proportion as man's social, moral, and
intellectual faculties became developed, his physical structure would
cease to be affected by the operation of "natural selection," we have a
most important clue to the origin of races. For it will follow, that
those great modifications of structure and of external form, which
resulted in the development of man out of some lower type of animal,
must have occurred before his intellect had raised him above the
condition of the brutes, at a period when he was gregarious, but
scarcely social, with a mind perceptive but not reflective, ere any
sense of _right_ or feelings of _sympathy_ had been developed in him. He
would be still subject, like the rest of the organic world, to the
action of "natural selection," which would retain his physical form and
constitution in harmony with the surrounding universe. He was probably
at a very early period a dominant race, spreading widely over the warmer
regions of the earth as it then existed, and in agreement with what we
see in the case of other dominant species, gradually becoming modified
in accordance with local conditions. As he ranged farther from his
original home, and became exposed to greater extremes of climate, to
greater changes of food, and had to contend with new enemies, organic
and inorganic, slight useful variations in his constitution would be
selected and rendered permanent, and would, on the principle of
"correlation of growth," be accompanied by corresponding external
physical changes. Thus might have arisen those striking characteristics
and special modifications which still distinguish the chief races of
mankind. The red, black, yellow, or blushing white skin; the straight,
the curly, the woolly hair; the scanty or abundant beard; the straight
or oblique eyes; the various forms of the pelvis, the cranium, and other
parts of the skeleton.
But while these changes had been going on, his mental development had,
from some unknown cause, greatly advanced, and had now reached that
condition in which it began powerfully to influence his whole existence,
and would therefore become subject to the irresistible action of
"natural selection." This action would quickly give the ascendency to
mind: speech would probably now be first developed, leading to a still
further advance of the mental faculties; and from that moment man, as
regards the form and structure of most parts of his body, would remain
almost stationary. The art of making weapons, division of labour,
anticipation of the future, restraint of the appetites, moral, social,
and sympathetic feelings, would now have a preponderating influence on
his well being, and would therefore be that part of his nature on which
"natural selection" would most powerfully act; and we should thus have
explained that wonderful persistence of mere physical characteristics,
which is the stumbling-block of those who advocate the unity of mankind.
We are now, therefore, enabled to harmonise the conflicting views of
anthropologists on this subject. Man may have been, indeed I believe
must have been, once a homogeneous race; but it was at a period of which
we have as yet discovered no remains, at a period so remote in his
history, that he had not yet acquired that wonderfully developed brain,
the organ of the mind, which now, even in his lowest examples, raises
him far above the highest brutes;--at a period when he had the form but
hardly the nature of man, when he neither possessed human speech, nor
those sympathetic and moral feelings which in a greater or less degree
everywhere now distinguish the race. Just in proportion as these truly
human faculties became developed in him, would his physical features
become fixed and permanent, because the latter would be of less
importance to his well being; he would be kept in harmony with the
slowly changing universe around him, by an advance in mind, rather than
by a change in body. If, therefore, we are of opinion that he was not
really man till these higher faculties were fully developed, we may
fairly assert that there were many originally distinct races of men;
while, if we think that a being closely resembling us in form and
structure, but with mental faculties scarcely raised above the brute,
must still be considered to have been human, we are fully entitled to
maintain the common origin of all mankind.
_The Bearing of these Views on the Antiquity of Man._
These considerations, it will be seen, enable us to place the origin of
man at a much more remote geological epoch than has yet been thought
possible. He may even have lived in the Miocene or Eocene period, when
not a single mammal was identical in form with any existing species.
For, in the long series of ages during which these primeval animals were
being slowly changed into the species which now inhabit the earth, the
power which acted to modify them would only affect the mental
organization of man. His brain alone would have increased in size and
complexity, and his cranium have undergone corresponding changes of
form, while the whole structure of lower animals was being changed. This
will enable us to understand how the fossil crania of Denise and Engis
agree so closely with existing forms, although they undoubtedly existed
in company with large mammalia now extinct. The Neanderthal skull may be
a specimen of one of the lowest races then existing, just as the
Australians are the lowest of our modern epoch. We have no reason to
suppose that mind and brain and skull modification, could go on quicker
than that of the other parts of the organization; and we must therefore
look back very far in the past, to find man in that early condition in
which his mind was not sufficiently developed, to remove his body from
the modifying influence of external conditions and the cumulative action
of "natural selection." I believe, therefore, that there is no _à
priori_ reason against our finding the remains of man or his works in
the tertiary deposits. The absence of all such remains in the European
beds of this age has little weight, because, as we go further back in
time, it is natural to suppose that man's distribution over the surface
of the earth was less universal than at present.
Besides, Europe was in a great measure submerged during the tertiary
epoch; and though its scattered islands may have been uninhabited by
man, it by no means follows that he did not at the same time exist in
warm or tropical continents. If geologists can point out to us the most
extensive land in the warmer regions of the earth, which has not been
submerged since Eocene or Miocene times, it is there that we may expect
to find some traces of the very early progenitors of man. It is there
that we may trace back the gradually decreasing brain of former races,
till we come to a time when the body also begins materially to differ.
Then we shall have reached the starting point of the human family.
Before that period, he had not mind enough to preserve his body from
change, and would, therefore, have been subject to the same
comparatively rapid modifications of form as the other mammalia.
_Their Bearing on the Dignity and Supremacy of Man._
If the views I have here endeavoured to sustain have any foundation,
they give us a new argument for placing man apart, as not only the head
and culminating point of the grand series of organic nature, but as in
some degree a new and distinct order of being. From those infinitely
remote ages, when the first rudiments of organic life appeared upon the
earth, every plant, and every animal has been subject to one great law
of physical change. As the earth has gone through its grand cycles of
geological, climatal, and organic progress, every form of life has been
subject to its irresistible action, and has been continually, but
imperceptibly moulded into such new shapes as would preserve their
harmony with the ever-changing universe. No living thing could escape
this law of its being; none (except, perhaps, the simplest and most
rudimentary organisms), could remain unchanged and live, amid the
universal change around it.
At length, however, there came into existence a being in whom that
subtle force we term _mind_, became of greater importance than his mere
bodily structure. Though with a naked and unprotected body, _this_ gave
him clothing against the varying inclemencies of the seasons. Though
unable to compete with the deer in swiftness, or with the wild bull in
strength, _this_ gave him weapons with which to capture or overcome
both. Though less capable than most other animals of living on the herbs
and the fruits that unaided nature supplies, this wonderful faculty
taught him to govern and direct nature to his own benefit, and make her
produce food for him, when and where he pleased. From the moment when
the first skin was used as a covering, when the first rude spear was
formed to assist in the chase, when fire was first used to cook his
food, when the first seed was sown or shoot planted, a grand revolution
was effected in nature, a revolution which in all the previous ages of
the earth's history had had no parallel, for a being had arisen who was
no longer necessarily subject to change with the changing universe--a
being who was in some degree superior to nature, inasmuch as he knew how
to control and regulate her action, and could keep himself in harmony
with her, not by a change in body, but by an advance of mind.
Here, then, we see the true grandeur and dignity of man. On this view of
his special attributes, we may admit, that even those who claim for him
a position as an order, a class, or a sub-kingdom by himself, have some
show of reason on their side. He is, indeed, a being apart, since he is
not influenced by the great laws which irresistibly modify all other
organic beings. Nay more; this victory which he has gained for himself,
gives him a directing influence over other existences. Man has not only
escaped "natural selection" himself, but he is actually able to take
away some of that power from nature which before his appearance she
universally exercised. We can anticipate the time when the earth will
produce only cultivated plants and domestic animals; when man's
selection shall have supplanted "natural selection;" and when the ocean
will be the only domain in which that power can be exerted, which for
countless cycles of ages ruled supreme over all the earth.
_Their Bearing on the future Development of Man._
We now find ourselves enabled to answer those who maintain, that if Mr.
Darwin's theory of the Origin of Species is true, man too must change in
form, and become developed into some other animal as different from his
present self as he is from the Gorilla or the Chimpanzee; and who
speculate on what this form is likely to be. But it is evident that such
will not be the case; for no change of conditions is conceivable, which
will render any important alteration of his form and organization so
universally useful and necessary to him, as to give those possessing it
always the best chance of surviving, and thus lead to the development
of a new species, genus, or higher group of man. On the other hand, we
know that far greater changes of conditions and of his entire
environment have been undergone by man, than any other highly organized
animal could survive unchanged, and have been met by mental, not
corporeal adaptation. The difference of habits, of food, clothing,
weapons, and enemies, between savage and civilized man, is enormous.
Difference in bodily form and structure there is practically none,
except a slightly increased size of brain, corresponding to his higher
mental development.
We have every reason to believe, then, that man may have existed and may
continue to exist, through a series of geological periods which shall
see all other forms of animal life again and again changed; while he
himself remains unchanged, except in the two particulars already
specified--the head and face, as immediately connected with the organ of
the mind and as being the medium of expressing the most refined emotions
of his nature,--and to a slight extent in colour, hair, and proportions,
so far as they are correlated with constitutional resistance to disease.
_Summary._
Briefly to recapitulate the argument;--in two distinct ways has man
escaped the influence of those laws which have produced unceasing change
in the animal world. 1. By his superior intellect he is enabled to
provide himself with clothing and weapons, and by cultivating the soil
to obtain a constant supply of congenial food. This renders it
unnecessary for his body, like those of the lower animals, to be
modified in accordance with changing conditions--to gain a warmer
natural covering, to acquire more powerful teeth or claws, or to become
adapted to obtain and digest new kinds of food, as circumstances may
require. 2. By his superior sympathetic and moral feelings, he becomes
fitted for the social state; he ceases to plunder the weak and helpless
of his tribe; he shares the game which he has caught with less active or
less fortunate hunters, or exchanges it for weapons which even the weak
or the deformed can fashion; he saves the sick and wounded from death;
and thus the power which leads to the rigid destruction of all animals
who cannot in every respect help themselves, is prevented from acting on
him.
This power is "natural selection;" and, as by no other means can it be
shown, that individual variations can ever become accumulated and
rendered permanent so as to form well-marked races, it follows that the
differences which now separate mankind from other animals, must have
been produced before he became possessed of a human intellect or human
sympathies. This view also renders possible, or even requires, the
existence of man at a comparatively remote geological epoch. For, during
the long periods in which other animals have been undergoing
modification in their whole structure, to such an amount as to
constitute distinct genera and families, man's _body_ will have
remained generically, or even specifically, the same, while his _head_
and _brain_ alone will have undergone modification equal to theirs. We
can thus understand how it is that, judging from the head and brain,
Professor Owen places man in a distinct sub-class of mammalia, while as
regards the bony structure of his body, there is the closest anatomical
resemblance to the anthropoid apes, "every tooth, every bone, strictly
homologous--which makes the determination of the difference between
_Homo_ and _Pithecus_ the anatomist's difficulty." The present theory
fully recognises and accounts for these facts; and we may perhaps claim
as corroborative of its truth, that it neither requires us to depreciate
the intellectual chasm which separates man from the apes, nor refuses
full recognition of the striking resemblances to them, which exist in
other parts of his structure.
_Conclusion._
In concluding this brief sketch of a great subject, I would point out
its bearing upon the future of the human race. If my conclusions are
just, it must inevitably follow that the higher--the more intellectual
and moral--must displace the lower and more degraded races; and the
power of "natural selection," still acting on his mental organization,
must ever lead to the more perfect adaptation of man's higher faculties
to the conditions of surrounding nature, and to the exigencies of the
social state. While his external form will probably ever remain
unchanged, except in the development of that perfect beauty which
results from a healthy and well organized body, refined and ennobled by
the highest intellectual faculties and sympathetic emotions, his mental
constitution may continue to advance and improve, till the world is
again inhabited by a single nearly homogeneous race, no individual of
which will be inferior to the noblest specimens of existing humanity.
Our progress towards such a result is very slow, but it still seems to
be a progress. We are just now living at an abnormal period of the
world's history, owing to the marvellous developments and vast practical
results of science, having been given to societies too low morally and
intellectually, to know how to make the best use of them, and to whom
they have consequently been curses as well as blessings. Among civilized
nations at the present day, it does not seem possible for natural
selection to act in any way, so as to secure the permanent advancement
of morality and intelligence; for it is indisputably the mediocre, if
not the low, both as regards morality and intelligence, who succeed best
in life and multiply fastest. Yet there is undoubtedly an advance--on
the whole a steady and a permanent one--both in the influence on public
opinion of a high morality, and in the general desire for intellectual
elevation; and as I cannot impute this in any way to "survival of the
fittest," I am forced to conclude that it is due, to the inherent
progressive power of those glorious qualities which raise us so
immeasurably above our fellow animals, and at the same time afford us
the surest proof that there are other and higher existences than
ourselves, from whom these qualities may have been derived, and towards
whom we may be ever tending.
X.
THE LIMITS OF NATURAL SELECTION AS APPLIED TO MAN.
Throughout this volume I have endeavoured to show, that the known laws
of variation, multiplication, and heredity, resulting in a "struggle for
existence" and the "survival of the fittest," have probably sufficed to
produce all the varieties of structure, all the wonderful adaptations,
all the beauty of form and of colour, that we see in the animal and
vegetable kingdoms. To the best of my ability I have answered the most
obvious and the most often repeated objections to this theory, and have,
I hope, added to its general strength, by showing how colour--one of the
strongholds of the advocates of special creation--may be, in almost all
its modifications, accounted for by the combined influence of sexual
selection and the need of protection. I have also endeavoured to show,
how the same power which has modified animals has acted on man; and
have, I believe, proved that, as soon as the human intellect became
developed above a certain low stage, man's body would cease to be
materially affected by natural selection, because the development of his
mental faculties would render important modifications of its form and
structure unnecessary. It will, therefore, probably excite some
surprise among my readers, to find that I do not consider that all
nature can be explained on the principles of which I am so ardent an
advocate; and that I am now myself going to state objections, and to
place limits, to the power of "natural selection." I believe, however,
that there are such limits; and that just as surely as we can trace the
action of natural laws in the development of organic forms, and can
clearly conceive that fuller knowledge would enable us to follow step by
step the whole process of that development, so surely can we trace the
action of some unknown higher law, beyond and independent of all those
laws of which we have any knowledge. We can trace this action more or
less distinctly in many phenomena, the two most important of which
are--the origin of sensation or consciousness, and the development of
man from the lower animals. I shall first consider the latter difficulty
as more immediately connected with the subjects discussed in this
volume.
_What Natural Selection can Not do._
In considering the question of the development of man by known natural
laws, we must ever bear in mind the first principle of "natural
selection," no less than of the general theory of evolution, that all
changes of form or structure, all increase in the size of an organ or in
its complexity, all greater specialization or physiological division of
labour, can only be brought about, in as much as it is for the good of
the being so modified. Mr. Darwin himself has taken care to impress
upon us, that "natural selection" has no power to produce absolute
perfection but only relative perfection, no power to advance any being
much beyond his follow beings, but only just so much beyond them as to
enable it to survive them in the struggle for existence. Still less has
it any power to produce modifications which are in any degree injurious
to its possessor, and Mr. Darwin frequently uses the strong expression,
that a single case of this kind would be fatal to his theory. If,
therefore, we find in man any characters, which all the evidence we can
obtain goes to show would have been actually injurious to him on their
first appearance, they could not possibly have been produced by natural
selection. Neither could any specially developed organ have been so
produced if it had been merely useless to him, or if its use were not
proportionate to its degree of development. Such cases as these would
prove, that some other law, or some other power, than "natural
selection" had been at work. But if, further, we could see that these
very modifications, though hurtful or useless at the time when they
first appeared, became in the highest degree useful at a much later
period, and are now essential to the full moral and intellectual
development of human nature, we should then infer the action of mind,
foreseeing the future and preparing for it, just as surely as we do,
when we see the breeder set himself to work with the determination to
produce a definite improvement in some cultivated plant or domestic
animal. I would further remark that this enquiry is as thoroughly
scientific and legitimate as that into the origin of species itself. It
is an attempt to solve the inverse problem, to deduce the existence of a
new power of a definite character, in order to account for facts which
according to the theory of natural selection ought not to happen. Such
problems are well known to science, and the search after their solution
has often led to the most brilliant results. In the case of man, there
are facts of the nature above alluded to, and in calling attention to
them, and in inferring a cause for them, I believe that I am as strictly
within the bounds of scientific investigation as I have been in any
other portion of my work.
_The Brain of the Savage shown to be Larger than he Needs it to be._
_Size of Brain an important Element of Mental Power._--The brain is
universally admitted to be the organ of the mind; and it is almost as
universally admitted, that size of brain is one of the most important of
the elements which determine mental power or capacity. There seems to be
no doubt that brains differ considerably in quality, as indicated by
greater or less complexity of the convolutions, quantity of grey matter,
and perhaps unknown peculiarities of organization; but this difference
of quality seems merely to increase or diminish the influence of
quantity, not to neutralize it. Thus, all the most eminent modern
writers see an intimate connection between the diminished size of the
brain in the lower races of mankind, and their intellectual
inferiority. The collections of Dr. J. B. Davis and Dr. Morton give the
following as the average internal capacity of the cranium in the chief
races:--Teutonic family, 94 cubic inches; Esquimaux, 91 cubic inches;
Negroes, 85 cubic inches; Australians and Tasmanians, 82 cubic inches;
Bushmen, 77 cubic inches. These last numbers, however, are deduced from
comparatively few specimens, and may be below the average, just as a
small number of Finns and Cossacks give 98 cubic inches, or considerably
more than that of the German races. It is evident, therefore, that the
absolute bulk of the brain is not necessarily much less in savage than
in civilised man, for Esquimaux skulls are known with a capacity of 113
inches, or hardly less than the largest among Europeans. But what is
still more extraordinary, the few remains yet known of pre-historic man
do not indicate any material diminution in the size of the brain case. A
Swiss skull of the stone age, found in the lake dwelling of Meilen,
corresponded exactly to that of a Swiss youth of the present day. The
celebrated Neanderthal skull had a larger circumference than the
average, and its capacity, indicating actual mass of brain, is estimated
to have been not less than 75 cubic inches, or nearly the average of
existing Australian crania. The Engis skull, perhaps the oldest known,
and which, according to Sir John Lubbock, "there seems no doubt was
really contemporary with the mammoth and the cave bear," is yet,
according to Professor Huxley, "a fair average skull, which might have
belonged to a philosopher, or might have contained the thoughtless
brains of a savage." Of the cave men of Les Eyzies, who were undoubtedly
contemporary with the reindeer in the South of France, Professor Paul
Broca says (in a paper read before the Congress of Pre-historic
Archæology in 1868)--"The great capacity of the brain, the development
of the frontal region, the fine elliptical form of the anterior part of
the profile of the skull, are incontestible characteristics of
superiority, such as we are accustomed to meet with in civilised races;"
yet the great breadth of the face, the enormous development of the
ascending ramus of the lower jaw, the extent and roughness of the
surfaces for the attachment of the muscles, especially of the
masticators, and the extraordinary development of the ridge of the
femur, indicate enormous muscular power, and the habits of a savage and
brutal race.
These facts might almost make us doubt whether the size of the brain is
in any direct way an index of mental power, had we not the most
conclusive evidence that it is so, in the fact that, whenever an adult
male European has a skull less than nineteen inches in circumference, or
has less than sixty-five cubic inches of brain, he is invariably
idiotic. When we join with this the equally undisputed fact, that great
men--those who combine acute perception with great reflective power,
strong passions, and general energy of character, such as Napoleon,
Cuvier, and O'Connell, have always heads far above the average size, we
must feel satisfied that volume of brain is one, and perhaps the most
important, measure of intellect; and this being the case, we cannot fail
to be struck with the apparent anomaly, that many of the lowest savages
should have as much brains as average Europeans. The idea is suggested
of a surplusage of power; of an instrument beyond the needs of its
possessor.
_Comparison of the Brains of Man and of Anthropoid Apes._--In order to
discover if there is any foundation for this notion, let us compare the
brain of man with that of animals. The adult male Orang-utan is quite as
bulky as a small sized man, while the Gorilla is considerably above the
average size of man, as estimated by bulk and weight; yet the former has
a brain of only 28 cubic inches, the latter, one of 30, or, in the
largest specimen yet known, of 34½ cubic inches. We have seen that the
average cranial capacity of the lowest savages is probably not less than
_five-sixths_ of that of the highest civilized races, while the brain of
the anthropoid apes scarcely amounts to _one-third_ of that of man, in
both cases taking the average; or the proportions may be more clearly
represented by the following figures--anthropoid apes, 10; savages, 26;
civilized man, 32. But do these figures at all approximately represent
the relative intellect of the three groups? Is the savage really no
farther removed from the philosopher, and so much removed from the ape,
as these figures would indicate? In considering this question, we must
not forget that the heads of savages vary in size, almost as much as
those of civilized Europeans. Thus, while the largest Teutonic skull in
Dr. Davis' collection is 112·4 cubic inches, there is an Araucanian of
115·5, an Esquimaux of 113·1, a Marquesan of 11O·6, a Negro of 105·8,
and even an Australian of 104·5 cubic inches. We may, therefore, fairly
compare the savage with the highest European on the one side, and with
the Orang, Chimpanzee, or Gorilla, on the other, and see whether there
is any relative proportion between brain and intellect.
_Range of intellectual power in Man._--First, let us consider what this
wonderful instrument, the brain, is capable of in its higher
developments. In Mr. Galton's interesting work on "Hereditary Genius,"
he remarks on the enormous difference between the intellectual power and
grasp of the well-trained mathematician or man of science, and the
average Englishman. The number of marks obtained by high wranglers, is
often more than thirty times as great as that of the men at the bottom
of the honour list, who are still of fair mathematical ability; and it
is the opinion of skilled examiners, that even this does not represent
the full difference of intellectual power. If, now, we descend to those
savage tribes who only count to three or five, and who find it
impossible to comprehend the addition of two and three without having
the objects actually before them, we feel that the chasm between them
and the good mathematician is so vast, that a thousand to one will
probably not fully express it. Yet we know that the mass of brain might
be nearly the same in both, or might not differ in a greater proportion
than as 5 to 6; whence we may fairly infer that the savage possesses a
brain capable, if cultivated and developed, of performing work of a kind
and degree far beyond what he ever requires it to do.
Again, let us consider the power of the higher or even the average
civilized man, of forming abstract ideas, and carrying on more or less
complex trains of reasoning. Our languages are full of terms to express
abstract conceptions. Our business and our pleasures involve the
continual foresight of many contingencies. Our law, our government, and
our science, continually require us to reason through a variety of
complicated phenomena to the expected result. Even our games, such as
chess, compel us to exercise all these faculties in a remarkable degree.
Compare this with the savage languages, which contain no words for
abstract conceptions; the utter want of foresight of the savage man
beyond his simplest necessities; his inability to combine, or to
compare, or to reason on any general subject that does not immediately
appeal to his senses. So, in his moral and æsthetic faculties, the
savage has none of those wide sympathies with all nature, those
conceptions of the infinite, of the good, of the sublime and beautiful,
which are so largely developed in civilized man. Any considerable
development of these would, in fact, be useless or even hurtful to him,
since they would to some extent interfere with the supremacy of those
perceptive and animal faculties on which his very existence often
depends, in the severe struggle he has to carry on against nature and
his fellow-man. Yet the rudiments of all these powers and feelings
undoubtedly exist in him, since one or other of them frequently manifest
themselves in exceptional cases, or when some special circumstances call
them forth. Some tribes, such as the Santals, are remarkable for as pure
a love of truth as the most moral among civilized men. The Hindoo and
the Polynesian have a high artistic feeling, the first traces of which
are clearly visible in the rude drawings of the palæolithic men who were
the contemporaries in France of the Reindeer and the Mammoth. Instances
of unselfish love, of true gratitude, and of deep religious feeling,
sometimes occur among most savage races.
On the whole, then, we may conclude, that the general moral and
intellectual development of the savage, is not less removed from that of
civilized man than has been shown to be the case in the one department
of mathematics; and from the fact that all the moral and intellectual
faculties do occasionally manifest themselves, we may fairly conclude
that they are always latent, and that the large brain of the savage man
is much beyond his actual requirements in the savage state.
_Intellect of Savages and of Animals compared._--Let us now compare the
intellectual wants of the savage, and the actual amount of intellect he
exhibits, with those of the higher animals. Such races as the Andaman
Islanders, the Australians, and the Tasmanians, the Digger Indians of
North America, or the natives of Fuegia, pass their lives so as to
require the exercise of few faculties not possessed in an equal degree
by many animals. In the mode of capture of game or fish, they by no
means surpass the ingenuity or forethought of the jaguar, who drops
saliva into the water, and seizes the fish as they come to eat it; or of
wolves and jackals, who hunt in packs; or of the fox, who buries his
surplus food till he requires it. The sentinels placed by antelopes and
by monkeys, and the various modes of building adopted by field mice and
beavers, as well as the sleeping place of the orang-utan, and the
tree-shelter of some of the African anthropoid apes, may well be
compared with the amount of care and forethought bestowed by many
savages in similar circumstances. His possession of free and perfect
hands, not required for locomotion, enable man to form and use weapons
and implements which are beyond the physical powers of brutes; but
having done this, he certainly does not exhibit more mind in using them
than do many lower animals. What is there in the life of the savage, but
the satisfying of the cravings of appetite in the simplest and easiest
way? What thoughts, ideas, or actions are there, that raise him many
grades above the elephant or the ape? Yet he possesses, as we have seen,
a brain vastly superior to theirs in size and complexity; and this brain
gives him, in an undeveloped state, faculties which he never requires to
use. And if this is true of existing savages, how much more true must
it have been of the men whose sole weapons were rudely chipped flints,
and some of whom, we may fairly conclude, were lower than any existing
race; while the only evidence yet in our possession shows them to have
had brains fully as capacious as those of the average of the lower
savage races.
We see, then, that whether we compare the savage with the higher
developments of man, or with the brutes around him, we are alike driven
to the conclusion that in his large and well-developed brain he
possesses an organ quite disproportionate to his actual requirements--an
organ that seems prepared in advance, only to be fully utilized as he
progresses in civilization. A brain slightly larger than that of the
gorilla would, according to the evidence before us, fully have sufficed
for the limited mental development of the savage; and we must therefore
admit, that the large brain he actually possesses could never have been
solely developed by any of those laws of evolution, whose essence is,
that they lead to a degree of organization exactly proportionate to the
wants of each species, never beyond those wants--that no preparation can
be made for the future development of the race--that one part of the
body can never increase in size or complexity, except in strict
co-ordination to the pressing wants of the whole. The brain of
pre-historic and of savage man seems to me to prove the existence of
some power, distinct from that which has guided the development of the
lower animals through their ever-varying forms of being.
_The Use of the Hairy Covering of Mammalia._
Let us now consider another point in man's organization, the bearing of
which has been almost entirely overlooked by writers on both sides of
this question. One of the most general external characters of the
terrestrial mammalia is the hairy covering of the body, which, whenever
the skin is flexible, soft, and sensitive, forms a natural protection
against the severities of climate, and particularly against rain. That
this is its most important function, is well shown by the manner in
which the hairs are disposed so as to carry off the water, by being
invariably directed downwards from the most elevated parts of the body.
Thus, on the under surface the hair is always less plentiful, and, in
many cases, the belly is almost bare. The hair lies downwards, on the
limbs of all walking mammals, from the shoulder to the toes, but in the
orang-utan it is directed from the shoulder to the elbow, and again from
the wrist to the elbow, in a reverse direction. This corresponds to the
habits of the animal, which, when resting, holds its long arms upwards
over its head, or clasping a branch above it, so that the rain would
flow down both the arm and fore-arm to the long hair which meets at the
elbow. In accordance with this principle, the hair is always longer or
more dense along the spine or middle of the back from the nape to the
tail, often rising into a crest of hair or bristles on the ridge of the
back. This character prevails through the entire series of the mammalia,
from the marsupials to the quadrumana, and by this long persistence it
must have acquired such a powerful hereditary tendency, that we should
expect it to reappear continually even after it had been abolished by
ages of the most rigid selection; and we may feel sure that it never
could have been completely abolished under the law of natural selection,
unless it had become so positively injurious as to lead to the almost
invariable extinction of individuals possessing it.
_The constant absence of Hair from certain parts of Man's Body a
remarkable Phenomenon._
In man the hairy covering of the body has almost totally disappeared,
and, what is very remarkable, it has disappeared more completely from
the back than from any other part of the body. Bearded and beardless
races alike have the back smooth, and even when a considerable quantity
of hair appears on the limbs and breast, the back, and especially the
spinal region, is absolutely free, thus completely reversing the
characteristics of all other mammalia. The Ainos of the Kurile Islands
and Japan are said to be a hairy race; but Mr. Bickmore, who saw some of
them, and described them in a paper read before the Ethnological
Society, gives no details as to where the hair was most abundant, merely
stating generally, that "their chief peculiarity is their great
abundance of hair, not only on the head and face, but over the whole
body." This might very well be said of any man who had hairy limbs and
breast, unless it was specially stated that his back was hairy, which
is not done in this case. The hairy family in Birmah have, indeed, hair
on the back rather longer than on the breast, thus reproducing the true
mammalian character, but they have still longer hair on the face,
forehead, and inside the ears, which is quite abnormal; and the fact
that their teeth are all very imperfect, shows that this is a case of
monstrosity rather than one of true reversion to the ancestral type of
man before he lost his hairy covering.
_Savage Man feels the Want of this Hairy Covering._
We must now enquire if we have any evidence to show, or any reason to
believe, that a hairy covering to the back would be in any degree
hurtful to savage man, or to man in any stage of his progress from his
lower animal form; and if it were merely useless, could it have been so
entirely and completely removed as not to be continually reappearing in
mixed races? Let us look to savage man for some light on these points.
One of the most common habits of savages is to use some covering for the
back and shoulders, even when they have none on any other part of the
body. The early voyagers observed with surprise, that the Tasmanians,
both men and women, wore the kangaroo-skin, which was their only
covering, not from any feeling of modesty, but over the shoulders to
keep the back dry and warm. A cloth over the shoulders was also the
national dress of the Maories. The Patagonians wear a cloak or mantle
over the shoulders, and the Fuegians often wear a small piece of skin on
the back, laced on, and shifted from side to side as the wind blows.
The Hottentots also wore a somewhat similar skin over the back, which
they never removed, and in which they were buried. Even in the tropics
most savages take precautions to keep their backs dry. The natives of
Timor use the leaf of a fan palm, carefully stitched up and folded,
which they always carry with them, and which, held over the back, forms
an admirable protection from the rain. Almost all the Malay races, as
well as the Indians of South America, make great palm-leaf hats, four
feet or more across, which they use during their canoe voyages to
protect their bodies from heavy showers of rain; and they use smaller
hats of the same kind when travelling by land.
We find, then, that so far from there being any reason to believe that a
hairy covering to the back could have been hurtful or even useless to
pre-historic man, the habits of modern savages indicate exactly the
opposite view, as they evidently feel the want of it, and are obliged to
provide substitutes of various kinds. The perfectly erect posture of
man, may be supposed to have something to do with the disappearance of
the hair from his body, while it remains on his head; but when walking,
exposed to rain and wind, a man naturally stoops forwards, and thus
exposes his back; and the undoubted fact, that most savages feel the
effects of cold and wet most severely in that part of the body,
sufficiently demonstrates that the hair could not have ceased to grow
there merely because it was useless, even if it were likely that a
character so long persistent in the entire order of mammalia, could have
so completely disappeared, under the influence of so weak a selective
power as a diminished usefulness.
_Man's Naked Skin could not have been produced by Natural Selection._
It seems to me, then, to be absolutely certain, that "Natural Selection"
could not have produced man's hairless body by the accumulation of
variations from a hairy ancestor. The evidence all goes to show that
such variations could not have been useful, but must, on the contrary,
have been to some extent hurtful. If even, owing to an unknown
correlation with other hurtful qualities, it had been abolished in the
ancestral tropical man, we cannot conceive that, as man spread into
colder climates, it should not have returned under the powerful
influence of reversion to such a long persistent ancestral type. But the
very foundation of such a supposition as this is untenable; for we
cannot suppose that a character which, like hairiness, exists throughout
the whole of the mammalia, can have become, in one form only, so
constantly correlated with an injurious character, as to lead to its
permanent suppression--a suppression so complete and effectual that it
never, or scarcely ever, reappears in mongrels of the most widely
different races of man.
Two characters could hardly be wider apart, than the size and
development of man's brain, and the distribution of hair upon the
surface of his body; yet they both lead us to the same conclusion--that
some other power than Natural Selection has been engaged in his
production.
_Feet and Hands of Man, considered as Difficulties on the Theory of
Natural Selection._
There are a few other physical characteristics of man, that may just be
mentioned as offering similar difficulties, though I do not attach the
same importance to them as to those I have already dwelt on. The
specialization and perfection of the hands and feet of man seems
difficult to account for. Throughout the whole of the quadrumana the
foot is prehensile; and a very rigid selection must therefore have been
needed to bring about that arrangement of the bones and muscles, which
has converted the thumb into a great toe, so completely, that the power
of opposability is totally lost in every race, whatever some travellers
may vaguely assert to the contrary. It is difficult to see why the
prehensile power should have been taken away. It must certainly have
been useful in climbing, and the case of the baboons shows that it is
quite compatible with terrestrial locomotion. It may not be compatible
with perfectly easy erect locomotion; but, then, how can we conceive
that early man, _as an animal_, gained anything by purely erect
locomotion? Again, the hand of man contains latent capacities and powers
which are unused by savages, and must have been even less used by
palæolithic man and his still ruder predecessors. It has all the
appearance of an organ prepared for the use of civilized man, and one
which was required to render civilization possible. Apes make little use
of their separate fingers and opposable thumbs. They grasp objects
rudely and clumsily, and look as if a much less specialized extremity
would have served their purpose as well. I do not lay much stress on
this, but, if it be proved that some intelligent power has guided or
determined the development of man, then we may see indications of that
power, in facts which, by themselves, would not serve to prove its
existence.
_The voice of man._--The same remark will apply to another peculiarly
human character, the wonderful power, range, flexibility, and sweetness,
of the musical sounds producible by the human larynx, especially in the
female sex. The habits of savages give no indication of how this faculty
could have been developed by natural selection; because it is never
required or used by them. The singing of savages is a more or less
monotonous howling, and the females seldom sing at all. Savages
certainly never choose their wives for fine voices, but for rude health,
and strength, and physical beauty. Sexual selection could not therefore
have developed this wonderful power, which only comes into play among
civilized people. It seems as if the organ had been prepared in
anticipation of the future progress of man, since it contains latent
capacities which are useless to him in his earlier condition. The
delicate correlations of structure that give it such marvellous powers,
could not therefore have been acquired by means of natural selection.
_The Origin of some of Man's Mental Faculties, by the preservation of
Useful Variations, not possible._
Turning to the mind of man, we meet with many difficulties in attempting
to understand, how those mental faculties, which are especially human,
could have been acquired by the preservation of useful variations. At
first sight, it would seem that such feelings as those of abstract
justice and benevolence could never have been so acquired, because they
are incompatible with the law of the strongest, which is the essence of
natural selection. But this is, I think, an erroneous view, because we
must look, not to individuals but to societies; and justice and
benevolence, exercised towards members of the same tribe, would
certainly tend to strengthen that tribe, and give it a superiority over
another in which the right of the strongest prevailed, and where
consequently the weak and the sickly were left to perish, and the few
strong ruthlessly destroyed the many who were weaker.
But there is another class of human faculties that do not regard our
fellow men, and which cannot, therefore, be thus accounted for. Such are
the capacity to form ideal conceptions of space and time, of eternity
and infinity--the capacity for intense artistic feelings of pleasure, in
form, colour, and composition--and for those abstract notions of form
and number which render geometry and arithmetic possible. How were all
or any of these faculties first developed, when they could have been of
no possible use to man in his early stages of barbarism? How could
"natural selection," or survival of the fittest in the struggle for
existence, at all favour the development of mental powers so entirely
removed from the material necessities of savage men, and which even now,
with our comparatively high civilization, are, in their farthest
developments, in advance of the age, and appear to have relation rather
to the future of the race than to its actual status?
_Difficulty as to the Origin of the Moral Sense._
Exactly the same difficulty arises, when we endeavour to account for the
development of the moral sense or conscience in savage man; for although
the _practice_ of benevolence, honesty, or truth, may have been useful
to the tribe possessing these virtues, that does not at all account for
the peculiar _sanctity_, attached to actions which each tribe considers
right and moral, as contrasted with the very different feelings with
which they regard what is merely _useful_. The utilitarian hypothesis
(which is the theory of natural selection applied to the mind) seems
inadequate to account for the development of the moral sense. This
subject has been recently much discussed, and I will here only give one
example to illustrate my argument. The utilitarian sanction for
truthfulness is by no means very powerful or universal. Few laws enforce
it. No very severe reprobation follows untruthfulness. In all ages and
countries, falsehood has been thought allowable in love, and laudable in
war; while, at the present day, it is held to be venial by the majority
of mankind, in trade, commerce, and speculation. A certain amount of
untruthfulness is a necessary part of politeness in the east and west
alike, while even severe moralists have held a lie justifiable, to elude
an enemy or prevent a crime. Such being the difficulties with which this
virtue has had to struggle, with so many exceptions to its practice,
with so many instances in which it brought ruin or death to its too
ardent devotee, how can we believe that considerations of utility could
ever invest it with the mysterious sanctity of the highest
virtue,--could ever induce men to value truth for its own sake, and
practice it regardless of consequences?
Yet, it is a fact, that such a mystical sense of wrong does attach to
untruthfulness, not only among the higher classes of civilized people,
but among whole tribes of utter savages. Sir Walter Elliott tells us (in
his paper "On the Characteristics of the Population of Central and
Southern India," published in the Journal of the Ethnological Society of
London, vol. i., p. 107) that the Kurubars and Santals, barbarous
hill-tribes of Central India, are noted for veracity. It is a common
saying that "a Kurubar _always_ speaks the truth;" and Major Jervis
says, "the Santals are the most truthful men I ever met with." As a
remarkable instance of this quality the following fact is given. A
number of prisoners, taken during the Santal insurrection, were allowed
to go free on parole, to work at a certain spot for wages. After some
time cholera attacked them and they were obliged to leave, but every man
of them returned and gave up his earnings to the guard. Two hundred
savages with money in their girdles, walked thirty miles back to prison
rather than break their word! My own experience among savages has
furnished me with similar, although less severely tested, instances; and
we cannot avoid asking, how is it, that in these few cases "experiences
of utility" have left such an overwhelming impression, while in so many
others they have left none? The experiences of savage men as regards the
utility of truth, must, in the long run, be pretty nearly equal. How is
it, then, that in some cases the result is a sanctity which overrides
all considerations of personal advantage, while in others there is
hardly a rudiment of such a feeling?
The intuitional theory, which I am now advocating, explains this by the
supposition, that there is a feeling--a sense of right and wrong--in our
nature, antecedent to and independent of experiences of utility. Where
free play is allowed to the relations between man and man, this feeling
attaches itself to those acts of universal utility or self-sacrifice,
which are the products of our affections and sympathies, and which we
term moral; while it may be, and often is, perverted, to give the same
sanction to acts of narrow and conventional utility which are really
immoral,--as when the Hindoo will tell a lie, but will sooner starve
than eat unclean food; and looks upon the marriage of adult females as
gross immorality.
The strength of the moral feeling will depend upon individual or racial
constitution, and on education and habit;--the acts to which its
sanctions are applied, will depend upon how far the simple feelings and
affections of our nature, have been modified by custom, by law, or by
religion.
It is difficult to conceive that such an intense and mystical feeling of
right and wrong, (so intense as to overcome all ideas of personal
advantage or utility), could have been developed out of accumulated
ancestral experiences of utility; and still more difficult to
understand, how feelings developed by one set of utilities, could be
transferred to acts of which the utility was partial, imaginary, or
altogether absent. But if a moral sense is an essential part of our
nature, it is easy to see, that its sanction may often be given to acts
which are useless or immoral; just as the natural appetite for drink, is
perverted by the drunkard into the means of his destruction.
_Summary of the Argument as to the Insufficiency of Natural Selection to
account for the Development of Man._
Briefly to resume my argument--I have shown that the brain of the lowest
savages, and, as far as we yet know, of the pre-historic races, is
little inferior in size to that of the highest types of man, and
immensely superior to that of the higher animals; while it is
universally admitted that quantity of brain is one of the most
important, and probably the most essential, of the elements which
determine mental power. Yet the mental requirements of savages, and the
faculties actually exercised by them, are very little above those of
animals. The higher feelings of pure morality and refined emotion, and
the power of abstract reasoning and ideal conception, are useless to
them, are rarely if ever manifested, and have no important relations to
their habits, wants, desires, or well-being. They possess a mental organ
beyond their needs. Natural Selection could only have endowed savage man
with a brain a little superior to that of an ape, whereas he actually
possesses one very little inferior to that of a philosopher.
The soft, naked, sensitive skin of man, entirely free from that hairy
covering which is so universal among other mammalia, cannot be explained
on the theory of natural selection. The habits of savages show that they
feel the want of this covering, which is most completely absent in man
exactly where it is thickest in other animals. We have no reason
whatever to believe, that it could have been hurtful, or even useless to
primitive man; and, under these circumstances, its complete abolition,
shown by its never reverting in mixed breeds, is a demonstration of the
agency of some other power than the law of the survival of the fittest,
in the development of man from the lower animals.
Other characters show difficulties of a similar kind, though not perhaps
in an equal degree. The structure of the human foot and hand seem
unnecessarily perfect for the needs of savage man, in whom they are as
completely and as humanly developed as in the highest races. The
structure of the human larynx, giving the power of speech and of
producing musical sounds, and especially its extreme development in the
female sex, are shown to be beyond the needs of savages, and from their
known habits, impossible to have been acquired either by sexual
selection, or by survival of the fittest.
The mind of man offers arguments in the same direction, hardly less
strong than those derived from his bodily structure. A number of his
mental faculties have no relation to his fellow men, or to his material
progress. The power of conceiving eternity and infinity, and all those
purely abstract notions of form, number, and harmony, which play so
large a part in the life of civilised races, are entirely outside of the
world of thought of the savage, and have no influence on his individual
existence or on that of his tribe. They could not, therefore, have been
developed by any preservation of useful forms of thought; yet we find
occasional traces of them amidst a low civilization, and at a time when
they could have had no practical effect on the success of the
individual, the family, or the race; and the development of a moral
sense or conscience by similar means is equally inconceivable.
But, on the other hand, we find that every one of these characteristics
is necessary for the full development of human nature. The rapid
progress of civilization under favourable conditions, would not be
possible, were not the organ of the mind of man prepared in advance,
fully developed as regards size, structure, and proportions, and only
needing a few generations of use and habit to co-ordinate its complex
functions. The naked and sensitive skin, by necessitating clothing and
houses, would lead to the more rapid development of man's inventive and
constructive faculties; and, by leading to a more refined feeling of
personal modesty, may have influenced, to a considerable extent, his
moral nature. The erect form of man, by freeing the hands from all
locomotive uses, has been necessary for his intellectual advancement;
and the extreme perfection of his hands, has alone rendered possible
that excellence in all the arts of civilization which raises him so far
above the savage, and is perhaps but the forerunner of a higher
intellectual and moral advancement. The perfection of his vocal organs
has first led to the formation of articulate speech, and then to the
development of those exquisitely toned sounds, which are only
appreciated by the higher races, and which are probably destined for
more elevated uses and more refined enjoyment, in a higher condition
than we have yet attained to. So, those faculties which enable us to
transcend time and space, and to realize the wonderful conceptions of
mathematics and philosophy, or which give us an intense yearning for
abstract truth, (all of which were occasionally manifested at such an
early period of human history as to be far in advance of any of the few
practical applications which have since grown out of them), are
evidently essential to the perfect development of man as a spiritual
being, but are utterly inconceivable as having been produced through the
action of a law which looks only, and can look only, to the immediate
material welfare of the individual or the race.
The inference I would draw from this class of phenomena is, that a
superior intelligence has guided the development of man in a definite
direction, and for a special purpose, just as man guides the development
of many animal and vegetable forms. The laws of evolution alone would,
perhaps, never have produced a grain so well adapted to man's use as
wheat and maize; such fruits as the seedless banana and bread-fruit; or
such animals as the Guernsey milch cow, or the London dray-horse. Yet
these so closely resemble the unaided productions of nature, that we may
well imagine a being who had mastered the laws of development of organic
forms through past ages, refusing to believe that any new power had been
concerned in their production, and scornfully rejecting the theory (as
my theory will be rejected by many who agree with me on other points),
that in these few cases a controlling intelligence had directed the
action of the laws of variation, multiplication, and survival, for his
own purposes. We know, however, that this has been done; and we must
therefore admit the possibility that, if we are not the highest
intelligences in the universe, some higher intelligence may have
directed the process by which the human race was developed, by means of
more subtle agencies than we are acquainted with. At the same time I
must confess, that this theory has the disadvantage of requiring the
intervention of some distinct individual intelligence, to aid in the
production of what we can hardly avoid considering as the ultimate aim
and outcome of all organized existence--intellectual, ever-advancing,
spiritual man. It therefore implies, that the great laws which govern
the material universe were insufficient for his production, unless we
consider (as we may fairly do) that the controlling action of such
higher intelligences is a necessary part of those laws, just as the
action of all surrounding organisms is one of the agencies in organic
development. But even if my particular view should not be the true one,
the difficulties I have put forward remain, and I think prove, that some
more general and more fundamental law underlies that of "natural
selection." The law of "unconscious intelligence" pervading all organic
nature, put forth by Dr. Laycock and adopted by Mr. Murphy, is such a
law; but to my mind it has the double disadvantage of being both
unintelligible and incapable of any kind of proof. It is more probable,
that the true law lies too deep for us to discover it; but there seems
to me, to be ample indications that such a law does exist, and is
probably connected with the absolute origin of life and organization.
(_Note A._)
_The Origin of Consciousness._
The question of the origin of sensation and of thought can be but
briefly discussed in this place, since it is a subject wide enough to
require a separate volume for its proper treatment. No physiologist or
philosopher has yet ventured to propound an intelligible theory, of how
sensation may possibly be a product of organization; while many have
declared the passage from matter to mind to be inconceivable. In his
presidential address to the Physical Section of the British Association
at Norwich, in 1868, Professor Tyndall expressed himself as follows:--
"The passage from the physics of the brain to the corresponding facts of
consciousness is unthinkable. Granted that a definite thought, and a
definite molecular action in the brain occur simultaneously, we do not
possess the intellectual organ, nor apparently any rudiment of the
organ, which would enable us to pass by a process of reasoning from the
one phenomenon to the other. They appear together, but we do not know
why. Were our minds and senses so expanded, strengthened, and
illuminated as to enable us to see and feel the very molecules of the
brain; were we capable of following all their motions, all their
groupings, all their electric discharges, if such there be, and were we
intimately acquainted with the corresponding states of thought and
feeling, we should be as far as ever from the solution of the problem,
'How are these physical processes connected with the facts of
consciousness?' The chasm between the two classes of phenomena would
still remain intellectually impassable."
In his latest work ("An Introduction to the Classification of Animals,")
published in 1869, Professor Huxley unhesitatingly adopts the "well
founded doctrine, that life is the cause and not the consequence of
organization." In his celebrated article "On the Physical Basis of
Life," however, he maintains, that life is a property of protoplasm, and
that protoplasm owes its properties to the nature and disposition of its
molecules. Hence he terms it "the matter of life," and believes that all
the physical properties of organized beings are due to the physical
properties of protoplasm. So far we might, perhaps, follow him, but he
does not stop here. He proceeds to bridge over that chasm which
Professor Tyndall has declared to be "intellectually impassable," and,
by means which he states to be logical, arrives at the conclusion, that
our "_thoughts are the expression of molecular changes in that matter of
life which is the source of our other vital phenomena_." Not having been
able to find any clue in Professor Huxley's writings, to the steps by
which he passes from those vital phenomena, which consist only, in their
last analysis, of movements of particles of matter, to those other
phenomena which we term thought, sensation, or consciousness; but,
knowing that so positive an expression of opinion from him will have
great weight with many persons, I shall endeavour to show, with as much
brevity as is compatible with clearness, that this theory is not only
incapable of proof, but is also, as it appears to me, inconsistent with
accurate conceptions of molecular physics. To do this, and in order
further to develop my views, I shall have to give a brief sketch of the
most recent speculations and discoveries, as to the ultimate nature and
constitution of matter.
_The Nature of Matter._
It has been long seen by the best thinkers on the subject, that
atoms,--considered as minute solid bodies from which emanate the
attractive and repulsive forces which give what we term matter its
properties,--could serve no purpose whatever; since it is universally
admitted that the supposed atoms never touch each other, and it cannot
be conceived that these homogeneous, indivisible, solid units, are
themselves the ultimate _cause_ of the forces that emanate from their
centres. As, therefore, none of the properties of matter can be due to
the atoms themselves, but only to the forces which emanate from the
points in space indicated by the atomic centres, it is logical
continually to diminish their size till they vanish, leaving only
localized centres of force to represent them. Of the various attempts
that have been made to show how the properties of matter may be due to
such modified atoms (considered as mere centres of force), the most
successful, because the simplest and the most logical, is that of Mr.
Bayma, who, in his "Molecular Mechanics," has demonstrated how, from the
simple assumption of such centres having attractive and repulsive forces
(both varying according to the same law of the inverse squares as
gravitation), and by grouping them in symmetrical figures, consisting of
a repulsive centre, an attractive nucleus, and one or more repulsive
envelopes, we may explain all the general properties of matter; and, by
more and more complex arrangements, even the special chemical,
electrical, and magnetic properties of special forms of matter.[I] Each
chemical element will thus consist of a molecule formed of simple atoms,
(or as Mr. Bayma terms them to avoid confusion, "material elements") in
greater or less number and of more or less complex arrangement; which
molecule is in stable equilibrium, but liable to be changed in form by
the attractive or repulsive influences of differently constituted
molecules, constituting the phenomena of chemical combination, and
resulting in new forms of molecule of greater complexity and more or
less stability.
+--------------------------------------------------------------+
| [I] Mr. Bayma's work, entitled "The Elements of Molecular |
| Mechanics," was published in 1866, and has received less |
| attention than it deserves. It is characterised by great |
| lucidity, by logical arrangement, and by comparatively |
| simple geometrical and algebraical demonstrations, so that |
| it may be understood and appreciated with a very moderate |
| knowledge of mathematics. It consists of a series of |
| Propositions, deduced from the known properties of matter; |
| from these are derived a number of Theorems, by whose help |
| the more complicated Problems are solved. Nothing is taken |
| for granted throughout the work, and the only valid mode of |
| escaping from its conclusions is, by either disproving the |
| fundamental Propositions, or by detecting fallacies in the |
| subsequent reasoning. |
+--------------------------------------------------------------+
Those organic compounds of which organized beings are built up, consist,
as is well known, of matter of an extreme complexity. and great
instability; whence result the changes of form to which it is
continually subject. This view enables us to comprehend the
_possibility_, of the phenomena of vegetative life being due to an
almost infinite complexity of molecular combinations, subject to
definite changes under the stimuli of heat, moisture, light,
electricity, and probably some unknown forces. But this greater and
greater complexity, even if carried to an infinite extent, cannot, of
itself, have the slightest tendency to originate consciousness in such
molecules or groups of molecules. If a material element, or a
combination of a thousand material elements in a molecule, are alike
unconscious, it is impossible for us to believe, that the mere addition
of one, two, or a thousand other material elements to form a more
complex molecule, could in any way tend to produce a self-conscious
existence. The things are radically distinct. To say that mind is a
product or function of protoplasm, or of its molecular changes, is to
use words to which we can attach no clear conception. You cannot have,
in the whole, what does not exist in any of the parts; and those who
argue thus should put forth a definite conception of matter, with
clearly enunciated properties, and show, that the necessary result of a
certain complex arrangement of the elements or atoms of that matter,
will be the production of self-consciousness. There is no escape from
this dilemma,--either all matter is conscious, or consciousness is
something distinct from matter, and in the latter case, its presence in
material forms is a proof of the existence of conscious beings, outside
of, and independent of, what we term matter. (_Note B._)
_Matter is Force._--The foregoing considerations lead us to the very
important conclusion, that matter is essentially force, and nothing but
force; that matter, as popularly understood, does not exist, and is, in
fact, philosophically inconceivable. When we touch matter, we only
really experience sensations of resistance, implying repulsive force;
and no other sense can give us such apparently solid proofs of the
reality of matter, as touch does. This conclusion, if kept constantly
present in the mind, will be found to have a most important bearing on
almost every high scientific and philosophical problem, and especially
on such as relate to our own conscious existence.
_All Force is probably Will-Force._--If we are satisfied that force or
forces are all that exist in the material universe, we are next led to
enquire what is force? We are acquainted with two radically distinct or
apparently distinct kinds of force--the first consists of the primary
forces of nature, such as gravitation, cohesion, repulsion, heat,
electricity, &c.; the second is our own will-force. Many persons will at
once deny that the latter exists. It will be said, that it is a mere
transformation of the primary forces before alluded to; that the
correlation of forces includes those of animal life, and that _will_
itself is but the result of molecular change in the brain. I think,
however, that it can be shown, that this latter assertion has neither
been proved, nor even been proved to be possible; and that in making it,
a great leap in the dark has been taken from the known to the unknown.
It may be at once admitted that the _muscular force_ of animals and men,
is merely the transformed energy derived from the primary forces of
nature. So much has been, if not rigidly proved, yet rendered highly
probable, and it is in perfect accordance with all our knowledge of
natural forces and natural laws. But it cannot be contended that the
physiological balance-sheet has ever been so accurately struck, that we
are entitled to say, not one-thousandth part of a grain more of force
has been exerted by any organized body or in any part of it, than has
been derived from the known primary forces of the material world. If
that were so, it would absolutely negative the existence of will; for if
will is anything, it is a power that _directs_ the action of the forces
stored up in the body, and it is not conceivable that this _direction_
can take place, without the exercise of some force in some part of the
organism. However delicately a machine may be constructed, with the most
exquisitely contrived detents to release a weight or spring by the
exertion of the smallest possible amount of force, _some_ external force
will always, be required; so, in the animal machine, however minute may
be the changes required in the cells or fibres of the brain, to set in
motion the nerve currents which loosen or excite the pent up forces of
certain muscles, _some force_ must be required to effect those changes.
If it is said, "those changes are automatic, and are set in motion by
external causes," then one essential part of our consciousness, a
certain amount of freedom in willing, is annihilated; and it is
inconceivable how or why there should have arisen any consciousness or
any apparent will, in such purely automatic organisms. If this were so,
our apparent WILL would be a delusion, and Professor Huxley's
belief--"that our volition counts for something as a condition of the
course of events," would be fallacious, since our volition would then be
but one link in the chain of events, counting for neither more nor less
than any other link whatever.
If, therefore, we have traced one force, however minute, to an origin in
our own WILL, while we have no knowledge of any other primary cause of
force, it does not seem an improbable conclusion that all force may be
will-force; and thus, that the whole universe, is not merely dependent
on, but actually _is_, the WILL of higher intelligences or of one
Supreme Intelligence. It has been often said that the true poet is a
seer; and in the noble verse of an American poetess, we find expressed,
what may prove to be the highest fact of science, the noblest truth of
philosophy:
God of the Granite and the Rose!
Soul of the Sparrow and the Bee!
The mighty tide of Being flows
Through countless channels, Lord, from thee.
It leaps to life in grass and flowers,
Through every grade of being runs,
While from Creation's radiant towers
Its glory flames in Stars and Suns.
_Conclusion._
These speculations are usually held to be far beyond the bounds of
science; but they appear to me to be more legitimate deductions from the
facts of science, than those which consist in reducing the whole
universe, not merely to matter, but to matter conceived and defined so
as to be philosophically inconceivable. It is surely a great step in
advance, to get rid of the notion that _matter_ is a thing of itself,
which can exist _per se_, and must have been eternal, since it is
supposed to be indestructible and uncreated,--that force, or the forces
of nature, are another thing, given or added to matter, or else its
necessary properties,--and that mind is yet another thing, either a
product of this matter and its supposed inherent forces, or distinct
from and co-existent with it;--and to be able to substitute for this
complicated theory, which leads to endless dilemmas and contradictions,
the far simpler and more consistent belief, that matter, as an entity
distinct from force, does not exist; and that FORCE is a product of
MIND. Philosophy had long demonstrated our incapacity to prove the
existence of matter, as usually conceived; while it admitted the
demonstration to each of us of our own self-conscious, ideal existence.
Science has now worked its way up to the same result, and this agreement
between them should give us some confidence in their combined teaching.
The view we have now arrived at seems to me more grand and sublime, as
well as far simpler, than any other. It exhibits the universe, as a
universe of intelligence and will-power; and by enabling us to rid
ourselves of the impossibility of thinking of mind, but as connected
with our old notions of matter, opens up infinite possibilities of
existence, connected with infinitely varied manifestations of force,
totally distinct from, yet as real as, what we term matter.
The grand law of continuity which we see pervading our universe, would
lead us to infer infinite gradations of existence, and to people all
space with intelligence and will-power; and, if so, we have no
difficulty in believing that for so noble a purpose as the progressive
development of higher and higher intelligences, those primal and general
will-forces, which have sufficed for the production of the lower
animals, should have been guided into new channels and made to converge
in definite directions. And if, as seems to me probable, this has been
done, I cannot admit that it in any degree affects the truth or
generality of Mr. Darwin's great discovery. It merely shows, that the
laws of organic development have been occasionally used for a special
end, just as man uses them for his special ends; and, I do not see that
the law of "natural selection" can be said to be disproved, if it can be
shown that man does not owe his entire physical and mental development
to its unaided action, any more than it is disproved by the existence of
the poodle or the pouter pigeon, the production of which may have been
equally beyond its undirected power.
The objections which in this essay I have taken, to the view,--that the
same law which appears to have sufficed for the development of animals,
has been alone the cause of man's superior physical and mental
nature,--will, I have no doubt, be over-ruled and explained away. But I
venture to think they will nevertheless maintain their ground, and that
they can only be met by the discovery of new facts or new laws, of a
nature very different from any yet known to us. I can only hope that my
treatment of the subject, though necessarily very meagre, has been clear
and intelligible; and that it may prove suggestive, both to the
opponents and to the upholders of the theory of Natural Selection.
NOTES.
_NOTE A._ (_Page_ 360.)
Some of my critics seem quite to have misunderstood my meaning in this
part of the argument. They have accused me of unnecessarily and
unphilosophically appealing to "first causes" in order to get over a
difficulty--of believing that "our brains are made by God and our lungs
by natural selection;" and that, in point of fact, "man is God's
domestic animal." An eminent French critic, M. Claparède, makes me
continually call in the aid of--"_une Force supérieure_," the capital F,
meaning I imagine that this "higher Force" is the Deity. I can only
explain this misconception by the incapacity of the modern cultivated
mind to realise the existence of any higher intelligence between itself
and Deity. Angels and archangels, spirits and demons, have been so long
banished from our belief as to have become actually unthinkable as
actual existences, and nothing in modern philosophy takes their place.
Yet the grand law of "continuity," the last outcome of modern science,
which seems absolute throughout the realms of matter, force, and mind,
so far as we can explore them, cannot surely fail to be true beyond the
narrow sphere of our vision, and leave an infinite chasm between man and
the Great Mind of the universe. Such a supposition seems to me in the
highest degree improbable.
Now, in referring to the origin of man, and its possible determining
causes, I have used the words "some other power"--"some intelligent
power"--"a superior intelligence"--"a controlling intelligence," and
only in reference to the origin of universal forces and laws have I
spoken of the will or power of "one Supreme Intelligence." These are the
only expressions I have used in alluding to the power which I believe
has acted in the case of man, and they were purposely chosen to show,
that I reject the hypothesis of "first causes" for any and every
_special_ effect in the universe, except in the same sense that the
action of man or of any other intelligent being is a first cause. In
using such terms I wished to show plainly, that I contemplated the
possibility that the development of the essentially human portions of
man's structure and intellect may have been determined by the directing
influence of some higher intelligent beings, acting through natural and
universal laws. A belief of this nature may or may not have a
foundation, but it is an intelligible theory, and is not, _in its
nature_, incapable of proof; and it rests on facts and arguments of an
exactly similar kind to those, which would enable a sufficiently
powerful intellect to deduce, from the existence on the earth of
cultivated plants and domestic animals, the presence of some intelligent
being of a higher nature than themselves.
_NOTE B._ (_Page_ 365.)
A friend has suggested that I have not here explained myself
sufficiently, and objects, that _life_ does not exist in matter any more
than _consciousness_, and if the one can be produced by the laws of
matter, why may not the other? I reply, that there is a radical
difference between the two. Organic or vegetative life consists
essentially in chemical transformations and molecular motions, occurring
under certain conditions and in a certain order. The matter, and the
forces which act upon it, are for the most part known; and if there are
any forces engaged in the manifestation of vegetative life yet
undiscovered (which is a moot question), we can conceive them as
analogous to such forces as heat, electricity, or chemical affinity,
with which we are already acquainted. We can thus clearly _conceive_ of
the transition from dead matter to living matter. A complex mass which
suffers decomposition or decay is dead, but if this mass has the power
of attracting to itself, from the surrounding medium, matter like that
of which it is composed, we have the first rudiment of vegetative life.
If the mass can do this for a considerable time, and if its absorption
of new matter more than replaces that lost by decomposition, and if it
is of such a nature as to resist the mechanical or chemical forces to
which it is usually exposed, and to retain a tolerably constant form, we
term it a living organism. We can _conceive_ an organism to be so
constituted, and we can further conceive that any fragments, which may
be accidentally broken from it, or which may fall away when its bulk has
become too great for the cohesion of all its parts, may begin to
increase anew and run the same course as the parent mass. This is growth
and reproduction in their simplest forms; and from such a simple
beginning it is possible to conceive a series of slight modifications of
composition, and of internal and external forces, which should
ultimately lead to the development of more complex organisms. The LIFE
of such an organism may, perhaps, be nothing added to it, but merely the
name we give to the result of a balance of internal and external forces
in maintaining the permanence of the form and structure of the
individual. The simplest conceivable form of such life would be the
dewdrop, which owes its existence to the balance between the
condensation of aqueous vapour in the atmosphere and the evaporation of
its substance. If either is in excess, it soon ceases to maintain an
individual existence. I do not maintain that vegetative life _is_ wholly
due to such a complex balance of forces, but only that it is
_conceivable_ as such.
With CONSCIOUSNESS the case is very different. Its phenomena are not
comparable with those of any kind of _matter_ subjected to any of the
known or conceivable _forces_ of nature; and we cannot _conceive_ a
gradual transition from absolute unconsciousness to consciousness, from
an unsentient organism to a sentient being. The merest rudiment of
sensation or self-consciousness is infinitely removed from absolutely
non-sentient or unconscious matter. We can conceive of no physical
addition to, or modification of, an unconscious mass which should create
consciousness; no step in the series of changes organised matter may
undergo, which should bring in sensation where there was no sensation
or power of sensation at the preceding step. It is because the things
are utterly incomparable and incommensurable that we can only conceive
of _sensation_ coming to matter from without, while _life_ may be
conceived as merely a specific combination and co-ordination of the
matter and the forces that compose the universe, and with which we are
separately acquainted. We may admit with Professor Huxley that
_protoplasm_ is the "matter of life" and the cause of organisation, but
we cannot admit or conceive that _protoplasm_ is the primary source of
sensation and consciousness, or that it can ever of itself become
_conscious_ in the same way as we may perhaps conceive that it may
become _alive_.
INDEX.
_ABRAXAS grossulariata_, 119.
_Acanthotritus dorsalis_, 94.
_Accipiter pileatus_, 107.
ACRÆIDÆ, the subjects of mimicry, 85, 86.
_Acronycta psi_, protective colouring of, 62.
ADAPTATION brought about by general laws, 276;
looks like design, 281.
ÆGERIIDÆ mimic Hymenoptera, 90.
AGASSIZ, or embryonic character of ancient animals, 301.
_Agnia fasciata_, mimics another Longicorn, 95.
_Agriopis aprilina_, protective colouring of, 62.
ALCEDINIDÆ, sexual colouring and nidification of, 240.
AMADINA, sexual colouring and nidification of, 243.
AMPELIDÆ, sexual colouring and nidification of, 243.
ANCYLOTHERIUM, 300.
ANDRENIDÆ, 98.
_Angræcum sesquipedale_, 272;
its fertilization by a large moth, 275.
ANIMALS, senses and faculties of, 127;
intellect of, compared with that of savages, 341.
ANISOCERINÆ, 92.
ANOA, 196.
ANOPLOTHERIUM, 299.
ANTHRIBIDÆ, mimicry of, 94;
dimorphism in, 155.
_Anthrocera filipendulæ_, 120.
ANTHROPOLOGISTS, wide difference of opinion among, as to origin of
human races, 304;
conflicting views of, harmonized, 321.
ANTIQUITY of man, 303, 322.
APATHUS, 98.
APPARENT exceptions to law of colour and nidification, 253.
AQUATIC BIRDS, why abundant, 32.
_Araschnia prorsa_, 154.
ARCHEGOSAURUS, 300.
ARCHÆOPTERYX, 300.
ARCHITECTURE of most nations derivative, 228;
Grecian, false in principle, 226.
ARCTIC animals, white colour of, 50, 51.
ARGYLL, Duke of, on colours of Woodcock, 53;
on mind in nature, 265;
criticism on Darwin's works, 269;
on humming birds 282;
on creation by birth, 287.
ASILUS, 97.
ASPECTS of nature as influencing man's development, 317.
BABIRUSA, 196.
BALANCE in nature, 42.
BARRINGTON, Hon. Daines, on song of birds, 220.
BASILORNIS, 196.
BATES, Mr., first adopted the word "mimicry," 75;
his observations on Leptalis and Heliconidæ, 82;
his paper explaining the theory of mimicry, 83;
objections to his theory, 108;
on variation, 165;
on recent immigration of Amazonian Indians, 214.
BAYMA, Mr., on "Molecular Mechanics," 363, 364.
BEAUTY in nature, 282;
not universal, 284;
of flowers useful to them, 285;
not given for its own sake, 285.
BIRDS, possible rapid increase of, 29;
numbers that die annually, 30;
mimicry among, 103;
dull colour of females, 114;
nidification as affecting colour of females, 116;
refusing the gooseberry caterpillar, 119;
the highest in rank and organization, 137;
dimorphism in, 155;
why peculiar nest built by each species, 215-219;
build more perfect nests as they grow older, 224, 227;
alter and improve their nests, 226;
sexual differences of colour in, 239.
_Bombus hortorum_, 90.
_Bombycilla, garrula_, colours and nidification of, 255.
BOMBYLIUS, 98.
BRAIN of the savage but slightly less than that of civilized man, 336;
size of, an important element of mental power, 335;
of savage races larger than their needs require, 338, 343;
of man and of anthropoid apes compared, 338.
BROCA, Professor Paul, on the fine crania of the cave men, 337.
_Bryophila glandifera_ and _B. perla_ protectively coloured, 63.
BUCEROTIDÆ, sexual colouring and nidification of, 241.
BUCCONIDÆ, sexual colouring and nidification of, 241.
BUFF-TIP moth, resembles a broken stick, 62.
BUILDINGS of various races do not change, 213.
BUPRESTIDÆ, resembling bird's dung, 57;
similar colours in two sexes, 114.
BUTTERFLIES, value of, in studying "natural selection," 131;
varieties of, in Sardinia and Isle of Man, 178.
_CACIA anthriboides_, 94.
_Callizona acesta_, protective colouring of, 59.
CALORNIS, 239.
CAPITONIDÆ, sexual colouring and nidification of, 241.
_Capnolymma stygium_, 94.
CARABIDÆ, special protection among, 72;
similar colouring of two sexes, 114.
CASSIDÆ, resemble dew drops, 58.
CATERPILLARS, mimicking a poisonous snake, 99;
gaudy colours of, 117;
various modes of protection of, 118;
gooseberry caterpillar, 119;
Mr. Jenner Weir's observations on, 119;
Mr. A. G. Butler's observations on, 121.
CELEBES, local modifications of form in, 170;
probable cause of these, 176;
remarkable zoological peculiarities of, 195-199.
CENTROPUS, sexual colouring and nidification of, 242.
_Cephalodonta spinipes_, 92.
_Ceroxylus laceratus_, imitates a moss-covered stick, 64.
CERTHIOLA, sexual colouring and nidification of, 244.
_Cethosia æole_, 172;
_biblis_, 172.
CETONIADÆ, how protected, 73;
similar colours of two sexes, 114.
CEYCOPSIS, 196.
_Charis melipona_, 96.
CHEMATOBIA, wintry colours of this genus, 62.
_Chlamys pilula_, resembles dung of caterpillars, 58.
CHRYSIDIDÆ, how protected, 72.
CHRYSOMELIDÆ, similar colouring of two sexes, 114.
CICINDELA, adaptive colour of various species of, 57.
_Cilix compressa_, resembles bird's dung, 63.
CLADOBATES, mimicking squirrels, 107.
CLASSIFICATION, form of true, 6;
circular, inadmissible, 8;
quinarian and circular, of Swainson, 46;
argument from, against Mr. Darwin, 295.
CLIMACTERIS, sexual colouring and nidification of, 243.
COCCINELLIDÆ, how protected, 72;
similar colouring of sexes, 114.
COEXISTING varieties, 159.
_Collyrodes lacordairei_, 95.
COLOUR, in animals, popular theories of, 47;
frequent variations of, in domesticated animals, 48;
influenced by need of concealment, 49;
in deserts, 49, 50;
in Arctic regions, 50, 51;
nocturnal, 51;
tropical, 52;
special modifications of, 52;
different distribution of, in butterflies and moths, 58;
of autumnal and winter moths, 62;
white, generally dangerous and therefore eliminated, 66;
why it exists so abundantly although often injurious, 69;
influenced by need of protection, 113;
of female birds, 114;
in relation to nidification of birds, 116;
gaudy colours of many caterpillars, 117;
in nature, general causes of, 126;
local variations of, 173;
sexual differences of, in birds, 239;
in female birds, how connected with their nidification, 240, 246;
more variable than structure or habits, and therefore more easily
modified, 249;
of flowers, as explained by Mr. Darwin, 262;
often correlated with disease, 316.
COMPSOGNATHUS, 300.
_Condylodera tricondyloides_, 97.
CONSCIOUSNESS, origin of, 360;
Professor Tyndall on, 361;
not a product of complex organization, 365.
CORRELATION of growth, 310.
_Corynomalus sp._, 92.
COTINGIDÆ, sexual colouring and nidification of, 244.
CRATOSOMUS, a hard weevil, 94.
CRICKETS mimicking sand wasps, 98.
CRYPTODONTIA, 299.
_Cucullia verbasci_, 120.
CURCULIONIDÆ, often protected by hard covering, 71;
similar colours of two sexes, 114.
_Cuviera squamata_, 258.
_Cyclopeplus batesii_, 92.
CYNOPITHECUS, 196.
_Cynthia arsinoë_, 172.
DANAIDÆ, the subjects of mimicry, 85, 86.
_Danais erippus_, 88;
_chysippus_, 112;
_sobrina_, 179;
_aglaia_, 179;
_tytia_, 180.
DARWIN, Mr., his principle of utility, 47;
on cause of colour in flowers, 127, 262;
on colours of caterpillars, 118;
on sexual colouration, 260;
his metaphors liable to misconception, 269;
criticism of, in _North British Review_, 291.
DESERT animals, colours of, 49, 50.
DIADEMA, species of, mimic Danaidæ, 86, 87;
female with male colouration, 112.
_Diadema misippus_, 112;
_D. anomala_, 113.
_Diaphora mendica_, 89.
DICNYODONTIA, 299.
DICROURUS, 253.
_Diloba coeruleocephala_, 120.
DIMORPHISM, 145;
in beetles, 155;
in birds, 155;
illustrated, 157.
DINOSAURIA, 298.
DIPTERA mimicking wasps and bees, 97.
_Doliops curculionides_, 94.
DOMESTICATED animals, their essential difference from wild
ones, 38-41.
DOTTERELL, 251.
DRUSILLA, mimicked by three genera, 181.
_Drusilla bioculata_, 180.
DYTISCUS, dimorphism in, 155.
EGYPTIAN architecture, introduced, 225.
_Elaps fulvius_, _E. corallinus_, _E. lemniscatus_, 101;
_E. mipartitus_, _E. lemniscatus_, _E. hemiprichii_, 102.
ENODES, 196.
ENNOMUS, autumnal colours of this genus, 62.
_Eos fuscata_, dimorphism of, 155.
EQUUS, 299.
_Eronia tritæa_, 172;
_valeria_, 172.
_Eroschema poweri_, 93.
ERYCINIDÆ mimic Heliconidæ, 84.
_Erythroplatis corallifer_, 92.
ESTRELDA, sexual colouring and nidification of, 243.
EUCNEMIDÆ, mimicking a Malacoderm, 93.
_Eudromias morinellus_, 251.
_Euglossa dimidiata_, 98.
EUMORPHIDÆ, a protected group 72;
imitated by Longicorns, 92.
EUPLOEA, local modifications of colour in, 173.
_Euploea midamus_, 87-113, 179;
_E. rhadamanthus_, 87, 179.
_Eurhinia megalonice_, 172;
_polynice_, 172.
EURYLÆMIDÆ, sexual colouring and nidification of, 243.
EXTINCT animals, intermediate forms of, 298.
EXTINCTION of lower races, 318.
FEMALE birds, colours of, 114;
sometimes connected with their mode of nidification, 240;
more exposed to enemies than the males, 248.
FEMALE butterflies generally dull-coloured, 259.
FEMALE insects, mimicry by, 110, 259;
colours of, 113.
FEMALE sex, has no incapacity for as brilliant colouration as the
male, 247;
in some groups requires more protection than the male, 258.
FISHES, protective colouring of, 55.
FISSIROSTRAL birds, nests of, 238.
FLOWERS, causes of colour in, 127.
FLYCATCHERS, genera of, absent from Celebes, 177.
FORBES, EDWARD, objections to his theory of Polarity, 17-23.
FORCE is probably all Will-force, 366.
GALAPAGOS, 10.
GALTON, Mr., on range of intellectual power, 339.
GANOCEPHALA, 298.
_Gastropacha querci_, protective colour and form of, 62.
GAUDRY, M., on fossil mammals of Greece, 299.
GEOGRAPHICAL distribution, dependent on geologic changes, 1;
its agreement with law of introduction of new species, 9;
of allied species and groups, 12.
GEOLOGICAL distribution analogous to geographical, 13.
GEOLOGY, facts proved by, 2-5.
GIRAFFE, how it acquired its long neck, 42.
GLÆA, autumnal colours of this genus, 62.
GOULD, Mr., on sexual plumage of Gray Phalarope, 115;
on incubation by male Dotterell, 115.
_Grallina australis_, 254.
GREEN birds almost confined to the tropics, 52.
_Gymnocerus cratosomoides_, 94.
_Gymnocerous capucinus_, 96.
_Gymnocerous dulcissimus_, 97.
GUNTHER, Dr., on arboreal snakes, 55;
on colouring of snakes, 102.
_Gynecia dirce_, 59.
HABITS, often persistent when use of them has ceased, 234;
of children and savages analogous to those of animals, 235;
if persistent and imitative may be termed hereditary, 235, 236.
HAIRY covering of Mammalia, use of, 344;
absence of, in man remarkable, 345;
the want of it felt by savages, 346;
could not have been abolished by natural selection, 348.
_Harpagus diodon_, 107.
HEILIPLUS, a hard genus of Curculionidæ, 94.
HELICONIDÆ, the objects of mimicry, 77;
their secretions, 88;
not attacked by birds, 79;
sometimes mimicked by other Heliconidæ, 85.
HELLADOTHERIUM, 300.
HEMIPTERA, protected by bad odour, 72.
HERBERT, Rev. W., on song of birds, 221.
HESPERIDÆ, probable means of protection of, 176.
HESTHESIS, longicorns resembling ants, 96.
_Hestia leuconoë_, 180.
HEWITSON, Mr., 131.
HIPPARION, 299.
HIPPOTHERIUM, 299.
HISPIDÆ, imitated by Longicorns, 92.
HOLOTHURIDÆ, 258.
_Homalocranium semicinctum_, 101.
HOOKER, Dr., on the value of the "specific term," 165.
HOUSES of American and Malay races contrasted, 213.
HUXLEY, Professor, on "Physical Basis of Life," 362;
on volition, 368.
HYÆNICTIS, 300.
HYBERNIA, wintry colours of this genus, 62.
HYMENOPTERA, large number of, peculiar to Celebes, 196.
ICTERIDÆ, sexual colouring and nidification of, 244.
ICTHYOPTERYGIA, 298.
_Ideopsis daos_, 180.
IMITATION, the effects of, in man's works, 212.
INDIANS, how they travel through trackless forests, 207.
INSECTS, protective colouring of, 56;
mimicking species of other orders, 97;
senses of, perhaps different from ours, 202, 203.
INSTINCT, how it may be best studied, 201;
definition of, 203;
in many cases assumed without proof, 205;
if possessed by man, 206;
supposed, of Indians, 207;
supposed to be shown in the construction of birds' nests, 211.
INTELLECT of savages compared with that of animals, 341.
INTELLECTUAL power, range of, in man, 339.
_Iphias glaucippe_, 172.
ITHOMIA, mimicked by Leptalis, 83.
_Ithomia ilerdina_, mimicked by four groups of Lepidoptera, 84.
JAVA, relations of, to Sumatra and Borneo, 193.
JAMAICA swift altering position of nest, 228.
JERDON, Mr., on incubation by males in Turnix, 115.
_Kallima inachis_ and _Kallima paralekta_, wonderful resemblance of,
to leaves, 59-61.
LABYRINTHODONTIA, 298, 300.
LAKES as cases of imperfect adaptation, 278.
LANIADÆ, sexual colouring and nidification of, 245.
LAMARCK'S hypothesis very different from the author's, 41.
_Larentia tripunctaria_, 63.
LAW which has regulated the introduction of new species, 5;
confirmed by geographical distribution, 9;
high organization of ancient animals consistent with, 14;
of multiplication in geometrical progression, 265;
of limited populations, 265;
of heredity, 266;
of variation, 266;
of change of physical conditions, 266;
of the equilibrium of nature, 266;
as opposed to continual interference, 268.
LAYCOCK, Dr., on law of "unconscious intelligence," 360.
LEAF BUTTERFLY, appearance and habits of, 59-61.
LEPIDOPTERA, especially subject to variation, 132.
LEPTALIS, species of mimic Heliconidæ, 82;
gain a protection thereby, 259.
LESTER, Mr. J. M., on wood-dove and robin, 53.
LEVAILLANT, on formation of a nest, 224.
_Limenitis archippus_, 88.
_Limenitis limire_, 172;
_procris_, 172.
LIZARDS refusing certain moths and caterpillars, 121;
devouring bees, 121.
LOCAL FORMS, 158.
LOCAL variation of form, 169;
of colour, 173;
general remarks on, 174;
in Celebesian butterflies, probable use of, 175.
LOCUSTIDÆ, adaptive colouring of, 64.
LUMINOUSNESS of some insects a protection, 71.
LYCÆNIDÆ, probable means of protection of, 176.
MAMMALS, mimicry among, 107.
MAN, does he build by reason or imitation, 212;
his works mainly imitative, 225;
antiquity of, 303, 322;
difference of opinion as to his origin, 304;
unity or plurality of species, 305;
persistence of type of, 306;
importance of mental and moral characters, 312;
his dignity and supremacy, 324;
his influence on nature, 326;
his future development, 326;
range of intellectual power in, 339;
rudiments of all the higher faculties in savage, 341;
his feet and hands, difficulties on the theory of natural
selection, 349;
his voice, 350;
his mental faculties, 351;
difficulty as to the origin of the moral sense in, 352;
development of, probably directed by a superior intelligence, 359.
MANTIDÆ, adaptive colouring of, 64;
mimicking white ants, 98.
MALACODERMS, a protected group, 93.
MALURIDÆ, 255.
MATTER, the nature of, 363;
Mr. Bayma on, 363;
is force, 365.
MECHANITIS and Methona, mimicked by _Leptalis_, 83.
MECOCERUS, dimorphism of, 155.
_Mecocerus gazella_, 94.
MEGACEPHALON, 196.
MEGAPODIDÆ, sexual colouring and nidification of, 246.
MEROPOGON, 196.
_Midas dives_, 97.
MIMETA, mimicking Tropidorhynchus, 104.
MIMICRY, meaning of the word, 74;
theory of, 76;
among Lepidoptera, 77;
how it acts as a protection, 80, 81;
of other insects by Lepidoptera, 89;
among beetles, 91;
of other insects by beetles, 95;
of insects by species of other orders, 97;
among the vertebrata, 99;
among snakes, 101;
among tree frogs, 103;
among birds, 103;
among mammals, 107;
objections to the theory of, 108;
by female insects, 110;
among Papilionidæ, 179;
never occurs in the male only, 260.
MOMOTIDÆ, sexual colouring and nidification of, 241.
MONTROUZIER, M., on butterflies of Woodlark Island, 152.
MORAL sense, difficulty as to the origin of, 352.
MORPHOS, how protected, 73.
MURRAY, Mr. Andrew, objections to theory of mimicry, 108.
MUSCICAPIDÆ, sexual colouring and nidification of, 245.
MUSOPHAGIDÆ, sexual colouring and nidification of, 242.
NAPEOGENES, all the species are mimickers, 85.
NATURAL selection, the principle stated, 41-43;
general acceptance of the theory of, 46;
tabular demonstration of, 302;
outline of theory of, 307;
its effects on man and animals different, 311;
hardly acts among civilized societies, 330;
what it can not do, 333;
cannot produce injurious or useless modifications, 334.
NECTARINEIDÆ, 254.
NECYDALIDÆ, mimic Hymenoptera, 96.
_Nemophas grayi_, a Longicorn mimicked by a Longicorn, 95.
NESTS of Birds, why different, 215;
of young birds, how built, 219;
construction of, described by Levaillant, 224;
imperfections in, 229;
influenced by changed conditions and persistent habits, 232;
classification of, according to function, 237.
NEW FORMS, how produced by variation and selection, 286.
NEW GUINEA, relation of the several Papuan islands to, 194.
NOCTURNAL animals, colours of, 51.
NOMADA, 98.
OBEREA, species resemble Tenthredinidæ, 96.
_Odontocera odyneroides_, 96.
ODONTOCHEILA, 97.
_Odyncrus sinuatus_, 90.
_Onthophilus sulcatus_, like a seed, 58.
_Onychocerus scorpio_, resembles bark, 56.
ORANGE-TIP butterfly, protective colouring of, 59.
ORCHIS, structure of an, explained by natural selection, 271.
_Orgyia antiqua_ and _O. gonostigma_, autumnal colours of, 62.
ORIOLIDÆ, 253.
_Ornithoptera priamus_, 145, 173;
_O. helena_, 173.
_Oxyrhopus petolarius_, _O. trigeminus_, _O. formosus_, 102.
OWEN, Professor, on more generalized structure of extinct
animals, 298.
_Pachyotris fabricii_, 96.
PACHYRHYNCHI, weevils mimicked by Longicorns, 95.
PALEOTHERIUM, 299.
PALOPLOTHERIUM, 299.
PAPILIO, black and red group imitated, 84.
_Papilio achates_, 147;
_P. adamantius_, 171;
_P. ænigma_, 87;
_P. agamemnon_, 141, 158, 170, 171;
_P. agestor_, 180;
_P. alphenor_, 148, 169;
_P. amanga_, 151;
_P. androcles_, 171;
_P. androgeus_, 88, 147, 180, 183;
_P. antiphates_, 141, 171;
_P. antiphus_, 87, 150, 170, 180, 183;
_P. aristæus_, 171;
_P. arjuna_, 141;
_P. ascalaphus_, 171;
_P. autolycus_, 160;
_P. bathycles_, 141;
_P. blumei_, 171;
_P. brama_, 171;
_P. caunus_, 87, 179;
_P. codrus_, 160, 171;
_P. cöon_, 88, 146, 180, 182;
_P. deiphobus_, 140;
_P. deiphontes_, 171;
_P. delessertii_, 180;
_P. demolion_, 171;
_P. diphilus_, 87, 170, 180, 183;
_P. doubledayi_, 88, 180;
_P. elyros_, 148;
_P. encelades_, 171;
_P. erectheus_, 151;
_P. euripilus_, 160;
_P. evemon_, 159;
_P. gigon_, 171;
_P. glaucus_, 152;
_P. hector_, 87, 150, 180, 183;
_P. helenus_, 160, 171;
_P. hospiton_, 178;
_P. idæoides_, 180;
_P. jason_, 159, 171;
_P. ledebouria_, 148;
_P. leucothoë_, 171;
_P. leodamas_, 170;
_P. liris_, 87, 180, 184;
_P. macareus_, 179;
_P. machaon_, 178;
_P. melanides_, 148, 150;
_P. memnon_, 88, 140, 146, 147, 152, 180, 183;
_P. milon_, 171;
_P. nephelus_, 140;
_P. nicanor_, 170;
_P. oenomaus_, 88, 180, 184;
_P. onesimus_, 151;
_P. ormenus_, 150, 152, 182;
_P. pammon_, 147, 152, 170, 180;
_P. pamphylus_, 171;
_P. pandion_, 152, 180;
_P. paradoxa_, 87, 179;
_P. peranthus_, 160, 171;
_P. pertinax_, 145;
_P. philoxenus_, 182;
_P. polydorus_, 88, 170, 182;
_P. polytes_, 147, 148;
_P. rhesus_, 171;
_P. romulus_, 87, 148, 150, 183;
_P. sarpedon_, 141, 158, 171;
_P. sataspes_, 171;
_P. severus_, 140, 144;
_P. theseus_, 87, 148, 150, 169, 170, 171, 180, 183;
_P. thule_, 179;
_P. torquatus_, 156;
_P. turnus_, 152;
_P. ulysses_, 140, 160, 173;
_P. varuna_, 88.
PAPILIONIDÆ, the question of their rank, 133;
peculiar characters possessed by, 134;
peculiarly diurnal, 136;
compared with groups of mammalia, 138;
distribution of, 140;
large forms of Celebes and Moluccas, 168;
large forms of Amboyna, 169;
local variation of form, 169;
arrangement of, 186;
geographical distribution of, 189;
of Indo-Malay and Austro-Malay regions, 192;
of Java, Sumatra, and Borneo, 193.
PARIDÆ, sexual colouring and nidification of, 243.
PASSENGER pigeon, cause of its great numbers, 308.
PATENT inventions, as illustrating classification, 295.
_Phacellocera batesii_, mimics one of the Anthribidæ, 94.
_Phalaropus fulicarius_, 115, 251.
PHASMIDÆ, imitate sticks and twigs, 64;
females resembling leaves, 112.
PHYLLIUM, wonderful protective colour and form of, 64.
PHYSALIA, 258.
PIERIDÆ, local modification of form in, 172.
PIERIS, females only imitating Heliconidæ, 112.
_Pieris coronis_, 172;
_eperia_, 172.
_Pieris pyrrha_, 113.
PICIDÆ, sexual colouring and nidification of, 242.
PIPRIDÆ, sexual colouring and nidification of, 245.
PITTIDÆ, 253.
_Pliocerus equalis_, 101;
_P. elapoides, P. euryzonus_, 102.
_Pæciloderma terminale_, 93.
POLARITY, Forbes' theory of, 17, 45.
POLYMORPHISM, 145;
illustration of, 157.
POPULATION of species, law of, 28;
does not permanently increase, 29;
not determined by abundance of offspring, 29;
checks to, 30;
difference in the case of cats and rabbits explained, 32.
PREVISION, a case of, 122.
PRIONITURUS, 196.
PROTECTION, various modes in which animals obtain it, 69-71, 258;
greater need of, in female insects and birds, 113.
PROTECTIVE colouring, theory of, 65.
PSITTACI (Parrots), sexual colouring and nidification of, 242.
PTEROSAURIA, 298.
PTYCHODERES, 94.
RACES, or subspecies, 160;
of man, origin of, 319.
REDBREAST and woodpigeon, protective colouring of, 53, 54.
REPRESENTATIVE groups, 9;
of Trogons, butterflies, &c., 12.
REPTILES, protective colouring of, 54.
RHAMPHASTIDÆ, sexual colouring and nidification of, 242.
RHINOCEROS, 299.
RIVER system, as illustrating self-adaptation, 276.
ROSES, Mr. Baker on varieties of, 165.
RUDIMENTARY organs, 23.
SALVIN, Mr. Osbert, on a case of bird mimicry, 107.
_Saturnia pavonia-minor_, protective colouring of larva of, 63.
SATYRIDÆ, probable means of protection of, 176.
SAUROPTERYGIA, 299.
SAVAGES, why they become extinct, 319;
undeveloped intellect of, 339, 341;
intellect of, compared with that of animals, 341, 343;
protect their backs from rain, 346.
SCANSORIAL birds, nests of, 238.
SCAPHURA, 98.
SCISSIROSTRUM, 165.
SCOPULIPEDES, brush-legged bees, 91.
SCUDDER, Mr., on fossil insects, 301.
SCUTELLERIDÆ, mimicked by Longicorns, 96.
_Sesia bombiliformis_, 90.
SESIIDÆ, mimic Hymenoptera, 90.
SEXES, comparative importance of, in different classes of
animals, 111;
diverse habits of, 156.
SEXUAL SELECTION, 156;
its normal action to develop colour in both sexes, 247;
among birds, 283.
SIDGWICK, Mr. A., on protective colouring of moths, 62.
SIMOCYONIDÆ, 300.
SITTA, sexual colouring and nidification of, 243.
SITTELLA, sexual colouring and nidification of, 243.
SNAKES, mimicry among, 101.
SONG of birds, instinctive or imitative, 220.
SPECIES, law of population of, 28;
abundance or rarity of, dependent on the adaptation to
conditions, 33;
definition of, 141, 161;
the range and constancy of, 143;
extreme variation in, 163, 164.
SPEED of animals, limits of, 292.
_Sphecia craboniforme_, 90.
_Sphecomorpha chalybea_, 96.
SPHEGIDÆ, mimicked by flies, 97.
SPIDERS, which mimic ants, 98;
and flower buds, 99.
_Spilosoma menthastri_, 88.
STAINTON, Mr., on moths rejected by turkeys, 78, 88.
STALACHTIS, a genus of Erycinidæ, the object of mimicry, 84.
STINGING insects generally conspicuously coloured, 72.
STREPTOCITTA, 196.
STURNIDÆ, sexual colouring and nidification of, 244.
STURNOPASTOR, 239.
ST. HELENA, 10.
_Streptolabis hispoides_, 93.
STRUGGLE for existence, 28, 33.
SURVIVAL of the fittest, law of, stated, 33;
its action in determining colour, 67.
SWAINSON'S circular and quinarian theory, 45.
SYLVIADÆ, sexual colouring and nidification of, 245.
SYNAPTA, 258.
_TACHORNIS phoenicobea_, 228.
_Tachyris hombronii_, 172;
_ithome_, 172;
_lycaste_, 172;
_lyncida_, 172;
_nephele_, 172;
_nero_, 172;
_zarinda_, 172.
TANAGRIDÆ, sexual colouring and nidification of, 245.
TAPIR, 299.
TELEPHORI, similar colouring of two sexes, 114.
TEMPERATE and cold climates favourable to civilization, 318.
THECODONTIA, 299.
THERATES, mimicked by Heteromera, 95.
_Thyca descombesi_, 172;
_hyparete_, 172;
_rosenbergii_, 172;
_zebuda_, 172.
TIGER, adaptive colouring of, 52.
TIMES newspaper on Natural Selection, 296.
TOOLS, importance of, to man, 314.
TREE FROGS, probable mimicry by, 103.
TRICONDYLA, 97.
TRIMEN, Mr., on rank of the Papilionidæ, 136.
TRISTRAM, Rev. H., on colours of desert animals, 50.
_Trochilium tipuliforme_, 90.
TROGONIDÆ, sexual colouring and nidification of, 241.
TROPICAL birds often green, 52.
TROPICS, most favourable to production of perfect adaptation among
animals, 68;
not favourable to growth of civilization, 318.
TROPIDORHYNCHUS mimicked by orioles, 104.
TRUTHFULNESS of some savages, 353;
not to be explained on utilitarian hypothesis, 354.
TURDIDÆ, sexual colouring and nidification of, 245.
TURNIX, 115, 251.
TYNDALL, Professor, on origin of consciousness, 361.
UPUPIDÆ, sexual colouring and nidification of, 241.
USEFUL and useless variations, 34.
UTILITY, importance of the principle of, 47, 127.
VARIABILITY, simple, 144.
VARIATIONS, useful and useless, 34;
laws of, 143, 266;
as influenced by locality, 166;
of size, 168;
universality of, 287-291;
are there limits to, 291;
of domestic dogs, 293;
of pigeons, 293.
VARIETIES, instability of, supposed to prove the permanent
distinctness of species, 26;
if superior will extirpate original species, 36;
its reversion then impossible, 37;
of domesticated animals may partially revert, 38, 40;
inconvenience of using the term, 161.
VERTEBRATA, mimicry among, 99.
VOICE of man, not explained by natural selection, 350.
VOLUCELLA, species of mimic bees, 75, 98.
WALSH, Mr., on dimorphism, of _Papilio turnus_, 153.
WEAPONS and tools, how they affect man's progress, 314.
WEEVILS often resemble small lumps of earth, 58.
WEIR, Mr. Jenner, on a moth refused by birds, 89;
on beetles refused by birds, 93;
on caterpillars eaten and rejected by birds, 119.
WESTWOOD, Professor, objections to theory of mimicry, 108.
WHITE colour in domesticated and wild animals, 66.
WILD and domesticated animals, essential differences of, 38-41.
WILL really exerts force, 367;
probably the primary source of force, 368.
WOOD, Mr. T. W., on orange-tip butterfly, 59.
WOODCOCKS and Snipes, protective colouring of, 53.
WOODPECKERS, why scarce in England, 32.
_XANTHIA_, autumnal colours of these moths, 62.
ZEBRAS, 299.
+--------------------------------------------------------------+
| Transcriber's Notes & Errata |
| |
| The following entries were added to the Table of Contents. |
| |
| In Chapter IV.--_The Malayan Papilionidæ, or Swallow-tailed |
| Butterflies, as illustrative of the Theory of Natural |
| Selection._: |
| |
| Arrangement and Geographical Distribution of the Malayan |
| Papilionidæ |
| |
| Range of the Groups of Malayan Papilionidæ |
| |
| |
| In Chapter VI.--_The Philosophy of Birds' Nests._: |
| |
| How young Birds may learn to build Nests. |
| |
| |
| Missing page number 94 supplied for the entry "_Phacellocera |
| batesii_, mimics one of the Anthribidæ," in the index. |
| |
| The following words were found in both hyphenated and |
| unhyphenated forms (incidence in parentheses). |
| |
| |Co-existing (2) |Coexisting (1) | |
| |Fly-catcher (1) |Flycatcher (2) | |
| |sea-weed (2) |seaweed (1) | |
| |bull-dog (1) |bulldog (1) | |
| |
| The following typographical errors have been corrected: |
| |
| |Error |Correction | |
| | | | |
| |sparrrow |sparrow | |
| |unwieldly |unwieldy | |
| |it |its | |
| |Perphaps |Perhaps | |
| |confimation |confirmation | |
| |Pharoahs |Pharaohs | |
| |receptable |receptacle | |
| |occured |occurred | |
| |that that |than that | |
+--------------------------------------------------------------+
End of the Project Gutenberg EBook of Contributions to the Theory of Natural
Selection, by Alfred Russel Wallace
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