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Title: Little Masterpieces of Science:
The Naturalist as Interpreter and Seer
Author: Various
Editor: George Iles
Release Date: August 20, 2009 [EBook #29739]
Language: English
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LITTLE MASTERPIECES OF SCIENCE
[Illustration: Charles R. Darwin.]
Little Masterpieces
of Science
Edited by George Iles
THE NATURALIST AS INTERPRETER AND SEER
_By_
Charles Darwin
Alfred R. Wallace
Thomas H. Huxley
Leland O. Howard
George Iles
NEW YORK
DOUBLEDAY, PAGE & COMPANY
1902
Copyright, 1902, by Doubleday, Page & Co.
Copyright, 1877, by D. Appleton & Co.
Copyright, 1901, by John Wanamaker
Copyright, 1895, by G. H. Buek & Co.
TRANSCRIBER'S NOTES: Obvious printer's errors have been silently
corrected. Hyphenated and accented words have been standardized. See
the end of this file for more information.
PREFACE
To gather stones and fallen boughs is soon to ask, what may be done with
them, can they be piled and fastened together for shelter? So begins
architecture, with the hut as its first step, with the Alhambra, St.
Peter's, the capitol at Washington, as its last. In like fashion the
amassing of fact suggests the ordering of fact: when observation is
sufficiently full and varied it comes to the reasons for what it sees.
The geologist delves from layer to layer of the earth beneath his tread,
he finds as he compares their fossils that the more recent forms of life
stand highest in the scale of being, that in the main the animals and
plants of one era are more allied to those immediately next than to
those of remoter times. He thus divines that he is but exploring the
proofs of lineal descent, and with this thought in his mind he finds
that the collections not only of his own district, but of every other,
take on a new meaning. The great seers of science do not await every jot
and tittle of evidence in such a case as this. They discern the drift of
a fact here, a disclosure there, and with both wisdom and boldness
assume that what they see is but a promise of what shall duly be
revealed. Thus it was that Darwin early in his studies became convinced
of the truth of organic evolution: the labours of a lifetime of all but
superhuman effort, a judicial faculty never exceeded among men, served
only to confirm his confidence that all the varied forms of life upon
earth have come to be what they are through an intelligible process,
mainly by "natural selection."
The present volume offers from the classic pages of Darwin his summary
of the argument of "The Origin of Species," his account of how that book
came to be written, and his recapitulation of "The Descent of Man." All
this affords a supreme lesson as to the value of observation with a
purpose. When Darwin was confronted with an organ or trait which puzzled
him, he was wont to ask, What use can it have had? And always the answer
was that every new peculiarity of plant, or beast, is seized upon and
held whenever it confers advantage in the unceasing conflict for place
and food. No hue of scale or plume, no curve of beak or note of song,
but has served a purpose in the plot of life, or advanced the action in
a drama where the penalty for failure is extinction.
As Charles Darwin stood first among the naturalists of the nineteenth
century, his advocacy of evolution soon wrought conviction among the
thinkers competent to follow his evidence and weigh his arguments. The
opposition to his theories though short was sharp, and here he found a
lieutenant of unflinching courage, of the highest expository power, in
Professor Huxley. This great teacher came to America in 1876, and
discoursed on the ancestry of the horse, as disclosed in fossils then
recently discovered in the Far West, maintaining that they afforded
unimpeachable proof of organic evolution. His principal lecture is here
given.
In a remarkable field of "natural selection" Bates, Wallace and Poulton
have explained the value of "mimicry" as an aid to beasts, birds,
insects, as they elude their enemies or lie unsuspected on the watch for
prey. The resemblances thus worked out through successive generations
attest the astonishing plasticity of bodily forms, a plasticity which
would be incredible were not its evidence under our eyes in every
quarter of the globe. Insects have high economic importance as agents of
destruction: we are learning how to pit one of them against another, so
as to leave a clear field to the farmer and the fruit grower. In this
department a leader is Professor Howard, who contributes a noteworthy
chapter on the successful fight against the pest which threatened with
ruin the orange groves of California.
To the every-day observer the most enticing field of natural history is
that in which common flowers and common insects work out their unending
co-partnery. A blossom by its scent, its beauty of tint, allures a moth
or bee and thus, in effect, is able to take flight and find a mate
across a county so as to perpetuate its race a hundred miles from home.
Our volume closes with a sketch of the singular ties which thus bind
together the fortunes of blossom and insect, so that at last the very
form of a flower may be cast in the mould of its winged ally. A word is
also spoken regarding the singular relations of late detected between
the world of vegetation and minute forms once deemed parasitic. The pea
and its kindred harbor on their rootlets certain tiny lodgers; the
tenants pay a liberal rent in the form of nitrogen compounds, a striking
interlacement of interests!
GEORGE ILES.
CONTENTS
DARWIN, CHARLES
THE ORIGIN OF SPECIES IN SUMMARY
Varieties merge gradually into species. Animals tend to
increase in geometrical ratio. Varieties diverge in consonance
with diversity of opportunity for life. In the struggle
for existence those which best accord with their surroundings
will survive and propagate their kind. Sexual selection
has put a premium on beauty. The causes which in brief
periods produce varieties, in long periods give rise to
species. Instincts, as of the hive bee, are slowly developed.
Geology supports the theory of Evolution: the changes in time
in the fossil record are gradual. Geographical distribution
lends its corroboration: in each region most of the inhabitants
in every great class are plainly related. A common ancestor
is suggested when we see the similarity of hand, wing and
fin. Embryos of birds, reptiles and fish are closely similar
and unlike adult forms. Slight changes in the course of
millions of years produce wide divergences. 3
DARWIN, CHARLES
HOW "THE ORIGIN OF SPECIES" CAME TO BE WRITTEN
During his voyage on the _Beagle_ Darwin saw fossil
armadillos like existing species, and on the islands of the
Galapagos group a gradually increased diversity of species of
every kind. All this suggested that species gradually become
modified. Notes gathered of facts bearing on the question.
Observes that it is the variation between one animal and
another which gives the breeder his opportunity. Reads
Malthus on Population, a work which points out the keen
struggle for existence and that favourable variations tend to
be preserved. In 1842 draws up a brief abstract of the theory
of "natural selection." In 1856 begins an elaborate work on
the same theme, but in 1858, hearing that Wallace has written
an essay advancing an independent theory of natural selection,
offers a summary of his argument to the Linnean Society
of London. Writes "The Origin of Species," which is published
most successfully, November, 1859. 35
DARWIN, CHARLES
THE DESCENT OF MAN: THE ARGUMENT IN BRIEF
Since evolution is probable for all other animals, it is
probable for man. The human form has so much in common with
the forms of other animals that community of descent is
strongly suggested. Man, like other creatures, is subject to
the struggle for existence. Evidence shows that it is likely
that man is descended from a tailed and hairy quadruped that
dwelt in trees. Man's mental power has been the chief factor
in his advance, especially in his development of language.
Conscience is due to social instincts, love of approbation,
memory, imagination and religious feeling. Sexual selection
in its effects upon human advancement. 45
WALLACE, ALFRED R.
MIMICRY AND OTHER PROTECTIVE RESEMBLANCES AMONG ANIMALS
The colours of animals are useful for concealment from their
prey, from the creatures upon which they prey. The lion is
scarcely visible as he crouches on the sand or among desert
rocks and stones. Larks, quails and many other birds are so
tinted and mottled that their detection is difficult. The
polar bear, living amid ice and snow, is white. Reptiles and
fish are so coloured as to be almost invisible in the grass
or gravel where they rest. Many beetles and other insects
are so like the leaves or bark on which they feed that
when motionless they cannot be discerned. Some butterflies
resemble dead, dry or decaying leaves so closely as to elude
discovery. Every individual better protected by colour than
others, has a better chance for life, and of transmitting his
hues. Harmless beetles and flies are so like wasps and bees
as to be left alone. 71
HUXLEY, THOMAS H.
EVOLUTION OF THE HORSE
The hoof of the horse is simply a greatly enlarged and
thickened nail: four of his five toes are reduced to mere
vestiges. His teeth are built of substances of varying
hardness: they wear away at different rates presenting uneven
grinding surfaces. Probable descent of the horse, link by
link, especially as traced in the fossils of North America.
Evolution has taken a long time: how long the physicist and
the astronomer must decide. 101
HOWARD, LELAND O.
FIGHTING PESTS WITH INSECT ALLIES
A scale insect threatened with ruin the orchards of California.
Professor C. V. Riley decided that the pest was a native
of Australia. Mr. A. Hoebele observes in Australia that
the pest is kept down by ladybirds. These are accordingly
sent to California where they destroy the scale insect and
restore prosperity among the fruit-growers. Another pest,
of olive trees, is devoured by an imported ladybird of
another species. This plan extended to Portugal and Egypt
with success. Grasshoppers killed by a fungus cultivated
for the purpose. Introduction into the United States of
the insect which fertilizes the Smyrna fig. 123
ILES, GEORGE
THE STRANGE STORY OF THE FLOWERS: A CHAPTER IN MODERN BOTANY
Dress is important, whether natural or artificial. Because
they catch dust on their clothes, bees, moths and butterflies
have brought about myriad espousals of flower with flower.
Colours and scents of blossoms attract insects. A flower
which in form, scent or hue varies gainfully is likely to
survive while others perish. All the parts of a flower are
leaves in disguise. Floral modes of repulsion and defence.
Plants which devour insects, a habit gradually acquired. The
mesquit tree tells of water. Plants believed to indicate
mineral veins. Seeds as emigrants equipped with wings or
hooks. Parasitic plants and their degradation. Tenants that
pay a liberal rent. The gardener as a creator of new flowers.
The modern sugar beet due to Mons. Vilmorin. 139
THE NATURALIST AS
INTERPRETER AND
SEER
THE ORIGIN OF SPECIES: THE ARGUMENT IN SUMMARY
CHARLES DARWIN
[Charles Darwin, one of the greatest men of all time, did
more to advance and prove the theory of evolution than
anybody else who ever lived. This he accomplished by virtue
of the highest gifts of observation, experiment, and
generalization. His truthfulness, patience, and calmness of
judgment have never been exceeded by mortal. His works are
published by D. Appleton & Co., New York, together with his
"Life and Letters," edited by his son Francis. From "The
Origin of Species" the argument in summary is here given.]
On the view that species are only strongly marked and permanent
varieties, and that each species first existed as a variety, we can see
why it is that no line of demarcation can be drawn between species,
commonly supposed to have been produced by special acts of creation, and
varieties which are acknowledged to have been produced by secondary
laws. On this same view we can understand how it is that in a region
where many species of a genus have been produced, and where they now
flourish, these same species should present many varieties; for where
the manufactory of species has been active, we might expect, as a
general rule, to find it still in action; and this is the case if
varieties be incipient species. Moreover, the species of the larger
genera, which afford the greater number of varieties or incipient
species, retain to a certain degree the character of varieties; for they
differ from each other by a less amount of difference than do the
species of smaller genera. The closely allied species also of a larger
genera apparently have restricted ranges, and in their affinities they
are clustered in little groups round other species--in both respects
resembling varieties. These are strange relations on the view that each
species was independently created, but are intelligible if each existed
first as a variety.
As each species tends by its geometrical rate of reproduction to
increase inordinately in number; and as the modified descendants of each
species will be enabled to increase by as much as they become more
diversified in habits and structure, so as to be able to seize on many
and widely different places in the economy of nature, there will be a
constant tendency in natural selection to preserve the most divergent
offspring of any one species. Hence, during a long-continued course of
modification, the slight differences of characteristic of varieties of
the same species, tend to be augmented into the greater differences
characteristic of the species of the same genus. New and improved
varieties will inevitably supplant and exterminate the older, less
improved, and intermediate varieties; and thus species are rendered to a
large extent defined and distinct objects. Dominant species belonging
to the larger groups within each class tend to give birth to new and
dominant forms; so that each large group tends to become still larger,
and at the same time more divergent in character. But as all groups
cannot thus go on increasing in size, for the world would not hold them,
the more dominant groups beat the less dominant. This tendency in the
large groups to go on increasing in size and diverging in character,
together with the inevitable contingency of much extinction, explains
the arrangement of all the forms of life in groups subordinate to
groups, all within a few great classes, which has prevailed throughout
all time. This grand fact of the grouping of all organic beings under
what is called the Natural System, is utterly inexplicable on the theory
of creation.
As natural selection acts solely by accumulating slight, successive,
favourable variations, it can produce no great or sudden modifications;
it can act only by short and slow steps. Hence, the canon of "Nature
makes no leaps," which every fresh addition to our knowledge tends to
confirm, is on this theory intelligible. We can see why throughout
nature the same general end is gained by an almost infinite diversity of
means, for every peculiarity when once acquired is long inherited, and
structures already modified in many different ways have to be adapted
for the same general purpose. We can, in short, see why nature is
prodigal in variety, though niggard in innovation. But why this should
be a law of nature if each species has been independently created no man
can explain.
Many other facts are, as it seems to me, explicable on this theory. How
strange it is that a bird, under the form of a woodpecker, should prey
on insects on the ground; that upland geese which rarely or never swim,
would possess webbed feet; that a thrush-like bird should dive and feed
on sub-aquatic insects; and that a petrel should have the habits and
structure fitting it for the life of an auk! and so in endless other
cases. But on the view of each species constantly trying to increase in
number, with natural selection always ready to adapt the slowly varying
descendants of each to any unoccupied or ill-occupied place in nature,
these facts cease to be strange, or might even have been anticipated.
We can to a certain extent understand how it is that there is so much
beauty throughout nature; for this may be largely attributed to the
agency of selection. That beauty, according to our sense of it, is not
universal, must be admitted by every one who will look at some venomous
snakes, at some fishes, and at certain hideous bats with a distorted
resemblance to the human face. Sexual selection has given the most
brilliant colours, elegant patterns, and other ornaments to the males,
and sometimes to both sexes of many birds, butterflies and other
animals. With birds it has often rendered the voice of the male musical
to the female, as well as to our ears. Flowers and fruit have been
rendered conspicuous by brilliant colours in contrast with the green
foliage, in order that the flowers may be easily seen, visited and
fertilized by insects, and the seeds disseminated by birds. How it comes
that certain colours, sounds and forms should give pleasure to man and
the lower animals, that is, how the sense of beauty in its simplest form
was first acquired, we do not know any more than how certain odours and
flavours were first rendered agreeable.
As natural selection acts by competition, it adopts and improves the
inhabitants of each country only in relation to their co-inhabitants; so
that we need feel no surprise at the species of any one country,
although on the ordinary view supposed to have been created and
specially adapted for that country, being beaten and supplanted by the
naturalized productions from another land. Nor ought we marvel if all
the contrivances in nature be not, as far as we can judge, absolutely
perfect, as in the case even of the human eye; or if some of them be
abhorrent to our ideas of fitness. We need not marvel at the sting of
the bee, when used against an enemy, causing the bee's own death; at
drones being produced in such great numbers for one single act, and
being then slaughtered by their sterile sisters; at the astonishing
waste of pollen by our fir trees; at the instinctive hatred of the queen
bee for her own fertile daughters; at ichneumonidæ feeding within the
living bodies of caterpillars; or at other such cases. The wonder
indeed, is, on the theory of natural selection, that more cases of the
want of absolute perfection have not been detected.
The complex and little known laws governing production of varieties are
the same, as far as we can judge, with the laws which have governed the
production of distinct species. In both cases physical conditions seem
to have produced some direct and definite effect, but how much we cannot
say. Thus, when varieties enter any new station, they occasionally
assume some of the characters proper to the species of that station.
With both varieties and species, use and disuse seem to have produced a
considerable effect; for it is impossible to resist this conclusion when
we look, for instance, at the logger-headed duck, which has wings
incapable of flight, in nearly the same condition as in the domestic
duck; or when we look at the burrowing tucu-tucu, which is occasionally
blind, and then at certain moles, which are habitually blind and have
their eyes covered with skin; or when we look at the blind animals
inhabiting the dark caves of America and Europe. With varieties and
species, correlated variation seems to have played an important part, so
that when one part has been modified other parts have been necessarily
modified. With both varieties and species, reversions to long-lost
characters occasionally occur. How inexplicable on the theory of
creation is the occasional appearance of stripes on the shoulders and
legs of the several species of the horse-genus and of their hybrids! How
simply is this fact explained if we believe that these species are all
descended from a striped progenitor, in the same manner as the several
domestic breeds of the pigeon are descended from the blue and barred
rock pigeon!
On the ordinary view of each species having been independently created,
why should specific characters, or those by which the species of the
same genus differ from each other, be more variable than generic
characters in which they all agree? Why, for instance, should the colour
of a flower be more likely to vary in any one species of genus, if the
other species possess differently coloured flowers, than if all
possessed the same coloured flowers? If species are only well-marked
varieties, of which the characters have become in a high degree
permanent, we can understand this fact; for they have already varied
since they branched off from a common progenitor in certain characters,
by which they have come to be specifically different from each other;
therefore these same characters would be more likely again to vary than
the generic characters which have been inherited without change for an
immense period. It is inexplicable on the theory of creation why a part
developed in a very unusual manner in one species alone of a genus, and
therefore, as we may naturally infer, of great importance to that
species, should be eminently liable to variation; but, on our view,
this part has undergone, since the several species branched off from a
common progenitor, an unusual amount of variability and modification,
and therefore we might expect the part generally to be still variable.
But a part may be developed in the most unusual manner, like the wing of
a bat, and yet not be more variable than any other structure, if the
part be common to many subordinate forms, that is, if it has been
inherited for a very long period; for in this case it will have been
rendered constant by long-continued natural selection.
Glancing at instincts, marvellous as some are, they offer no greater
difficulty than do corporeal structures on the theory of the natural
selection of successive, slight, but profitable modifications. We can
thus understand why nature moves by graduated steps in endowing certain
animals of the same class with their several instincts. I have attempted
to show how much light the principle of gradation throws on the
admirable architectural powers of the hive-bee. Habit no doubt often
comes into play in modifying instincts; but it certainly is not
indispensable, as we see in the case of neuter insects, which leave no
progeny to inherit the effects of long-continued habit. On the view of
all the species of the same genus having descended from a common parent,
and having inherited much in common, we can understand how it is that
allied species, when placed under widely different conditions of life,
yet follow nearly the same instincts; why the thrushes of temperate and
tropical South America, for instance, line their nests with mud like our
British species. On the view of instincts having been slowly acquired
through natural selection, we need not marvel at some instincts being
not perfect and liable to mistakes, and at many instincts causing other
animals to suffer.
If species be only well-marked and permanent varieties, we can see at
once why their crossed offspring should follow the same complex laws in
their degrees and kinds of resemblance to their parents--in being
absorbed into each other by successive crosses, and in other such
points--as do the crossed offspring of acknowledged varieties. This
similarity would be a strange fact, if species had been independently
created and varieties had been produced through secondary laws.
If we admit that the geological record is imperfect to an extreme
degree, then the facts, which the record does give, strongly support the
theory of descent with modification. New species have come on the stage
slowly and at successive intervals; and the amount of change after equal
intervals of time, is widely different in different groups. The
extinction of species and of whole groups of species, which has played
so conspicuous a part in the history of the organic world, almost
inevitably follows from the principle of natural selection; for old
forms are supplanted by new and improved forms. Neither single species
nor groups of species reappear when the chain of ordinary generation is
once broken. The gradual diffusion of dominant forms, with the slow
modification of their descendants, causes the forms of life, after long
intervals of time, to appear as if they had changed simultaneously
throughout the world. The fact of the fossil remains of each formation
being in some degree intermediate in character between the fossils in
the formations above and below, is simply explained by their
intermediate position in the chain of descent. The grand fact that all
extinct beings can be classed with all recent beings, naturally follows
from the living and the extinct being the offspring of common parents.
As species have generally diverged in character during their long course
of descent and modification, we can understand why it is that the more
ancient forms, or early progenitors of each group, so often occupy a
position in some degree intermediate between existing groups. Recent
forms are generally looked upon as being, on the whole, higher in the
scale of organization than ancient forms; and they must be higher, in so
far as the later and more improved forms have conquered the older and
less improved forms in the struggle for life; they have also generally
had their organs more specialized for different functions. This fact is
perfectly compatible with numerous beings still retaining simple but
little improved structures, fitted for simple conditions of life; it is
likewise compatible with some forms having retrograded in organization,
by having become at each stage of descent better fitted for new and
degraded habits of life. Lastly, the wonderful law of the long endurance
of allied forms on the same continent--of marsupials [as kangaroos] in
Australia, of edentata [as armadillos, sloths, and anteaters] in
America, and other such cases--is intelligible, for within the same
country the existing and the extinct will be closely allied by descent.
Looking to geographical distribution, if we admit that there has been
during the long course of ages much migration from one part of the world
to another, owing to former climatical and geographical changes and to
the many occasional and unknown means of dispersal, then we can
understand, on the theory of descent with modification, most of the
great leading facts in distribution. We can see why there should be so
striking a parallelism in the distribution of organic beings throughout
space, and in their geological succession throughout time; for in both
cases the beings have been connected by the bond of ordinary generation,
and the means of modification have been the same. We see the full
meaning of the wonderful fact, which has struck every traveller, namely,
that on the same continent, under the most diverse conditions, under
heat and cold, on mountain and lowland, on deserts and marshes, most of
the inhabitants within each great class are plainly related; for they
are the descendants of the same progenitors and early colonists. On this
same principle of former migration, combined in most cases with
modification, we can understand by the aid of the Glacial period, the
identity of some few plants and the close alliance of many others, on
the most distant mountains, and in the northern and southern temperate
zones; and likewise the close alliance of some of the inhabitants of the
sea in the northern and southern temperate latitudes, though separated
by the whole inter-tropical ocean. Although two countries may present
physical conditions as closely similar as the same species ever acquire,
we need feel no surprise at their inhabitants being widely different, if
they have been for a long period completely sundered from each other;
for as the relation of organism to organism is the most important of all
relations, and as the two countries will have received colonists at
various periods and in different proportions, from some other country or
from each other, the course of modification in the two areas will
inevitably have been different.
On this view of migration, with subsequent modification, we see why
oceanic islands are inhabited by only few species, but of these, why
many are peculiar or endemic forms. We clearly see why species belonging
to those groups of animals which cannot cross wide spaces of the ocean,
as frogs and terrestrial mammals, do not inhabit oceanic islands; and
why, on the other hand, new and peculiar species of bats, animals which
can traverse the ocean, are often found on islands far distant from any
continent. Such cases as the presence of peculiar species of bats on
oceanic islands and the absence of all other terrestrial mammals, are
facts utterly inexplicable on the theory of independent acts of
creation.
The existence of closely allied representative species in any two areas,
implies on the theory of descent with modification, that the same
parent-forms formerly inhabited both areas: and we almost invariably
find that wherever many closely allied species inhabit two areas, some
identical species are still common to both. Wherever many closely allied
yet distant species occur, doubtful forms and varieties belonging to the
same groups likewise occur. It is a rule of high generality that the
inhabitants of each area are related to the inhabitants of the nearest
source whence immigrants might have been derived. We see this in the
striking relation of nearly all the plants and animals of the Galapagos
Archipelago, of Juan Fernandez, and of the other American islands, to
the plants and animals of the neighbouring American mainland; and of
those of the Cape Verde Archipelago, and of the other African islands to
the African mainland. It must be admitted that these facts receive no
explanation on the theory of creation.
The fact, as we have seen, that all past and present organic beings can
be arranged within a few great classes, in groups subordinate to groups,
and with the extinct groups often falling in between the recent groups,
is intelligible on the theory of natural selection with its
contingencies of extinction and divergence of character. On these same
principles we see how it is that the mutual affinities of the forms
within each class are so complex and circuitous. We see why certain
characters are far more serviceable than others for classification; why
adaptive characters derived from rudimentary parts, though of no service
to the beings, are often of high classificatory value; and why
embryological characters are often the most valuable of all. The real
affinities of all organic beings, in contradistinction to their adaptive
resemblances, are due to inheritance or community of descent. The
Natural System is a genealogical arrangement, with the acquired grades
of difference, marked by the terms, varieties, species, genera,
families, etc.; and we have to discover the lines of descent by the most
permanent characters, whatever they may be, and of however slight vital
importance.
The similar framework of bones in the hand of a man, wing of a bat, fin
of the porpoise, and leg of the horse--the same number of vertebræ
forming the neck of the giraffe and of the elephant--and innumerable
other such facts, at once explain themselves on the theory of descent
with slow and slight successive modifications. The similarity of pattern
in the wing and in the leg of a bat, though used for such different
purpose--in the jaws and legs of a crab--in the petals, stamens, and
pistils of a flower, is likewise, to a large extent, intelligible on
the view of the gradual modification of parts or organs, which were
aboriginally alike in an early progenitor in each of these classes. On
the principle of successive variations not always supervening at an
early age, and being inherited at a corresponding not early period of
life, we clearly see why the embryos of mammals, birds, reptiles, and
fishes should be so closely similar, and so unlike the adult forms. We
may cease marvelling at the embryo of an air-breathing mammal or bird
having branchial slits and arteries running in loops, like those of a
fish which has to breathe the air dissolved in water by the aid of
well-developed branchiæ [gills].
Disuse, aided sometimes by natural selection, will often have reduced
organs when rendered useless under changed habits or conditions of life;
and we can understand on this view the meaning of rudimentary organs.
But disuse and selection will generally act on each creature, when it
has come to maturity and has to play its full part in the struggle for
existence, and will thus have little power in an organ during early
life; hence the organ will not be reduced or rendered rudimentary at
this early age. The calf, for instance, has inherited teeth, which never
cut through the gums of the upper jaw, from an early progenitor having
well-developed teeth; and we may believe, that the teeth in the mature
animal were formerly reduced by disuse, owing to the tongue and palate,
or lips, having become excellently fitted through natural selection to
browse without their aid; whereas in the calf, the teeth have been left
unaffected, and on the principle of inheritance at corresponding ages
have been inherited from a remote period to the present day. On the view
of each organism with all its separate parts having been specially
created, how utterly inexplicable is it that organs bearing the plain
stamp of inutility, such as the teeth in the embryonic calf or the
shrivelled wings under the soldered wing covers of many beetles, should
so frequently occur. Nature may be said to have taken pains to reveal
her scheme of modification, by means of rudimentary organs, of
embryological and homologous [corresponding] structures, but we are too
blind to understand her meaning.
I have now recapitulated the facts and considerations which have
thoroughly convinced me that species have been modified, during a long
course of descent. This has been effected chiefly through the natural
selection of numerous successive, slight, favourable variations; aided
in an important manner by the inherited effects of the use and disuse of
parts; and in an unimportant manner, that is, in relation to adaptive
structures, whether past or present, by the direct action of external
conditions, and by variations which seem to us in our ignorance to arise
spontaneously. It appears that I formerly underrated the frequency and
value of these latter forms of variation, as leading to permanent
modifications of structure independently of natural selection. But as
my conclusions have lately been much misrepresented, and it has been
stated that I attribute the modification of species exclusively to
natural selection, I may be permitted to remark that in the first
edition of this work, and subsequently, I placed in a most conspicuous,
position--namely, at the close of the Introduction--the following words:
"I am convinced that natural selection has been the main but not the
exclusive means of modification." This has been of no avail. Great is
the power of steady misrepresentation; but the history of science shows
that fortunately this power does not long endure.
It can hardly be supposed that a false theory would explain, in so
satisfactory a manner as does the theory of natural selection, the
several large classes of facts above specified. It has recently been
objected that this is an unsafe method of arguing; but it is a method
used in judging the common events of life, and has often been used by
the greatest natural philosophers. The undulatory theory of light has
thus been arrived at; and the belief in the revolution of the earth on
its own axis was until lately supported by hardly any direct evidence.
It is no valid objection that science as yet throws no light on the far
higher problems of the essence of the origin of life. Who can explain
what is the essence of the attraction of gravity? No one now objects to
following out the results consequent on this unknown element of
attraction; notwithstanding that Leibnitz formerly accused Newton of
introducing "occult qualities and miracles into philosophy."
I see no good reasons why the views given in this volume should shock
the religious feelings of any one. It is satisfactory, as showing how
transient such impressions are, to remember that the greatest discovery
ever made by man, namely, the law of the attraction of gravity, was also
attacked by Leibnitz, "as subversive of natural, and inferentially of
revealed religion." A celebrated author and divine has written to me
that "he has gradually learned to see that it is just as noble a
conception of the Deity to believe that He created a few original forms
capable of self-development into other and needful forms, as to believe
that He required a fresh act of creation to supply the voids caused by
the action of His laws."
Why, it may be asked, until recently did nearly all the most eminent
living naturalists and geologists disbelieve in the mutability of
species? It cannot be asserted that organic beings in a state of nature
are subject to no variation; it cannot be proved that the amount of
variation in the course of long ages is a limited quantity; no clear
distinction has been, or can be, drawn between species and well-marked
varieties. It cannot be maintained that species when intercrossed are
invariably sterile and varieties invariably fertile; or that sterility
is a special endowment and sign of creation. The belief that species
were immutable productions was almost unavoidable as long as the
history of the world was thought to be of short duration; and now that
we have acquired some idea of the lapse of time, we are too apt to
assume, without proof, that the geological record is so perfect that it
would have afforded us plain evidence of the mutation of species, if
they had undergone mutation.
But the chief cause of our natural unwillingness to admit that one
species has given birth to other and distinct species, is that we are
always slow in admitting great changes of which we do not see the steps.
The difficulty is the same as that felt by so many geologists, when
Lyell first insisted that long lines of inland cliffs had been formed,
and great valleys excavated, by the agencies which we still see at work.
The mind cannot possibly grasp the full meaning of the term of even a
million years; it cannot add up and perceive the full effects of many
slight variations, accumulated during an almost infinite number of
generations.
Although I am fully convinced of the truth of the views given in this
volume under the form of an abstract, I by no means expect to convince
experienced naturalists whose minds are stocked with a multitude of
facts all viewed, during a long course of years, from a point of view
directly opposite to mine. It is so easy to hide our ignorance under
such expressions as the "plan of creation," "unity of design," etc., and
to think that we give an explanation when we only restate a fact. Any
one whose disposition leads him to attach more weight to unexplained
difficulties than to the explanation of a certain number of facts will
certainly reject the theory. A few naturalists, endowed with much
flexibility of mind, and who have already begun to doubt the
immutability of species, may be influenced by this volume; but I look
with confidence to the future, to young and rising naturalists, who will
be able to view both sides of the question with impartiality. Whoever is
led to believe that species are mutable will do good service by
conscientiously expressing his conviction; for thus only can the load of
prejudice by which this subject is overwhelmed be removed.
Several eminent naturalists have of late published their belief that a
multitude of reputed species in each genus are not real species; but
that other species are real, that is, have been independently created.
This seems to me a strange conclusion to arrive at. They admit that a
multitude of forms, which till lately they themselves thought were
special creations, and which are still thus looked at by the majority of
naturalists, and which consequently have all the external characteristic
features of true species--they admit that these have been produced by
variation, but they refuse to extend the same view to other and slightly
different forms. Nevertheless, they do not pretend that they can define,
or even conjecture, which are the created forms of life, and which are
those produced by secondary laws. They admit variation as a true cause
in one case, they arbitrarily reject it in another, without assigning
any distinction in the two cases. The day will come when this will be
given as a curious illustration of the blindness of preconceived
opinion. These authors seem no more startled at a miraculous act of
creation than at an ordinary birth. But do they really believe that at
innumerable periods in the earth's history certain elemental atoms have
been commanded suddenly to flash into living tissues? Do they believe
that at each supposed act of creation one individual or many were
produced? Were all the infinite numerous kinds of animals and plants
created as eggs or seed, or as full grown? and in the case of mammals,
were they created bearing the false marks of nourishment from the
mother's womb? Undoubtedly some of these same questions cannot be
answered by those who believe in the appearance or creation of only a
few forms of life, or of some one form alone. It has been maintained by
several authors that it is as easy to believe in the creation of a
million beings as of one; but Maupertuis's philosophical axiom "of least
action" leads the mind more willingly to admit the smaller number; and
certainly we ought not to believe that innumerable beings within each
great class have been created with plain, but deceptive, marks of
descent from a single parent.
As a record of a former state of things, I have retained in the
foregoing paragraphs, and elsewhere, several sentences which imply that
naturalists believe in the separate creation of each species; and I have
been much censured for having thus expressed myself. But undoubtedly
this was the general belief when the first edition of the present work
appeared. I formerly spoke to very many naturalists on the subject of
evolution, and never once met with any sympathetic agreement. It is
probable that some did then believe in evolution, but they were either
silent or expressed themselves so ambiguously that it was not easy to
understand their meaning. Now, things are wholly changed, and almost
every naturalist admits the great principle of evolution. There are,
however, some who still think that species have suddenly given birth,
through quite unexplained means, to new and totally different forms.
But, as I have attempted to show, weighty evidence can be opposed to the
admission of great and abrupt modifications. Under a scientific point of
view, and as leading to further investigation, but little advantage is
gained by believing that new forms are suddenly developed in an
inexplicable manner from old and widely different forms, over the old
belief in the creation of species from the dust of the earth.
It may be asked how far I extend the doctrine of the modification of
species. The question is difficult to answer, because the more distinct
the forms are which we consider, by so much the arguments in favour of
community of descent become fewer in number and less in force. But some
arguments of the greatest weight extend very far. All the members of
whole classes are connected together by a chain of affinities, and all
can be classed on the same principle, in groups subordinate to groups.
Fossil remains sometimes tend to fill up very wide intervals between
existing orders.
Organs in a rudimentary condition plainly show that an early progenitor
had the organ in a fully developed condition, and this in some cases
implies an enormous amount of modification in the descendants.
Throughout whole classes various structures are formed on the same
pattern, and at a very early age the embryos closely resemble each
other. Therefore I cannot doubt that the theory of descent with
modification embraces all the members of the same great class or
kingdom. I believe that animals are descended from at most only four or
five progenitors, and plants from an equal or lesser number.
Analogy would lead me one step further, namely, to the belief that all
animals and plants are descended from some one prototype. But analogy
may be a deceitful guide. Nevertheless all living things have much in
common, in their chemical composition, their cellular structure, their
laws of growth, and their liability to injurious influences. We see this
even in so trifling a fact as that the same poison often similarly
affects plants and animals; or that the poison secreted by the gall-fly
produces monstrous growths on the wild rose or oak tree. With all
organic beings, excepting perhaps some of the very lowest, sexual
reproduction seems to be essentially similar. With all, as far as is at
present known, the germinal vesicle is the same; so that all organisms
start from a common origin. If we look even to the two main
divisions--namely, to the animal and vegetable kingdoms--certain low
forms are so far intermediate in character that naturalists have
disputed to which kingdom they should be referred. As Professor Asa Gray
has remarked, "the spores and other reproductive bodies of many of the
lower algæ may claim to have first a characteristically animal, and then
an unequivocally vegetable existence." Therefore, on the principle of
natural selection with divergence of character, it does not seem
incredible that, from some such low and intermediate form, both animals
and plants may have been developed; and, if we admit this, we must
likewise admit that all the organic beings which have ever lived on this
earth may be descended from some one primordial form. But this inference
is chiefly grounded on analogy, and it is immaterial whether or not it
is accepted. No doubt it is possible, as Mr. G. H. Lewes has urged, that
at the first commencement of life many different forms were evolved; but
if so, we may conclude that only a very few have left modified
descendants. For, as I have recently remarked in regard to the members
of each great kingdom, such as the Vertebrata, Articulata, etc., we
have distinct evidence in their embryological, homologous, and
rudimentary structures, that within each kingdom all the members are
descended from a single progenitor.
When the views advanced by me in this volume, and by Mr. Wallace, or
when analogous views on the origin of species are generally admitted, we
can dimly foresee that there will be a considerable revolution in
natural history. Systematists will be able to pursue their labours as at
present; but they will not be incessantly haunted by the shadowy doubt
whether this or that form be a true species. This, I feel sure and I
speak after experience, will be no slight relief. The endless disputes
whether or not some fifty species of British brambles are good species
will cease. Systematists will have only to decide (not that this will be
easy) whether any form be sufficiently constant and distinct from other
forms, to be capable of definition; and if definable, whether the
differences be sufficiently important to deserve a specific name. This
latter point will become a far more essential consideration than it is
at present; for differences, however slight, between any two forms, if
not blended by intermediate gradations, are looked at by most
naturalists as sufficient to raise both forms to the rank of species.
Hereafter we shall be compelled to acknowledge that the only distinction
between species and well-marked varieties is, that the latter are known,
or believed to be connected at the present day by intermediate
gradations, whereas species were formerly thus connected. Hence, without
rejecting the considerations of the present existence of intermediate
gradations between any two forms, we shall be led to weigh more
carefully and to value higher the actual amount of difference between
them. It is quite possible that forms now generally acknowledged to be
merely varieties may hereafter be thought worthy of specific names; and
in this case scientific and common language will come into accordance.
In short, we shall have to treat species in the same manner as those
naturalists treat genera, who admit that genera are merely artificial
combinations made for convenience. This may not be a cheering prospect;
but we shall at least be freed from the vain search for the undiscovered
and undiscoverable essence of the term species.
The other and more general departments of natural history will rise
greatly in interest. The terms used by naturalists, of affinity,
relationship, community of type, paternity, morphology [the science of
organic form], adaptive characters, rudimentary and aborted organs,
etc., will cease to be metaphorical and will have a plain signification.
When we no longer look at an organic being as a savage looks at a ship,
as something wholly beyond his comprehension; when we regard every
production of nature as one which has had a long history; when we
contemplate every complex structure and instinct as the summing up of
many contrivances, each useful to the possessor, in the same way as any
great mechanical invention is the summing up of the labour, the
experience, the reason, and even the blunders of numerous workmen; when
we thus view each organic being, how far more interesting--I speak from
experience--does the study of natural history become!
A grand and almost untrodden field of inquiry will be opened, on the
causes and laws of variation, on correlation, on the effects of use and
disuse, on the direct action of external conditions, and so forth. The
study of domestic productions will rise immensely in value. A new
variety raised by man will be a more important and interesting subject
for study than one more species added to the infinitude of already
recorded species. Our classifications will come to be, as far as they
can be so made, genealogies; and will then truly give what may be called
the plan of creation. The rules for classifying will no doubt become
simpler when we have a definite object in view. We possess no pedigree
or armorial bearings; and we have to discover and trace the many
diverging lines of descent in our natural genealogies, by characters of
any kind which have long been inherited. Rudimentary[1] organs will
speak infallibly with respect to the nature of long-lost structures.
Species and groups of species which are called aberrant, and which may
fancifully be called living fossils, will aid us in forming a picture of
the ancient forms of life. Embryology will often reveal to us the
structure, in some degree obscured, of the prototypes of each great
class.
When we can feel assured that all the individuals of the same species,
and all the closely allied species of most genera, have, within a not
very remote period descended from one parent, and have migrated from
some one birth-place; and when we better know the many means of
migration, then, by the light which geology now throws, and will
continue to throw, on former changes of climate and of the level of the
land, we shall surely be enabled to trace in an admirable manner the
former migrations of the inhabitants of the whole world. Even at
present, by comparing the differences between the inhabitants of the sea
on the opposite sides of a continent, and the nature of the various
inhabitants on that continent in relation to their apparent means of
immigration, some light can be thrown on ancient geography.
The noble science of geology loses glory from the extreme imperfection
of the record. The crust of the earth, with its imbedded remains, must
not be looked at as a well-filled museum, but as a poor collection made
at hazard and at rare intervals. The accumulation of each great
fossiliferous formation will be recognized as having depended on an
unusual occurrence of favourable circumstances, and the blank intervals
between the successive stages as having been of vast duration. But we
shall be able to gauge with some security the duration of these
intervals by a comparison of the preceding and succeeding organic forms.
We must be cautious in attempting to correlate as strictly
contemporaneous two formations, which do not include many identical
species, by the general succession of the forms of life.
As species are produced and exterminated by slowly acting and still
existing causes, and not by miraculous acts of creation; and as the most
important of all causes of organic change is one which is almost
independent of altered and perhaps suddenly altered physical conditions,
namely, the mutual relation of organism to organism--the improvement of
one organism entailing the improvement or the extermination of others;
it follows, that the amount of organic change in the fossils of
consecutive formations probably serves as a fair measure of the
relative, though not actual lapse of time. A number of species, however,
keeping in a body might remain for a long period unchanged, while within
the same period, several of these species, by migrating into new
countries and coming into competition with foreign associates, might
become modified; so that we must not overrate the accuracy of organic
change as a measure of time.
In the future I see open fields for far more important researches.
Psychology will be securely based on the foundation already well laid by
Mr. Herbert Spencer, that of the necessary acquirement of each mental
power and capacity by gradation. Much light will be thrown on the
origin of man and his history.
Authors of the highest eminence seem to be fully satisfied with the view
that each species has been independently created. To my mind it accords
better with what we know of the laws impressed on matter by the Creator,
that the production and extinction of the past and present inhabitants
of the world should have been due to secondary causes, like those
determining the birth and death of the individual. When I view all
beings as not special creations, but as the lineal descendants of some
few beings which lived long before the first bed of the Cambrian system
was deposited, they seem to me to become ennobled. Judging from the
past, we may safely infer that not one living species will transmit its
unaltered likeness to a distant futurity. And of the species now living
very few will transmit progeny of any kind to a far distant futurity;
for the manner in which all organic beings are grouped, shows that the
greater number of species in each genus, and all the species in many
genera, have left no descendants, but have become utterly extinct. We
can so far take a prophetic glance into futurity as to foretell that it
will be the common and widely spread species, belonging to the larger
and dominant groups within each class, which will ultimately prevail and
procreate new and dominant species. As all the living forms of life are
the lineal descendants of those which lived long before the Cambrian
epoch, we may feel certain that the ordinary succession by generation
has never once been broken, and that no cataclysm has desolated the
whole world. Hence, we may look with some confidence to a secure future
of great length. And as natural selection works solely by and for the
good of each being, all corporeal and mental endowments will tend to
progress toward perfection.
It is interesting to contemplate a tangled bank, clothed with many
plants of many kinds, with birds singing on the bushes, with various
insects flitting about, and with worms crawling through the damp earth,
and to reflect that these elaborately constructed forms, so different
from each other, and dependent upon each other in so complex a manner,
have all been produced by laws acting around us. These laws taken in the
largest sense, being growth with reproduction; Inheritance which is
almost implied by reproduction; Variability from the indirect and direct
action of the conditions of life, and from use and disuse: a Ratio of
Increase so high as to lead to a Struggle for Life, and as a consequence
to Natural Selection, entailing divergence of Character and the
Extinction of less improved forms. Thus, from the war of nature, from
famine and death, the most exalted object which we are capable of
conceiving, namely, the production of the higher animals, directly
follows. There is grandeur in this view of life, with its several
powers, having been originally breathed by the Creator into a few forms
or into one; and that, while this planet has gone circling on according
to the fixed law of gravity, from so simple a beginning endless forms
most beautiful and most wonderful have been, and are being evolved.
FOOTNOTES:
[1] _Vestigial_ is now preferred to _rudimentary_ as a term.--Ed.
HOW "THE ORIGIN OF SPECIES" CAME TO BE WRITTEN.
[An extract from the autobiography of Charles Darwin, in "The
Life and Letters of Charles Darwin," New York, D. Appleton &
Co.]
From September, 1854, I devoted my whole time to arranging my huge pile
of notes, to observing and to experimenting in relation to the
transmutation of species. During the voyage of the _Beagle_ I had been
deeply impressed by discovering in the Pampean formation great fossil
animals covered with armour like that on the existing armadillos;
secondly, by the manner in which closely allied animals replace one
another in proceeding southwards over the continent; and, thirdly, by
the South American character of most of the productions of the Galapagos
Archipelago, and more especially by the manner in which these differ
slightly on each island of the group, none of these islands appearing to
be very ancient in a geological sense.
It was evident that such facts as these, as well as many others, could
only be explained on the supposition that species gradually become
modified; and the subject haunted me. But it was equally evident that
neither the action of the surrounding conditions, nor the will of the
organisms (especially in the case of plants) could account for the
innumerable cases in which organisms of every kind are beautifully
adapted to their habits of life--for instance, a woodpecker or a
tree-frog to climb trees, or a seed for dispersal by hooks or plumes. I
had always been much struck by such adaptations, and until these could
be explained it seemed to me almost useless to endeavour to prove by
indirect evidence that species have been modified.
After my return to England it appeared to me that by following the
example of Lyell in geology,[2] and by collecting all facts that bore in
any way on the variation of animals and plants under domestication and
nature, some light might perhaps be thrown on the whole subject. My
first note-book was opened in July, 1837. I worked on true Baconian
principles, and without any theory collected facts on a wholesale scale,
more especially with respect to domesticated productions, by printed
enquiries, by conversation with skilful breeders and gardeners and by
extensive reading. When I see the list of books of all kinds which I
read and abstracted, including whole series of journals and
translations, I am surprised at my industry. I soon perceived that
selection was the keystone of man's success in making useful races of
animals and plants. But how selection could be applied to organisms
living in a state of nature remained for some time a mystery to me.
In October, 1838, that is fifteen months after I had begun my systematic
enquiry, I happened to read for amusement "Malthus on Population," and
being well prepared to appreciate the struggle for existence which
everywhere goes on from long-continued observation of the habits of
animals and plants, it at once struck me that under these circumstances
favourable variations would tend to be preserved and unfavourable ones
to be destroyed. The result of this would be the formation of a new
species. Here then I had at last got a theory by which to work; but I
was so anxious to avoid prejudice that I determined not for some time to
write even the briefest sketch of it. In June, 1842, I first allowed
myself the satisfaction of writing a very brief abstract of my theory in
pencil in 35 pages; and this was enlarged during the summer of 1844 into
one of 230 pages, which I had fairly copied out and still possess.
But at that time I overlooked one problem of great importance; and it is
astonishing to me, except on the principle of Columbus and his egg, how
I could have overlooked it and its solution. This problem is the
tendency in organic beings descended from the same stock to diverge in
character as they become, modified. That they have diverged greatly is
obvious from the manner in which species of all kinds can be classed
under genera, genera under families, families under sub-orders and so
forth; and I can remember the very spot on the road, whilst in my
carriage, when to my joy the solution occurred to me; and this was long
after I had come to Down. This solution, as I believe, is that the
modified offspring of all dominant and increasing forms tend to become
adapted to many and highly diversified places in the economy of nature.
Early in 1856 Lyell advised me to write out my views pretty fully, and I
began at once to do so on a scale three or four times as extensive as
that which was afterwards followed in my "Origin of Species;" yet it was
only an abstract of the materials which I had collected and I got
through about half the work on this scale. But my plans were overthrown,
for early in the summer of 1858 Mr. Wallace, who was then in the Malay
Archipelago, sent me an essay "On the tendency of varieties to depart
indefinitely from the original type;" and this essay contained exactly
the same theory as mine.[3] Mr. Wallace expressed the wish that if I
thought well of his essay I should send it to Lyell for perusal.
The circumstances under which I consented at the request of Lyell and
Hooker to allow of an abstract from my MS., together with a letter to
Asa Gray, dated September 5, 1857, to be published at the same time
with Wallace's essay, are given in the "Journal of the Proceedings of
the Linnean Society," 1858, p. 45. I was at first very unwilling to
consent, as I thought Mr. Wallace might consider my doing so
unjustifiable, for I did not then know how generous and noble was his
disposition. The extract from my MS. and the letter to Asa Gray had
neither been intended for publication, and were badly written. Mr.
Wallace's essay, on the other hand, was admirably expressed and quite
clear. Nevertheless, our joint productions excited very little
attention, and the only published notice of them which I can remember
was by Professor Haughton of Dublin, whose verdict was that all that was
new in them was false, and what was true was old. This shows how
necessary it is that any new idea should be explained at considerable
length in order to arouse public attention.
In September, 1858, I set to work by the strong advice of Lyell and
Hooker to prepare a volume on the transmutation of species, but was
often interrupted by ill health and short visits to Dr. Lane's
delightful hydropathic establishment at Moor Park. I abstracted the MS.
begun on a much larger scale in 1856, and completed the volume on the
same reduced scale. It cost me thirteen months and ten days' hard labor.
It was published under the title of the "Origin of Species," in
November, 1859. Though considerably added to and corrected in the later
editions, it has remained substantially the same book.
It is no doubt the chief work of my life. It was from the first highly
successful. The first small edition of 1,250 copies was sold on the day
of publication, and a second edition of 3,000 copies soon afterwards.
Sixteen thousand copies have now (1876) been sold in England; and
considering how stiff a book it is, this is a large sale. It has been
translated into almost every European tongue, even into such languages
as Spanish, Bohemian, Polish and Russian. Even an essay in Hebrew has
appeared on it, showing that the theory is contained in the Old
Testament! The reviews were very numerous; for some time all that
appeared on the "Origin" and on my related books, and these amount
(excluding newspaper reviews) to 265; but after a time I gave up the
attempt in despair. Many separate essays and books on the subject have
appeared; and in Germany a catalogue or bibliography on "Darwinismus"
has appeared every year or two.
The success of the "Origin" may, I think, be attributed in large part to
my having long before written two condensed sketches and to my having
abstracted a much larger manuscript, which was itself an abstract. By
this means I was enabled to select the more striking facts and
conclusions. I had also, during many years followed a golden rule,
namely, that whenever a published fact, a new observation or thought
came across me, which was opposed to my general results, to make a
memorandum of it without fail and at once; for I had found by experience
that such facts and thoughts were far more apt to escape from the memory
than favourable ones. Owing to this habit very few objections were
raised against my views which I had not at least noticed and attempted
to answer.
It has sometimes been said that the success of the "Origin" proved "that
the subject was in the air," or "that men's minds were prepared for it."
I do not think that this is strictly true, for I occasionally sounded
not a few naturalists, and never happened to come across a single one
who seemed to doubt about the permanence of species. Even Lyell and
Hooker, though they listened with interest to me, never seemed to agree.
I tried once or twice to explain to able men what I meant by Natural
Selection, but signally failed. What I believe was strictly true is that
innumerable well-observed facts were stored in the minds of naturalists
ready to take their proper places as soon as any theory which would
receive them was sufficiently explained. Another element in the success
of the book was its moderate size; and this I owe to the appearance of
Mr. Wallace's essay; had I published on the scale on which I began to
write in 1856, the book would have been four or five times as large as
the "Origin," and very few would have had the patience to read it.
I gained much by my delay an publishing from about, 1839, when the
theory was clearly conceived, to 1859; and I lost nothing by it, for I
cared very little whether men attributed most originality to me or
Wallace; and his essay no doubt aided in the reception of the theory. I
was forestalled in only one important point, which my vanity has always
made me regret, namely, the explanation by means of the Glacial period
of the presence of the same species of plants and of some few animals on
distant mountain summits and in the arctic regions. This view pleased me
so much that I wrote it out _in extenso_, and I believe that it was read
by Hooker some years before E. Forbes published in 1846 his celebrated
memoir on the subject. In the very few points in which we differed, I
still think that I was in the right. I have never, of course, alluded in
print to my having independently worked out this view.
Hardly any point gave me so much satisfaction when I was at work on the
"Origin," as the explanation of the wide difference in many classes
between the embryo and the adult animal, and of the close resemblance of
the embryos within the same class. No notice of this point was taken, as
far as I remember, in the early reviews of the "Origin," and I recollect
expressing my surprise on this head in a letter to Asa Gray. Within late
years several reviewers have given the whole credit to Fritz Muller and
Haeckel, who undoubtedly have worked it out much more fully and in some
respects more correctly than I did. I had materials for a whole chapter
on the subject, and I ought to have made the discussion longer; for it
is clear that I failed to impress my readers; and he who succeeds in
doing so deserves, in my opinion, all the credit.
This leads me to remark that I have almost always been treated honestly
by my reviewers, passing over those without scientific knowledge as not
worthy of notice. My views have been grossly misrepresented, bitterly
opposed and ridiculed, but this has been generally done as, I believe,
in good faith. On the whole, I do not doubt that my works have been over
and over again greatly overpraised. I rejoice that I have avoided
controversies, and this I owe to Lyell, who many years ago, in reference
to my geological works, strongly advised me never to get entangled in a
controversy, as it rarely did any good and caused a miserable loss of
time and temper.
Whenever I have found out that I have blundered, or that my work has
been imperfect, and when I have been contemptuously criticised, and even
when I have been overpraised, so that I have felt mortified, it has been
my greatest comfort to say hundreds of times to myself that "I have
worked as hard and as well as I could, and no man can do more than
this." I remember when in Good Success Bay, in Tierra del Fuego,
thinking (and, I believe, that I wrote home to the effect) that I could
not employ my life better than in adding a little to Natural Science.
This I have done to the best of my abilities, and critics may say what
they like, but they can not destroy this conviction.
FOOTNOTES:
[2] See Masterpieces of Science, Vol. I, "Earth and Sky," Sir Charles
Lyell on Uniformity in geological change.
[3] The essay appears in "Natural Selection," London, 1870.
THE DESCENT OF MAN
CHARLES DARWIN
[Concluding chapter of "The Descent of Man," New York, D.
Appleton & Co.]
A brief summary will be sufficient to recall to the reader's mind the
more salient points in this work. Many of the views which have been
advanced are highly speculative, and some, no doubt, will prove
erroneous; but I have in every case given the reasons which have led me
to one view rather than to another. It seemed worth while to try how far
the principle of evolution would throw light on some of the more complex
problems in the natural history of man. False facts are highly injurious
to the progress of science, for they often endure long; but false views,
if supported by some evidence, do little harm, for every one takes a
salutary pleasure in proving their falseness; and, when this is done,
one path toward error is closed and the road to truth is often at the
same time opened.
The main conclusion arrived at in this work, and now held by many
naturalists who are well competent to form a sound judgment, is that man
is descended from some less highly organized form. The grounds upon
which this conclusion rests will never be shaken, for the close
similarity between man and the lower animals in embryonic development,
as well as in innumerable points of structure and constitution, both of
high and of the most trifling importance--the rudiments which he
retains, and the abnormal reversions to which he is occasionally
liable--are facts which cannot be disputed. They have long been known,
but, until recently, they told us nothing with respect to the origin of
man. Now, when viewed by the light of our knowledge of the whole organic
world, their meaning is unmistakable. The great principle of evolution
stands up clear and firm when these groups of facts are considered in
connection with others, such as the mutual affinities of the members of
the same group, their geographical distribution in past and present
times, and their geological succession. It is incredible that all these
facts should speak falsely. He who is not content to look, like a
savage, at the phenomena of Nature as disconnected, cannot any longer
believe that man is the work of a separate act of creation. He will be
forced to admit that the close resemblance of the embryo of man to that,
for instance, of a dog--the construction of his skull, limbs and whole
frame on the same plan with that of other mammals--the occasional
appearance of various structures, for instance, of several distinct
muscles, which man does not normally possess, but which are common to
the Quadrumana--and a crowd of analogous facts--all point in the
plainest manner to the conclusion that man is the co-descendant of other
mammals of a common progenitor.
We have seen that man incessantly presents individual differences in all
parts of his body and in his mental faculties. These differences or
variations seem to be induced by the same general causes, and to obey
the same laws as with the lower animals. In both cases similar laws of
inheritance prevail. Man tends to increase at a greater rate than his
means of subsistence; consequently he is occasionally subjected to a
severe struggle for existence, and natural selection will have effected
whatever lies within its scope. A succession of strongly marked
variations of a similar nature is by no means requisite; slight
fluctuating differences in the individual suffice in the work of natural
selection. We may feel assured that the inherited effects of the
long-continued use or disuse of parts will have done much in the same
direction with natural selection. Modifications formerly of importance,
though no longer of any special use, are long-inherited. When one part
is modified other parts change through the principle of correlation, of
which we have instances in many curious cases of correlated
monstrosities. Something may be attributed to the direct and definite
action of the surrounding conditions of life, such as abundant food,
heat or moisture; and, lastly, many characters of slight physiological
importance, some indeed of considerable importance, have been gained
through sexual selection.
No doubt man, as well as every other animal, presents structures, which,
as far as we can judge with our little knowledge, are not now of any
service to him, nor to have been so during any former period of his
existence, either in relation to his general conditions of life, or of
one sex to the other. Such structures cannot be accounted for by any
form of selection, or by the inherited effects of the use and disuse of
parts. We know, however, that many strange and strongly marked
peculiarities of structure occasionally appear in our domesticated
productions, and if the unknown causes which produce them were to act
more uniformly, they would probably become common to all the individuals
of the species. We may hope hereafter to understand something about the
causes of such occasional modifications, especially through the study of
monstrosities; hence, the labours of experimentalists, such as those of
M. Camille Dareste, are full of promise for the future. In general we
can only say that the cause of each slight variation and of each
monstrosity lies much more in the constitution of the organism than in
the nature of the surrounding conditions; though new and changed
conditions certainly play an important part in exciting organic changes
of many kinds.
Through the means just specified, aided perhaps by others as yet
undiscovered, man has been raised to his present state. But since he
attained to the rank of manhood, he has diverged into distinct races,
or, as they may be more fitly called, subspecies. Some of these, such as
the negro and European, are so distinct that, if specimens had been
brought to a naturalist without any further information, they would
undoubtedly have been considered by him as good and true species.
Nevertheless, all the races agree in so many unimportant details of
structure and in so many mental peculiarities, that these can be
accounted for only by inheritance from a common progenitor; and a
progenitor thus characterized would probably deserve to rank as man.
It must not be supposed that the divergence of each race from the other
races, and of all from a common stock, can be traced back to any one
pair of progenitors. On the contrary, at every stage in the process of
modification, all the individuals which were in any way best fitted for
their conditions of life, though in different degrees, would have
survived in greater numbers than the less well-fitted. The process would
have been like that followed by man, when he does not intentionally
select particular individuals, but breeds from all the superior
individuals and neglects all the inferior individuals. He thus slowly
but surely modifies his stock and unconsciously forms a new strain. So
with respect to modifications acquired independently of selection, and
due to variations arising from the nature of the organism and the
action of the surrounding conditions, or from changed habits of life, no
single pair will have been modified in a much greater degree than the
other pairs which inhabit the same country, for all will have been
continually blended through free intercrossing.
By considering the embryological structure of man--the homologies
[parallels] which he presents with the lower animals--the rudiments
which he retains--and the reversions to which he is liable, we can
partly recall in imagination the former condition of our early
progenitors; and can approximately place them in their proper place in
the zoological series. We thus learn that man is descended from a hairy,
tailed quadruped, probably arboreal in its habits [living on or among
trees] and an inhabitant of the Old World. This creature, if its whole
structure had been examined by a naturalist, would have been classed
among the Quadrumana, as surely as the still more ancient progenitor of
the Old and New World monkeys. The Quadrumana and all the higher mammals
are probably derived from an ancient marsupial animal [usually provided
with a pouch for the reception and nourishment of the young, as in the
case of the kangaroo] and this through a long line of diversified forms,
from some reptile-like or some amphibian-like creature, and this again
from some fish-like animal. In the dim obscurity of the past we can see
that the early progenitor of all the Vertebrata must have been an
aquatic animal, provided with branchiæ [gills], with the two sexes
united in the same individual, and with the most important organs of the
body (such as the brain and heart) imperfectly or not at all developed.
This animal seems to have been more like the larvæ of the existing
marine Ascidians than any other known form.
The greatest difficulty which presents itself when we are driven to the
above conclusion on the origin of man is the high standard of
intellectual power and of moral disposition which he has attained. But
every one who admits the principle of evolution must see that the mental
powers of the higher animals, which are the same in kind with those of
man, though so different in degree, are capable of advancement. Thus the
interval between the mental powers of one of the higher apes and of a
fish, or between those of an ant and scale-insect, is immense; yet their
development does not offer any special difficulty; for with our
domesticated animals the mental faculties are certainly variable, and
the variations are inherited. No one doubts that they are of the utmost
importance to animals in a state of nature. Therefore, the conditions
are favourable for their development through natural selection.
The same conclusion may be extended to man; the intellect must have been
all-important to him, even at a very remote period, as enabling him to
invent and use language, to make weapons, tools, traps, etc., whereby
with the aid of his social habits he long ago became the most dominant
of all living creatures.
A great stride in the development of the intellect will have followed,
as soon as the half-art and half-instinct of language came into use; for
the continued use of language will have reacted on the brain and
produced an inherited effect; and this again will have reacted on the
improvement of language. As Mr. Chauncey Wright has well remarked, the
largeness of the brain in man relatively to his body, compared with the
lower animals, may be attributed in chief part to the early use of some
simple form of language--that wonderful engine which affixes signs to
all sorts of objects and qualities, and excites trains of thought which
would never arise from the mere impression of the senses, or if they did
arise could not be followed out. The higher intellectual powers of man,
such as those of ratiocination, abstraction, self-consciousness, etc.,
will have followed from the continued improvement of other mental
faculties; but without considerable culture of the mind, both in the
race and in the individual, it is doubtful whether these high powers
would be exercised and thus fully attained.
The development of the moral qualities is a more interesting problem.
The foundation lies in the social instincts, including under this term
the family ties. These instincts are highly complex, and in the case of
the lower animals give special tendencies toward certain definite
actions; but the more important elements are love and the distinct
emotion of sympathy. Animals endowed with the social instincts take
pleasure in one another's company, warn one another of danger, defend
and aid one another in many ways. These instincts do not extend to all
the individuals of the species, but only to those of the same community.
As they are highly beneficial to the species they have in all
probability been acquired through natural selection.
A moral being is one who is capable of reflecting on his past actions
and their motives--of approving of some and disapproving of others; and
the fact that man is the one being who certainly deserves this
designation is the greatest of all distinctions between him and the
lower animals. But in the fourth chapter I have endeavoured to show that
the moral sense follows, firstly, from the enduring and ever-present
nature of the social instincts; secondly, from man's appreciation of the
approbation and disapprobation of his fellows; and, thirdly, from the
high activity of his mental faculties, with past impressions extremely
vivid; and in these latter respects he differs from the lower animals.
Owing to this condition of mind, man cannot avoid looking both backward
and forward and comparing past impressions. Hence, after some temporary
desire or passion has mastered his social instincts, he reflects and
compares the now weakened impression of such past impulses with the
ever-present social instincts; and he then feels that sense of
dissatisfaction which all unsatisfied instincts leave behind them, he
therefore resolves to act differently for the future--and this is
conscience. Any instinct permanently stronger or more enduring than
another gives rise to a feeling which we express by saying that it ought
to be obeyed. A pointer dog if able to reflect on his past conduct would
say to himself, I ought (as indeed we say of him) to have pointed at
that hare and not have yielded to the passing temptation of hunting it.
Social animals are impelled partly by a wish to aid the members of their
community in a general manner, but more commonly to perform certain
definite actions. Man is impelled by the same general wish to aid his
fellows; but has few or no special instincts. He differs also from the
lower animals in the power of expressing his desires by words, which
thus become a guide to the aid required and bestowed. The motive to give
aid is likewise much modified in man; it no longer consists solely of a
blind instinctive impulse, but is much influenced by the praise or blame
of his fellows. The appreciation and bestowal of praise and blame both
rest on sympathy; and this emotion, as we have seen, is one of the most
important elements of the social instincts. Sympathy, though gained as
an instinct, is also much strengthened by exercise or habit. As all men
desire their own happiness, praise or blame is bestowed on actions or
motives according as they lead to this end; and as happiness is an
essential part of the general good the greatest-happiness principle
indirectly serves as a nearly safe standard of right and wrong. As the
reasoning powers advance and experience is gained the remoter effects of
certain lines of conduct on the character of the individual and on the
general good are perceived; and then the self-regarding virtues come
within the scope of public opinion and receive praise and their
opposites blame. But with the less civilized nations reason often errs,
and many bad customs and base superstitions come within the same scope
and are then esteemed as high virtues and their breach as heavy crimes.
The moral faculties are generally and justly esteemed as of higher value
than the intellectual powers. But we should bear in mind that the
activity of the mind in vividly recalling past impressions is one of the
fundamental though secondary bases of conscience. This affords the
strongest argument for educating and stimulating in all possible ways
the intellectual faculties of every human being. No doubt, a man with a
torpid mind, if his social affections and sympathies are well developed,
will be led to good actions and may have a fairly sensitive conscience.
But whatever renders the imagination more vivid and strengthens the
habit of recalling and comparing past impressions will make the
conscience more sensitive, and may even somewhat compensate for weak
social affections and sympathies.
The moral nature of man has reached its present standard partly through
the advancement of his reasoning powers and consequently of a just
public opinion, but especially from his sympathies having been rendered
more tender and widely diffused through the effects of habit, example,
instruction and reflection. It is not improbable that after long
practice virtuous tendencies may be inherited. With the more civilized
races the conviction of the existence of an all-seeing Deity has had a
potent influence on the advance of morality. Ultimately man does not
accept the praise or blame of his fellows as his sole guide, though few
escape this influence, but his habitual convictions, controlled by
reason, afford him the safest rule. His conscience then becomes the
supreme judge and monitor. Nevertheless, the first foundation or origin
of the moral sense lies in the social instincts, including sympathy; and
these instincts, no doubt, were primarily gained, as in the case of the
lower animals, through natural selection.
The belief in God has often been advanced as not only the greatest but
the most complete of all the distinctions between man and the lower
animals. It is, however, impossible, as we have seen, to maintain that
this belief is innate or instinctive in man. On the other hand, a
belief in all-pervading spiritual agencies seems to be universal, and
apparently follows from a considerable advance in man's reason and from
a still greater advance in his faculties of imagination, curiosity and
wonder. I am aware that the assumed instinctive belief in God has been
used by many persons as an argument for His existence. But this is a
rash judgment, as we should thus be compelled to believe in the
existence of many cruel and malignant spirits, only a little more
powerful than man; for the belief in them is far more general than in a
beneficent Deity. The idea of a universal and beneficent Creator does
not seem to arise in the mind of man until he has been elevated by
long-continued culture.
He who believes in the advancement of man from some low organized form
will naturally ask, How does this bear on the belief in the immortality
of the soul? The barbarous races of man, as Sir J. Lubbock has shown,
possess no clear belief of this kind; but arguments derived from the
primeval beliefs of savages are, as we have just seen, of little or no
avail. Few persons feel any anxiety from the impossibility of
determining at what precise period in the development of the individual,
from the first trace of a minute germinal vesicle, man becomes an
immortal being; and there is no greater cause for anxiety because the
period in the gradually ascending organic scale cannot possibly be
determined.
I am aware that the conclusions arrived at in this work will be
denounced by some as highly irreligious; but he who denounces them is
bound to show why it is more irreligious to explain the origin of man as
a distinct species by descent from some lower form, through the laws of
variation and natural selection, than to explain the birth of the
individual through the laws of ordinary reproduction. The birth both of
the species and of the individual are equally parts of that grand
sequence of events, which our minds refuse to accept as the result of
blind chance. The understanding revolts at such a conclusion, whether or
not we are able to believe that every slight variation of structure, the
union of each pair in marriage, the dissemination of each seed, and
other such events have all been ordained for some special purpose.
Sexual selection has been treated at great length in this work; for, as
I have attempted to show, it has played an important part in the history
of the organic world. I am aware that much remains doubtful, but I have
endeavoured to give a fair view of the whole case. In the lower
divisions of the animal kingdom sexual selection seems to have done
nothing; such animals are often affixed for life to the same spot, or
have the sexes combined in the same individual, or, what is still more
important, their perceptive and intellectual faculties are not
sufficiently advanced to allow of the feelings of love and jealousy, or
of the exertion of choice. When, however, we come to the Arthropoda and
Vertebrata, even to the lowest classes in these two great sub-kingdoms,
sexual selection has effected much; and it deserves notice that we here
find the intellectual faculties developed, but in two very distinct
lines, to the highest standard, namely in the Hymenoptera [ants, bees,
etc.], among the Arthropoda [many insects, spiders, etc.], and in the
Mammalia, including man, among the Vertebrata.
In the most distinct classes of the animal kingdom--in mammals, birds,
fishes, insects and even crustaceans--the differences between the sexes
follow almost exactly the same rules. The males are almost always the
wooers; and they alone are armed with special weapons for fighting with
their rivals. They are generally stronger and larger than the females,
and are endowed with the requisite qualities of courage and pugnacity.
They are provided, either exclusively or in a much higher degree than
the females, with organs for vocal or instrumental music, and with
odoriferous glands. They are ornamented with infinitely diversified
appendages and with the most brilliant or conspicuous colors, often
arranged in elegant patterns, while the females are unadorned. When the
sexes differ in more important structures it is the male which is
provided with special sense-organs for discovering the female, with
locomotive organs for reaching her, and often with prehensile organs
for holding her. These various structures for charming or securing the
female are often developed in the male during only part of the year;
namely, the breeding season. They have in many cases been transferred in
a greater or less degree to the females; and in the latter case they
often appear in her as mere rudiments. They are lost or never gained by
the males after emasculation. Generally they are not developed in the
male during early youth, but appear a short time before the age for
reproduction. Hence, in most cases the young of both sexes resemble each
other; and the female somewhat resembles her young offspring throughout
life. In almost every great class a few anomalous cases occur, where
there has been an almost complete transposition of the characters proper
to the two sexes; the females assuming characters which properly belong
to the males. This surprisingly uniformity in the laws regulating the
differences between the sexes in so many and such widely separated
classes is intelligible if we admit the action throughout all the higher
divisions of the animal kingdom of one common cause; namely, sexual
selection.
Sexual selection depends on the success of certain individuals over
others of the same sex, in relation to the propagation of the species;
while natural selection depends on the success of both sexes, at all
ages, in relation to the general conditions of life. The sexual
struggle is of two kinds; in the one it is between the individuals of
the same sex, generally the males, in order to drive away or kill their
rivals, the females remaining passive; while in the other, the struggle
is likewise between the individuals of the same sex, in order to excite
or charm those of the opposite sex, generally the females, which no
longer remain passive, but select the more agreeable partners. This
latter kind of selection is closely analogous to that which man
unintentionally, yet effectually, brings to bear on his domesticated
productions, when he preserves during a long period the most pleasing or
useful individuals, without any wish to modify the breed.
The laws of inheritance determine whether characters gained through
sexual selection by either sex shall be transmitted to the same sex, or
to both; as well as the age at which they shall be developed. It appears
that variations arising late in life are commonly transmitted to one and
the same sex. Variability is the necessary basis for the action of
selection and is wholly independent of it. It follows from this that
variations of the same general nature have often been taken advantage of
and accumulated through sexual selection in relation to the propagation
of the species, as well as through natural selection in relation to the
general purposes of life. Hence secondary sexual characters, when
equally transmitted to both sexes, can be distinguished from ordinary
specific characters only by the light of analogy. The modifications
acquired through sexual selection are often so strongly pronounced that
the two sexes have frequently been ranked as distinct species, or even
as distinct genera. Such strongly marked differences must be in some
manner highly important; and we know that they have been acquired in
some instances at the cost not only of inconvenience, but of exposure to
actual danger.
The belief in the power of sexual selection rests chiefly on the
following considerations: The characters which we have the best reasons
for supposing to have been thus acquired are confined to one sex; and
this alone renders it probable that in most cases they are connected
with the act of reproduction. These characters in innumerable instances
are fully developed only at maturity; and often during only a part of
the year, which is always the breeding season. The males (passing over a
few exceptional cases) are the more active in courtship; they are the
best armed, and are rendered the most attractive in various ways. It is
to be especially observed that the males display their attractions with
elaborate care in the presence of the females; and that they rarely or
never display them excepting during the season of love. It is incredible
that all this should be purposeless. Lastly, we have distinct evidence
with some quadrupeds and birds that the individuals of one sex are
capable of feeling a strong antipathy or preference for certain
individuals of the other sex.
Bearing in mind these facts and not forgetting the marked results of
man's unconscious selection, it seems to me almost certain that if the
individuals of one sex were during a long series of generations to
prefer pairing with certain individuals of the other sex, characterized
in some peculiar manner, the offspring would slowly but surely become
modified in this same manner. I have not attempted to conceal that,
excepting when the males are more numerous than the females, or when
polygamy prevails, it is doubtful how the more attractive males succeed
in leaving a larger number of offspring to inherit their superiority in
ornaments or other charms than the less attractive males; but I have
shown that this would probably follow from the females--especially the
more vigorous ones, which would be the first to breed--preferring not
only the more attractive but at the same time the more vigorous and
victorious males.
Although we have some positive evidence that birds appreciate bright and
beautiful objects, as with the bower-birds of Australia, and although
they certainly appreciate the power of song, yet I fully admit that it
is astonishing that the females of many birds and some mammals should be
endowed with sufficient taste to appreciate ornaments, which we have
reason to attribute to sexual selection; and this is even more
astonishing in the case of reptiles, fish and insects. But we really
know little about the minds of the lower animals. It cannot be supposed,
for instance, that male birds of paradise or peacocks should take such
pains in erecting, spreading and vibrating their beautiful plumes before
the males for no purpose. We should remember the fact given on excellent
authority in a former chapter that several peahens, when debarred from
an admired male, remained widows during a whole season rather than pair
with another bird.
Nevertheless, I know of no fact in natural history more wonderful than
that the female Argus pheasant should appreciate the exquisite shading
of the ball-and-socket ornaments and the elegant patterns on the wing
feathers of the male. He who thinks that the male was created as he now
exists must admit that the great plumes, which prevent the wings from
being used for flight and which, as well as the primary feathers, are
displayed in a manner quite peculiar to this one species during the act
of courtship, and at no other time, were given to him as an ornament. If
so, he must likewise admit that the female was created and endowed with
the capacity of appreciating such ornaments. I differ only in the
conviction that the male Argus pheasant acquired his beauty gradually,
through the females having preferred during many generations the more
highly ornamented males; the esthetic capacity of the females having
been advanced through exercise or habit just as our own taste is
gradually improved. In the male, through the fortunate chance of a few
feathers not having been modified, we can distinctly see how simple
spots with a little fulvous [tawny] shading on one side may have been
developed by small steps into the wonderful ball-and-socket ornaments;
and it is probable that they were actually thus developed.
Every one who admits the principle of evolution, and yet feels great
difficulty in admitting that female mammals, birds, reptiles and fish,
could have acquired the high taste implied by the beauty of the males,
and which generally coincides with our own standard, should reflect that
the nerve-cells of the brain in the highest as well as in the lowest
members of the Vertebrate series, are derived from those of the common
progenitor of the whole group. It thus becomes intelligible that the
brain and mental faculties should be capable under similar conditions of
nearly the same course of development, and consequently of performing
nearly the same functions.
The reader who has taken the trouble to go through the several chapters
devoted to sexual selection will be able to judge how far the
conclusions at which I have arrived are supported by sufficient
evidence. If he accepts these conclusions he may, I think, safely extend
them to mankind; but it would be superfluous here to repeat what I have
so lately said on the manner in which sexual selection apparently has
acted on man, both on the male and female side, causing the two sexes of
man to differ in body and mind, and the several races to differ from
each other in various characters, as well as from their ancient and
lowly organized progenitors.
He who admits the principle of sexual selection will be led to the
remarkable conclusion that the cerebral system not only regulates most
of the existing functions of the body, but has indirectly influenced the
progressive development of various bodily structures and of certain
mental qualities. Courage, pugnacity, perseverance, strength and size of
body, weapons of all kinds, musical organs, both vocal and instrumental,
bright colours, stripes and marks, and ornamental appendages, have all
been indirectly gained by the one sex or the other, through the
influence of love and jealousy, through the appreciation of the
beautiful in sound, colour or form, and through the exertion of a
choice; and those powers of the mind manifestly depend on the
development of the cerebral system.
Man scans with scrupulous care the character and pedigree of his horses,
cattle and dogs before he matches them; but when he comes to his own
marriage he rarely, or never takes any such care. He is impelled by
nearly the same motives as the lower animals when left to their own free
choice, though he is in so far superior to them that he highly values
mental charms and virtues. On the other hand he is strongly attracted
by mere wealth or rank. Yet he might by selection do something not only
for the bodily constitution and frame of his offspring, but for their
intellectual and moral qualities. Both sexes ought to refrain from
marriage if they are in any marked degree inferior in body or mind; but
such hopes are Utopian and will never be even partially realized until
the laws of inheritance are thoroughly known. All do good service who
aid toward this end. When the principles of breeding and inheritance are
better understood, we shall not hear ignorant members of our legislature
rejecting with scorn a plan for ascertaining whether or not
consanguineous marriages are injurious to man.
The advancement of the welfare of mankind is a most intricate problem;
all ought to refrain from marriage who cannot avoid abject poverty for
their children; for poverty is not only a great evil, but tends to its
own increase by leading to recklessness in marriage. On the other hand,
as Mr. Galton has remarked, if the prudent avoid marriage, while the
reckless marry, the inferior members tend to supplant the better members
of society. Man, like every other animal, has no doubt advanced to his
present high condition through a struggle for existence consequent on
his rapid multiplication; and if he is to advance still higher, he must
remain subject to a severe struggle. Otherwise he would sink into
indolence, and the more gifted men would not be more successful in the
battle of life than the less gifted. Hence our natural rate of
increase, though leading to many and obvious evils, must not be greatly
diminished by any means. There should be open competition for all men;
and the most able should not be prevented by laws or customs from
succeeding best and rearing the largest number of offspring. Important
as the struggle for existence has been and even still is, yet as far as
the highest part of man's nature is concerned there are other agencies
more important. For the moral qualities are advanced, either directly or
indirectly, much more through the effects of habit, the reasoning
powers, instruction, religion, etc., than through natural selection;
though to this latter agency the social instincts, which afforded the
basis for the development of the moral sense, may be safely attributed.
The main conclusion arrived at in this work, namely, that man is
descended from some lowly organized form, will, I regret to think, be
highly distasteful to many. But there can hardly be a doubt that we are
descended from barbarians. The astonishment I felt on first seeing a
party of Fuegians on a wild and broken shore will never be forgotten by
me, for the reflection at once rushed into my mind--such were our
ancestors. These men were absolutely naked and bedaubed with paint,
their long hair was tangled, their mouths frothed with excitement, and
their expression was wild, startled and distrustful. They possessed
hardly any arts, and like wild animals lived on what they could catch;
they had no government, and were merciless to every one not of their
own small tribe. He who has seen a savage in his native land will not
feel much shame, if forced to acknowledge that the blood of some more
humble creature flows in his veins. For my own part I would as soon be
descended from that heroic little monkey who braved his dreaded enemy in
order to save the life of his keeper; or from that old baboon, who,
descending from the mountains, carried away in triumph his young comrade
from a crowd of astonished dogs--as from a savage who delights to
torture his enemies, offers up bloody sacrifices, practises infanticide
without remorse, treats his wives like slaves, knows no decency, and is
haunted by the grossest superstitions.
Man may be excused for feeling some pride at having risen, though not
through his own exertions, to the very summit of the organic scale; and
the fact of his having thus risen, instead of having been aboriginally
placed there, may give him hope for a still higher destiny in the
distant future. But we are not here concerned with hopes or fears, only
with the truth as far as our reason permits us to discover it. I have
given the evidence to the best of my ability, and we must acknowledge,
as it seems to me, that man, with all his noble qualities, with sympathy
which feels for the most debased, with benevolence which extends not
only to other men but to the humblest living creature, with his godlike
intellect which has penetrated into the movements and constitution of
the solar system--with all these exalted powers--Man still bears in his
bodily frame the indelible stamp of his lowly origin.
MIMICRY AND OTHER PROTECTIVE RESEMBLANCES AMONG ANIMALS
ALFRED RUSSEL WALLACE
[Mr. Wallace, one of the greatest naturalists of the age,
discovered the law of natural selection independently of
Darwin, and about the same time. Among his works are "The
Malay Archipelago," "Island Life," and "Darwinism." From
"Natural Selection," which was published by Macmillan & Co.,
1871, the following extracts are taken. The theme has
received important development at the hands of Professor E.
B. Poulton, in his "The Colours of Animals," International
Scientific Series, 1890: and in F. E. Beddard's "Animal
Colouration"; London, Swan Sonnenschein; N. Y., Macmillan,
1892.]
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 phenomena 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 has been supported. The course of a true
theory 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.
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 races which possess them. This great principle gives
us a clue which we can follow out in the study of many recondite
phenomena, 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.
The adaptation of the external colouring of animals to their conditions
of life has long been recognized, 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 phenomena, and to
be contradicted by many well-known facts. For example, wild rabbits are
always of gray 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 food, since in
many cases the species does not feed on the substance it resembles, and
when it does, no reasonable connection 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 phenomena which may be classed under the head of useful
or protective resemblances.
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 stone-chats, 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 first volume of the "Ibis," says: "In
the desert, where neither trees, brushwood, 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 jerfalcon, 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.
The conformity of tint which has been so far shown to exist between
animals and their habitations is of 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 in 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 until 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 on 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 they must 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 in 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. Gunthner 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-horse (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 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 Tapiriba, 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 Para, 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 powdery black dots gathered into patches and spots, so
closely resembling the various kinds of minute fungi that grow on dead
leaves that is it 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 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 wings 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....
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 are 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.
[Here are given many detailed examples of insects which gainfully mimic
one another.]
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
pedicle, 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.
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 (Saphura), 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.
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
travesty? 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.
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 fertilization, 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.[4]
FOOTNOTES:
[4] The author continues this study in Chapter ix of "Darwinism": New
York, Macmillan Co., 1889.--Ed.
THE EVOLUTION OF THE HORSE
THOMAS HENRY HUXLEY
[Professor Huxley as a naturalist, educator, and
controversialist was one of the commanding figures of the
nineteenth century. To physiology and morphology his
researches added much of importance: as an expositor he stood
unapproached. As the bold and witty champion of Darwinism he
gave natural selection an acceptance much more early and wide
than it would otherwise have enjoyed. In 1876 he delivered in
America three lectures on Evolution: the third of the series
is here given. All three are copyrighted and published by D.
Appleton & Co., New York, in a volume which also contains a
lecture on the study of biology. Since 1876 the arguments of
Professor Huxley have been reinforced by the discovery of
many fossils connecting not only the horse, but other
quadrupeds, with species widely different and now extinct.
The most comprehensive collection illustrating the descent of
the horse is to be seen at the American Museum of Natural
History, New York, where also the evolution of tapirs,
camels, llamas, rhinoceroses, dinosaurs, great ground sloths
and other animals are clearly to be traced--in most cases by
remains discovered in America. A capital book on the theme
broached by Professor Huxley is "Animals of the Past," by
Frederic A. Lucas, Curator of the Division of Comparative
Anatomy, United States National Museum, Washington, D. C.,
published by McClure, Phillips & Co., New York.
"The Life and Letters of Professor Huxley," edited by his
son, Leonard Huxley, is a work of rare interest: it is
published by D. Appleton & Co., New York.]
The occurrence of historical facts is said to be demonstrated, when the
evidence that they happened is of such a character as to render the
assumption that they did not happen in the highest degree improbable;
and the question I now have to deal with is, whether evidence in favour
of the evolution of animals of this degree of cogency is, or is not,
obtainable from the record of the succession of living forms which is
presented to us by fossil remains.
Those who have attended to the progress of palæontology are aware that
evidence of the character which I have defined has been produced in
considerable and continually-increasing quantity during the last few
years. Indeed, the amount and the satisfactory nature of that evidence
are somewhat surprising, when we consider the conditions under which
alone we can hope to obtain it.
It is obviously useless to seek for such evidence, except in localities
in which the physical conditions have been such as to permit of the
deposit of an unbroken, or but rarely interrupted, series of strata
through a long period of time; in which the group of animals to be
investigated has existed in such abundance as to furnish the requisite
supply of remains; and in which, finally, the materials composing the
strata are such as to insure the preservation of these remains in a
tolerably perfect and undisturbed state.
It so happens that the case which, at present, most nearly fulfils all
these conditions is that of the series of extinct animals which
culminates in the horses; by which term I mean to denote not merely the
domestic animals with which we are all so well acquainted, but their
allies, the ass, zebra, quagga, and the like. In short, I use "horses"
as the equivalent of the technical name _Equidæ_, which is applied to
the whole group of existing equine animals.
The horse is in many ways a remarkable animal; not least so in the fact
that it presents us with an example of one of the most perfect pieces of
machinery in the living world. In truth, among the works of human
ingenuity it cannot be said that there is any locomotive so perfectly
adapted to its purposes, doing so much work with so small a quantity of
fuel, as this machine of nature's manufacture--the horse. And, as a
necessary consequence of any sort of perfection, of mechanical
perfection as of others, you find that the horse is a beautiful
creature, one of the most beautiful of all land animals. Look at the
perfect balance of its form, and the rhythm and force of its action. The
locomotive machinery is, as you are aware, resident in its slender fore
and hind limbs; they are flexible and elastic levers, capable of being
moved by very powerful muscles; and, in order to supply the engines
which work these levers with the force which they expend, the horse is
provided with a very perfect apparatus for grinding its food and
extracting therefrom the requisite fuel.
Without attempting to take you very far into the region of osteological
detail, I must nevertheless trouble you with some statements respecting
the anatomical structure of the horse; and, more especially, will it be
needful to obtain a general conception of the structure of its fore and
hind limbs, and of its teeth. But I shall only touch upon these points
which are absolutely essential to our inquiry.
Let us turn in the first place to the fore-limb. In most quadrupeds, as
in ourselves, the fore-arms contains distinct bones called the radius
and the ulna. The corresponding region in the horse seem at first to
possess but one bone. Careful observation, however, enables us to
distinguish in this bone a part which clearly answers to the upper end
of the ulna. This is closely united with the chief mass of the bone
which represents the radius, and runs out into a slender shaft which may
be traced for some distance downwards upon the back of the radius, and
then in most cases thins out and vanishes. It takes still more trouble
to make sure of what is nevertheless the fact, that a small part of the
lower end of the bone of the horse's fore-arm, which is only distinct in
a very young foal, is really the lower extremity of the ulna.
What is commonly called the knee of a horse is its wrist. The "cannon
bone" answers to the middle bone of the five metacarpal bones, which
support the palm of the hand in ourselves. The "pastern," "coronary,"
and "coffin" bones of veterinarians answer to the joints of our middle
fingers, while the hoof is simply a greatly enlarged and thickened nail.
But if what lies below the horse's "knee" thus corresponds to the middle
finger in ourselves, what has become of the four other fingers or
digits? We find in the places of the second and fourth digits only two
slender splint-like bones, about two-thirds as long as the cannon bone,
which gradually taper to their lower ends and bear no finger joints, or,
as they are termed, phalanges. Sometimes, small bony or gristly nodules
are to be found at the bases of these two metacarpal splints, and it is
probable that these represent rudiments of the first and fifth toes.
Thus, the part of the horse's skeleton, which corresponds with that of
the human hand, contains one overgrown middle digit, and at least two
imperfect lateral digits; and these answer, respectively, to the third,
the second and the fourth fingers in man.
Corresponding modifications are found in the hind limb. In ourselves,
and in most quadrupeds, the leg contains two distinct bones, a large
bone, the tibia, and a smaller and more slender bone, the fibula. But,
in the horse, the fibula seems, at first, to be reduced to its upper
end; a short slender bone united with the tibia and ending in a point
below, occupying its place. Examination of the lower end of a young
foal's shin-bone, however, shows a distinct portion of osseous matter,
which is the lower end of the fibula; so that the, apparently single,
lower end of the shin-bone is really made up of the coalesced ends of
the tibia and fibula, just as the, apparently single, lower end of the
fore-arm bone is composed of the coalesced radius and ulna.
The heel of the horse is the part commonly known as the hock. The hinder
cannon bone answers to the middle metatarsal bone of the human foot, the
pastern, coronary, and coffin bones, to the middle toe bones; the hind
hoof to the nail; as in the fore-foot. And, as in the fore-foot, there
are merely two splints to represent the second and the fourth toes.
Sometimes a rudiment of a fifth toe appears to be traceable.
The teeth of a horse are not less peculiar than its limbs. The living
engine, like all others, must be well stoked if it is to do its work;
and the horse, if it is to make good its wear and tear, and to exert the
enormous amount of force required for its propulsion, must be well and
rapidly fed. To this end good cutting instruments and powerful and
lasting crushers are needful. Accordingly, the twelve cutting teeth of a
horse are close-set and concentrated in the fore-part of its mouth, like
so many adzes or chisels. The grinders or molars are large, and have an
extremely complicated structure, being composed of a number of different
substances of unequal hardness. The consequence of this is that they
wear away at different rates; and, hence, the surface of each grinder
is always as uneven as that of a good millstone.
I have said that the structure of the grinding teeth is very
complicated, the harder and the softer parts being, as it were,
interlaced with one another. The result of this is that, as the tooth
wears, the crown presents a peculiar pattern, the nature of which is not
very easily deciphered at first, but which it is important we should
understand clearly. Each grinding tooth of the upper jaw has an _outer
wall_ so shaped that, on the worn crown, it exhibits the form of two
crescents, one in front and one behind, with their concave sides turned
outwards. From the inner side of the front crescent, a crescentic _front
ridge_ passes inwards and backwards, and its inner face enlarges into a
strong longitudinal fold or _pillar_. From the front part of the hinder
crescent, a _back ridge_ takes a like direction, and also has its
_pillar_.
The deep interspaces or _valleys_ between these ridges and the outer
wall are filled by bony substance, which is called _cement_, and coats
the whole tooth.
The pattern of the worn face of each grinding tooth of the lower jaw is
quite different. It appears to be formed of two crescent-shaped ridges,
the convexities of which are turned outwards. The free extremity of each
crescent has a _pillar_, and there is a large double _pillar_ where the
two crescents meet. The whole structure is, as it were, imbedded in
cement, which fills up the valleys, as in the upper grinders.
If the grinding faces of an upper and of a lower molar of the same side
are applied together, it will be seen that the opposed ridges are
nowhere parallel, but that they frequently cross; and that thus, in the
act of mastication, a hard surface in the one is constantly applied to a
soft surface in the other, and _vice versa_. They thus constitute a
grinding apparatus of great efficiency, and one which is repaired as
fast as it wears, owing to the long-continued growth of the teeth.
Some other peculiarities of the dentition of the horse must be noticed,
as they bear upon what I shall have to say by and by. Thus the crowns of
the cutting teeth have a peculiar deep pit, which gives rise to the
well-known "mark" of the horse. There is a large space between the outer
incisors and the front grinders. In this space the adult male horse
presents, near the incisors on each side, above and below, a canine or
"tush," which is commonly absent in mares. In a young horse, moreover,
there is not unfrequently to be seen, in front of the first grinder, a
very small tooth, which soon falls out. If this small tooth be counted
as one, it will be found that there are seven teeth behind the canine on
each side; namely, the small tooth in question, and the six great
grinders, among which, by an unusual peculiarity, the foremost tooth is
rather larger than those which follow it.
I have now enumerated those characteristic structures of the horse which
are of most importance for the purpose we have in view.
To any one who is acquainted with the morphology [comparative forms] of
vertebrated animals, they show that the horse deviates widely from the
general structure of mammals; and that the horse type is, in many
respects, an extreme modification of the general mammalian plan. The
least modified mammals, in fact, have the radius and ulna, the tibia and
fibula, distinct and separate. They have five distinct and complete
digits on each foot, and no one of these digits is very much larger than
the rest. Moreover, in the least modified mammals the total number of
the teeth is very generally forty-four, while in horses the usual number
is forty, and in the absence of the canines it may be reduced to
thirty-six; the incisor teeth are devoid of the fold seen in those of
the horse: the grinders regularly diminish in size from the middle of
the series to its front end; while their crowns are short, early attain
their full length, and exhibit simple ridges or tubercles, in place of
the complex foldings of the horse's grinders.
Hence the general principles of the hypothesis of evolution lead to the
conclusion that the horse must have been derived from some quadruped
which possessed five complete digits on each foot; which had the bones
of the fore-arm and of the leg complete and separate; and which
possessed forty-four teeth, among which the crowns of the incisors and
grinders had a simple structure; while the latter gradually increased in
size from before backwards, at any rate in the anterior part of the
series, and had short crowns.
And if the horse has been thus evolved, and the remains of the different
stages of its evolution have been preserved, they ought to present us
with a series of forms in which the number of the digits becomes
reduced; the bones of the fore-arm and leg gradually take on the equine
condition; and the form and arrangement of the teeth successively
approximate to those which obtain in existing horses.
Let us turn to the facts, and see how far they fulfil these requirements
of the doctrine of evolution.
In Europe abundant remains of horses are found in the Quaternary and
later Tertiary strata as far as the Pliocene formation. But these
horses, which are so common in the cave-deposits and in the gravels of
Europe, are in all essential respects like existing horses. And that is
true of all the horses of the latter part of the Pliocene epoch. But in
deposits which belong to the earlier Pliocene and later Miocene epochs,
and which occur in Britain, in France, in Germany, in Greece, in India,
we find animals which are extremely like horses--which, in fact, are so
similar to horses that you may follow descriptions given in works upon
the anatomy of the horse upon the skeletons of these animals--but which
differ in some important particulars. For example, the structure of
their fore and hind limbs is somewhat different. The bones which, in the
horse, are represented by two splints, imperfect below, are as long as
the middle metacarpal and metatarsal bones; and attached to the
extremity of each is a digit with three joints of the same general
character as those of the middle digit, only very much smaller. These
small digits are so disposed that they could have had but very little
functional importance, and they must have been rather of the nature of
the dew-claws, such as are to be found in many ruminant animals. The
_Hipparion_, as the extinct European three-toed horse is called, in
fact, presents a foot similar to that of the American _Protohippus_
(Fig. 9), except that in the _Hipparion_ the smaller digits are situated
farther back and are of smaller proportional size than in the
_Protohippus_.
The ulna is slightly more distinct than in the horse; and the whole
length of it, as a very slender shaft intimately united with the radius,
is completely traceable. The fibula appears to be in the same condition
as in the horse. The teeth of the _Hipparion_ are essentially similar to
those of the horse, but the pattern of the grinders is in some respects
a little more complex, and there is a depression on the face of the
skull in front of the orbit, which is not seen in existing horses.
In the earlier Miocene, and perhaps the later Eocene deposits of some
parts of Europe, another extinct animal has been discovered, which
Cuvier, who first described some fragments of it, considered to be a
_Palæotherium_. But as further discoveries threw new light on its
structure, it was recognized as a distinct genus under the name of
_Anchitherium_.
In its general characters, the skeleton of _Anchitherium_ is very
similar to that of the horse. In fact, Lartet and De Blainville called
it _Palæotherium equinum_ or _hippoides_; and De Christol, in 1847, said
that it differed from _Hipparion_ in little more than the characters of
its teeth, and gave it the name of _Hipparitherium_. Each foot possesses
three complete toes; while the lateral toes are much larger in
proportion to the middle toe than in _Hipparion_, and doubtless rested
on the ground in ordinary locomotion.
The ulna is complete and quite distinct from that radius, though firmly
united with the latter. The fibula seems also to have been complete. Its
lower end, though intimately united with that of the tibia, is clearly
marked off from the latter bone.
There are forty-four teeth. The incisors have no strong pit. The canines
seem to have been well developed in both sexes. The first of the seven
grinders, which, as I have said, is frequently absent, and when it does
exist, is small in the horse, is a good-sized and permanent tooth,
while the grinder which follows it is but little larger than the hinder
ones. The crowns of the grinders are short, and though the fundamental
pattern of the horse-tooth is discernible, the front and back ridges are
less curved, the accessory pillars, are wanting, and the valleys, much
shallower, are not filled up with cement.
Seven years ago, when I happened to be looking critically into the
bearing of palæontological facts upon the doctrine of evolution, it
appeared to me that the _Anchitherium_, the _Hipparion_, and the modern
horses, constitute a series in which the modifications of structure
coincide with the order of chronological occurrence, in the manner in
which they must coincide, if the modern horses really are the result of
the gradual metamorphosis, in the course of the Tertiary epoch, of a
less specialized ancestral form. And I found by correspondence with the
late eminent French anatomist and palæontologist, M. Lartet, that he had
arrived at the same conclusion from the same data.
That the _Anchitherium_ type had become metamorphosed into the
_Hipparion_ type, and the latter into the _Equine_ type,[5] in the
course of that period of time which is represented by the latter half
of the Tertiary deposits, seemed to me to be the only explanation of the
facts for which there was even a shadow of probability.
And, hence, I have ever since held that these facts afford evidence of
the occurrence of evolution, which, in the sense already defined, may be
termed demonstrative.
All who have occupied themselves with the structure of _Anchitherium_,
from Cuvier onwards, have acknowledged its many points of likeness to a
well-known genus of extinct Eocene mammals, _Palæotherium_. Indeed, as
we have seen, Cuvier regarded his remains of _Anchitherium_ as those of
a species of _Palæotherium_. Hence, in attempting to trace the pedigree
of the horse beyond the Miocene epoch and the Anchitheroid form, I
naturally sought among the various species of Palæotheroid animals for
its nearest ally, and I was led to the conclusion that the _Palæotherium
minus_ (_Plagiolophus_) represented the next step more nearly than any
form then known.
I think that this opinion was fully justifiable; but the progress of
investigation has thrown an unexpected light on the question, and has
brought us much nearer than could have been anticipated to a knowledge
of the true series of the progenitors of the horse.
You are all aware that, when your country was first discovered by
Europeans, there were no traces of the existence of the horse on any
part of the American Continent. The accounts of the conquest of Mexico
dwell upon the astonishment of the natives of that country when they
first became acquainted with that astounding phenomenon--a man seated
upon a horse. Nevertheless, the investigations of American geologists
have proved that the remains of horses occur in the most superficial
deposits of both North and South America, just as they do in Europe.
Therefore, for some reason or other--no feasible suggestion on that
subject, so far as I know, has been made--the horse must have died out
on this continent at some period preceding the discovery of America. Of
late years there has been discovered in your Western Territories that
marvellous accumulation of deposits, admirably adapted for the
preservation of organic remains, to which I referred the other evening,
and which furnishes us with a consecutive series of records of the fauna
of the older half of the Tertiary epoch, for which we have no parallel
in Europe. They have yielded fossils in an excellent state of
conservation and in unexampled numbers and variety. The researches of
Leidy and others have shown that forms allied to the _Hipparion_ and the
_Anchitherium_ are to be found among these remains. But it is only
recently that the admirably conceived and most thoroughly and patiently
worked-out investigations of Professor Marsh have given us a just idea
of the vast fossil wealth, and of the scientific importance, of these
deposits. I have had the advantage of glancing over the collections in
Yale Museum; and I can truly say, that so far as my knowledge extends,
there is no collection from any one region and series of strata
comparable, for extent, or for the care with which the remains have been
got together, or for their scientific importance, to the series of
fossils which he has deposited there. This vast collection has yielded
evidence bearing upon the question of the pedigree of the horse of the
most striking character. It tends to show that we must look to America,
rather than to Europe, for the original seat of the equine series; and
that the archaic forms and successive modifications of the horse's
ancestry are far better preserved here than in Europe.
Professor Marsh's kindness has enabled me to put before you a diagram,
every figure of which is an actual representation of some specimen which
is to be seen at Yale at this present time (Fig. 9).
The succession of forms which he has brought together carries us from
the top to the bottom of the Tertiaries. Firstly, there is the true
horse. Next we have the American Pliocene form of the horse
(_Pliohippus_); in the conformation of its limbs it presents some very
slight deviations from the ordinary horse, and the crowns of the
grinding teeth are shorter. Then comes the _Protohippus_, which
represents the European _Hipparion_, having one large digit and two
small ones on each foot, and the general characters of the fore-arm and
leg to which I have referred. But it is more valuable than the European
_Hipparion_ for the reason that it is devoid of some of the
peculiarities of that form--peculiarities which tend to show that the
European _Hipparion_ is rather a member of a collateral branch, than a
form in the direct line of succession. Next, in the backward order in
time, is the _Miohippus_, which corresponds pretty nearly with the
_Anchitherium_ of Europe. It presents three complete toes--one large
median and two smaller lateral ones; and there is a rudiment of that
digit, which answers to the little finger of the human hand.
The European record of the pedigree of the horse stops here; in the
American Tertiaries, on the contrary, the series of ancestral equine
forms is continued into the Eocene formations. An older Miocene form,
termed _Mesohippus_, has three toes in front, with a large splint-like
rudiment representing the little finger; and three toes behind. The
radius and ulna, the tibia and the fibula, are distinct, and the short
crowned molar teeth are anchitheroid in pattern.
But the most important discovery of all is the _Orohippus_, which comes
from the Eocene formation, and which is the oldest member of the equine
series, as yet known. Here we find four complete toes on the front-limb,
three toes on the hind-limb, a well-developed ulna, a well-developed
fibula, and short-crowned grinders of simple pattern.
Thus, thanks to these important researches, it has become evident that,
so far as our present knowledge extends, the history of the horse-type
is exactly and precisely that which could have been predicted from a
knowledge of the principles of evolution. And the knowledge we now
possess justifies us completely in the anticipation, that when the still
lower Eocene deposits, and those which belong to the Cretaceous epoch,
have yielded up their remains of ancestral equine animals, we shall
find, first, a form with four complete toes and a rudiment of the
innermost or first digit in front, with probably, a rudiment of the
fifth digit in the hind foot;[6] while, in still older forms, the series
of the digits will be more and more complete, until we come to the
five-toed animals, in which, if the doctrine of evolution is well
founded, the whole series must have taken its origin.
That is what I mean by demonstrative evidence of evolution. An inductive
hypothesis is said to be demonstrated when the facts are shown to be in
entire accordance with it. If that is not scientific proof, there are no
merely inductive conclusions which can be said to be proved. And the
doctrine of evolution, at the present time, rests upon exactly as secure
a foundation as the Copernican theory of the motions of the heavenly
bodies did at the time of its promulgation. Its logical basis is
precisely of the same character--the coincidence of the observed facts
with theoretical requirements.
The only way of escape, if it be a way of escape, from the conclusions
which I have just indicated, is the supposition that all these different
equine forms have been created separately at separate epochs of time;
and, I repeat, that of such an hypothesis as this there neither is, nor
can be, any scientific evidence; and, assuredly, so far as I know, there
is none which is supported, or pretends to be supported, by evidence or
authority of any other kind. I can but think that the time will come
when such suggestions as these, such obvious attempts to escape the
force of demonstration, will be put upon the same footing as the
supposition made by some writers, who are, I believe, not completely
extinct at present, that fossils are mere simulacra [images], are no
indications of the former existence of the animals to which they seem to
belong; but that they are either sports of Nature, or special creations,
intended--as I heard suggested the other day--to test our faith.
In fact, the whole evidence is in favour of evolution, and there is none
against it. And I say this, although perfectly well aware of the seeming
difficulties which have been built up upon what appears to the
uninformed to be a solid foundation. I meet constantly with the argument
that the doctrine of evolution cannot be well founded because it
requires the lapse of a very vast period of time; while the duration of
life upon the earth, thus implied, is inconsistent with the conclusions
arrived at by the astronomer and the physicist. I may venture to say
that I am familiar with those conclusions, inasmuch as some years ago,
when president of the Geological Society of London, I took the liberty
of criticising them, and of showing in what respects, as it appeared to
me, they lacked complete and thorough demonstration. But, putting that
point aside, suppose that, as the astronomers, or some of them, and some
physical philosophers tell us, it is impossible that life could have
endured upon the earth for so long a period as is required by the
doctrine of evolution--supposing that to be proved--I desire to be
informed, what is the foundation for the statement that evolution does
require so great a time? The biologist knows nothing whatever of the
amount of time which may be required for the process of evolution. It is
a matter of fact that the equine forms, which I have described to you,
occur, in the order stated, in the Tertiary formations. But I have not
the slightest means of guessing whether it took a million of years, or
ten millions, or a hundred millions, or a thousand millions of years, to
give rise to that series of changes. A biologist has no means of
arriving at any conclusions as to the amount of time which may be needed
for a certain quantity of organic change. He takes his time from the
geologist. The geologist, considering the rate at which deposits are
formed and the rate at which denudation goes on upon the surface of the
earth, arrives at more or less justifiable conclusions as to the time
which is required for the deposit of a certain thickness of rocks; and
if he tells me that the Tertiary formations required 500,000,000 years
for their deposit, I suppose he has good ground for what he says, and I
take that as a measure of the duration of the evolution of the horse
from the _Orohippus_ up to its present condition. And, if he is right,
undoubtedly evolution is a very slow process, and requires a great deal
of time. But suppose now, that an astronomer or a physicist--for
instance, my friend Sir William Thomson--tells me that my geological
authority is quite wrong; and that he has weighty evidence to show that
life could not possibly have existed upon the surface of the earth
500,000,000 years ago, because the earth would have then been too hot to
allow of life, my reply is: "That is not my affair; settle that with the
geologist, and when you have come to an agreement among yourselves I
will adopt your conclusions." We take our time from the geologists and
physicists, and it is monstrous that, having taken our time from the
physical philosopher's clock, the physical philosopher should turn round
upon us, and say we are too fast or too slow. What we desire to know is,
is it a fact that evolution took place? As to the amount of time which
evolution may have occupied, we are in the hands of the physicist and
the astronomer, whose business it is to deal with those questions.
[Illustration: Fig. 9]
Fore Foot. Hind Foot. Fore-arm. Leg. Upper Molar. Lower Molar.
RECENT.
EQUUS.
PLIOCENE.
PLIOHIPPUS.
PROTOHIPPUS
(_Hipparion_).
MIOCENE.
MIOHIPPUS
(_Anchitherium_).
MESOHIPPUS.
EOCENE.
OROHIPPUS.
FOOTNOTES:
[5] I use the word "type" because it is highly probable that many of the
forms of _Anchitherium_-like and _Hipparion_-like animals existed in the
Miocene and Pliocene epochs, just as many species of the horse tribe
exist now; and it is highly improbable that the particular species of
_Anchitherium_ or _Hipparion_, which happen to have been discovered,
should be precisely those which have formed part of the direct line of
the horse's pedigree.
[6] Since this lecture was delivered, Professor Marsh has discovered a
new genus of equine mammals (_Eohippus_) from the lowest Eocene
deposits of the West, which corresponds very nearly to this
description.--_American Journal of Science_, November, 1876.
FIGHTING PESTS WITH INSECT ALLIES
LELAND O. HOWARD
[Dr. Howard is Chief of the Division of Entomology in the
United States Department of Agriculture at Washington. He is
a lecturer at Swarthmore College and at Georgetown
University. He has written "The Insect Book," published by
Doubleday, Page & Co., New York; and a work on Mosquitoes,
issued by McClure, Phillips & Co., New York. Both are books
of interest from the hand of a master: they are fully
illustrated. The narrative which follows appeared in
_Everybody's Magazine_, June, 1901.]
Some twenty-five years ago there appeared suddenly upon certain acacia
trees at Menlo Park, California, a very destructive scale bug. It
rapidly increased and spread from tree to tree, attacking apples, figs,
pomegranates, quinces, and roses, and many other trees and plants, but
seeming to prefer to all other food the beautiful orange and lemon trees
which grow so luxuriantly on the Pacific Coast, and from which a large
share of the income of so many fruit-growers is gained. This insect,
which came to be known as the _white scale_ or _fluted scale_ or the
_Icerya_ (from its scientific name), was an insignificant creature in
itself, resembling a small bit of fluted wax a little more than a
quarter of an inch long. But when the scales had once taken possession
of a tree, they swarmed over it until the bark was hidden; they sucked
its sap through their minute beaks until the plant became so feeble that
the leaves and young fruit dropped off, a hideous black smut-fungus
crept over the young twigs, and the weakened tree gradually died.
In this way orchard after orchard of oranges, worth a thousand dollars
or more an acre, was utterly destroyed; the best fruit-growing sections
of the State were invaded, and ruin stared many a fruit-grower in the
face. This spread of the pest was gradual, extending through a series of
years, and not until 1886 did it become so serious a matter as to
attract national attention.
In this year an investigation was begun by the late Professor C. V.
Riley, the Government entomologist then connected with the Department of
Agriculture at Washington. He sent two agents to California, both of
whom immediately began to study the problem of remedies. In 1887 he
visited California himself, and during that year published an elaborate
report giving the results of the work up to that point. The complete
life-history of the insect had been worked out, and a number of washes
had been discovered which could be applied to the trees in the form of a
spray, and which would kill a large proportion of the pests at a
comparatively small expense. But it was soon found that the average
fruit-grower would not take the trouble to spray his trees, largely from
the fact that he had experimented for some years with inferior washes
and quack nostrums, and from lack of success had become disgusted with
the whole idea of using liquid compounds. Something easier, something
more radical was necessary in his disheartened condition.
Meantime, after much sifting of evidence and much correspondence with
naturalists in many parts of the world, Professor Riley had decided that
the white scale was a native of Australia, and had been first brought
over to California accidentally upon Australian plants. In the same way
it was found to have reached South Africa and New Zealand, in both of
which colonies it had greatly increased, and had become just such a pest
as it is in California. In Australia, however, its native home, it did
not seem to be abundant, and was not known as a pest--a somewhat
surprising state of affairs, which put the entomologist on the track of
the results which proved of such great value to California. He reasoned
that, in his native home, with the same food plants upon which it
flourished abroad in such great abundance, it would undoubtedly do the
same damage that it does in South Africa, New Zealand, and California,
if there were not in Australia some natural enemy, probable some insect
parasite or predatory beetle, which killed it off. It became therefore
important to send a trained man to Australia to investigate this
promising line.
After many difficulties in arranging preliminaries relating to the
payment of expenses (in which finally the Department of State kindly
assisted), one of Professor Riley's assistants, a young German named
Albert Koebele, who had been with him for a number of years, sailed for
Australia in August, 1888. Koebele was a skilled collector and an
admirable man for the purpose. He at once found that Professor Riley's
supposition was correct: there existed in Australia small flies which
laid their eggs in the white scales, and these eggs hatched into grubs
which devoured the pests. He also found a remarkable little ladybird, a
small, reddish-brown convex beetle, which breeds with marvellous
rapidity and which, with voracious appetite, and at the same time with
discriminating taste, devours scale after scale, but eats fluted scales
only--does not attack other insects. This beneficial creature, now known
as the Australian ladybird, or the Vedalia, Mr. Koebele at once began to
collect in large numbers, together with several other insects found
doing the same work. He packed many hundreds of living specimens of the
ladybird, with plenty of food, in tin boxes, and had them placed on ice
in the ice-box of the steamer at Sydney; they were carried carefully to
California, where they were liberated upon orange trees at Los Angeles.
[Illustration: Vedalia, or Australian Ladybird]
These sendings were repeated for several months, and Mr. Koebele, on his
return in April, 1889, brought with him many more living specimens which
he had collected on his way home in New Zealand, where the same Vedalia
had been accidentally introduced a year or so before.
[Illustration: Larvæ of Vedalia eating White Scale]
The result more than justified the most sanguine expectations. The
ladybirds reached Los Angeles alive, and, with appetites sharpened by
their long ocean voyage, immediately fell upon the devoted scales and
devoured them one after another almost without rest. Their hunger
temporarily satisfied, they began to lay eggs. These eggs hatched in a
few days into active grub-like creatures--the larvæ of the beetles--and
these grubs proved as voracious as their parents. They devoured the
scales right and left, and in less than a month transformed once more to
beetles.
And so the work of extermination went on. Each female beetle laid on an
average 300 eggs, and each of these eggs hatched into a hungry larva.
Supposing that one-half of these larvæ produced female beetles, a simple
calculation will show that in six months a single ladybird became the
ancestor of 75,000,000,000 of other ladybirds, each capable of
destroying very many scale insects.
[Illustration: Twig of olive infected with Black Scale]
Is it any wonder, then, that the fluted scales soon began to disappear?
Is it any wonder that orchard after orchard was entirely freed from the
pest, until now over a large section of the State hardly an Icerya is to
be found? And could a more striking illustration of the value of the
study of insects possibly be instanced? In less than a year from the
time when the first of these hungry Australians was liberated from his
box in Los Angeles the orange trees were once more in bloom and were
resuming their old-time verdure--the Icerya had become practically a
thing of the past.
[Illustration: Rhizobius, the imported enemy of the Black Scale of the
Olive.]
This wonderful success encouraged other efforts in the same direction.
The State of California some years later sent the same entomologist,
Koebele, to Australia to search for some insect enemy of the black
scale, an insect which threatened the destruction of the extensive olive
orchards of California. He found and successfully introduced another
ladybird beetle, known as _Rhizobius ventralis_, a little dark-coloured
creature which has thrived in the California climate, especially near
the seacoast, and in the damp air of those regions has successfully held
the black scale in check. It was found, however, that back from the
seacoast this insect did not seem to thrive with the same vigor, and the
black scale held its own. Then a spirited controversy sprung up among
the olive-growers, those near the seacoast contending that the
_Rhizobius_ was a perfect remedy for the scale, while those inland
insisted that it was worthless. A few years later it was discovered that
this olive enemy in South Europe is killed by a little caterpillar,
which burrows through scale after scale eating out their contents, and
an effort was made to introduce the caterpillar into California, but
these efforts failed. Within the past two years it has been found that a
small parasitic fly exists in South Africa which lays its eggs in the
same black scale, and its grub-like larvæ eat out the bodies of the
scales and destroy them. The climate of the region in which this
parasite exists is dry through a large part of the year, and therefore
this little parasitic fly, known as _Scutellista_, was thought to be
the needed insect for the dry California regions. With the help of Mr.
C. P. Lounsbury, the Government entomologist of Cape Colony, living
specimens of this fly were brought to this country, and were colonized
in the Santa Clara Valley, near San José, California, where they have
perpetuated themselves and destroyed many of the black scales, and
promise to be most successful in their warfare against the injurious
insect.
This same _Scutellista_ parasite had, curiously enough, been previously
introduced in an accidental manner into Italy, probably from India, and
probably in scale-insects living on ornamental plants brought from
India. But in Italy it lives commonly in another scale insect, and with
the assistance of the learned Italian, Professor Antonio Berlese, the
writer made an unsuccessful attempt to introduce and establish it a year
earlier in some of our Southern States, where it was hoped it would
destroy certain injurious insects known as "wax scales."
In the meantime the United States, not content with keeping all the good
things to herself, has spread the first ladybird imported--the
_Vedalia_--to other countries. Four years ago the white scale was
present in enormous numbers in orange groves on the left bank of the
river Tagus, in Portugal, and threatened to wipe out the orange-growing
industry in that country. The California people, in pursuance of a
far-sighted policy, had with great difficulty, owing to lack of food,
kept alive some colonies of the beneficial beetle, and specimens were
sent to Portugal which reached there alive and flourishing. They were
tended for a short time, and then liberated in the orange groves, with
precisely the same result as in California. In a few months the scale
insects were almost entirely destroyed, and the Portuguese
orange-growers saved from enormous loss.
This good result in Portugal was not accomplished without opposition. It
was tried experimentally at the advice of the writer, and in the face of
great incredulity on the part of certain Portuguese newspapers and of
some officials. By many prominent persons the account published of the
work of the insect in the United States was considered as untrustworthy,
and simply another instance of American boasting. But the opposition was
overruled, and the triumphant result silenced all opposition. It is safe
to say that the general opinion among Portuguese orange-growers to-day
is very favourable to American enterprise and practical scientific
acumen.
The _Vedalia_ was earlier sent to the people in Alexandria and Cairo,
Egypt, where a similar scale was damaging the fig trees and other
valuable plants, and the result was again the same, the injurious
insects were destroyed. This was achieved only after extensive
correspondence and several failures. The active agent in Alexandria was
Rear Admiral Blomfield, of the British Royal Navy, a man apparently of
wide information, good judgment, and great energy.
The same thing occurred when the California people sent this saviour of
horticulture to South Africa, where the white scale had also made its
appearance.
It is not only beneficial insects, however, which are being imported,
but diseases of injurious insects. In South Africa the colonists suffer
severely from swarms of migratory grasshoppers, which fly from the north
and destroy their crops. They have discovered out there a fungus
disease, which under favorable conditions kills off the grasshoppers in
enormous numbers. At the Bacteriological Institute in Grahamstown,
Natal, they have cultivated this fungus in culture tubes, and have
carried it successfully throughout the whole year; and they have used it
practically by distributing these culture tubes wherever swarms of
grasshoppers settle and lay their eggs. The disease, once started in an
army of young grasshoppers, soon reduces them to harmless numbers. The
United States Government last year secured culture tubes of this
disease, and experiments carried on in Colorado and in Mississippi show
that the vitality of the fungus had not been destroyed by its long ocean
voyage, and many grasshoppers were killed by its spread. During the past
winter other cultures were brought over from Cape Colony, and the fungus
is being propagated in the Department of Agriculture for distribution
during the coming summer in parts of the country where grasshoppers may
prove to be destructively abundant.
[Illustration: Grasshopper dying from Fungus Disease]
Although we practically no longer have those tremendous swarms of
migratory grasshoppers which used to come down like devastating armies
in certain of our Western States and in a night devour everything green,
still, almost every year, and especially in the West and South, there
is somewhere a multiplication of grasshoppers to a very injurious
degree, and it is hoped that the introduced fungus can be used in such
cases.
Persons officially engaged in searching for remedies for injurious
insects all over the world have banded themselves together in a society
known as the Association of Economic Entomologists. They are constantly
interchanging ideas regarding the destruction of insects, and at present
active movements are on foot in this direction of interchanging
beneficial insects. Entomologists in Europe will try the coming summer
to send to the United States living specimens of a tree-inhabiting
beetle which eats the caterpillar of the gipsy moth, and which will
undoubtedly also eat the caterpillar so common upon the shade-trees of
our principal Eastern cities, which is known as the Tussock moth
caterpillar. An entomologist from the United States, Mr. C. L. Marlatt,
has started for Japan, China, and Java, for the purpose of trying to
find the original home of the famous San José scale--an insect which has
been doing enormous damage in the apple, pear, peach, and plum orchards
of the United States--and if he finds the original home of this scale,
it is hoped that some natural enemy or parasite will be discovered which
can be introduced into the United States to the advantage of our
fruit-growers. Professor Berlese of Italy, and Dr. Reh, of Germany,
will attempt the introduction into Europe of some of the parasites of
injurious insects which occur in the United States, and particularly
those of the woolly root-louse of the apple, known in Europe as the
"American blight"--one of the few injurious insects which probably went
to Europe from this country, and which in the United States is not so
injurious as it is in Europe.
It is a curious fact, by the way, that while we have had most of our
very injurious insects from Europe, American insects, when accidentally
introduced into Europe, do not seem to thrive. The insect just
mentioned, and the famous grape-vine _Phylloxera_, a creature which
caused France a greater economic loss than the enormous indemnity which
she had to pay to Germany after the Franco-Prussian War, are practically
the only American insects with which we have been able to repay Europe
for the insects which she has sent us. Climatic differences, no doubt,
account for this strange fact, and our longer and warmer summers are the
principal factor.
It is not alone the parasitic and predaceous insects which are
beneficial. A new industry has been brought into the United States
during the past two years by the introduction and acclimatization of the
little insect which fertilizes the Smyrna fig in Mediterranean
countries. The dried-fig industry in this country has never amounted to
anything. The Smyrna fig has controlled the dried-fig markets of the
world, but in California the Smyrna fig has never held its fruit, the
young figs dropping from the trees without ripening. It was found that
in Mediterranean regions a little insect, known as the _Blastophaga_,
fertilizes the flowers of the Smyrna fig with pollen from the wild fig
which it inhabits. The United States Department of Agriculture in the
spring of 1899 imported successfully some of these insects through one
of its travelling agents, Mr. W. T. Swingle, and the insect was
successfully established at Fresno in the San Joaquin Valley. A
far-sighted fruit-grower, Mr. George C. Roeding, of Fresno, had planted
some years previously an orchard of 5,000 Smyrna fig trees and wild fig
trees, and his place was the one chosen for the successful experiment.
The little insect multiplied with astonishing rapidity, was carried
successfully through the winter of 1899-1900, and in the summer of 1900
was present in such great numbers that it fertilized thousands of figs,
and fifteen tons of them ripened. When these figs were dried and packed
it was discovered that they were superior to the best imported figs.
They contained more sugar and were of a finer flavor than those brought
from Smyrna and Algeria. The _Blastophaga_ has come to stay, and the
prospects for a new and important industry are assured.
With all these experiments the criticism is constantly made that
unwittingly new and serious enemies to agriculture may be introduced.
The unfortunate introduction of the English sparrow into this country is
mentioned, and the equally unfortunate introduction of the East Indian
mongoose into the West Indies as well. The fear is expressed that the
beneficial parasitic insects, after they have destroyed the injurious
insects, will either themselves attack valuable crops or do something
else of an equally harmful nature. But there is no reason for such
alarm. The English sparrow feeds on all sorts of things, and the East
Indian mongoose, while it was introduced into Jamaica to kill snakes,
was found, too late, to be also a very general feeder. As a matter of
fact, after the snakes were destroyed, and even before, it attacked
young pigs, kids, lambs, calves, puppies, and kittens, and also
destroyed bananas, pineapples, corn, sweet potatoes, cocoanuts, peas,
sugar corn, meat, and salt provisions and fish. But with the parasitic
and predatory insects the food habits are definite and fixed. They can
live on nothing but their natural food, and in its absence they die. The
Australian ladybird originally imported, for example, will feed upon
nothing but scale insects of a particular genus, and, as a matter of
fact, as soon as the fluted scales became scarce the California
officials had the greatest difficulty in keeping the little beetles
alive, and were actually obliged to cultivate for food the very insects
which they were formerly so anxious to wipe out of existence! With the
_Scutellista_ parasite the same fact holds. The fly itself does not
feed, and its young feed only upon certain scale insects, and so with
all the rest.
All of these experiments are being carried on by men learned in the ways
of insects, and only beneficial results, or at the very least negative
ones, can follow. And even where only one such experiment out of a
hundred is successful, what a saving it will mean!
We do not expect the time to come when the farmer, finding Hessian fly
in his wheat, will have only to telegraph the nearest experiment
station, "Send at once two dozen first-class parasites;" but in many
cases, and with a number of different kinds of injurious insects,
especially those introduced from foreign countries, it is probable that
we can gain much relief by the introduction of their natural enemies
from their original home.
THE STRANGE STORY OF THE FLOWERS
GEORGE ILES
[From "The Wild Flowers of America," copyright by G. H. Buek
& Co., New York, 1894, by their kind permission. The American
edition is out of print: the Canadian edition, "Wild Flowers
of Canada," is published by Graham & Co., Montreal, Canada.
The work describes and illustrates in their natural tints
nearly three hundred beautiful flowers.]
Imagine a Venetian doge, a French crusader, a courtier of the time of
the second Charles, an Ojibway chief, a Justice of the Supreme Court, in
the formal black of evening dress, and how much each of them would lose!
Where there is beauty, strength or dignity, dress can heighten it; where
all these are lacking, their absence is kept out of mind by raiment in
itself worthy to be admired. If dress artificial has told for much in
the history of human-kind, dress natural has told for yet more in the
lesser world of plant and insect life. In some degree the tiny folk that
reign in the air, like ourselves, are drawn by grace of form, by charm
of colour; of elaborate display of their attractions moths, butterflies
and beetles are just as fond as any belles of the ball-room. Now let us
bear in mind that of all the creatures that share the earth with man,
the one that stands next to him in intelligence is neither a biped nor
a quadruped, but that king of the insect tribe, the ant, which can be a
herdsman and warehouse-keeper, an engineer and builder, an explorer and
a general. With all his varied powers the ant lacks a peculiarity in his
costume which has denied him enlistment in a task of revolution in which
creatures far his inferiors have been able to change the face of the
earth. And the marvel of this peculiarity of garb which has meant so
much, is that it consists in no detail of graceful outline, or beauty of
tint, but solely in the minor matter of texture. The ant, warrior that
he is, wears smooth and shining armour; the bee, the moth and the
butterfly are clad in downy vesture, and simply because thus enabled to
catch dust on their clothes these insects, as weavers of the web of
life, have counted for immensely more than the ant with all his brains
and character. To understand the mighty train of consequences set in
motion by this mere shagginess of coat, let us remember that, like a
human babe, every flowering plant has two parents. These two parents,
though a county's breadth divide them, are wedded the instant that
pollen from the anther of one of them meets the stigma of the other.
Many flowers find their mates upon their own stem; but, as in the races
of animals, too close intermarriage is hurtful, and union with a distant
stock promotes both health and vigor. Hence the great gain which has
come to plants by engaging the wind as their matchmaker--as every
summer shows us in its pollen-laden air, the oaks, the pines, the
cottonwoods, and a host of other plants commit to the breeze the winged
atoms charged with the continuance of their kind. Nevertheless, long as
the wind has been employed at this work, it has not yet learned to do it
well; nearly all the pollen entrusted to it is wasted, and this while
its production draws severely upon the strength of a plant. As good
fortune will have it, a great many flowers close to their pollen yield
an ample supply of nectar: a food esteemed delicious by the whole round
of insects, winged and wingless. While ants might sip this nectar of
ages without plants being any the better or the worse; a very different
result has followed upon the visits of bees, wasps, and other
hairy-coated callers. These, as they devour nectar, dust themselves with
the pollen near by. Yellowed or whitened with this freightage, moth and
butterfly, as they sail through the air, know not that they are
publishing the banns of marriage between two blossoms acres or, it may
be, miles apart. Yet so it is. Alighting on a new flower the insect rubs
a pollen grain on a stigma ready to receive it, and lo! the rites of
matrimony are solemnized then and there. Unwittingly the little visitor
has wrought a task bigger with fate than many an act loudly trumpeted
among the mightiest deeds of men! On the threshold of a Lady's Slipper a
bee may often be detected in the act of entrance. In the Sage-flower he
finds an anther of the stamen which, pivoted on its spring, dusts him
even more effectually.
[Illustration: Sage-flower and Bee]
Bountifully to spread a table is much, but not enough, for without
invitation how can hospitality be dispensed? To the feast of nectar the
blossoms join their bidding; and those most conspicuously borne and
massed, gayest of hue, richest in odor, secure most guests, and are
therefore most likely to transmit to their kind their own excellences as
hosts and entertainers. Thus all the glories of the blossoms have arisen
in doing useful work; their beauty is not mere ornament, but the sign
and token of duty well performed. Our opportunity to admire the radiancy
and perfume of a jessamine or a pond-lily is due to the previous
admiration of uncounted winged attendants. If a winsome maid adorns
herself with a wreath from the garden, and carries a posy gathered at
the brookside, it is for the second time that their charms are impressed
into service; for the flowers' own ends of attraction all their scent
and loveliness were called into being long before.
Let us put flowers of the blue flag beside those of the maple, and we
shall have a fair contrast between the brilliancy of blossoms whose
marrier has been an insect, and the dinginess of flowers indebted to the
services of the wind. Can it be that both kinds of flowers are descended
from forms resembling each other in want of grace and colour? Such,
indeed, is the truth. But how, as the generations of the flowers
succeeded one another, did differences so striking come about? In our
rambles afield let us seek a clue to the mystery. It is late in
springtime, and near the border of a bit of swamp we notice a clump of
violets: they are pale of hue, and every stalk of them rises to an
almost weedy height.
[Illustration: Wild Rose, Single]
Twenty paces away, on a knoll of dry ground, we find more violets, but
these are in much deeper tints of azure and yellow, while their stalks
are scarcely more than half as tall as their brethren near the swamp.
Six weeks pass by. This time we walk to a wood-lot close to a brimming
pond. At its edge are more than a score wild-rose bushes. On the very
first of them we see that some of the blossoms are a light pink, others
a pink so deep as to seem dashed with vivid red. And while a flower here
and there is decidedly larger and more vigorous than its fellows, a few
of the blossoms are undersized and puny: the tide of life flows high and
merrily in a fortunate rose or two, it seems to ebb and falter by the
time it reaches one or two of their unhappy mates. As we search bush
after bush we are at last repaid for sundry scratches from their thorns
by securing a double rose, a "sport," as the gardener would call it. And
in the broad meadow between us and home we well know that for the quest
we can have not only four-leaved clovers, but perchance a handful of
five and six-leaved prizes. The secret is out. Flowers and leaves are
not cast like bullets in rigid moulds, but differ from their parents
much as children do. Usually the difference is slight, at times it is as
marked as in our double rose. Whenever the change in a flower is for the
worse, as in the sickly violets and roses we have observed, that
particular change ends there--with death. But when the change makes a
healthy flower a little more attractive to its insect ministers, it will
naturally be chosen by them for service, and these choosings, kept up
year after year, and century upon century, have at last accomplished
much the same result as if the moth, the bee, and the rest of them had
been given power to create blossoms of the most welcome forms, the most
alluring tints, the most bewitching perfumes.
In farther jaunts afield we shall discover yet more. It is May, and a
heavy rainstorm has caused the petals of a trillium to forget
themselves and return to their primitive hue of leafy green. A month
later we come upon a buttercup, one of whose sepals has grown out as a
small but perfect leaf. Later still in summer we find a rose in the same
surprising case, while not far off is a columbine bearing pollen on its
spurs instead of its anthers. What family tie is betrayed in all this?
No other than that sepals, petals, anthers and pistils are but leaves in
disguise, and that we have detected nature returning to the form from
which ages ago she began to transmute the parts of flowers in all their
teeming diversity. The leaf is the parent not only of all these but of
delicate tendrils, which save a vine the cost of building a stem stout
enough to lift it to open air and sunshine. However thoroughly, or
however long, a habit may be impressed upon a part of a plant, it may on
occasion relapse into a habit older still, resume a shape all but
forgotten, and thus tell a story of its past that otherwise might remain
forever unsuspected. Thus it is with the somewhat rare "sport" that
gives us a morning glory or a harebell in its primitive form of unjoined
petals. The bell form of these and similar flowers has established
itself by being much more effective than the original shape in dusting
insect servitors with pollen. Not only the forms of flowers but their
massing has been determined by insect preferences; a wide profusion of
blossoms grow in spikes, umbels, racemes and other clusters, all
economizing the time of winged allies, and attracting their attention
from afar as scattered blossoms would fail to do. Besides this massing,
we have union more intimate still as in the dandelion, the sun-flower
and the marigold. These and their fellow composites each seem an
individual; a penknife discloses each of them to be an aggregate of
blossoms. So gainful has this kind of co-operation proved that
composites are now dominant among plants in every quarter of the globe.
As to how composites grew before they learned that union is strength, a
hint is dropped in the "sport" of the daisy known as "the hen and
chickens," where perhaps as many as a dozen florets, each on a stalk of
its own, ray out from a mother flower.
While for the most part insects have been mere choosers from among
various styles of architecture set before them by plants, they have
sometimes risen to the dignity of builders on their own account, and
without ever knowing it. The buttress of the larkspur has sprung forth
in response to the pressure of one bee's weight after another, and many
a like structure has had the very same origin,--or shall we say,
provocation? In these and in other examples unnumbered, culminating in
the marvellous orchids and their ministers, there has come about the
closest adaptation of flower-shape to insect-form, the one now clearly
the counterpart of the other.
We must not forget that the hospitality of a flower is after all the
hospitality of an inn-keeper who earns and requires payment. Vexed as
flowers are apt to be by intruders that consume their stores without
requital, no wonder that they present so ample an array of repulsion and
defence. Best of all is such a resource as that of the red clover, which
hides its honey at the bottom of a tube so deep that only a friendly
bumblebee can sip it. Less effective, but well worth a moment's
examination, are the methods by which leaves are opposed as fences for
the discouragement of thieves. Here, in a Bellwort, is a perfoliate leaf
that encircles the stem upon which it grows; and there in a Honeysuckle
is a connate leaf on much the same plan, formed of two leaves, stiff and
strong, soldered at their bases. Sometimes the pillager meets prickles
that sting him, as in the roses and briers; and if he is a little fellow
he is sure to regard him with intense disgust, a bristly guard of wiry
hair--hence the commonness of that kind of fortification. Against
enemies of larger growth a tree or shrub will often aim sharp
thorns--another piece of masquerade, for thorns are but branches checked
in growth, and frowning with a barb in token of disappointment at not
being able to smile in a blossom. In every jot and tittle of barb and
prickle, of the glossiness which disheartens or the gumminess which
ensnares, we may be sure that equally with all the lures of hue, form
and scent, nothing, however trifling it may seem, is as we find it,
except through usefulness long tested and approved. In flowers, much
that at first glance looks like idle decoration, on closer scrutiny
reveals itself as service in disguise. In penetrating these disguises
and many more of other phases, the student of flowers delights to busy
himself. He loves, too, to detect the cousinship of plants through all
the change of dress and habit due to their rearing under widely
different skies and nurture, to their being surrounded by strangely
contrasted foes and friends. Often he can link two plants together only
by going into partnership with a student of the rocks, by turning back
the records of the earth until he comes upon a flower long extinct, a
plant which ages ago found the struggle for life too severe for it. He
ever takes care to observe his flowers accurately and fully, but chiefly
that he may rise from observation to explanation, from bare facts to
their causes, from declaring What, to understanding, Whence and How.
One of the stock resources of novelists, now somewhat out of date, was
the inn-keeper who beamed in welcome of his guest, grasped his hand in
gladness, and loaded a table for him in tempting array, and all with
intent that later in the day (or night) he might the more securely
plunge a dagger into his victim's heart--if, indeed, he had not already
improved an opportunity to offer to that victim's lips a poisoned cup.
This imagined treachery might well have been suggested by the behaviour
of certain alluring plants that so far from repelling thieves, or
discouraging pillagers, open their arms to all comers--with purpose of
the deadliest. Of these betrayers the chief is the round-leaved sun-dew,
which plies its nefarious vocation all the way from Labrador to Florida.
Its favourite site is a peat-bog or a bit of swampy lowland, where in
July and August we can see its pretty little white blossoms beckoning to
wayfaring flies and moths their token of good cheer! Circling the
flower-stalk, in rosette fashion, are a dozen or more round leaves, each
of them wearing scores of glands, very like little pins, a drop of gum
glistening on each and every pin by way of head. This appetizing gum is
no other than a fatal stick-fast, the raying pins closing in its aid the
more certainly to secure a hapless prisoner. Soon his prison-house
becomes a stomach for his absorption. Its duty of digestion done, the
leaf in all seeming guilessness once more expands itself for the
enticement of a dupe. To see how much the sun-dew must depend upon its
meal of insects we have only to pull it up from the ground. A touch
suffices--it has just root enough to drink by; the soil in which it
makes, and perhaps has been obliged to make, its home has nothing else
but drink to give it.
Less accomplished in its task of assassination is the common butterwort
to be found on wet rocks in scattered districts of Canada and the States
adjoining Canada. Surrounding its pretty violet flowers, of funnel
shape, are gummy leaves which close upon their all too trusting guests,
but with less expertness than the sun-dew's. The butterwort is but a
'prentice hand in the art of murder, and its intended victims often
manage to get away from it. Built on a very different model is the
bladderwort, busy in stagnant ponds near the sea coast from Nova Scotia
to Texas. Its little white spongy bladders, about a tenth of an inch
across, encircle the flowering stem by scores. From each bladder a bunch
of twelve or fifteen hairy prongs protrude, giving the structure no
slight resemblance to an insect form. These prongs hide a valve which,
as many an unhappy little swimmer can attest, opens inward easily
enough, but opens outward never. As in the case of its cousinry a-land,
the bladderwort at its leisure dines upon its prey.
[Illustration: Venus' Fly Trap--Open with a Welcome]
In marshy places near the mouth of the Cape Fear River, in the vicinity
of Wilmington, North Carolina, grows the Venus' fly-trap, most wonderful
of all the death-dealers of vegetation. Like much else in nature's
handiwork this plant might well have given inventors a hint worth
taking. The hairy fringes of its leaves are as responsive to a touch
from moth or fly as the sensitive plant itself. And he must be either a
very small or a particularly sturdy little captive that can escape
through the sharp opposed teeth of its formidable snare. It is one of
the unexplained puzzles of plant life that the Venus' fly-trap, so
marvellous in its ingenuity, should not only be confined to a single
district, but should seem to be losing its hold of even that small
kingdom. Of still another type is the pitcher plant, or side-saddle
flower, which flaunts its deep purple petals in June in many a peat-bog
from Canada southward to Louisiana and Florida. Its leaves develop
themselves into lidded cups, half-filled with sweetish juice, which
first lures a fly or ant, then makes him tipsy, and then despatches him.
The broth resulting is both meat and drink to the plant, serving as a
store and reservoir against times of drought and scarcity.
[Illustration: Shut for Slaughter]
Now the question is, How came about this strange and somewhat horrid
means of livelihood? How did plants of so diverse families turn the
tables on the insect world, and learn to eat instead of being themselves
devoured? A beginner in the builder's art finds it much more gainful to
examine the masonry of foundations, the rearing of walls, the placing of
girders and joists, the springing of arches and buttresses, than to look
at a cathedral, a courthouse, or a bank, finished and in service. In
like manner a student of insect-eating plants tries to find their leaves
in the making, in all the various stages which bridge their common forms
with the shapes they assume when fully armed and busy. Availing himself
of the relapses into old habits which plants occasionally exhibit under
cultivation, Mr. Dickson has taught us much regarding the way the
pitcher plant of Australia, the _Cephalotus_, has come to be what it is.
He has arranged in a connected series all the forms of its leaf from
that of a normal leaf with a mere dimple in it, to the deeply pouched
and lidded pitcher ready for deceitful hospitalities. And similar
transformations have without doubt taken place in the pitcher plants of
America. Observers in the Cape of Good Hope have noted two plants
_Roridula dentata_ and _Biblys gigantea_, which are evidently following
in the footsteps of the sundews, and may be expected in the fulness of
years to be their equal partners in crime. But why need we wander so far
as South Africa to find the germs of this strange rapacity when we can
see at home a full dozen species of catch-fly, sedums, primulas, and
geraniums pouring out glutinous juices in which insects are entangled?
Let stress of hunger, long continued, force any of these to turn its
attention to the dietary thus proffered, and how soon might not the
plant find in felony the sustenance refused to honest toil?
But after all the plants that have meat for dinner are only a few. The
greater part of the vegetable kingdom draws its supplies from the air
and the soil. Those plants, and they are many, that derive their chief
nourishment from the atmosphere have a decidedly thin diet. Which of us
would thrive on milk at the rate of a pint to five hogsheads of water?
Such is the proportion in which air contains carbonic acid gas, the main
source of strength for many thousands of trees, shrubs, and other
plants. No wonder that they array themselves in so broad an expanse of
leafage. An elm with a spread of seventy feet is swaying in the summer
breeze at least five acres of foliage as its lungs and stomach. Beyond
the shade of elms and maples let us stroll past yonder stretch of
pasture and we shall notice how the grass in patches here and there
deepens into green of the richest--a plain token of moisture in the
hollows--a blessing indeed in this dry weather. In the far West and
Northwest the buffalo grass has often to contend with drought for months
together, so that it has learned to strike deep in quest of water to
quench its thirst. It is a by-word among the ranchmen that the roots go
clear through the earth and are clinched as they sprout from the ground
in China. Joking apart, they have been found sixty-eight feet below the
surface of the prairie, and often in especially dry seasons cattle would
perish were not these faithful little well-diggers and pumpers
constantly at work for them. In the river valleys of Arizona although
the air is dry the subsoil water is near the surface of the ground. Here
flourishes the mesquit tree, _Prosopis juliflora_, with a tale to tell
well worth knowing. When a mesquit seems stunted, it is because its
strength is withdrawn for the task of delving to find water; where a
tree grows tall with goodly branches, it betokens success in reaching
moisture close at hand. Thus in shrewdly reading the landscape a
prospector can choose the spot where with least trouble he can sink his
well. And plants discover provender in the soil as well as drink. Nearer
home than Arizona we have only to dislodge a beach pea from the ground
to see how far in search of food its roots have dug amid barren stones
and pebbles. Often one finds a plant hardly a foot high with roots
extending eight feet from its stem.
And beyond the beaches where the beach peas dig so diligently are the
seaweeds--with a talent for picking and choosing all their own. Dr.
Julius Sachs, a leading German botanist, believes that the parts of
plants owe their form, as crystals do, to their peculiarities of
substance; that just as salt crystallizes in one shape and sugar in
another, so a seaweed or a tulip is moulded by the character of its
juices. Something certainly of the crystal's faculty for picking out
particles akin to itself, and building with them, is shown by the kelp
which attracts from the ocean both iodine and bromine--often dissolved
though they are in a million times their bulk of sea water. This trait
of choosing this or that dish from the feast afforded by sea or soil or
air is not peculiar to the seaweeds; every plant displays it. Beech
trees love to grow on limestone and thus declare to the explorer the
limestone ridge he seeks. In the Horn silver mine, of Utah, the zinc
mingled with the silver ore is betrayed by the abundance of the zinc
violet, a delicate and beautiful cousin of the pansy. In Germany this
little flower is admittedly a signal of zinc in the earth, and zinc is
found in its juices. The late Mr. William Dorn, of South Carolina, had
faith in a bush, of unrecorded name, as betokening gold-bearing veins
beneath it. That his faith was not without foundation is proved by the
large fortune he won as a gold miner in the Blue Ridge country--his
guide the bush aforesaid. Mr. Rossiter W. Raymond, the eminent mining
engineer of New York, has given some attention to this matter of
"indicative plants." He is of the opinion that its unwritten lore among
practical miners, prospectors, hunters, and Indians is well worth
sifting. Their observations, often faulty, may occasionally be sound and
valuable enough richly to repay the trouble of separating truth from
error. When we see how important as signs of water many plants can be,
why may we not find other plants denoting the minerals which they
especially relish as food or condiment?
Of more account than gold or silver are the harvests of wheat and corn
that ripen in our fields. There the special appetites of plants have
much more than merely curious interest for the farmer. He knows full
well that his land is but a larder which serves him best when not part
but all its stores are in demand. Hence his crop "rotation," his
succession of wheat to clover, of grass to both. Were he to grow barley
every year he would soon find his soil bared of all the food that barley
asks, while fare for peas or clover stood scarcely broached. If he
insists on planting barley always, then he must perforce restore to the
land the food for barley constantly withdrawn.
[Illustration: Maple Seed, with pair of wings]
A plant may diligently find food and drink, pour forth delicious nectar,
array itself with flowers as gayly as it can, and still behold its work
unfinished. Its seed may be produced in plenty, and although as far as
that goes it is well, it is not enough. Of what avail is all this seed
if it falls as it ripens upon soil already overcrowded with its kind?
Hence the vigorous emigration policy to be observed in plants of every
name. Hence the fluffy sails set to catch the passing breeze by the
dandelion, the thistle and by many more, including the southern plant of
snowy wealth whose wings are cotton. With the same intent of seeking new
fields are the hooks of the burdock, the unicorn plant, and the
bur-parsley which impress as carriers the sheep and cattle upon a
thousand hills. The Touch-me-not and the herb Robert adopt a different
plan, and convert their seed-cases into pistols for the firing of seeds
at as wide range as twenty feet or more. The maple, the ash, the
hornbeam, the elm and the birch have yet another method of escape from
the home acre. Their seeds are winged, and torn off in a gale are
frequently borne two hundred yards away. And stronger wings than these
are plied in the cherry tree's service. The birds bide the time when a
blush upon the fruit betrays its ripeness. Then the cherries are
greedily devoured, and their seed, preserved from digestion in their
stony cases are borne over hill, dale, and river to some islet or
brookside where a sprouting cherry plant will be free from the stifling
rivalries suffered by its parent. Yoked in harness with sheep, ox, and
bird as planter is yonder nimble squirrel. We need not begrudge him the
store of nuts he hides. He will forget some of them, he will be
prevented by fright or frost from nibbling yet more, and so without
intending it he will ensure for others and himself a sure succession of
acorns and butternuts.
Very singular are the seeds that have come to resemble beetles; among
these may be mentioned the seeds of the castor-oil plant and of the
_Iatropha_. The pod of the _Biserrula_ looks like a worm, and a worm
half-coiled might well have served as a model for the mimicry of the
_Scorpiurus vermiculata_. All these are much more likely to enlist the
services of birds than if their resemblances to insects were less
striking.
Nature elsewhere rich in hints to the gardener and the farmer is not
silent here. A lesson plainly taught in all this apparatus for the
dispersal of seeds is that the more various the planting the fuller the
harvest. Now that from the wheat fields comes a cry of disappearing
gains, it is time to heed the story told in the unbroken prairie that
diversity in sowing means wealth in reaping.
In a field of growing flax we can find--somewhat oftener than the farmer
likes--a curious tribe of plants, the dodders. Their stems are thin and
wiry, and their small white flowers, globular in shape, make the azure
blossoms of the flax all the lovelier by contrast. As their cousins the
morning glories are to this day, the dodders in their first estate were
true climbers. Even now they begin life in an honest kind of way with
roots of their own that go forth as roots should, seeking food where it
is to be found in the soil. But if we pull up one of these little
club-shaped roots we shall see that it has gone to work feebly and
doubtfully; it seems to have a skulking expectation of dinner without
having to dig and delve for it in the rough dirty ground. Nor is this
expectation unfounded. Watch the stem of a sister dodder as it rises
from the earth day by day, and it will be observed to clasp a stalk of
flax very tightly; so tightly that its suckers will absorb the juices of
its unhappy host. When, so very easily, it can regale itself with food
ready to hand why should it take the trouble to drudge for a living?
Like many another pauper demoralized by being fed in idleness, the plant
now abandons honest toil, its roots from lack of exercise wither away,
and for good and all it ceases to claim any independence whatever.
Indeed, so deep is the dodder's degradation that if it cannot find a
stem of flax, or hop, or other plant whereon to climb and thrive, it
will simply shrivel and die rather than resume habits of industry so
long renounced as to be at last forgotten.
Like the lowly dodder the mistletoe is a climber that has discovered
large opportunities of theft in ascending the stem of a supporting
plant. On this continent the mistletoe scales a wide variety of trees
and shrubs, preferring poplars and apple trees, where these are to be
had. Its extremely slender stem, its meagre leaves, its small flowers,
greenish and leathery, are all eloquent as to the loss of strength and
beauty inevitable to a parasite. Rising as this singular plant does out
of the branches of another with a distinct life all its own, it is no
other than a natural graft, and it is very probable that from the hint
it so unmistakably gives the first gardeners were not slow to adopt
grafts artificial--among the resources which have most enriched and
diversified both flowers and fruits. The dodders and mistletoes rob
juices from the stem and branches of their unfortunate hosts; more
numerous still are the unbidden guests that fasten themselves upon the
roots of their prey. The broom-rape, a comparatively recent immigrant
from Europe, lays hold of the roots of thyme in preference to other
place of entertainment; the Yellow Rattle, the Lousewort, and many more
attach themselves to the roots of grasses--frequently with a serious
curtailment of crop.
Yet in this very department of hers Nature has for ages hidden away what
has been disclosed within twenty years as one of her least suspected
marvels. It is no other than that certain parasites of field and meadow
so far from being hurtful, are well worth cultivating for the good they
do. For a long time the men who devoted themselves to the study of peas,
beans, clovers, and other plants of the pulse family, were confronted
with a riddle they could not solve. These plants all manage to enrich
themselves with compounds of nitrogen, which make them particularly
valuable as food, and these compounds often exist in a degree far
exceeding the rate at which their nitrogen comes out of the soil. And
this while they have no direct means of seizing upon the nitrogen
contained in its great reservoir--the atmosphere. Upon certain roots of
beans and peas it was noted that there were little round excrescences
about the size of a small pin's head. These excrescences on examination
with a microscope proved to be swarming with bacteria of minute
dimensions. Further investigation abundantly showed that these little
guests paid a handsome price for their board and lodging--while they
subsisted in part on the juices of their host they passed into the bean
or pea certain valuable compounds of nitrogen which they built from
common air. At the Columbian Exposition, of 1893, one of the striking
exhibits in the Agricultural Building set this forth in detail. Vials
were shown containing these tiny subterranean aids to the farmer, and
large photographs showed in natural size the vast increase of crop due
to the farmer's taking bacteria into partnership. To-day these little
organisms are cultivated of set purpose, and quest is being made for
similar bacteria suitable to be harnessed in producing wheat, corn, and
other harvests.
These are times when men of science are discontented with mere
observation. They wish to pass from watching things as nature presents
them to putting them into relations wholly new. In 1866 DeBary, a close
observer of lichens, felt confident that a lichen was not the simple
growth it seems, but a combination of fungus and algæ. This opinion, so
much opposed to honoured tradition, was scouted, but not for long.
Before many months had passed Stahl took known algæ, and upon them sowed
a known fungus, the result was a known lichen! The fungus turns out to
be no other than a slave-driver that captures algæ in colonies and makes
them work for him. He is, however, a slave-driver of an intelligent
sort; his captives thrive under his mastery, and increase more rapidly
for the healthy exercise he insists that they shall take.
It is an afternoon in August and the sultry air compels us to take
shelter in a grove of swaying maples. Beneath their shade every square
yard of ground bears a score of infant trees, very few of them as much
as a foot in stature. How vain their expectation of one day enjoying an
ample spread of branch and root, of rising to the free sunshine of upper
air! The scene, with its quivering rounds of sunlight, seems peace
itself, but the seeming is only a mask for war as unrelenting as that
of weaponed armies. For every ray of the sunbeam, for every atom of
food, for every inch of standing room, there is deadly rivalry. To begin
the fight is vastly easier than to maintain it, and not one in a hundred
of these bantlings will ever know maturity. We have only to do what
Darwin did--count the plants that throng a foot of sod in spring, count
them again in summer, and at the summer's end, to find how great the
inexorable carnage in this unseen combat, how few its survivors. So hard
here is the fight for a foothold, for daily bread, that the playfulness
inborn in every healthy plant can peep out but timidly and seldom. But
when strife is exchanged for peace, when a plant is once safely
sheltered behind a garden fence, then the struggles of the battlefield
give place to the diversions of the garrison--diversions not
infrequently hilarious enough. Now food abounds and superabounds;
henceforth neither drought nor deluge can work their evil will; insect
foes, as well as may be, are kept at bay; there is room in plenty
instead of dismal overcrowding. The grateful plant repays the care
bestowed upon it by bursting into a sportiveness unsuspected, and indeed
impossible, amidst the alarms and frays incessant in the wilderness. It
departs from parental habits in most astonishing fashion, puts forth
blossoms of fresh grace of form, of new dyes, of doubled magnitude. The
gardener's opportunity has come. He can seize upon such of these
"sports" as he chooses and make them the confirmed habits of his wards.
Take a stroll through his parterres and greenhouses, where side by side
he shows you pansies of myriad tints and the modest little wild violets
of kindred to the pansies' ancestral stock. Let him contrast for you
roses, asters, tuberous begonias, hollyhocks, dahlias, pelargoniums,
before cultivation and since. Were wild flowers clay, were the gardener
both painter and sculptor, he could not have wrought marvels more
glorious than these. In a few years the brethren of his guild have
brought about a revolution for which, if possible at all to her, nature
in the open fields would ask long centuries. And the gardener's
experiments with these strange children of his have all the charm of
surprise. No passive chooser is he of "sports" of promise, but an active
matchmaker between flowers often brought together from realms as far
apart as France and China. Sometimes his experiment is an instant
success. Mr. William Paul, a famous creator of splendid flowers, tells
us that at a time when climbing roses were either white or yellow, he
thought he would like to produce one of bright dark colour. Accordingly
he mated the Rose Athelin, of vivid crimson, with Russelliana, a hardy
climber, and lo, the flower he had imagined and longed for stood
revealed! But this hitting the mark at the first shot is uncommon good
fortune with the gardener. No experience with primrose or chrysanthemum
is long and varied enough to tell him how the crossing of two different
stocks will issue. A rose which season after season opposes only
indifference to all his pains may be secretly gathering strength for a
bound beyond its ancestral paths which will carry it much farther than
his hopes, or, perhaps, his wishes.
Most flowers are admired for their own sweet sake, but who thinks less
of an apple or cherry blossom because it bears in its beauty the promise
of delicious fruit? Put a red Astrachan beside a sorry crab, a Bartlett
pear next a tough, diminutive wild pear such as it is descended from, an
ear of milky corn in contrast with an ear one-fourth its size, each
grain of which, small and dry, is wrapped in a sheath by itself; and
rejoice that fruits and grains as well as flowers can learn new lessons
and remember them. At Concord, Massachusetts, in an honoured old age,
dwells Mr. Ephraim W. Bull. In his garden he delights to show the mother
vine of the Concord grape which he developed from a native wild grape
planted as long ago as 1843. Another "sport" of great value was the
nectarine, which was seized upon as it made its appearance on a peach
bough. Throughout America are scattered experiment stations, part of
whose business it is to provoke fresh varieties of wheat, or corn, or
other useful plant, and make permanent such of them as show special
richness of yield; earliness in ripening; stoutness of resistance to
Jack Frost, or blight, or insect pests. Suppose that dire disaster
swept from off the earth every cereal used as food. Professor Goodale,
Professor Asa Gray's successor at Harvard University, has so much
confidence in the experiment stations of America that he deems them well
able to repair the loss we have imagined; within fifty years, he thinks,
from plants now uncultivated the task could be accomplished. Among the
men who have best served the world by hastening nature's steps in the
improvement of flowers and fruits, stands Mr. Vilmorin, of Paris. He it
was who in creating the sugar beet laid the foundation for one of the
chief industries of our time. One of his rules is to select at first not
the plant which varies most in the direction he wishes, but the plant
that varies most in any direction whatever. From it, from the
instability of its very fibres, its utter forgetfulness of ancestral
traditions, he finds it easiest in the long run to obtain and to
establish the character he seeks of sweetness, or size, or colour.
Of flowering plants there are about 110,000, of these the farmer and the
gardener between them have scarcely tamed and trained 1,000. What new
riches, therefore, may we not expect from the culture of the future?
Already in certain northern flower-pots the trillium, the bloodroot, the
dog's-tooth violet, and the celandine are abloom in May; as June
advances, the wild violet, the milkweed, the wild lily-of-the-valley,
unfold their petals; later in summer the dog-rose displays its charms
and breathes its perfume. All respond kindly to care, and were there
more of this hospitality, were the wild roses which the botanist calls
_blanda_ and _lucida_, were the cardinal flowers, the May flowers, and
many more of the treasures of glen and meadow, made welcome with
thoughtful study of their wants and habits, much would be done to extend
the wealth of our gardens. Let a hepatica be plucked from its home in a
rocky crevice where one marvels how it ever contrived to root itself and
find subsistence. Transplant it to good soil, give it a little care--it
asks none--and it will thrive as it never throve before; proving once
again that plants do not grow where they like, but where they can. The
Russian columbine rewards its cultivator with a wealth of blossoms that
plainly say how much it rejoices in his nurture of it, in its escape
from the frost and tempest that have assailed it for so many
generations.
But here we must be content to take a leaf out of nature's book, and
look for small results unless our experiments are broadly planned. It is
in great nurseries and gardens, not in little door-yards that "sports"
are likely to arise, and to meet the skill which can confirm them as new
varieties.
Japan has much to teach us with regard to flowers: nowhere else on earth
are they so sedulously cultivated, or so faithfully studied in all their
changeful beauty. Perhaps the most striking revelation of the Japanese
gardener is his treatment of flowering shrubs and flowering trees
disposed in masses. Happy the visitors to Tokio who sees in springtime
the cherry blossoms ready to lend their witchery to the Empress's
reception! Much is done to extend the reign of beauty in a garden when
it is fitly bordered with berry-bearers. Rows of mountain ash,
snow-berry, and hawthorn trees give colour just when colour is most
effective, at the time when most flowers are past and gone.
In the practical bit of ground where the kitchen garden meets the
flowers, Japan has long since enlarged its bill of fare with the tuber
of a cousin of our common hedge nettle, with the roots of the large
burdock, commoner still. In Florida, the calla lily has use as well as
beauty; it is cultivated for its potato-like tubers.
Much as the study of flowers heightens our interest in them, their
first, their chief enduring charm consists in their simple beauty--their
infinitely varied grace of form, their exhaustless wealth of changeful
tints. Off we go with delight from desk and book to a breezy field, a
wimpling brook, a quiet pond in woodland shade. A dozen rambles from May
to October will show us all the floral procession, which, beginning with
the trilliums and the violets, ends at the approach of frost with the
golden-rod and aster. But who ever formed an engaging acquaintance
without wishing it might become a close friendship? Never yet did the
observant culler of bloodroot and columbine rest satisfied with merely
knowing their names, and how can more be known unless flowers are set
up in a portrait gallery of their own for the leisurely study of their
lineaments and lineage?
A word then as to the best way to gather wild flowers. A case for them
in the form of a round tube, closed at the ends, with a hinged cover,
can be made by a tinsmith at small cost. Its dimensions should be about
thirty inches in length by five inches in diameter, with a strap
attached to carry it by. At still less expense a frame can be made, or
bought, formed of two boards, one-eighth of an inch thick, twenty-four
inches long and eighteen inches broad, with two thin battens fastened
across them to prevent warping. A quire of soft brown paper, newspaper
will do, and a strap to hold all together, complete the outfit.
Our gathered treasures at home, we may wish to deck a table or a mantel
with a few of them. The lives of impressed blossoms can be, much
prolonged by exercising a little care. Punch holes in a round of
cardboard and put the stalks through these holes before placing the
flowers in a vase. This prevents the stalks touching each other, and so
decaying before their time. A little charcoal in the water tends to keep
it pure; the water should be changed daily.
A flower will fade at last be it tended ever so carefully. If we wish to
preserve it dried we can best do so as soon as we bring it home, by
placing it between sheets of absorbent paper (newspaper will do) well
weighted down, the paper to be renewed if the plants are succulent and
if there is any risk of mildew. But a dried plant after all is only a
mummy. Its colours are gone; its form bruised and crumpled, gives only a
faint suggestion of it as it lived and breathed. Other and more pleasant
reminders of our summer rambles can be ours. With a camera of fair size
it is easy to take pictures of flowers at their best; these pictures can
be coloured in their natural tints with happy effect. In this art Mrs.
Cornelius Van Brunt, of New York, has attained extraordinary success.
Or, instead of the camera, why not at first invoke the brush and
colour-box? Only a little skill in handling them is enough for a
beginning. Practice soon increases deftness in this art as in every
other, and in a few short weeks floral portraits are painted with a
truth to nature denied the unaided pencil. For what flower, however meek
and lowly, could ever tell its story in plain black and white?
The amateur painter of flowers learns a good many things by the way; at
the very outset, that drawing accurate and clear must be the groundwork
of any painting worthy the name. Both in the use of pencil and brush
there must be a degree of painstaking observation, wholesome as a
discipline and delightful in its harvests. How many of us, unused to the
task of careful observation, can tell the number of the musk-mallow's
petals, or mark on paper the depth of fringe on a gentian, or match from
a series of dyed silks the hues of a common buttercup? Drawing and
painting sharpen the eye, and make the fingers its trained and ready
servants. From the very beginning of one's task in limning bud and
blossom, we see them richer in grace and loveliness than ever before.
When wild flowers are sketched as they grow it is often easy to give
them a new interest by adding the portraits of their insect servitors.
Amateurs who are so fortunate as to visit the West Indies have an
opportunity to paint the wonderful blossoms of the Marcgravia, whose
minister, a humming bird, quivers above it like a bit of rainbow
loosened from the sky.
Early in the history of art the wild flowers lent their aid to
decoration. The acanthus which gave its leaves to crest the capital of
the Corinthian column, the roses conventionalized in the rich fabrics of
ancient Persia, until they have been thought sheer inventions of the
weaver, are among the first items of an indebtedness which has steadily
grown in volume until to-day, when the designers who find their
inspiration in the flowers are a vast and increasing host. In a modern
mansion of the best type the outer walls are enriched with the leonine
beauty of the sun-flower; within, the mosaic floors, the silk, and paper
hangings, repeat themes suggested by the vine, the wild clematis and the
Mayflower. The stained glass windows from New York, where their
manufacture excels that of any other city in the world, are exquisite
with boldly treated lilies, poppies, and columbines. In the
drawing-room are embroideries designed by two young women of Salem,
Massachusetts, who have established a thriving industry in transferring
the glow of wild flowers to the adornment of noble houses such as this.
As one goes from studio to studio, it is cheering to find so many men
and women busy at work which is more joyful than play,--which in many
cases first taken up as a recreation disclosed a vein of genuine talent
and so pointed to a career more delightful than any other,--because it
chimes in with the love of beauty and the power of giving it worthy
expression.
TRANSCRIBER'S NOTE: Unable to verify "partnery" nor "tucu-tucu", but
they have been left as in the original.
The word "sylvain" has been verified as a valid word, and therefore
it has been left as in the original.
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