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Title: The Foundations of the Origin of Species
Two Essays written in 1842 and 1844
Author: Charles Darwin
Editor: Francis Darwin
Release Date: September 22, 2007 [EBook #22728]
Language: English
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THE FOUNDATIONS OF THE ORIGIN OF SPECIES
CAMBRIDGE UNIVERSITY PRESS
London: FETTER LANE, E.C.
C. F. CLAY, MANAGER
{Illustration}
Edinburgh: 100, PRINCES STREET
ALSO
London: H. K. LEWIS, 136, GOWER STREET, W.C.
Berlin: A. ASHER AND CO.
Leipzig: F. A. BROCKHAUS
New York: G. P. PUTNAM'S SONS
Bombay and Calcutta: MACMILLAN AND Co., LTD.
_All rights reserved_
{Illustration: Charles Darwin from a photograph by Maull & Fox in 1854}
THE FOUNDATIONS OF THE ORIGIN OF SPECIES
TWO ESSAYS WRITTEN IN 1842 AND 1844
by
CHARLES DARWIN
Edited by his son
FRANCIS DARWIN
Honorary Fellow of Christ's College
Cambridge:
at the University Press
1909
Astronomers might formerly have said that God ordered each planet
to move in its particular destiny. In same manner God orders each
animal created with certain form in certain country. But how much
more simple and sublime power,--let attraction act according to
certain law, such are inevitable consequences,--let animal(s) be
created, then by the fixed laws of generation, such will be their
successors.
From DARWIN'S _Note Book_, 1837, p. 101.
TO THE MASTER AND FELLOWS
OF CHRIST'S COLLEGE, THIS
BOOK IS DEDICATED BY THE
EDITOR IN TOKEN OF RESPECT
AND GRATITUDE
CONTENTS
ESSAY OF 1842
PAGES
INTRODUCTION xi
PART I
§ i. On variation under domestication, and on the principles
of selection 1
§ ii. On variation in a state of nature and on the natural
means of selection 4
§ iii. On variation in instincts and other mental attributes 17
PART II
§§ iv. and v. On the evidence from Geology. (The reasons for
combining the two sections are given in the Introduction) 22
§ vi. Geographical distribution 29
§ vii. Affinities and classification 35
§ viii. Unity of type in the great classes 38
§ ix. Abortive organs 45
§ x. Recapitulation and conclusion 48
ESSAY OF 1844
PART I
CHAPTER I 57-80
ON THE VARIATION OF ORGANIC BEINGS UNDER DOMESTICATION;
AND ON THE PRINCIPLES OF SELECTION.
Variation
On the hereditary tendency
Causes of Variation
On Selection
Crossing Breeds
Whether our domestic races have descended from one or more wild stocks
Limits to Variation in degree and kind
In what consists Domestication--Summary
CHAPTER II 81-111
ON THE VARIATION OF ORGANIC BEINGS IN A WILD STATE;
ON THE NATURAL MEANS OF SELECTION; AND ON THE
COMPARISON OF DOMESTIC RACES AND TRUE SPECIES.
Variation
Natural means of Selection
Differences between "Races" and "Species":-first, in their trueness
or variability
Difference between "Races" and "Species" in fertility when crossed
Causes of Sterility in Hybrids
Infertility from causes distinct from hybridisation
Points of Resemblance between "Races" and "Species"
External characters of Hybrids and Mongrels
Summary
Limits of Variation
CHAPTER III 112-132
ON THE VARIATION OF INSTINCTS AND OTHER MENTAL
ATTRIBUTES UNDER DOMESTICATION AND IN A STATE OF
NATURE; ON THE DIFFICULTIES IN THIS SUBJECT; AND
ON ANALOGOUS DIFFICULTIES WITH RESPECT TO CORPOREAL
STRUCTURES.
Variation of mental attributes under domestication
Hereditary habits compared with instincts
Variation in the mental attributes of wild animals
Principles of Selection applicable to instincts
Difficulties in the acquirement of complex instincts by Selection
Difficulties in the acquirement by Selection of complex corporeal
structures
PART II
ON THE EVIDENCE FAVOURABLE AND OPPOSED TO THE VIEW
THAT SPECIES ARE NATURALLY FORMED RACES, DESCENDED
FROM COMMON STOCKS.
CHAPTER IV 133-143
ON THE NUMBER OF INTERMEDIATE FORMS REQUIRED ON THE
THEORY OF COMMON DESCENT; AND ON THEIR ABSENCE
IN A FOSSIL STATE
CHAPTER V 144-150
GRADUAL APPEARANCE AND DISAPPEARANCE OF SPECIES.
Gradual appearance of species
Extinction of species
CHAPTER VI
ON THE GEOGRAPHICAL DISTRIBUTION OF ORGANIC BEINGS
IN PAST AND PRESENT TIMES.
SECTION FIRST 151-174
Distribution of the inhabitants in the different continents
Relation of range in genera and species
Distribution of the inhabitants in the same continent
Insular Faunas
Alpine Floras
Cause of the similarity in the floras of some distant mountains
Whether the same species has been created more than once
On the number of species, and of the classes to which they belong
in different regions
SECOND SECTION 174-182
Geographical distribution of extinct organisms
Changes in geographical distribution
Summary on the distribution of living and extinct organic beings
SECTION THIRD 183-197
An attempt to explain the foregoing laws of geographical
distribution, on the theory of allied species having a
common descent
Improbability of finding fossil forms intermediate between
existing species
CHAPTER VII 198-213
ON THE NATURE OF THE AFFINITIES AND CLASSIFICATION
OF ORGANIC BEINGS.
Gradual appearance and disappearance of groups
What is the Natural System?
On the kind of relation between distinct groups
Classification of Races or Varieties
Classification of Races and Species similar
Origin of genera and families
CHAPTER VIII 214-230
UNITY OF TYPE IN THE GREAT CLASSES; AND
MORPHOLOGICAL STRUCTURES.
Unity of Type
Morphology
Embryology
Attempt to explain the facts of embryology
On the graduated complexity in each great class
Modification by selection of the forms of immature animals
Importance of embryology in classification
Order in time in which the great classes have first appeared
CHAPTER IX 231-238
ABORTIVE OR RUDIMENTARY ORGANS.
The abortive organs of Naturalists
The abortive organs of Physiologists
Abortion from gradual disuse
CHAPTER X 239-255
RECAPITULATION AND CONCLUSION.
Recapitulation
Why do we wish to reject the Theory of Common Descent?
Conclusion
INDEX 257
Portrait _frontispiece_
Facsimile _to face_ p. 50
INTRODUCTION
We know from the contents of Charles Darwin's Note Book of 1837 that he
was at that time a convinced Evolutionist{1}. Nor can there be any doubt
that, when he started on board the _Beagle_, such opinions as he had
were on the side of immutability. When therefore did the current of his
thoughts begin to set in the direction of Evolution?
{1} See the extracts in _Life and Letters of Charles Darwin_, ii.
p. 5.
We have first to consider the factors that made for such a change. On
his departure in 1831, Henslow gave him vol. I. of Lyell's _Principles_,
then just published, with the warning that he was not to believe what he
read{2}. But believe he did, and it is certain (as Huxley has forcibly
pointed out{3}) that the doctrine of uniformitarianism when applied to
Biology leads of necessity to Evolution. If the extermination of a
species is no more catastrophic than the natural death of an individual,
why should the birth of a species be any more miraculous than the birth
of an individual? It is quite clear that this thought was vividly
present to Darwin when he was writing out his early thoughts in the 1837
Note Book{4}:--
"Propagation explains why modern animals same type as extinct, which is
law almost proved. They die, without they change, like golden pippins;
it is a _generation of species_ like generation _of individuals_."
"If _species_ generate other _species_ their race is not utterly cut
off."
{2} The second volume,--especially important in regard to
Evolution,--reached him in the autumn of 1832, as Prof. Judd has
pointed out in his most interesting paper in _Darwin and Modern
Science_. Cambridge, 1909.
{3} Obituary Notice of C. Darwin, _Proc. R. Soc._ vol. 44.
Reprinted in Huxley's _Collected Essays_. See also _Life and
Letters of C. Darwin_, ii. p. 179.
{4} See the extracts in the _Life and Letters_, ii. p. 5.
These quotations show that he was struggling to see in the origin of
species a process just as scientifically comprehensible as the birth of
individuals. They show, I think, that he recognised the two things not
merely as similar but as identical.
It is impossible to know how soon the ferment of uniformitarianism began
to work, but it is fair to suspect that in 1832 he had already begun to
see that mutability was the logical conclusion of Lyell's doctrine,
though this was not acknowledged by Lyell himself.
There were however other factors of change. In his Autobiography{5} he
wrote:--"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
southward 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 they differ slightly on each
island of the group; none of the 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."
{5} _Life and Letters_, i. p. 82.
Again we have to ask: how soon did any of these influences produce an
effect on Darwin's mind? Different answers have been attempted.
Huxley{6} held that these facts could not have produced their essential
effect until the voyage had come to an end, and the "relations of the
existing with the extinct species and of the species of the different
geographical areas with one another were determined with some
exactness." He does not therefore allow that any appreciable advance
towards evolution was made during the actual voyage of the _Beagle_.
{6} _Obituary Notice_, _loc. cit._
Professor Judd{7} takes a very different view. He holds that November
1832 may be given with some confidence as the "date at which Darwin
commenced that long series of observations and reasonings which
eventually culminated in the preparation of the _Origin of Species_."
{7} _Darwin and Modern Science._
Though I think these words suggest a more direct and continuous march
than really existed between fossil-collecting in 1832 and writing the
_Origin of Species_ in 1859, yet I hold that it was during the voyage
that Darwin's mind began to be turned in the direction of Evolution, and
I am therefore in essential agreement with Prof. Judd, although I lay
more stress than he does on the latter part of the voyage.
Let us for a moment confine our attention to the passage, above quoted,
from the Autobiography and to what is said in the Introduction to the
_Origin_, Ed. i., viz. "When on board H.M.S. 'Beagle,' as naturalist, I
was much struck with certain facts in the distribution of the
inhabitants of South America, and in the geological relations of the
present to the past inhabitants of that continent." These words,
occurring where they do, can only mean one thing,--namely that the facts
suggested an evolutionary interpretation. And this being so it must be
true that his thoughts _began to flow in the direction of Descent_ at
this early date.
I am inclined to think that the "new light which was rising in his
mind{8}" had not yet attained any effective degree of steadiness or
brightness. I think so because in his Pocket Book under the date 1837 he
wrote, "In July opened first note-book on 'transmutation of species.'
Had been greatly struck _from about month of previous March_{9} on
character of South American fossils, and species on Galapagos
Archipelago. These facts origin (_especially latter_), of all my views."
But he did not visit the Galapagos till 1835 and I therefore find it
hard to believe that his evolutionary views attained any strength or
permanence until at any rate quite late in the voyage. The Galapagos
facts are strongly against Huxley's view, for Darwin's attention was
"thoroughly aroused{10}" by comparing the birds shot by himself and by
others on board. The case must have struck him at once,--without waiting
for accurate determinations,--as a microcosm of evolution.
{8} Huxley, _Obituary_, p. xi.
{9} In this citation the italics are mine.
{10} _Journal of Researches_, Ed. 1860, p. 394.
It is also to be noted, in regard to the remains of extinct animals,
that, in the above quotation from his Pocket Book, he speaks of March
1837 as the time at which he began to be "greatly struck on character of
South American fossils," which suggests at least that the impression
made in 1832 required reinforcement before a really powerful effect was
produced.
We may therefore conclude, I think, that the evolutionary current in my
father's thoughts had continued to increase in force from 1832 onwards,
being especially reinforced at the Galapagos in 1835 and again in 1837
when he was overhauling the results, mental and material, of his
travels. And that when the above record in the Pocket Book was made he
unconsciously minimised the earlier beginnings of his theorisings, and
laid more stress on the recent thoughts which were naturally more vivid
to him. In his letter{11} to Otto Zacharias (1877) he wrote, "On my
return home in the autumn of 1836, I immediately began to prepare my
Journal for publication, and then saw how many facts indicated the
common descent of species." This again is evidence in favour of the view
that the later growths of his theory were the essentially important
parts of its development.
{11} F. Darwin's _Life of Charles Darwin_ (in one volume), 1892, p.
166.
In the same letter to Zacharias he says, "When I was on board the
_Beagle_ I believed in the permanence of species, but as far as I can
remember vague doubts occasionally flitted across my mind." Unless Prof.
Judd and I are altogether wrong in believing that late or early in the
voyage (it matters little which) a definite approach was made to the
evolutionary standpoint, we must suppose that in 40 years such advance
had shrunk in his recollection to the dimensions of "vague doubts." The
letter to Zacharias shows I think some forgetting of the past where the
author says, "But I did not become convinced that species were mutable
until, I think, two or three years had elapsed." It is impossible to
reconcile this with the contents of the evolutionary Note Book of 1837.
I have no doubt that in his retrospect he felt that he had not been
"convinced that species were mutable" until he had gained a clear
conception of the mechanism of natural selection, _i.e._ in 1838-9.
But even on this last date there is some room, not for doubt, but for
surprise. The passage in the Autobiography{12} is quite clear, namely
that in October 1838 he read Malthus's _Essay on the principle of
Population_ and "being well prepared to appreciate the struggle for
existence ..., 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 new
species. Here then I had at last got a theory by which to work."
{12} _Life and Letters_, i. p. 83.
It is surprising that Malthus should have been needed to give him the
clue, when in the Note Book of 1837 there should occur--however
obscurely expressed--the following forecast{13} of the importance of the
survival of the fittest. "With respect to extinction, we can easily see
that a variety of the ostrich (Petise{14}), may not be well adapted, and
thus perish out; or on the other hand, like Orpheus{15}, being
favourable, many might be produced. This requires the principle that the
permanent variations produced by confined breeding and changing
circumstances are continued and produce according to the adaptation of
such circumstances, and therefore that death of species is a consequence
(contrary to what would appear in America) of non-adaptation of
circumstances."
{13} _Life and Letters_, ii. p. 8.
{14} Avestruz Petise, _i.e. Rhea Darwini_.
{15} A bird.
I can hardly doubt, that with his knowledge of the interdependence of
organisms and the tyranny of conditions, his experience would have
crystallized out into "a theory by which to work" even without the aid
of Malthus.
In my father's Autobiography{16} he writes, "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{17}, which I had fairly copied out and still
possess." These two Essays, of 1842 and 1844, are now printed under the
title _The Foundations of the Origin of Species_.
{16} _Life and Letters_, i. p. 84.
{17} It contains as a fact 231 pp. It is a strongly bound folio,
interleaved with blank pages, as though for notes and additions.
His own MS. from which it was copied contains 189 pp.
It will be noted that in the above passage he does not mention the MS.
of 1842 as being in existence, and when I was at work on _Life and
Letters_ I had not seen it. It only came to light after my mother's
death in 1896 when the house at Down was vacated. The MS. was hidden in
a cupboard under the stairs which was not used for papers of any value,
but rather as an overflow for matter which he did not wish to destroy.
The statement in the Autobiography that the MS. was written in 1842
agrees with an entry in my fathers Diary:--
"1842. May 18th went to Maer. June 15th to Shrewsbury, and on 18th to
Capel Curig.... During my stay at Maer and Shrewsbury (five years after
commencement) wrote pencil sketch of my species theory." Again in a
letter to Lyell (June 18, 1858) he speaks of his "MS. sketch written out
in 1842{18}." In the _Origin of Species_, Ed. i. p. 1, he speaks of
beginning his speculations in 1837 and of allowing himself to draw up
some "short notes" after "five years' work," _i.e._ in 1842. So far
there seems no doubt as to 1842 being the date of the first sketch; but
there is evidence in favour of an earlier date{19}. Thus across the
Table of Contents of the bound copy of the 1844 MS. is written in my
father's hand "This was sketched in 1839." Again in a letter to Mr
Wallace{20} (Jan. 25, 1859) he speaks of his own contributions to the
Linnean paper{21} of July 1, 1858, as "written in 1839, now just twenty
years ago." This statement as it stands is undoubtedly incorrect, since
the extracts are from the MS. of 1844, about the date of which no doubt
exists; but even if it could be supposed to refer to the 1842 Essay, it
must, I think, be rejected. I can only account for his mistake by the
supposition that my father had in mind the date (1839) at which the
framework of his theory was laid down. It is worth noting that in his
Autobiography (p. 88) he speaks of the time "about 1839, when the theory
was clearly conceived." However this may be there can be no doubt that
1842 is the correct date. Since the publication of _Life and Letters_ I
have gained fresh evidence on this head. A small packet containing 13
pp. of MS. came to light in 1896. On the outside is written "First
Pencil Sketch of Species Theory. Written at Maer and Shrewsbury during
May and June 1842." It is not however written in pencil, and it consists
of a single chapter on _The Principles of Variation in Domestic
Organisms_. A single unnumbered page is written in pencil, and is headed
"Maer, May 1842, useless"; it also bears the words "This page was
thought of as introduction." It consists of the briefest sketch of the
geological evidence for evolution, together with words intended as
headings for discussion,--such as "Affinity,--unity of type,--foetal
state,--abortive organs."
{18} _Life and Letters_, ii. p. 116.
{19} _Life and Letters_, ii. p. 10.
{20} _Life and Letters_, ii. p. 146.
{21} _J. Linn. Soc. Zool._ iii. p. 45.
The back of this "useless" page is of some interest, although it does
not bear on the question of date,--the matter immediately before us.
It seems to be an outline of the Essay or sketch of 1842, consisting of
the titles of the three chapters of which it was to have consisted.
"I. The Principles of Var. in domestic organisms.
"II. The possible and probable application of these same principles to
wild animals and consequently the possible and probable production of
wild races, analogous to the domestic ones of plants and animals.
"III. The reasons for and against believing that such races have really
been produced, forming what are called species."
It will be seen that Chapter III as originally designed corresponds to
Part II (p. 22) of the Essay of 1842, which is (p. 7) defined by the
author as discussing "whether the characters and relations of animated
things are such as favour the idea of wild species being races descended
from a common stock." Again at p. 23 the author asks "What then is the
evidence in favour of it (the theory of descent) and what the evidence
against it." The generalised section of his Essay having been originally
Chapter III{22} accounts for the curious error which occurs in pp. 18
and 22 where the second Part of the Essay is called Part III.
{22} It is evident that _Parts_ and _Chapters_ were to some extent
interchangeable in the author's mind, for p. 1 (of the MS. we have
been discussing) is headed in ink Chapter I, and afterwards altered
in pencil to Part I.
The division of the Essay into two parts is maintained in the enlarged
Essay of 1844, in which he writes: "The Second Part of this work is
devoted to the general consideration of how far the general economy of
nature justifies or opposes the belief that related species and genera
are descended from common stocks." The _Origin of Species_ however is
not so divided.
We may now return to the question of the date of the Essay. I have found
additional evidence in favour of 1842 in a sentence written on the back
of the Table of Contents of the 1844 MS.--not the copied version but the
original in my father's writing: "This was written and enlarged from a
sketch in 37 pages{23} in Pencil (the latter written in summer of 1842
at Maer and Shrewsbury) in beginning of 1844, and finished it <_sic_> in
July; and finally corrected the copy by Mr Fletcher in the last week in
September." On the whole it is impossible to doubt that 1842 is the date
of the earlier of the two Essays.
{23} On p. 23 of the MS. of the _Foundations_ is a reference to the
"back of p. 21 bis": this suggests that additional pages had been
interpolated in the MS. and that it may once have had 37 in place
of 35 pp.
The sketch of 1842 is written on bad paper with a soft pencil, and is in
many parts extremely difficult to read, many of the words ending in mere
scrawls and being illegible without context. It is evidently written
rapidly, and is in his most elliptical style, the articles being
frequently omitted, and the sentences being loosely composed and often
illogical in structure. There is much erasure and correction, apparently
made at the moment of writing, and the MS. does not give the impression
of having been re-read with any care. The whole is more like hasty
memoranda of what was clear to himself, than material for the convincing
of others.
Many of the pages are covered with writing on the back, an instance of
his parsimony in the matter of paper{24}. This matter consists partly of
passages marked for insertion in the text, and these can generally
(though by no means always) be placed where he intended. But he also
used the back of one page for a preliminary sketch to be rewritten on a
clean sheet. These parts of the work have been printed as footnotes, so
as to allow what was written on the front of the pages to form a
continuous text. A certain amount of repetition is unavoidable, but much
of what is written on the backs of the pages is of too much interest to
be omitted. Some of the matter here given in footnotes may, moreover,
have been intended as the final text and not as the preliminary sketch.
{24} _Life and Letters_, i. p. 153.
When a word cannot be deciphered, it is replaced by:--, the
angular brackets being, as already explained, a symbol for an insertion
by the editor. More commonly, however, the context makes the
interpretation of a word reasonably sure although the word is not
strictly legible. Such words are followed by an inserted mark of
interrogation . Lastly, words inserted by the editor, of which the
appropriateness is doubtful, are printed thus .
Two kinds of erasure occur in the MS. of 1842. One by vertical lines
which seem to have been made when the 35 pp. MS. was being expanded into
that of 1844, and merely imply that such a page is done with: and
secondly the ordinary erasures by horizontal lines. I have not been
quite consistent in regard to these: I began with the intention of
printing (in square brackets) all such erasures. But I ultimately found
that the confusion introduced into the already obscure sentences was
greater than any possible gain; and many such erasures are altogether
omitted. In the same way I have occasionally omitted hopelessly obscure
and incomprehensible fragments, which if printed would only have
burthened the text with a string of s and queried words. Nor have I
printed the whole of what is written on the backs of the pages, where it
seemed to me that nothing but unnecessary repetition would have been the
result.
In the matter of punctuation I have given myself a free hand. I may no
doubt have misinterpreted the author's meaning in so doing, but without
such punctuation, the number of repellantly crabbed sentences would have
been even greater than at present. In dealing with the Essay of 1844, I
have corrected some obvious slips without indicating such alterations,
because the MS. being legible, there is no danger of changing the
author's meaning.
The sections into which the Essay of 1842 is divided are in the original
merely indicated by a gap in the MS. or by a line drawn across the page.
No titles are given except in the case of § VIII.; and § II. is the only
section which has a number in the original. I might equally well have
made sections of what are now subsections, _e.g. Natural Selection_ p.
7, or _Extermination_ p. 28. But since the present sketch is the germ of
the Essay of 1844, it seemed best to preserve the identity between the
two works, by using such of the author's divisions as correspond to the
chapters of the enlarged version of 1844. The geological discussion with
which Part II begins corresponds to two chapters (IV and V) of the 1844
Essay. I have therefore described it as §§ IV. and V., although I cannot
make sure of its having originally consisted of two sections. With this
exception the ten sections of the Essay of 1842 correspond to the ten
chapters of that of 1844.
The _Origin of Species_ differs from the sketch of 1842 in not being
divided into two parts. But the two volumes resemble each other in
general structure. Both begin with a statement of what may be called the
mechanism of evolution,--variation and selection: in both the argument
proceeds from the study of domestic organisms to that of animals and
plants in a state of nature. This is followed in both by a discussion of
the _Difficulties on Theory_ and this by a section _Instinct_ which in
both cases is treated as a special case of difficulty.
If I had to divide the _Origin_ (first edition) into two parts without
any knowledge of earlier MS., I should, I think, make Part II begin with
Ch. VI, _Difficulties on Theory_. A possible reason why this part of the
argument is given in Part I of the Essay of 1842 may be found in the
Essay of 1844, where it is clear that the chapter on instinct is placed
in Part I because the author thought it of importance to show that
heredity and variation occur in mental attributes. The whole question is
perhaps an instance of the sort of difficulty which made the author give
up the division of his argument into two Parts when he wrote the
_Origin_. As matters stand §§ IV. and V. of the 1842 Essay correspond to
the geological chapters, IX and X, in the _Origin_. From this point
onwards the material is grouped in the same order in both works:
geographical distribution; affinities and classification; unity of type
and morphology; abortive or rudimentary organs; recapitulation and
conclusion.
In enlarging the Essay of 1842 into that of 1844, the author retained
the sections of the sketch as chapters in the completer presentment. It
follows that what has been said of the relation of the earlier Essay to
the _Origin_ is generally true of the 1844 Essay. In the latter,
however, the geological discussion is, clearly instead of obscurely,
divided into two chapters, which correspond roughly with Chapters IX and
X of the _Origin_. But part of the contents of Chapter X (_Origin_)
occurs in Chapter VI (1844) on Geographical Distribution. The treatment
of distribution is particularly full and interesting in the 1844 Essay,
but the arrangement of the material, especially the introduction of §
III. p. 183, leads to some repetition which is avoided in the _Origin_.
It should be noted that Hybridism, which has a separate chapter (VIII)
in the _Origin_, is treated in Chapter II of the Essay. Finally that
Chapter XIII (_Origin_) corresponds to Chapters VII, VIII and IX of the
work of 1844.
The fact that in 1842, seventeen years before the publication of the
_Origin_, my father should have been able to write out so full an
outline of his future work, is very remarkable. In his Autobiography{25}
he writes of the 1844 Essay, "But at that time I overlooked one problem
of great importance.... This problem is the tendency in organic beings
descended from the same stock to diverge in character as they become
modified." The absence of the principle of divergence is of course also
a characteristic of the sketch of 1842. But at p. 37, the author is not
far from this point of view. The passage referred to is: "If any
species, _A_, in changing gets an advantage and that advantage ... is
inherited, _A_ will be the progenitor of several genera or even families
in the hard struggle of nature. _A_ will go on beating out other forms,
it might come that _A_ would people earth,--we may now not have one
descendant on our globe of the one or several original creations{26}."
But if the descendants of _A_ have peopled the earth by beating out
other forms, they must have diverged in occupying the innumerable
diverse modes of life from which they expelled their predecessors. What
I wrote{27} on this subject in 1887 is I think true: "Descent with
modification implies divergence, and we become so habituated to a belief
in descent, and therefore in divergence, that we do not notice the
absence of proof that divergence is in itself an advantage."
{25} _Life and Letters_, i. p. 84.
{26} In the footnotes to the Essay of 1844 attention is called to
similar passages.
{27} _Life and Letters_, ii. p. 15.
The fact that there is no set discussion on the principle of divergence
in the 1844 Essay, makes it clear why the joint paper read before the
Linnean Society on July 1, 1858, included a letter{28} to Asa Gray, as
well as an extract{29} from the Essay of 1844. It is clearly because the
letter to Gray includes a discussion on divergence, and was thus,
probably, the only document, including this subject, which could be
appropriately made use of. It shows once more how great was the
importance attached by its author to the principle of divergence.
{28} The passage is given in the _Life and Letters_, ii. p. 124.
{29} The extract consists of the section on _Natural Means of
Selection_, p. 87.
I have spoken of the hurried and condensed manner in which the sketch of
1842 is written; the style of the later Essay (1844) is more finished.
It has, however, the air of an uncorrected MS. rather than of a book
which has gone through the ordeal of proof sheets. It has not all the
force and conciseness of the _Origin_, but it has a certain freshness
which gives it a character of its own. It must be remembered that the
_Origin_ was an abstract or condensation of a much bigger book, whereas
the Essay of 1844 was an expansion of the sketch of 1842. It is not
therefore surprising that in the _Origin_ there is occasionally evident
a chafing against the author's self-imposed limitation. Whereas in the
1844 Essay there is an air of freedom, as if the author were letting
himself go, rather than applying the curb. This quality of freshness and
the fact that some questions were more fully discussed in 1844 than in
1859, makes the earlier work good reading even to those who are familiar
with the _Origin_.
The writing of this Essay "during the summer of 1844," as stated in the
Autobiography{30}, and "from memory," as Darwin says elsewhere{31}, was
a remarkable achievement, and possibly renders more conceivable the
still greater feat of the writing of the _Origin_ between July 1858 and
September 1859.
{30} _Life and Letters_, i. p. 84.
{31} _Life and Letters_, ii. p. 18.
It is an interesting subject for speculation: what influence on the
world the Essay of 1844 would have exercised, had it been published in
place of the Origin. The author evidently thought of its publication in
its present state as an undesirable expedient, as appears clearly from
the following extracts from the _Life and Letters_, vol. ii. pp.
16--18:
_C. Darwin to Mrs Darwin._
DOWN, _July 5, 1844_.
"... I have just finished my sketch of my species theory. If, as I
believe, my theory in time be accepted even by one competent judge, it
will be a considerable step in science.
"I therefore write this in case of my sudden death, as my most solemn
and last request, which I am sure you will consider the same as if
legally entered in my will, that you will devote £400 to its
publication, and further will yourself, or through Hensleigh{32}, take
trouble in promoting it. I wish that my sketch be given to some
competent person, with this sum to induce him to take trouble in its
improvement and enlargement. I give to him all my books on Natural
History, which are either scored or have references at the end to the
pages, begging him carefully to look over and consider such passages as
actually bearing, or by possibility bearing, on this subject. I wish you
to make a list of all such books as some temptation to an editor. I also
request that you will hand over him all those scraps roughly divided
into eight or ten brown paper portfolios. The scraps, with copied
quotations from various works, are those which may aid my editor. I also
request that you, or some amanuensis, will aid in deciphering any of the
scraps which the editor may think possibly of use. I leave to the
editor's judgment whether to interpolate these facts in the text, or as
notes, or under appendices. As the looking over the references and
scraps will be a long labour, and as the _correcting_ and enlarging and
altering my sketch will also take considerable time, I leave this sum of
£400 as some remuneration, and any profits from the work. I consider
that for this the editor is bound to get the sketch published either at
a publisher's or his own risk. Many of the scraps in the portfolios
contain mere rude suggestions and early views, now useless, and many of
the facts will probably turn out as having no bearing on my theory.
{32} Mrs Darwin's brother.
"With respect to editors, Mr Lyell would be the best if he would
undertake it; I believe he would find the work pleasant, and he would
learn some facts new to him. As the editor must be a geologist as well
as a naturalist, the next best editor would be Professor Forbes of
London. The next best (and quite best in many respects) would be
Professor Henslow. Dr Hooker would be _very_ good. The next, Mr
Strickland{33}. If none of these would undertake it, I would request you
to consult with Mr Lyell, or some other capable man, for some editor, a
geologist and naturalist. Should one other hundred pounds make the
difference of procuring a good editor, I request earnestly that you will
raise £500.
{33} After Mr Strickland's name comes the following sentence, which
has been erased, but remains legible. "Professor Owen would be very
good; but I presume he would not undertake such a work."
"My remaining collections in Natural History may be given to any one or
any museum where would be accepted...."
"Lyell, especially with the aid of Hooker (and of any good zoological
aid), would be best of all. Without an editor will pledge himself to
give up time to it, it would be of no use paying such a sum.
"If there should be any difficulty in getting an editor who would go
thoroughly into the subject, and think of the bearing of the passages
marked in the books and copied out of scraps of paper, then let my
sketch be published as it is, stating that it was done several years
ago{34}, and from memory without consulting any works, and with no
intention of publication in its present form."
{34} The words "several years ago, and" seem to have been added at
a later date.
The idea that the sketch of 1844 might remain, in the event of his
death, as the only record of his work, seems to have been long in his
mind, for in August, 1854, when he had finished with the Cirripedes, and
was thinking of beginning his "species work," he added on the back of
the above letter, "Hooker by far best man to edit my species volume.
August 1854."
I have called attention in footnotes to many points in which the
_Origin_ agrees with the _Foundations_. One of the most interesting is
the final sentence, practically the same in the Essays of 1842 and 1844,
and almost identical with the concluding words of the _Origin_. I have
elsewhere pointed out{35} that the ancestry of this eloquent passage may
be traced one stage further back,--to the Note Book of 1837. I have
given this sentence as an appropriate motto for the _Foundations_ in its
character of a study of general laws. It will be remembered that a
corresponding motto from Whewell's _Bridgewater Treatise_ is printed
opposite the title-page of the _Origin of Species_.
{35} _Life and Letters_, ii. p. 9.
Mr Huxley who, about the year 1887, read the Essay of 1844, remarked
that "much more weight is attached to the influence of external
conditions in producing variation and to the inheritance of acquired
habits than in the _Origin_." In the _Foundations_ the effect of
conditions is frequently mentioned, and Darwin seems to have had
constantly in mind the need of referring each variation to a cause. But
I gain the impression that the slighter prominence given to this view in
the _Origin_ was not due to change of opinion, but rather because he had
gradually come to take this view for granted; so that in the scheme of
that book, it was overshadowed by considerations which then seemed to
him more pressing. With regard to the inheritance of acquired characters
I am not inclined to agree with Huxley. It is certain that the
_Foundations_ contains strong recognition of the importance of germinal
variation, that is of external conditions acting indirectly through the
"reproductive functions." He evidently considered this as more important
than the inheritance of habit or other acquired peculiarities.
Another point of interest is the weight he attached in 1842-4 to
"sports" or what are now called "mutations." This is I think more
prominent in the _Foundations_ than in the first edition of the
_Origin_, and certainly than in the fifth and sixth editions.
Among other interesting points may be mentioned the "good effects of
crossing" being "possibly analogous to good effects of change in
condition,"--a principle which he upheld on experimental grounds in his
_Cross and Self-Fertilisation_ in 1876.
In conclusion, I desire to express my thanks to Mr Wallace for a
footnote he was good enough to supply: and to Professor Bateson, Sir W.
Thiselton-Dyer, Dr Gadow, Professor Judd, Dr Marr, Col. Prain and Dr
Stapf for information on various points. I am also indebted to Mr
Rutherford, of the University Library, for his careful copy of the
manuscript of 1842.
CAMBRIDGE,
_June 9, 1909._
EXPLANATION OF SIGNS, &c.
[] Means that the words so enclosed are erased in the original MS.
<> Indicates an insertion by the Editor.
_Origin_, Ed. vi. refers to the Popular Edition.
PART I.
§ I.
An individual organism placed under new conditions [often] sometimes
varies in a small degree and in very trifling respects such as stature,
fatness, sometimes colour, health, habits in animals and probably
disposition. Also habits of life develope certain parts. Disuse
atrophies. [Most of these slight variations tend to become hereditary.]
When the individual is multiplied for long periods by buds the variation
is yet small, though greater and occasionally a single bud or individual
departs widely from its type (example){36} and continues steadily to
propagate, by buds, such new kind.
{36} Evidently a memorandum that an example should be given.
When the organism is bred for several generations under new or varying
conditions, the variation is greater in amount and endless in kind
[especially{37} holds good when individuals have long been exposed to
new conditions]. The nature of the external conditions tends to effect
some definite change in all or greater part of offspring,--little food,
small size--certain foods harmless &c. &c. organs affected and
diseases--extent unknown. A certain degree of variation (Müller's
twins){38} seems inevitable effect of process of reproduction. But more
important is that simple generation, especially under new conditions
[when no crossing] infinite variation and not direct effect of
external conditions, but only in as much as it affects the reproductive
functions{39}. There seems to be no part (_beau ideal_ of liver){40} of
body, internal or external, or mind or habits, or instincts which does
not vary in some small degree and [often] some to a great amount.
{37} The importance of exposure to new conditions for several
generations is insisted on in the _Origin_, Ed. i. p. 7, also p.
131. In the latter passage the author guards himself against the
assumption that variations are "due to chance," and speaks of "our
ignorance of the cause of each particular variation." These
statements are not always remembered by his critics.
{38} Cf. _Origin_, Ed. i. p. 10, vi. p. 9, "Young of the same
litter, sometimes differ considerably from each other, though both
the young and the parents, as Müller has remarked, have apparently
been exposed to exactly the same conditions of life."
{39} This is paralleled by the conclusion in the _Origin_, Ed. i.
p. 8, that "the most frequent cause of variability may be
attributed to the male and female reproductive elements having been
affected prior to the act of conception."
{40} The meaning seems to be that there must be some variability in
the liver otherwise anatomists would not speak of the 'beau ideal'
of that organ.
[All such] variations [being congenital] or those very slowly acquired
of all kinds [decidedly evince a tendency to become hereditary], when
not so become simple variety, when it does a race. Each{41} parent
transmits its peculiarities, therefore if varieties allowed freely to
cross, except by the _chance_ of two characterized by same peculiarity
happening to marry, such varieties will be constantly demolished{42}.
All bisexual animals must cross, hermaphrodite plants do cross, it seems
very possible that hermaphrodite animals do cross,--conclusion
strengthened: ill effects of breeding in and in, good effects of
crossing possibly analogous to good effects of change in condition {43}.
{41} The position of the following passage is uncertain. "If
individuals of two widely different varieties be allowed to cross,
a third race will be formed--a most fertile source of the variation
in domesticated animals. If freely allowed, the characters of
pure parents will be lost, number of races thus but
differences besides the . But if varieties differing
in very slight respects be allowed to cross, such small variation
will be destroyed, at least to our senses,--a variation [clearly]
just to be distinguished by long legs will have offspring not to be
so distinguished. Free crossing great agent in producing uniformity
in any breed. Introduce tendency to revert to parent form."
{42} The swamping effect of intercrossing is referred to in the
_Origin_, Ed. i. p. 103, vi. p. 126.
{43} A discussion on the intercrossing of hermaphrodites in
relation to Knight's views occurs in the _Origin_, Ed. i. p. 96,
vi. p. 119. The parallelism between crossing and changed conditions
is briefly given in the _Origin_, Ed. i. p. 267, vi. p. 391, and
was finally investigated in _The Effects of Cross and
Self-Fertilisation in the Vegetable Kingdom_, 1876.
Therefore if in any country or district all animals of one species be
allowed freely to cross, any small tendency in them to vary will be
constantly counteracted. Secondly reversion to parent form--analogue of
_vis medicatrix_{44}. But if man selects, then new races rapidly
formed,--of late years systematically followed,--in most ancient times
often practically followed{45}. By such selection make race-horse,
dray-horse--one cow good for tallow, another for eating &c.--one plant's
good lay in leaves another in fruit &c. &c.: the same plant
to supply his wants at different times of year. By former means animals
become adapted, as a direct effect to a cause, to external conditions,
as size of body to amount of food. By this latter means they may also be
so adapted, but further they may be adapted to ends and pursuits, which
by no possibility can affect growth, as existence of tallow-chandler
cannot tend to make fat. In such selected races, if not removed to new
conditions, and preserved from all cross, after several generations
become very true, like each other and not varying. But man{46} selects
only what is useful and curious--has bad judgment, is
capricious,--grudges to destroy those that do not come up to his
pattern,--has no [knowledge] power of selecting according to internal
variations,--can hardly keep his conditions uniform,--[cannot] does not
select those best adapted to the conditions under which form lives,
but those most useful to him. This might all be otherwise.
{44} There is an article on the _vis medicatrix_ in Brougham's
_Dissertations_, 1839, a copy of which is in the author's library.
{45} This is the classification of selection into methodical and
unconscious given in the _Origin_, Ed. i. p. 33, vi. p. 38.
{46} This passage, and a similar discussion on the power of the
Creator (p. 6), correspond to the comparison between the selective
capacities of man and nature, in the _Origin_, Ed. i. p. 83, vi. p.
102.
§ II.
Let us see how far above principles of variation apply to wild animals.
Wild animals vary exceedingly little--yet they are known as
individuals{47}. British Plants, in many genera number quite uncertain
of varieties and species: in shells chiefly external conditions{48}.
Primrose and cowslip. Wild animals from different [countries can be
recognized]. Specific character gives some organs as varying. Variations
analogous in kind, but less in degree with domesticated animals--chiefly
external and less important parts.
{47} i.e. they are individually distinguishable.
{48} See _Origin_, Ed. i. p. 133, vi. p. 165.
Our experience would lead us to expect that any and every one of these
organisms would vary if taken away and placed
under new conditions. Geology proclaims a constant round of change,
bringing into play, by every possible change of climate and the death
of pre-existing inhabitants, endless variations of new conditions. These
generally very slow, doubtful though how far the
slowness would produce tendency to vary. But Geolog show
change in configuration which, together with the accidents of air and
water and the means of transportal which every being possesses, must
occasionally bring, rather suddenly, organism to new conditions and
expose it for several generations. Hence we should expect every now
and then a wild form to vary{49}; possibly this may be cause of some
species varying more than others.
{49} When the author wrote this sketch he seems not to have been so
fully convinced of the general occurrence of variation in nature as
he afterwards became. The above passage in the text possibly
suggests that at this time he laid more stress on _sports_ or
_mutations_ than was afterwards the case.
According to nature of new conditions, so we might expect all or
majority of organisms born under them to vary in some definite way.
Further we might expect that the mould in which they are cast would
likewise vary in some small degree. But is there any means of selecting
those offspring which vary in the same manner, crossing them and keeping
their offspring separate and thus producing selected races: otherwise as
the wild animals freely cross, so must such small heterogeneous
varieties be constantly counter-balanced and lost, and a uniformity of
character [kept up] preserved. The former variation as the direct and
necessary effects of causes, which we can see can act on them, as size
of body from amount of food, effect of certain kinds of food on certain
parts of bodies &c. &c.; such new varieties may then become adapted to
those external [natural] agencies which act on them. But can varieties
be produced adapted to end, which cannot possibly influence their
structure and which it is absurd to look as effects of chance. Can
varieties like some vars of domesticated animals, like almost all wild
species be produced adapted by exquisite means to prey on one animal or
to escape from another,--or rather, as it puts out of question effects
of intelligence and habits, can a plant become adapted to animals, as a
plant which cannot be impregnated without agency of insect; or hooked
seeds depending on animal's existence: woolly animals cannot have any
direct effect on seeds of plant. This point which all theories about
climate adapting woodpecker{50} to crawl up trees,
miseltoe, . But if every part of a plant or animal
was to vary , and if a being infinitely more sagacious than
man (not an omniscient creator) during thousands and thousands of years
were to select all the variations which tended towards certain ends ([or
were to produce causes which tended to the same end]), for instance,
if he foresaw a canine animal would be better off, owing to the country
producing more hares, if he were longer legged and keener
sight,--greyhound produced{51}. If he saw that aquatic skinned toes. If for some unknown cause he found it would
advantage a plant, which like most plants is occasionally visited by
bees &c.: if that plant's seed were occasionally eaten by birds and were
then carried on to rotten trees, he might select trees with fruit more
agreeable to such birds as perched, to ensure their being carried to
trees; if he perceived those birds more often dropped the seeds, he
might well have selected a bird who would rotten trees or
[gradually select plants which had proved to live on less and less
rotten trees]. Who, seeing how plants vary in garden, what blind foolish
man has done{52} in a few years, will deny an all-seeing being in
thousands of years could effect (if the Creator chose to do so), either
by his own direct foresight or by intermediate means,--which will
represent the creator of this universe. Seems usual means. Be it
remembered I have nothing to say about life and mind and _all_ forms
descending from one common type{53}. I speak of the variation of the
existing great divisions of the organised kingdom, how far I would go,
hereafter to be seen.
{50} The author may possibly have taken the case of the woodpecker
from Buffon, _Histoire Nat. des Oiseaux_, T. vii. p. 3, 1780, where
however it is treated from a different point of view. He uses it
more than once, see for instance _Origin_, Ed. i. pp. 3, 60, 184,
vi. pp. 3, 76, 220. The passage in the text corresponds with a
discussion on the woodpecker and the mistletoe in _Origin_, Ed. i.
p. 3, vi. p. 3.
{51} This illustration occurs in the _Origin_, Ed. i. pp. 90, 91,
vi. pp. 110, 111.
{52} See _Origin_, Ed. i. p. 83, vi. p. 102, where the word
_Creator_ is replaced by _Nature_.
{53} Note in the original. "Good place to introduce, saying reasons
hereafter to be given, how far I extend theory, say to all
mammalia--reasons growing weaker and weaker."
Before considering whether be any natural means of selection, and
secondly (which forms the 2nd Part of this sketch) the far more
important point whether the characters and relations of animated
are such as favour the idea of wild species being races
descended from a common stock, as the varieties of potato or dahlia or
cattle having so descended, let us consider probable character of
[selected races] wild varieties.
_Natural Selection._ De Candolle's war of nature,--seeing contented face
of nature,--may be well at first doubted; we see it on borders of
perpetual cold{54}. But considering the enormous geometrical power of
increase in every organism and as every country, in ordinary cases
must be stocked to full extent, reflection will show that
this is the case. Malthus on man,--in animals no moral [check] restraint
--they breed in time of year when provision most abundant, or season
most favourable, every country has its seasons,--calculate
robins,--oscillating from years of destruction{55}. If proof were wanted
let any singular change of climate here , how astoundingly
some tribes increase, also introduced animals{56}, the pressure is
always ready,--capacity of alpine plants to endure other
climates,--think of endless seeds scattered abroad,--forests regaining
their percentage{57},--a thousand wedges{58} are being forced into the
oeconomy of nature. This requires much reflection; study Malthus and
calculate rates of increase and remember the resistance,--only
periodical.
{54} See _Origin_, Ed. i. pp. 62, 63, vi. p. 77, where similar
reference is made to De Candolle; for Malthus see _Origin_, p. 5.
{55} This may possibly refer to the amount of destruction going on.
See _Origin_, Ed. i. p. 68, vi. p. 84, where there is an estimate
of a later date as to death-rate of birds in winter. "Calculate
robins" probably refers to a calculation of the rate of increase of
birds under favourable conditions.
{56} In the _Origin_, Ed. i. pp. 64, 65, vi. p. 80, he instances
cattle and horses and certain plants in S. America and American
species of plants in India, and further on, as unexpected effects
of changed conditions, the enclosure of a heath, and the relation
between the fertilisation of clover and the presence of cats
(_Origin_, Ed. i. p. 74, vi. p. 91).
{57} _Origin_, Ed. i. p. 74, vi. p. 91. "It has been observed that
the trees now growing on ... ancient Indian mounds ... display the
same beautiful diversity and proportion of kinds as in the
surrounding virgin forests."
{58} The simile of the wedge occurs in the _Origin_, Ed. i. p. 67;
it is deleted in Darwin's copy of the first edition: it does not
occur in Ed. vi.
The unavoidable effect of this that many of every species are
destroyed either in egg or [young or mature (the former state the more
common)]. In the course of a thousand generations infinitesimally small
differences must inevitably tell{59}; when unusually cold winter, or hot
or dry summer comes, then out of the whole body of individuals of any
species, if there be the smallest differences in their structure,
habits, instincts [senses], health &c, will on an average tell; as
conditions change a rather larger proportion will be preserved: so if
the chief check to increase falls on seeds or eggs, so will, in the
course of 1000 generations or ten thousand, those seeds (like one with
down to fly{60}) which fly furthest and get scattered most ultimately
rear most plants, and such small differences tend to be hereditary like
shades of expression in human countenance. So if one parent fish
deposits its egg in infinitesimally different circumstances, as in
rather shallower or deeper water &c., it will then tell.
{59} In a rough summary at the close of the Essay, occur the
words:--"Every creature lives by a struggle, smallest grain in
balance must tell."
{60} Cf. _Origin_, Ed. i. p. 77, vi. p. 94.
Let hares{61} increase very slowly from change of climate affecting
peculiar plants, and some other rabbit decrease in same
proportion [let this unsettle organisation of], a canine animal, who
formerly derived its chief sustenance by springing on rabbits or
running them by scent, must decrease too and might thus readily become
exterminated. But if its form varied very slightly, the long legged
fleet ones, during a thousand years being selected, and the less fleet
rigidly destroyed must, if no law of nature be opposed to it, alter
forms.
{61} This is a repetition of what is given at p. 6.
Remember how soon Bakewell on the same principle altered cattle and
Western, sheep,--carefully avoiding a cross (pigeons) with any breed.
We cannot suppose that one plant tends to vary in fruit and another
in flower, and another in flower and foliage,--some have been selected
for both fruit and flower: that one animal varies in its covering and
another not,--another in its milk. Take any organism and ask what is
it useful for and on that point it will be found to vary,--cabbages
in their leaf,--corn in size quality of grain, both in times
of year,--kidney beans for young pod and cotton for envelope of seeds
&c. &c.: dogs in intellect, courage, fleetness and smell : pigeons
in peculiarities approaching to monsters. This requires
consideration,--should be introduced in first chapter if it holds, I
believe it does. It is hypothetical at best{62}.
{62} Compare _Origin_, Ed. i. p. 41, vi. p. 47. "I have seen it
gravely remarked, that it was most fortunate that the strawberry
began to vary just when gardeners began to attend closely to this
plant. No doubt the strawberry had always varied since it was
cultivated, but the slight varieties had been neglected."
Nature's variation far less, but such selection far more rigid and
scrutinising. Man's races not [even so well] only not better adapted to
conditions than other races, but often not one race adapted to its
conditions, as man keeps and propagates some alpine plants in garden.
Nature lets animal live, till on actual proof it is found less able
to do the required work to serve the desired end, man judges solely by
his eye, and knows not whether nerves, muscles, arteries, are developed
in proportion to the change of external form.
Besides selection by death, in bisexual animals the
selection in time of fullest vigour, namely struggle of males; even in
animals which pair there seems a surplus and a battle, possibly as in
man more males produced than females, struggle of war or charms{63}.
Hence that male which at that time is in fullest vigour, or best armed
with arms or ornaments of its species, will gain in hundreds of
generations some small advantage and transmit such characters to its
offspring. So in female rearing its young, the most vigorous and skilful
and industrious, instincts best developed, will rear more
young, probably possessing her good qualities, and a greater number will
thus prepared for the struggle of nature. Compared to man using a
male alone of good breed. This latter section only of limited
application, applies to variation of [specific] sexual characters.
Introduce here contrast with Lamarck,--absurdity of habit, or chance??
or external conditions, making a woodpecker adapted to tree{64}.
{63} Here we have the two types of sexual selection discussed in
the _Origin_, Ed. i. pp. 88 et seq., vi. pp. 108 et seq.
{64} It is not obvious why the author objects to "chance" or
"external conditions making a woodpecker." He allows that variation
is ultimately referable to conditions and that the nature of the
connexion is unknown, i.e. that the result is fortuitous. It is not
clear in the original to how much of the passage the two ? refer.
Before considering difficulties of theory of selection let us consider
character of the races produced, as now explained, by nature. Conditions
have varied slowly and the organisms best adapted in their whole course
of life to the changed conditions have always been selected,--man
selects small dog and afterwards gives it profusion of food,--selects a
long-backed and short-legged breed and gives it no particular exercise
to suit this function &c. &c. In ordinary cases nature has not allowed
her race to be contaminated with a cross of another race, and
agriculturists know how difficult they find always to prevent
this,--effect would be trueness. This character and sterility when
crossed, and generally a greater amount of difference, are two main
features, which distinguish domestic races from species.
[Sterility not universal admitted by all{65}. _Gladiolus_, _Crinum_,
_Calceolaria_{66} must be species if there be such a thing. Races of
dogs and oxen: but certainly very general; indeed a gradation of
sterility most perfect{67} very general. Some nearest species will not
cross (crocus, some heath ), some genera cross readily (fowls{68} and
grouse, peacock &c.). Hybrids no ways monstrous quite perfect except
secretions{69} hence even the mule has bred,--character of sterility,
especially a few years ago thought very much more universal than it now
is, has been thought the distinguishing character; indeed it is obvious
if all forms freely crossed, nature would be a chaos. But the very
gradation of the character, even if it always existed in some degree
which it does not, renders it impossible as marks those suppose
distinct as species{70}]. Will analogy throw any light on the fact of
the supposed races of nature being sterile, though none of the domestic
ones are? Mr Herbert Koelreuter have shown external differences will
not guide one in knowing whether hybrids will be fertile or not, but the
chief circumstance is constitutional differences{71}, such as being
adapted to different climate or soil, differences which [must] probably
affect the whole body of the organism and not any one part. Now wild
animals, taken out of their natural conditions, seldom breed. I do not
refer to shows or to Zoological Societies where many animals unite, but
breed, and others will never unite, but to wild animals caught
and kept _quite tame_ left loose and well fed about houses and living
many years. Hybrids produced almost as readily as pure breds. St Hilaire
great distinction of tame and domestic,--elephants,--ferrets{72}.
Reproductive organs not subject to disease in Zoological Garden.
Dissection and microscope show that hybrid is in exactly same condition
as another animal in the intervals of breeding season, or those animals
which taken wild and _not bred_ in domesticity, remain without breeding
their whole lives. It should be observed that so far from domesticity
being unfavourable in itself makes more fertile: [when animal is
domesticated and breeds, productive power increased from more food and
selection of fertile races]. As far as animals go might be thought
effect on their mind and a special case.
{65} The meaning is "That sterility is not universal is admitted by
all."
{66} See _Var. under Dom._, Ed. 2, i. p. 388, where the garden
forms of _Gladiolus_ and _Calceolaria_ are said to be derived from
crosses between distinct species. Herbert's hybrid _Crinums_ are
discussed in the _Origin_, Ed. i. p. 250, vi. p. 370. It is well
known that the author believed in a multiple origin of domestic
dogs.
{67} The argument from gradation in sterility is given in the
_Origin_, Ed. i. pp. 248, 255, vi. pp. 368, 375. In the _Origin_, I
have not come across the cases mentioned, viz. crocus, heath, or
grouse and fowl or peacock. For sterility between closely allied
species, see _Origin_, Ed. i. p. 257, vi. p. 377. In the present
essay the author does not distinguish between fertility between
species and the fertility of the hybrid offspring, a point on which
he insists in the _Origin_, Ed. i. p. 245, vi. p. 365.
{68} Ackermann (_Ber. d. Vereins f. Naturkunde zu Kassel_, 1898, p.
23) quotes from Gloger that a cross has been effected between a
domestic hen and a _Tetrao tetrix_; the offspring died when three
days old.
{69} No doubt the sexual cells are meant. I do not know on what
evidence it is stated that the mule has bred.
{70} The sentence is all but illegible. I think that the author
refers to forms usually ranked as varieties having been marked as
species when it was found that they were sterile together. See the
case of the red and blue _Anagallis_ given from Gärtner in the
_Origin_, Ed. i. p. 247, vi. p. 368.
{71} In the _Origin_, Ed. i. p. 258, where the author speaks of
constitutional differences in this connexion, he specifies that
they are confined to the reproductive system.
{72} The sensitiveness of the reproductive system to changed
conditions is insisted on in the _Origin_, Ed. i. p. 8, vi. p. 10.
The ferret is mentioned, as being prolific in captivity, in _Var.
under Dom._, Ed. 2, ii. p. 90.
But turning to plants we find same class of facts. I do not refer to
seeds not ripening, perhaps the commonest cause, but to plants not
setting, which either is owing to some imperfection of ovule or pollen.
Lindley says sterility is the [curse] bane of all propagators,--Linnæus
about alpine plants. American bog plants,--pollen in exactly same state
as in hybrids,--same in geraniums. Persian and Chinese{73} lilac will
not seed in Italy and England. Probably double plants and all fruits owe
their developed parts primarily to sterility and extra food thus
applied{74}. There is here gradation sterility and then parts, like
diseases, are transmitted hereditarily. We cannot assign any cause why
the Pontic Azalea produces plenty of pollen and not American{75}, why
common lilac seeds and not Persian, we see no difference in healthiness.
We know not on what circumstances these facts depend, why ferret breeds,
and cheetah{76}, elephant and pig in India will not.
{73} Lindley's remark is quoted in the _Origin_, Ed. i. p. 9.
Linnæus' remark is to the effect that Alpine plants tend to be
sterile under cultivation (see _Var. under Dom._, Ed. 2, ii. p.
147). In the same place the author speaks of peat-loving plants
being sterile in our gardens,--no doubt the American bog-plants
referred to above. On the following page (p. 148) the sterility of
the lilac (_Syringa persica_ and _chinensis_) is referred to.
{74} The author probably means that the increase in the petals is
due to a greater food supply being available for them owing to
sterility. See the discussion in _Var. under Dom._, Ed. 2, ii. p.
151. It must be noted that doubleness of the flower may exist
without noticeable sterility.
{75} I have not come across this case in the author's works.
{76} For the somewhat doubtful case of the cheetah (_Felis jubata_)
see _Var. under Dom._, Ed. 2, ii. p. 133. I do not know to what
fact "pig in India" refers.
Now in crossing it is certain every peculiarity in form and constitution
is transmitted: an alpine plant transmits its alpine tendency to its
offspring, an American plant its American-bog constitution, and
animals, those peculiarities, on which{77} when placed out of their
natural conditions they are incapable of breeding; and moreover they
transmit every part of their constitution, their respiration, their
pulse, their instinct, which are all suddenly modified, can it be
wondered at that they are incapable of breeding? I think it may be truly
said it would be more wonderful if they did. But it may be asked why
have not the recognised varieties, supposed to have been produced
through the means of man, [not refused to breed] have all bred{78}.
Variation depends on change of condition and selection{79}, as far as
man's systematic or unsystematic selection gone; he takes external
form, has little power from ignorance over internal invisible
constitutional differences. Races which have long been domesticated, and
have much varied, are precisely those which were capable of bearing
great changes, whose constitutions were adapted to a diversity of
climates. Nature changes slowly and by degrees. According to many
authors probably breeds of dogs are another case of modified species
freely crossing. There is no variety which has been
adapted to peculiar soil or situation for a thousand years and another
rigorously adapted to another, till such can be produced, the question
is not tried{80}. Man in past ages, could transport into different
climates, animals and plants which would freely propagate in such new
climates. Nature could effect, with selection, such changes slowly, so
that precisely those animals which are adapted to submit to great
changes have given rise to diverse races,--and indeed great doubt on
this head{81}.
{77} This sentence should run "on which depends their incapacity to
breed in unnatural conditions."
{78} This sentence ends in confusion: it should clearly close with
the words "refused to breed" in place of the bracket and the
present concluding phrase.
{79} The author doubtless refers to the change produced by the
_summation_ of variation by means of selection.
{80} The meaning of this sentence is made clear by a passage in the
MS. of 1844:--"Until man selects two varieties from the same stock,
adapted to two climates or to other different external conditions,
and confines each rigidly for one or several thousand years to such
conditions, always selecting the individuals best adapted to them,
he cannot be said to have even commenced the experiment." That is,
the attempt to produce mutually sterile domestic breeds.
{81} This passage is to some extent a repetition of a previous one
and may have been intended to replace an earlier sentence. I have
thought it best to give both. In the _Origin_, Ed. i. p. 141, vi.
p. 176, the author gives his opinion that the power of resisting
diverse conditions, seen in man and his domestic animals, is an
example "of a very common flexibility of constitution."
Before leaving this subject well to observe that it was shown that a
certain amount of variation is consequent on mere act of reproduction,
both by buds and sexually,--is vastly increased when parents exposed for
some generations to new conditions{82}, and we now find that many
animals when exposed for first time to very new conditions, are
incapable of breeding as hybrids. It [probably] bears also on supposed
fact of crossed animals when not infertile, as in mongrels, tending to
vary much, as likewise seems to be the case, when true hybrids possess
just sufficient fertility to propagate with the parent breeds and _inter
se_ for some generations. This is Koelreuter's belief. These facts throw
light on each other and support the truth of each other, we see
throughout a connection between the reproductive faculties and exposure
to changed conditions of life whether by crossing or exposure of the
individuals{83}.
{82} In the _Origin_, Ed. i. Chs. I. and V., the author does not
admit reproduction, apart from environment, as being a cause of
variation. With regard to the cumulative effect of new conditions
there are many passages in the _Origin_, Ed. i. e.g. pp. 7, 12, vi.
pp. 8, 14.
{83} As already pointed out, this is the important principle
investigated in the author's _Cross and Self-Fertilisation_.
Professor Bateson has suggested to me that the experiments should
be repeated with gametically pure individuals.
_Difficulties on theory of selection_{84}. It may be objected such
perfect organs as eye and ear, could never be formed, in latter less
difficulty as gradations more perfect; at first appears monstrous and to
end appears difficulty. But think of gradation, even now manifest,
(Tibia and Fibula). Everyone will allow if every fossil preserved,
gradation infinitely more perfect; for possibility of selection a
perfect gradation is required. Different groups of structure, slight
gradation in each group,--every analogy renders it probable that
intermediate forms have existed. Be it remembered what strange
metamorphoses; part of eye, not directly connected with vision, might
come to be [thus used] gradually worked in for this end,--swimming
bladder by gradation of structure is admitted to belong to the ear
system,--rattlesnake. [Woodpecker best adapted to climb.] In some cases
gradation not possible,--as vertebræ,--actually vary in domestic
animals,--less difficult if growth followed. Looking to whole animals, a
bat formed not for flight{85}. Suppose we had flying fish{86} and not
one of our now called flying fish preserved, who would have guessed
intermediate habits. Woodpeckers and tree-frogs both live in countries
where no trees{87}.
{84} In the _Origin_ a chapter is given up to "difficulties on
theory": the discussion in the present essay seems slight even when
it is remembered how small a space is here available. For _Tibia_
&c. see p. 48.
{85} This may be interpreted "The general structure of a bat is the
same as that of non-flying mammals."
{86} That is truly winged fish.
{87} The terrestrial woodpecker of S. America formed the subject of
a paper by Darwin, _Proc. Zool. Soc._, 1870. See _Life and
Letters_, vol. iii. p. 153.
The gradations by which each individual organ has arrived at its present
state, and each individual animal with its aggregate of organs has
arrived, probably never could be known, and all present great
difficulties. I merely wish to show that the proposition is not so
monstrous as it at first appears, and that if good reason can be
advanced for believing the species have descended from common parents,
the difficulty of imagining intermediate forms of structure not
sufficient to make one at once reject the theory.
§ III.
The mental powers of different animals in wild and tame state [present
still greater difficulties] require a separate section. Be it remembered
I have nothing to do with origin of memory, attention, and the different
faculties of the mind{88}, but merely with their differences in each of
the great divisions of nature. Disposition, courage, pertinacity ,
suspicion, restlessness, ill-temper, sagacity and reverse
unquestionably vary in animals and are inherited (Cuba wildness dogs,
rabbits, fear against particular object as man Galapagos{89}). Habits
purely corporeal, breeding season &c., time of going to rest &c., vary
and are hereditary, like the analogous habits of plants which vary and
are inherited. Habits of body, as manner of movement d^o. and d^o.
Habits, as pointing and setting on certain occasions d^o. Taste for
hunting certain objects and manner of doing so,--sheep-dog. These are
shown clearly by crossing and their analogy with true instinct thus
shown,--retriever. Do not know objects for which they do it. Lord
Brougham's definition{90}. Origin partly habit, but the amount
necessarily unknown, partly selection. Young pointers pointing stones
and sheep--tumbling pigeons--sheep{91} going back to place where born.
Instinct aided by reason, as in the taylor-bird{92}. Taught by parents,
cows choosing food, birds singing. Instincts vary in wild state (birds
get wilder) often lost{93}; more perfect,--nest without roof. These
facts [only clear way] show how incomprehensibly brain has power of
transmitting intellectual operations.
{88} The same proviso occurs in the _Origin_, Ed. i. p. 207, vi. p.
319.
{89} The tameness of the birds in the Galapagos is described in the
_Journal of Researches_ (1860), p. 398. Dogs and rabbits are
probably mentioned as cases in which the hereditary fear of man has
been lost. In the 1844 MS. the author states that the Cuban feral
dog shows great natural wildness, even when caught quite young.
{90} In the _Origin_, Ed. i. p. 207, vi. p. 319, he refuses to
define instinct. For Lord Brougham's definition see his
_Dissertations on Subjects of Science etc._, 1839, p. 27.
{91} See James Hogg (the Ettrick Shepherd), Works, 1865, _Tales and
Sketches_, p. 403.
{92} This refers to the tailor-bird making use of manufactured
thread supplied to it, instead of thread twisted by itself.
{93} _Often lost_ applies to _instinct_: _birds get wilder_ is
printed in a parenthesis because it was apparently added as an
after-thought. _Nest without roof_ refers to the water-ousel
omitting to vault its nest when building in a protected situation.
Faculties{94} distinct from true instincts,--finding [way]. It must I
think be admitted that habits whether congenital or acquired by practice
[sometimes] often become inherited{95}; instincts, influence, equally
with structure, the preservation of animals; therefore selection must,
with changing conditions tend to modify the inherited habits of animals.
If this be admitted it will be found _possible_ that many of the
strangest instincts may be thus acquired. I may observe, without
attempting definition, that an inherited habit or trick (trick because
may be born) fulfils closely what we mean by instinct. A habit is often
performed unconsciously, the strangest habits become associated, d^o.
tricks, going in certain spots &c. &c., even against will, is excited by
external agencies, and looks not to the end,--a person playing a
pianoforte. If such a habit were transmitted it would make a marvellous
instinct. Let us consider some of the most difficult cases of instincts,
whether they could be _possibly_ acquired. I do not say _probably_, for
that belongs to our 3rd Part{96}, I beg this may be remembered, nor do I
mean to attempt to show exact method. I want only to show that whole
theory ought not at once to be rejected on this score.
{94} In the MS. of 1844 is an interesting discussion on _faculty_
as distinct from _instinct_.
{95} At this date and for long afterwards the inheritance of
acquired characters was assumed to occur.
{96} Part II. is here intended: see the Introduction.
Every instinct must, by my theory, have been acquired gradually by
slight changes of former instinct, each change being useful
to its then species. Shamming death struck me at first as remarkable
objection. I found none really sham death{97}, and that there is
gradation; now no one doubts that those insects which do it either more
or less, do it for some good, if then any species was led to do it more,
and then escaped &c. &c.
{97} The meaning is that the attitude assumed in _shamming_ is not
accurately like that of death.
Take migratory instincts, faculty distinct from instinct, animals have
notion of time,--like savages. Ordinary finding way by memory, but how
does savage find way across country,--as incomprehensible to us, as
animal to them,--geological changes,--fishes in river,--case of sheep in
Spain{98}. Architectural instincts,--a manufacturer's employee in making
single articles extraordinary skill,--often said seem to make it almost
, child born with such a notion of playing{99},--we can
fancy tailoring acquired in same perfection,--mixture of
reason,--water-ouzel,--taylor-bird,--gradation of simple nest to most
complicated.
{98} This refers to the _transandantes_ sheep mentioned in the MS.
of 1844, as having acquired a migratory instinct.
{99} In the _Origin_, Ed. i. p. 209, vi. p. 321, Mozart's
pseudo-instinctive skill in piano-playing is mentioned. See _Phil.
Trans._, 1770, p. 54.
Bees again, distinction of faculty,--how they make a
hexagon,--Waterhouse's theory{100},--the impulse to use whatever faculty
they possess,--the taylor-bird has the faculty of sewing with beak,
instinct impels him to do it.
{100} In the discussion on bees' cells, _Origin_, Ed. i. p. 225,
vi. p. 343, the author acknowledges that his theory originated in
Waterhouse's observations.
Last case of parent feeding young with different food (take case of
Galapagos birds, gradation from Hawfinch to Sylvia) selection and habit
might lead old birds to vary taste and form, leaving their instinct of
feeding their young with same food{101},--or I see no difficulty in
parents being forced or induced to vary the food brought, and selection
adapting the young ones to it, and thus by degree any amount of
diversity might be arrived at. Although we can never hope to see the
course revealed by which different instincts have been acquired, for we
have only present animals (not well known) to judge of the course of
gradation, yet once grant the principle of habits, whether congenital or
acquired by experience, being inherited and I can see no limit to the
[amount of variation] extraordinariness of the habits thus acquired.
{101} The hawfinch-and _Sylvia-_types are figured in the _Journal
of Researches_, p. 379. The discussion of change of form in
relation to change of instinct is not clear, and I find it
impossible to suggest a paraphrase.
_Summing up this Division._ If variation be admitted to occur
occasionally in some wild animals, and how can we doubt it, when we see
[all] thousands organisms, for whatever use taken by man, do vary.
If we admit such variations tend to be hereditary, and how can we doubt
it when we resemblances of features and character,--disease
and monstrosities inherited and endless races produced (1200 cabbages).
If we admit selection is steadily at work, and who will doubt it, when
he considers amount of food on an average fixed and reproductive powers
act in geometrical ratio. If we admit that external conditions vary, as
all geology proclaims, they have done and are now doing,--then, if no
law of nature be opposed, there must occasionally be formed races,
[slightly] differing from the parent races. So then any such law{102},
none is known, but in all works it is assumed, in flat contradiction
to all known facts, that the amount of possible variation is soon
acquired. Are not all the most varied species, the oldest domesticated:
who think that horses or corn could be produced? Take dahlia and
potato, who will pretend in 5000 years{103} : perfectly adapted to conditions and then again brought
into varying conditions. Think what has been done in few last years,
look at pigeons, and cattle. With the amount of food man can produce he
may have arrived at limit of fatness or size, or thickness of wool ,
but these are the most trivial points, but even in these I conclude it
is impossible to say we know the limit of variation. And therefore with
the [adapting] selecting power of nature, infinitely wise compared to
those of man, that it is impossible to say we know the limit
of races, which would be true kind; if of different
constitutions would probably be infertile one with another, and which
might be adapted in the most singular and admirable manner, according to
their wants, to external nature and to other surrounding
organisms,--such races would be species. But is there any evidence
species been thus produced, this is a question wholly independent
of all previous points, and which on examination of the kingdom of
nature ought to answer one way or another.
{102} I should interpret this obscure sentence as follows, "No such
opposing law is known, but in all works on the subject a law is (in
flat contradiction to all known facts) assumed to limit the
possible amount of variation." In the _Origin_, the author never
limits the power of variation, as far as I know.
{103} In _Var. under Dom._ Ed. 2, ii. p. 263, the _Dahlia_ is
described as showing sensitiveness to conditions in 1841. All the
varieties of the _Dahlia_ are said to have arisen since 1804
(_ibid._ i. p. 393).
PART II{104}.
{104} In the original MS. the heading is: Part III.; but Part II.
is clearly intended; for details see the Introduction. I have not
been able to discover where § IV. ends and § V. begins.
§§ IV. & V.
I may premise, that according to the view ordinarily received, the
myriads of organisms peopling this world have been created by so many
distinct acts of creation. As we know nothing of the will of a
Creator,--we can see no reason why there should exist any relation
between the organisms thus created; or again, they might be created
according to any scheme. But it would be marvellous if this scheme
should be the same as would result from the descent of groups of
organisms from [certain] the same parents, according to the
circumstances, just attempted to be developed.
With equal probability did old cosmogonists say fossils were created, as
we now see them, with a false resemblance to living beings{105}; what
would the Astronomer say to the doctrine that the planets moved
according to the law of gravitation, but from the Creator having willed
each separate planet to move in its particular orbit? I believe such a
proposition (if we remove all prejudices) would be as legitimate as to
admit that certain groups of living and extinct organisms, in their
distribution, in their structure and in their relations one to another
and to external conditions, agreed with the theory and showed signs of
common descent, and yet were created distinct. As long as it was thought
impossible that organisms should vary, or should anyhow become adapted
to other organisms in a complicated manner, and yet be separated from
them by an impassable barrier of sterility{106}, it was justifiable,
even with some appearance in favour of a common descent, to admit
distinct creation according to the will of an Omniscient Creator; or,
for it is the same thing, to say with Whewell that the beginnings of all
things surpass the comprehension of man. In the former sections I have
endeavoured to show that such variation or specification is not
impossible, nay, in many points of view is absolutely probable. What
then is the evidence in favour of it and what the evidence against it.
With our imperfect knowledge of past ages [surely there will be some] it
would be strange if the imperfection did not create some unfavourable
evidence.
{105} This passage corresponds roughly to the conclusion of the
_Origin_, see Ed. i. p. 482, vi. p. 661.
{106} A similar passage occurs in the conclusion of the _Origin_,
Ed. i. p. 481, vi. p. 659.
Give sketch of the Past,--beginning with facts appearing hostile under
present knowledge,--then proceed to geograph. distribution,--order of
appearance,--affinities,--morphology &c., &c.
Our theory requires a very gradual introduction of new forms{107}, and
extermination of the old (to which we shall revert). The extermination
of old may sometimes be rapid, but never the introduction. In the groups
descended from common parent, our theory requires a perfect gradation
not differing more than breed of cattle, or potatoes, or cabbages in
forms. I do not mean that a graduated series of animals must have
existed, intermediate between horse, mouse, tapir{108}, elephant [or
fowl and peacock], but that these must have had a common parent, and
between horse and this parent &c., &c., but the common parent may
possibly have differed more from either than the two do now from each
other. Now what evidence of this is there? So perfect gradation in some
departments, that some naturalists have thought that in some large
divisions, if all existing forms were collected, a near approach to
perfect gradation would be made. But such a notion is preposterous with
respect to all, but evidently so with mammals. Other naturalists have
thought this would be so if all the specimens entombed in the strata
were collected{109}. I conceive there is no probability whatever of
this; nevertheless it is certain all the numerous fossil forms fall
in, as Buckland remarks, _not_ present classes, families and genera,
they fall between them: so is it with new discoveries of existing forms.
Most ancient fossils, that is most separated space of time, are most
apt to fall between the classes--(but organisms from those countries
most separated by space also fall between the classes <_e.g._>
Ornithorhyncus?). As far as geological discoveries they tend towards
such gradation{110}. Illustrate it with net. Toxodon,--tibia and
fibula,--dog and otter,--but so utterly improbable is , in _ex. gr._
Pachydermata, to compose series as perfect as cattle, that if, as many
geologists seem to infer, each separate formation presents even an
approach to a consecutive history, my theory must be given up. Even if
it were consecutive, it would only collect series of one district in our
present state of knowledge; but what probability is there that any one
formation during the _immense_ period which has elapsed during each
period will _generally_ present a consecutive history. [Compare number
living at one period to fossils preserved--look at enormous periods of
time.]
{107} See _Origin_, Ed. i. p. 312, vi. p. 453.
{108} See _Origin_, Ed. i. pp. 280, 281, vi. p. 414. The author
uses his experience of pigeons for examples for what he means by
_intermediate_; the instance of the horse and tapir also occurs.
{109} The absence of intermediate forms between living organisms
(and also as regards fossils) is discussed in the _Origin_, Ed. i.
pp. 279, 280, vi. p. 413. In the above discussion there is no
evidence that the author felt this difficulty so strongly as it is
expressed in the _Origin_, Ed. i. p. 299,--as perhaps "the most
obvious and gravest objection that can be urged against my theory."
But in a rough summary written on the back of the penultimate page
of the MS. he refers to the geological evidence:--"Evidence, as far
as it does go, is favourable, exceedingly incomplete,--greatest
difficulty on this theory. I am convinced not insuperable."
Buckland's remarks are given in the _Origin_, Ed. i. p. 329, vi. p.
471.
{110} That the evidence of geology, as far as it goes, is
favourable to the theory of descent is claimed in the _Origin_, Ed.
i. pp. 343-345, vi. pp. 490-492. For the reference to _net_ in the
following sentence, see Note 1, p. 48, {Note 161} of this Essay.
Referring only to marine animals, which are obviously most likely to be
preserved, they must live where sediment (of a kind favourable for
preservation, not sand and pebble){111} is depositing quickly and over
large area and must be thickly capped, littoral deposits:
for otherwise denudation ,--they must live in a
shallow space which sediment will tend to fill up,--as movement is
progress if soon brought up subject to denudation,--[if] as
during subsidence favourable, accords with facts of European
deposits{112}, but subsidence apt to destroy agents which produce
sediment{113}.
{111} See _Origin_, Ed. i. p. 288, vi. p. 422. "The remains that do
become embedded, if in sand and gravel, will, when the beds are
upraised, generally be dissolved by the percolation of rain-water."
{112} The position of the following is not clear:--"Think of
immense differences in nature of European deposits,--without
interposing new causes,--think of time required by present slow
changes, to cause, on very same area, such diverse deposits,
iron-sand, chalk, sand, coral, clay!"
{113} The paragraph which ends here is difficult to interpret. In
spite of obscurity it is easy to recognize the general resemblance
to the discussion on the importance of subsidence given in the
_Origin_, Ed. i. pp. 290 et seq., vi. pp. 422 et seq.
I believe safely inferred groups of marine fossils only
preserved for future ages where sediment goes on long
continuous and with rapid but not too rapid deposition in area
of subsidence. In how few places in any one region like Europe will
these contingencies be going on? Hence in past ages mere [gaps]
pages preserved{114}. Lyell's doctrine carried to extreme,--we shall
understand difficulty if it be asked:--what chance of series of
gradation between cattle by at age as far back
as Miocene{115}? We know then cattle existed. Compare number of
living,--immense duration of each period,--fewness of fossils.
{114} See Note 3, p. 27.
{115} Compare _Origin_, Ed. i. p. 298, vi. p. 437. "We shall,
perhaps, best perceive the improbability of our being enabled to
connect species by numerous, fine, intermediate, fossil links, by
asking ourselves whether, for instance, geologists at some future
period will be able to prove that our different breeds of cattle,
sheep, horses, and dogs have descended from a single stock or from
several aboriginal stocks."
This only refers to consecutiveness of history of organisms of each
formation.
The foregoing argument will show firstly, that formations are distinct
merely from want of fossils , and secondly, that
each formation is full of gaps, has been advanced to account for
_fewness_ of _preserved_ organisms compared to what have lived on the
world. The very same argument explains why in older formations the
organisms appear to come on and disappear suddenly,--but in [later]
tertiary not quite suddenly{116}, in later tertiary gradually,--becoming
rare and disappearing,--some have disappeared within man's time. It is
obvious that our theory requires gradual and nearly uniform
introduction, possibly more sudden extermination,--subsidence of
continent of Australia &c., &c.
{116} The sudden appearance of groups of allied species in the
lowest known fossiliferous strata is discussed in the _Origin_, Ed.
i. p. 306, vi. p. 446. The gradual appearance in the later strata
occurs in the _Origin_, Ed. i. p. 312, vi. p. 453.
Our theory requires that the first form which existed of each of the
great divisions would present points intermediate between existing ones,
but immensely different. Most geologists believe Silurian{117} fossils
are those which first existed in the whole world, not those which have
chanced to be the oldest not destroyed,--or the first which existed in
profoundly deep seas in progress of conversion from sea to land: if they
are first they give up. Not so Hutton or Lyell: if first
reptile{118} of Red Sandstone really was first which existed: if
Pachyderm{119} of Paris was first which existed: fish of Devonian:
dragon fly of Lias: for we cannot suppose them the progenitors: they
agree too closely with existing divisions. But geologists consider
Europe as a passage from sea to island to continent (except
Wealden, see Lyell). These animals therefore, I consider then mere
introduction from continents long since submerged.
{117} Compare _Origin_, Ed. i. p. 307, vi. p. 448.
{118} I have interpreted as _Sandstone_ a scrawl which I first read
as _Sea_; I have done so at the suggestion of Professor Judd, who
points out that "footprints in the red sandstone were known at that
time, and geologists were not then particular to distinguish
between Amphibians and Reptiles."
{119} This refers to Cuvier's discovery of _Palæotherium_ &c. at
Montmartre.
Finally, if views of some geologists be correct, my theory must be given
up. [Lyell's views, as far as they go, are in _favour_, but they go so
little in favour, and so much more is required, that it may viewed as
objection.] If geology present us with mere pages in chapters, towards
end of history, formed by tearing out bundles of leaves, and each page
illustrating merely a small portion of the organisms of that time, the
facts accord perfectly with my theory{120}.
{120} This simile is more fully given in the _Origin_, Ed. i. p.
310, vi. p. 452. "For my part, following out Lyell's metaphor, I
look at the natural geological record, as a history of the world
imperfectly kept, and written in a changing dialect; of this
history we possess the last volume alone, relating only to two or
three countries. Of this volume, only here and there a short
chapter has been preserved; and of each page, only here and there a
few lines. Each word of the slowly-changing language, in which the
history is supposed to be written, being more or less different in
the interrupted succession of chapters, may represent the
apparently abruptly changed forms of life, entombed in our
consecutive, but widely separated formations." Professor Judd has
been good enough to point out to me, that Darwin's metaphor is
founded on the comparison of geology to history in Ch. i. of the
_Principles of Geology_, Ed. i. 1830, vol. i. pp. 1-4. Professor
Judd has also called my attention to another
passage,--_Principles_, Ed. i. 1833, vol. iii. p. 33, when Lyell
imagines an historian examining "two buried cities at the foot of
Vesuvius, immediately superimposed upon each other." The historian
would discover that the inhabitants of the lower town were Greeks
while those of the upper one were Italians. But he would be wrong
in supposing that there had been a sudden change from the Greek to
the Italian language in Campania. I think it is clear that Darwin's
metaphor is partly taken from this passage. See for instance (in
the above passage from the _Origin_) such phrases as "history ...
written in a changing dialect"--"apparently abruptly changed forms
of life." The passage within [] in the above paragraph:--"Lyell's
views as far as they go &c.," no doubt refers, as Professor Judd
points out, to Lyell not going so far as Darwin on the question of
the imperfection of the geological record.
_Extermination._ We have seen that in later periods the organisms have
disappeared by degrees and [perhaps] probably by degrees in earlier, and
I have said our theory requires it. As many naturalists seem to think
extermination a most mysterious circumstance{121} and call in
astonishing agencies, it is well to recall what we have shown concerning
the struggle of nature. An exterminating agency is at work with every
organism: we scarcely see it: if robins would increase to thousands in
ten years how severe must the process be. How imperceptible a small
increase: fossils become rare: possibly sudden extermination as
Australia, but as present means very slow and many means of escape, I
shall doubt very sudden exterminations. Who can explain why some species
abound more,--why does marsh titmouse, or ring-ouzel, now little
change,--why is one sea-slug rare and another common on our coasts,--why
one species of Rhinoceros more than another,--why is tiger of
India so rare? Curious and general sources of error, the place of an
organism is instantly filled up.
{121} On rarity and extinction see _Origin_, Ed. i. pp. 109, 319,
vi. pp. 133, 461.
We know state of earth has changed, and as earthquakes and tides go on,
the state must change,--many geologists believe a slow gradual cooling.
Now let us see in accordance with principles of [variation]
specification explained in Sect. II. how species would probably be
introduced and how such results accord with what is known.
The first fact geology proclaims is immense number of extinct forms, and
new appearances. Tertiary strata leads to belief, that forms gradually
become rare and disappear and are gradually supplied by others. We see
some forms now becoming rare and disappearing, we know of no sudden
creation: in older periods the forms _appear_ to come in suddenly, scene
shifts: but even here Devonian, Permian &c. [keep on supplying new links
in chain]--Genera and higher forms come on and disappear, in same way
leaving a species on one or more stages below that in which the form
abounded.
§ VI. Let us consider the absolute state of distribution of organisms of
earth's face.
Referring chiefly, but not exclusively (from difficulty of transport,
fewness, and the distinct characteristics of groups) to Mammalia; and
first considering the three or four main [regions] divisions; North
America, Europe, Asia, including greater part of E. Indian Archipelago
and Africa are intimately allied. Africa most distinct, especially most
southern parts. And the Arctic regions, which unite N. America, Asia and
Europe, only separated (if we travel one way by Behring's St.) by a
narrow strait, is most intimately allied, indeed forms but one
restricted group. Next comes S. America,--then Australia, Madagascar
(and some small islands which stand very remote from the land). Looking
at these main divisions separately, the organisms vary according to
changes in condition{122} of different parts. But besides this, barriers
of every kind seem to separate regions in a greater degree than
proportionally to the difference of climates on each side. Thus great
chains of mountains, spaces of sea between islands and continents, even
great rivers and deserts. In fact the amount difference in the
organisms bears a certain, but not invariable relation to the amount of
physical difficulties to transit{123}.
{122} In the _Origin_, Ed. i. p. 346, vi. p. 493, the author begins
his discussion on geographical distribution by minimising the
effect of physical conditions. He lays great stress on the effect
of _barriers_, as in the present Essay.
{123} Note in the original, "Would it be more striking if we took
animals, take Rhinoceros, and study their habitats?"
There are some curious exceptions, namely, similarity of fauna of
mountains of Europe and N. America and Lapland. Other cases just
reverse, mountains of eastern S. America, Altai , S. India {124}:
mountain summits of islands often eminently peculiar. Fauna generally of
some islands, even when close, very dissimilar, in others very similar.
[I am here led to observe one or more centres of creation{125}.]
{124} Note by Mr A. R. Wallace. "The want of similarity referred
to, is, between the mountains of Brazil and Guiana and those of the
Andes. Also those of the Indian peninsula as compared with the
Himalayas. In both cases there is continuous intervening land.
"The islands referred to were, no doubt, the Galapagos for
dissimilarity from S. America; our own Islands as compared with
Europe, and perhaps Java, for similarity with continental Asia."
{125} The arguments against multiple centres of creation are given
in the _Origin_, Ed. i. p. 352, vi. p. 499.
The simple geologist can explain many of the foregoing cases of
distribution. Subsidence of a continent in which free means of
dispersal, would drive the lowland plants up to the mountains, now
converted into islands, and the semi-alpine plants would take place of
alpine, and alpine be destroyed, if mountains originally were not of
great height. So we may see, during gradual changes{126} of climate on a
continent, the propagation of species would vary and adapt themselves to
small changes causing much extermination{127}. The mountains of Europe
were quite lately covered with ice, and the lowlands probably partaking
of the Arctic climate and Fauna. Then as climate changed, arctic fauna
would take place of ice, and an inundation of plants from different
temperate countries seize the lowlands, leaving islands of arctic
forms. But if this had happened on an island, whence could the new forms
have come,--here the geologist calls in creationists. If island formed,
the geologist will suggest many of the forms might have been
borne from nearest land, but if peculiar, he calls in creationist,--as
such island rises in height &c., he still more calls in creation. The
creationist tells one, on a spot the American spirit of
creation makes _Orpheus_ and _Tyrannus_ and American doves, and in
accordance with past and extinct forms, but no persistent relation
between areas and distribution, Geologico-Geograph.-Distribution.
{126} In the _Origin_, Ed. i. p. 366, vi. p. 516, the author does
not give his views on the distribution of alpine plants as original
but refers to Edward Forbes' work (_Geolog. Survey Memoirs_, 1846).
In his autobiography, Darwin refers to this. "I was forestalled" he
says, "in only one important point, which my vanity has always made
me regret." (_Life and Letters_, i. p. 88.)
{127}
Discuss one or more centres of creation: allude strongly to
facilities of dispersal and amount of geological change: allude to
mountain-summits afterwards to be referred to. The distribution
varies, as everyone knows, according to adaptation, explain going
from N. to S. how we come to fresh groups of species in the same
general region, but besides this we find difference, according to
greatness of barriers, in greater proportion than can be well
accounted for by adaptation. This very striking when we think of
cattle of Pampas, plants &c. &c. Then go into discussion; this
holds with 3 or 4 main divisions as well as the endless minor ones
in each of these 4 great ones: in these I chiefly refer to mammalia
&c. &c. The similarity of type, but not in species, in same
continent has been much less insisted on than the dissimilarity of
different great regions generically: it is more striking.
Galapagos
Islands, Tristan d'Acunha, _volcanic_ islands covered with craters
we know lately did not support any organisms. How unlike these
islands in nature to neighbouring lands. These facts perhaps more
striking than almost any others. [Geology apt to affect geography
therefore we ought to expect to find the above.]
Geological-geographical distribution. In looking to past times we
find Australia equally distinct. S. America was distinct, though
with more forms in common. N. America its nearest neighbour more in
common,--in some respects more, in some less allied to Europe.
Europe we find equally European. For Europe is now part of Asia
though not . Africa unknown,--examples, Elephant,
Rhinoceros, Hippopotamus, Hyaena. As geology destroys geography we
cannot be surprised in going far back we find Marsupials and
Edentata in Europe: but geology destroys geography.
Now according to analogy of domesticated animals let us see what would
result. Let us take case of farmer on Pampas, where everything
approaches nearer to state of nature. He works on organisms having
strong tendency to vary: and he knows only way to make a
distinct breed is to select and separate. It would be useless to
separate the best bulls and pair with best cows if their offspring run
loose and bred with the other herds, and tendency to reversion not
counteracted; he would endeavour therefore to get his cows on islands
and then commence his work of selection. If several farmers in different
_rincons_{128} were to set to work, especially if with different
objects, several breeds would soon be produced. So would it be with
horticulturist and so history of every plant shows; the number of
varieties{129} increase in proportion to care bestowed on their
selection and, with crossing plants, separation. Now, according to this
analogy, change of external conditions, and isolation either by chance
landing a form on an island, or subsidence dividing a continent, or
great chain of mountains, and the number of individuals not being
numerous will best favour variation and selection{130}. No doubt change
could be effected in same country without any barrier by long continued
selection on one species: even in case of a plant not capable of
crossing would easier get possession and solely occupy an island{131}.
Now we can at once see that two parts of a continent isolated, new
species thus generated in them, would have closest affinities, like
cattle in counties of England: if barrier afterwards destroyed one
species might destroy the other or both keep their ground. So if island
formed near continent, let it be ever so different, that continent would
supply inhabitants, and new species (like the old) would be allied with
that continent. An island generally very different soil and climate, and
number and order of inhabitants supplied by chance, no point so
favourable for generation of new species{132},--especially the
mountains, hence, so it is. As isolated mountains formed in a plain
country (if such happens) is an island. As other islands formed, the old
species would spread and thus extend and the fauna of distant island
might ultimately meet and a continent formed between them. No one doubts
continents formed by repeated elevations and depressions{133}. In
looking backwards, but not so far that all geographical boundaries are
destroyed, we can thus at once see why existing forms are related to the
extinct in the same manner as existing ones are in some part of existing
continent. By chance we might even have one or two absolute parent
fossils.
{128} _Rincon_ in Spanish means a _nook_ or _corner_, it is here
probably used to mean a small farm.
{129} The following is written across the page: "No one would
expect a set of similar varieties to be produced in the different
countries, so species different."
{130} The parent of an organism, we may generally suppose to be in
less favourable condition than the selected offspring and therefore
generally in fewer numbers. (This is not borne out by horticulture,
mere hypothesis; as an organism in favourable conditions might by
selection be adapted to still more favourable conditions.)
Barrier would further act in preventing species formed in one part
migrating to another part.
{131} Number
of species not related to capabilities of the country: furthermore
not always those best adapted, perhaps explained by creationists by
changes and progress.
Although creationists can, by help of geology, explain much, how
can he explain the marked relation of past and present in same
area, the varying relation in other cases, between past and
present, the relation of different parts of same great area. If
island, to adjoining continent, if quite different, on mountain
summits,--the number of individuals not being related to
capabilities, or how &c.--our theory, I believe, can throw much
light and all facts accord.
{132} See _Origin_, Ed. i. p. 390, vi. p. 543.
{133} On oscillation see _Origin_, Ed. i. p. 291, vi. p. 426.
The detection of transitional forms would be rendered more difficult on
rising point of land.
The distribution therefore in the above enumerated points, even the
trivial ones, which on any other can be viewed as so many
ultimate facts, all follow a simple manner on the theory of the
occurrence of species by and being adapted by selection to
, conjoined with their power of dispersal, and the steady
geographico-geological changes which are now in progress and which
undoubtedly have taken place. Ought to state the opinion of the
immutability of species and the creation by so many separate acts of
will of the Creator{134}.
{134} Effect of climate on stationary island
and on continent, but continent once island. Moreover repeated
oscillations fresh diffusion when non-united, then isolation, when
rising again immigration prevented, new habitats formed, new
species, when united free immigration, hence uniform characters.
Hence more forms the island. Mountain summits. Why not true
species. First let us recall in Part I, conditions of variation:
change of conditions during several generations, and if frequently
altered so much better [perhaps excess of food]. Secondly, continued
selection [while in wild state]. Thirdly, isolation in all or nearly
all,--as well to recall advantages of.
[In continent, if we look to terrestrial animal, long continued
change might go on, which would only cause change in numerical
number : if continued long enough might ultimately
affect all, though to most continents chance of
immigration. Some few of whole body of species must be long affected
and entire selection working same way. But here isolation absent,
without barrier, cut off such . We can see advantage of
isolation. But let us take case of island thrown up by volcanic
agency at some distances, here we should have occasional visitants,
only in few numbers and exposed to new conditions and
more important,--a quite new grouping of organic beings, which would
open out new sources of subsistence, or control old
ones. The number would be few, can old have the very best opportunity.
Moreover as the island continued changing,--continued slow
changes, river, marshes, lakes, mountains &c. &c., new races as
successively formed and a fresh occasional visitant.
If island formed continent, some species would emerge and
immigrate. Everyone admits continents. We can see why Galapagos and
C. Verde differ ], depressed and raised.
We can see from this repeated action and the time required for a
continent, why many more forms than in New Zealand no
mammals or other classes . We can at once see how it comes when there
has been an old channel of migration,--Cordilleras; we can see why
Indian Asiatic Flora,--[why species] having a wide range gives
better chance of some arriving at new points and being selected, and
adapted to new ends. I need hardly remark no necessity for change.
Finally, as continent (most extinction during formation of
continent) is formed after repeated elevation and depression, and
interchange of species we might foretell much extinction, and that
the survivor would belong to same type, as the extinct, in same
manner as different part of same continent, which were once
separated by space as they are by time .
As all mammals have descended from one stock, we ought to expect
that every continent has been at some time connected, hence
obliteration of present ranges. I do not mean that the fossil
mammifers found in S. America are the lineal successors
of the present forms of S. America: for it is highly improbable
that more than one or two cases (who will say how many races after
Plata bones) should be found. I believe this from numbers, who have
lived,--mere chance of fewness. Moreover in every case from
very existence of genera and species only few at one time will
leave progeny, under form of new species, to distant ages; and the
more distant the ages the fewer the progenitors. An observation may
be here appended, bad chance of preservation on rising island, the
nurseries of new species, appeal to experience . This observation may be extended, that in all cases,
subsiding land must be, in early stages, less favourable to
formation of new species; but it will isolate them, and then if
land recommences rising how favourable. As preoccupation is bar to
diffusion to species, so would it be to a selected variety. But it
would not be if that variety was better fitted to some not fully
occupied station; so during elevation or the formation of new
stations, is scene for new species. But during elevation not
favourable to preservation of fossil (except in caverns ); when
subsidence highly favourable in early stages to preservation of
fossils; when subsidence, less sediment. So that our strata, as
general rule will be the tomb of old species (not undergoing any
change) when rising land the nursery. But if there be vestige will
generally be preserved to future ages, the new ones will not be
entombed till fresh subsidence supervenes. In this long gap we
shall have no record: so that wonderful if we should get
transitional forms. I do not mean every stage, for we cannot expect
that, as before shown, until geologists will be prepared to say
that although under unnaturally favourable condition we can trace
in future ages short-horn and Herefordshire .
{Note 115}
§ VII.
Looking now to the affinities of organisms, without relation to their
distribution, and taking all fossil and recent, we see the degrees of
relationship are of different degrees and
arbitrary,--sub-genera,--genera,--sub-families, families, orders and
classes and kingdoms. The kind of classification which everyone feels is
most correct is called the natural system, but no can define this. If we
say with Whewell undefined instinct of the importance
of organs{135}, we have no means in lower animals of saying which is
most important, and yet everyone feels that some one system alone
deserves to be called natural. The true relationship of organisms is
brought before one by considering relations of analogy, an otter-like
animal amongst mammalia and an otter amongst marsupials. In such cases
external resemblance and habit of life and _the final end of whole
organization_ very strong, yet no relation{136}. Naturalists cannot
avoid these terms of relation and affinity though they use them
metaphorically. If used in simple earnestness the natural system ought
to be a genealogical ; and our knowledge of the points which are
most easily affected in transmission are those which we least value in
considering the natural system, and practically when we find they do
vary we regard them of less value{137}. In classifying varieties the
same language is used and the same kind of division: here also (in
pine-apple){138} we talk of the natural classification, overlooking
similarity of the fruits, because whole plant differs. The origin of
sub-genera, genera, &c., &c., is not difficult on notion of genealogical
succession, and accords with what we know of similar gradations of
affinity in domesticated organisms. In the same region the organic
beings are related to each other and the external conditions
in many physical respects are allied{139} and their differences of same
kind, and therefore when a new species has been selected and has
obtained a place in the economy of nature, we may suppose that
generally it will tend to extend its range during geographical changes,
and thus, becoming isolated and exposed to new conditions, will slightly
alter and its structure by selection become slightly remodified, thus we
should get species of a sub-genus and genus,--as varieties of
merino-sheep,--varieties of British and Indian cattle. Fresh species
might go on forming and others become extinct and all might become
extinct, and then we should have extinct genus; a case formerly
mentioned, of which numerous cases occur in Palæontology. But more often
the same advantages which caused the new species to spread and become
modified into several species would favour some of the species being
preserved: and if two of the species, considerably different, each gave
rise to group of new species, you would have two genera; the same thing
will go on. We may look at case in other way, looking to future.
According to mere chance every existing species may generate another,
but if any species, A, in changing gets an advantage and that advantage
(whatever it may be, intellect, &c., &c., or some particular structure
or constitution) is inherited{140}, A will be the progenitor of several
genera or even families in the hard struggle of nature. A will go on
beating out other forms, it might come that A would people earth,--we
may now not have one descendant on our globe of the one or several
original creations{141}. External conditions air, earth, water being
same{142} on globe, and the communication not being perfect, organisms
of widely different descent might become adapted to the same end and
then we should have cases of analogy{143}, [they might even tend to
become numerically representative]. From this often happening each of
the great divisions of nature would have their representative eminently
adapted to earth, to {144}, to water, and to these in
and then these great divisions would show numerical relations in their
classification.
{135} After "organs" is inserted, apparently as an
afterthought:--"no, and instance metamorphosis, afterwards
explicable."
{136} For analogical resemblances see _Origin_, Ed. i. p. 427, vi.
p. 582.
{137} "Practically when naturalists are at work, they do not
trouble themselves about the physiological value of the
characters.... If they find a character nearly uniform, ... they
use it as one of high value," _Origin_, Ed. i. p. 417, vi. p. 573.
{138} "We are cautioned ... not to class two varieties of the
pine-apple together, merely because their fruit, though the most
important part, happens to be nearly identical," _Origin_, Ed. i.
p. 423, vi. p. 579.
{139} The whole of this passage is obscure, but the text is quite
clear, except for one illegible word.
{140}
"just as it is not likely every present breed of fancy birds
and cattle will propagate, only some of the best."
{141} This suggests that the author was not far from the principle
of divergence on which he afterwards laid so much stress. See
_Origin_, Ed. i. p. 111, vi. p. 134, also _Life and Letters_, i. p.
84.
{142} That is to say the same conditions occurring in different
parts of the globe.
{143} The position of the following is uncertain, "greyhound and
racehorse have an analogy to each other." The same comparison
occurs in the _Origin_, Ed. i. p. 427, vi. p. 583.
{144} _Air_ is evidently intended; in the MS. _water_ is written
twice.
§ VIII. UNITY [OR SIMILARITY] OF TYPE IN THE GREAT CLASSES.
Nothing more wonderful in Nat. Hist. than looking at the vast number of
organisms, recent and fossil, exposed to the most diverse conditions,
living in the most distant climes, and at immensely remote periods,
fitted to wholely different ends, yet to find large groups united by a
similar type of structure. When we for instance see bat, horse,
porpoise-fin, hand, all built on same structure{145}, having bones{146}
with same name, we see there is some deep bond of union between
them{147}, to illustrate this is the foundation and objects
what is called the Natural System; and which is foundation of
distinction of true and adaptive characters{148}. Now this wonderful
fact of hand, hoof, wing, paddle and claw being the same, is at once
explicable on the principle of some parent-forms, which might either be
or walking animals, becoming through infinite number of small
selections adapted to various conditions. We know that proportion,
size, shape of bones and their accompanying soft parts vary, and hence
constant selection would alter, to almost any purpose the framework
of an organism, but yet would leave a general, even closest similarity in
it.
{145} Written between the lines occurs:--"extend to birds and other
classes."
{146} Written between the lines occurs:--"many bones merely
represented."
{147} In the _Origin_, Ed. i. p. 434, vi. p. 595, the term
_morphology_ is taken as including _unity of type_. The paddle of
the porpoise and the wing of the bat are there used as instances of
morphological resemblance.
{148} The sentence is difficult to decipher.
[We know the number of similar parts, as vertebræ and ribs can vary,
hence this also we might expect.] Also the changes carried on to a
certain point, doubtless type will be lost, and this is case with
Plesiosaurus{149}. The unity of type in past and present ages of certain
great divisions thus undoubtedly receives the simplest explanation.
{149} In the _Origin_, Ed. i. p. 436, vi. p. 598, the author speaks
of the "general pattern" being obscured in the paddles of "extinct
gigantic sea-lizards."
There is another class of allied and almost identical facts, admitted by
the soberest physiologists, [from the study of a certain set of organs
in a group of organisms] and refers to a unity of type of
different organs in the same individual, denominated the science of
"Morphology." The discovered by beautiful and regular series,
and in the case of plants from monstrous changes, that certain organs in
an individual are other organs metamorphosed. Thus every botanist
considers petals, nectaries, stamens, pistils, germen as metamorphosed
leaf. They thus explain, in the most lucid manner, the position and
number of all parts of the flower, and the curious conversion under
cultivation of one part into another. The complicated double set of jaws
and palpi of crustaceans{150}, and all insects are considered as
metamorphosed and to see the series is to admit this phraseology.
The skulls of the vertebrates are undoubtedly composed of three
metamorphosed vertebræ; thus we can understand the strange form of the
separate bones which compose the casket holding man's brain. These{151}
facts differ but slightly from those of last section, if with wing,
paddle, hand and hoof, some common structure was yet visible, or could
be made out by a series of occasional monstrous conversions, and if
traces could be discovered of whole having once existed as walking or
swimming instruments, these organs would be said to be metamorphosed, as
it is they are only said to exhibit a common type.
{150} See _Origin_, Ed. i. p. 437, vi. p. 599.
{151} The following passage seems to have been meant to precede the
sentence beginning "These facts":--"It is evident, that when in
each individual species, organs are metamorph. a unity of type
extends."
This distinction is not drawn by physiologists, and is only implied by
some by their general manner of writing. These facts, though affecting
every organic being on the face of the globe, which has existed, or does
exist, can only be viewed by the Creationist as ultimate and
inexplicable facts. But this unity of type through the individuals of a
group, and this metamorphosis of the same organ into other organs,
adapted to diverse use, necessarily follows on the theory of
descent{152}. For let us take case of Vertebrata, which if{153} they
descended from one parent and by this theory all the Vertebrata have
been altered by slow degrees, such as we see in domestic animals. We
know that proportions alter, and even that occasionally numbers of
vertebræ alter, that parts become soldered, that parts are lost, as tail
and toes, but we know here we can see that possibly a walking organ
might be converted into swimming or into a gliding organ and so on to a
flying organ. But such gradual changes would not alter the unity of type
in their descendants, as parts lost and soldered and vertebræ. But we
can see that if this carried to extreme, unity lost,--Plesiosaurus. Here
we have seen the same organ is formed different purposes
: and if, in several orders of vertebrata, we could
trace origin spinous processes and monstrosities &c. we should say,
instead of there existing a unity of type, morphology{154}, as we do
when we trace the head as being the vertebræ metamorphosed. Be it
observed that Naturalists, as they use terms of affinity without
attaching real meaning, here also they are obliged to use metamorphosis,
without meaning that any parent of crustacean was really an animal with
as many legs as crustacean has jaws. The theory of descent at once
explains these wonderful facts.
{152} This is, I believe, the first place in which the author uses
the words "theory of descent."
{153} The sentence should probably run, "Let us take the case of
the vertebrata: if we assume them to be descended from one parent,
then by this theory they have been altered &c."
{154} That is "we should call it a morphological fact."
Now few of the physiologists who use this language really suppose that
the parent of insect with the metamorphosed jaw, was an insect with
[more] so many legs, or that the parent of flowering plants, originally
had no stamens, or pistils or petals, but some other means of
propagation,--and so in other cases. Now according to our theory during
the infinite number of changes, we might expect that an organ used for a
purpose might be used for a different one by his descendant, as must
have been the case by our theory with the bat, porpoise, horse, &c.,
which are descended from one parent. And if it so chanced that traces of
the former use and structure of the part should be retained, which is
manifestly possible if not probable, then we should have the organs, on
which morphology is founded and which instead of being metaphorical
becomes plain and utterly unintelligible becomes
simple matter of fact{155}.
{155} In the _Origin_, Ed. i. p. 438, vi. p. 602, the author,
referring to the expressions used by naturalists in regard to
morphology and metamorphosis, says "On my view these terms may be
used literally."
<_Embryology._> This general unity of type in great groups of organisms
(including of course these morphological cases) displays itself in a
most striking manner in the stages through which the foetus passes{156}.
In early stage, the wing of bat, hoof, hand, paddle are not to be
distinguished. At a still earlier there is no difference between
fish, bird, &c. &c. and mammal. It is not that they cannot be
distinguished, but the arteries{157} . It is not true that
one passes through the form of a lower group, though no doubt fish more
nearly related to foetal state{158}.
{156} See _Origin_, Ed. i. p. 439, vi. p. 605.
{157} In the _Origin_, Ed. i. p. 440, vi. p. 606, the author argues
that the "loop-like course of the arteries" in the vertebrate
embryo has no direct relation to the conditions of existence.
{158} The following passages are written across the page:--"They
pass through the same phases, but some, generally called the higher
groups, are further metamorphosed.
? Degradation and complication? no tendency to perfection.
? Justly argued against Lamarck?"
This similarity at the earliest stage is remarkably shown in the course
of the arteries which become greatly altered, as foetus advances in life
and assumes the widely different course and number which characterize
full-grown fish and mammals. How wonderful that in egg, in water or air,
or in womb of mother, artery{159} should run in same course.
{159} An almost identical passage occurs in the _Origin_, Ed. i. p.
440, vi. p. 606.
Light can be thrown on this by our theory. The structure of each
organism is chiefly adapted to the sustension of its life, when
full-grown, when it has to feed itself and propagate{160}. The structure
of a kitten is quite in secondary degree adapted to its habits, whilst
fed by its mother's milk and prey. Hence variation in the structure of
the full-grown species will _chiefly_ determine the preservation of a
species now become ill-suited to its habitat, or rather with a better
place opened to it in the economy of Nature. It would not matter to the
full-grown cat whether in its young state it was more or less eminently
feline, so that it become so when full-grown. No doubt most variation,
(not depending on habits of life of individual) depends on early
change{161} and we must suspect that at whatever time of life the
alteration of foetus is effected, it tends to appear at same period.
When we a tendency to particular disease in old age transmitted by
the male, we know some effect is produced during conception, on the
simple cell of ovule, which will not produce its effect till half a
century afterwards and that effect is not visible{162}. So we see in
grey-hound, bull-dog, in race-horse and cart-horse, which have been
selected for their form in full-life, there is much less (?) difference
in the few first days after birth{163}, than when full-grown: so in
cattle, we see it clearly in cases of cattle, which differ obviously in
shape and length of horns. If man were during 10,000 years to be able to
select, far more diverse animals from horse or cow, I should expect
there would be far less differences in the very young and foetal state:
and this, I think, throws light on above marvellous fact. In larvæ,
which have long life selection, perhaps, does much,--in the pupa not so
much{164} There is no object gained in varying form &c. of foetus
(beyond certain adaptations to mother's womb) and therefore selection
will not further act on it, than in giving to its changing tissues a
tendency to certain parts afterwards to assume certain forms.
{160} The following: "Deaths of brothers old by same peculiar
disease" which is written between the lines seems to have been a
memorandum which is expanded a few lines lower. I believe the case
of the brothers came from Dr R. W. Darwin.
{161} See the discussion to this effect in the _Origin_, Ed. i. pp.
443-4, vi. p. 610. The author there makes the distinction between a
cause affecting the germ-cell and the reaction occurring at a late
period of life.
{162} Possibly the sentence was meant to end "is not visible till
then."
{163} See _Origin_, Ed. i. pp. 444-5, vi. p. 611. The query
appended to _much less_ is justified, since measurement was
necessary to prove that the greyhound and bulldog puppies had not
nearly acquired "their full amount of proportional difference."
{164} I think light can be thrown on
these facts. From the following peculiarities being hereditary, [we
know that some change in the germinal vesicle is effected, which
will only betray itself years after] diseases--man, goitre, gout,
baldness, fatness, size, [longevity time of reproduction,
shape of horns, case of old brothers dying of same disease]. And we
know that the germinal vesicle must have been affected, though no
effect is apparent or can be apparent till years afterwards,--no
more apparent than when these peculiarities appear by the exposure
of the full-grown individual. So that when we see
a variety in cattle, even if the variety be due to act of
reproduction, we cannot feel sure at what period this change became
apparent. It may have been effected during early age of free life
foetal existence, as monsters show. From arguments before used,
and crossing, we may generally suspect in germ; but I repeat it
does not follow, that the change should be apparent till life fully
developed; any more than fatness depending on heredity should be
apparent during early childhood, still less during foetal
existence. In case of horns of cattle, which when inherited must
depend on germinal vesicle, obviously no effect till cattle
full-grown. Practically it would appear that the [hereditary]
peculiarities characterising our domestic races, therefore
resulting from vesicle, do not appear with their full characters
in very early states; thus though two breeds of cows have calves
different, they are not so different,--grey-hound and bull-dog.
And this is what is be expected, for man is indifferent to
characters of young animals and hence would select those full-grown
animals which possessed the desirable characteristics. So that from
mere chance we might expect that some of the characters would be
such only as became fully apparent in mature life. Furthermore we
may suspect it to be a law, that at whatever time a new character
appears, whether from vesicle, or effects of external conditions,
it would appear at corresponding time .
Thus diseases appearing in old age produce children with d^o.,--early
maturity,--longevity,--old men, brothers, of same disease--young
children of d^o. I said men do not select for quality of
young,--calf with big bullocks. Silk-worms, peculiarities which,
appear in caterpillar state or cocoon state, are transmitted to
corresponding states. The effect of this would be that if some
peculiarity was born in a young animal, but never exercised, it
might be inherited in young animal; but if exercised that part of
structure would be increased and would be inherited in
corresponding time of life after such training.
I have said that man selects in full-life, so would it be in
Nature. In struggle of existence, it matters nothing to a feline
animal, whether kitten eminently feline, as long as it sucks.
Therefore natural selection would act equally well on character
which was fully only in full age. Selection could tend
to alter no character in foetus, (except relation to mother) it would
alter less in young state (putting on one side larva condition) but
alter every part in full-grown condition. Look to a foetus and its
parent, and again after ages foetus and its descendant; the parent more variable than
foetus, which explains all.]
Thus there is no power to change the course of the arteries, as long as
they nourish the foetus; it is the selection of slight changes which
supervene at any time during of life.
The less differences of foetus,--this has obvious meaning on this view:
otherwise how strange that a [monkey] horse, a man, a bat should at one
time of life have arteries, running in a manner, which is only
intelligibly useful in a fish! The natural system being on theory
genealogical, we can at once see, why foetus, retaining traces of the
ancestral form, is of the highest value in classification.
§ IX.
There is another grand class of facts relating to what are called
abortive organs. These consist of organs which the same reasoning power
that shows us how beautifully these organs in some cases are adapted to
certain end, declares in other cases are absolutely useless. Thus teeth
in Rhinoceros{165}, whale, narwhal,--bone on tibia, muscles which do not
move,--little bone of wing of Apteryx,--bone representing extremities in
some snake,--little wings within soldered cover of beetles,--men and
bulls, mammæ: filaments without anthers in plants, mere scales
representing petals in others, in feather-hyacinth whole flower. Almost
infinitely numerous. No one can reflect on these without astonishment,
can anything be clearer than that wings are to fly and teeth ,
and yet we find these organs perfect in every detail in situations where
they cannot possibly be of their normal use{166}.
{165} Some of these examples occur in _Origin_, Ed. i. pp. 450-51,
vi. pp. 619-20.
{166} The two following sentences are written, one down the margin,
the other across the page. "Abortive organs eminently useful in
classification. Embryonic state of organs. Rudiments of organs."
The term abortive organ has been thus applied to above structure (as
_invariable_ as all other parts{167}) from their absolute similarity to
monstrous cases, where from _accident_, certain organs are not
developed; as infant without arms or fingers with mere stump
representing them: teeth represented by mere points of ossification:
headless children with mere button,--viscera represented by small
amorphous masses, &c.,--the tail by mere stump,--a solid horn by minute
hanging one{168}. There is a tendency in all these cases, when life is
preserved, for such structures to become hereditary. We see it in
tailless dogs and cats. In plants we see this strikingly,--in Thyme, in
_Linum flavum_,--stamen in _Geranium pyrenaicum_{169}. Nectaries abort
into petals in Columbine <_Aquilegia_>, produced from some accident and
then become hereditary, in some cases only when propagated by buds, in
other cases by seed. These cases have been produced suddenly by accident
in early growth, but it is part of law of growth that when any organ is
not used it tends to diminish (duck's wing{170}?) muscles of dog's ears,
rabbits, muscles wither, arteries grow up. When eye born
defective, optic nerve (Tuco Tuco) is atrophied. As every part whether
useful or not (diseases, double flowers) tends to be transmitted to
offspring, the origin of abortive organs whether produced at the birth
or slowly acquired is easily understood in domestic races of organisms:
[a struggle between the atrophy and hereditariness. Abortive organs in
domestic races.] There will always be a struggle between atrophy of an
organ rendered useless, and hereditariness{171}. Because we can
understand the origin of abortive organs in certain cases, it would be
wrong to conclude absolutely that all must have had same origin, but the
strongest analogy is in favour of it. And we can by our theory, for
during infinite changes some organ, we might have anticipated, would
have become useless. readily explain the fact, so astounding
on any other view, namely that organs possibly useless have been formed
often with the same exquisite care as when of vital importance.
{167} I imagine the meaning to be that abortive organs are specific
characters in contrast to monstrosities.
{168} Minute hanging horns are mentioned in the _Origin_, Ed. i. p.
454, vi. p. 625, as occurring in hornless breeds of cattle.
{169} _Linum flavum_ is dimorphic: thyme gynodiæcious. It is not
clear what point is referred to under _Geranium pyrenaicum_.
{170} The author's work on duck's wings &c. is in _Var. under
Dom._, Ed. 2, i. p. 299.
{171} The words _vis medicatrix_ are inserted after "useless,"
apparently as a memorandum.
Our theory, I may remark would permit an organ become abortive with
respect to its primary use, to be turned to any other purpose, (as the
buds in a cauliflower) thus we can see no difficulty in bones of male
marsupials being used as fulcrum of muscles, or style of
marygold{172},--indeed in one point of view, the heads of [vertebrated]
animal may be said to be abortive vertebræ turned into other use: legs
of some crustacea abortive jaws, &c., &c. De Candolle's analogy of table
covered with dishes{173}.
{172} In the male florets of certain Compositæ the style functions
merely as a piston for forcing out the pollen.
{173} If abortive organs
are a trace preserved by hereditary tendency, of organ in ancestor
of use, we can at once see why important in natural classification,
also why more plain in young animal because, as in last section, the
selection has altered the old animal most. I repeat, these wondrous
facts, of parts created for no use in past and present time, all
can by my theory receive simple explanation; or they receive none
and we must be content with some such empty metaphor, as that of De
Candolle, who compares creation to a well covered table, and says
abortive organs may be compared to the dishes (some should be empty)
placed symmetrically!
Degradation and complication see Lamarck: no tendency to perfection: if
room, [even] high organism would have greater power in beating lower
one, thought to be selected for a degraded end.
§ X. RECAPITULATION AND CONCLUSION.
Let us recapitulate the whole these latter sections by taking
case of the three species of Rhinoceros, which inhabit Java, Sumatra,
and mainland of Malacca or India. We find these three close neighbours,
occupants of distinct but neighbouring districts, as a group having a
different aspect from the Rhinoceros of Africa, though some of these
latter inhabit very similar countries, but others most diverse stations.
We find them intimately related [scarcely differences more than some
breeds of cattle] in structure to the Rhinoceros, which for immense
periods have inhabited this one, out of three main zoological divisions
of the world. Yet some of these ancient animals were fitted to very
different stations: we find all three of the generic character
of the Rhinoceros, which form a [piece of net]{174} set of links in the
broken chain representing the Pachydermata, as the chain likewise forms
a portion in other and longer chains. We see this wonderfully in
dissecting the coarse leg of all three and finding nearly the same bones
as in bat's wings or man's hand, but we see the clear mark in solid
tibia of the fusion into it of the fibula. In all three we find their
heads composed of three altered vertebræ, short neck, same bones as
giraffe. In the upper jaws of all three we find small teeth like
rabbit's. In dissecting them in foetal state we find at a not very early
stage their form exactly alike the most different animals, and even with
arteries running as in a fish: and this similarity holds when the young
one is produced in womb, pond, egg or spawn. Now these three undoubted
species scarcely differ more than breeds of cattle, are probably
subject to many the same contagious diseases; if domesticated these
forms would vary, and they might possibly breed together, and fuse into
something{175} different their aboriginal forms; might be selected
to serve different ends.
{174} The author doubtless meant that the complex relationships
between organisms can be roughly represented by a net in which the
knots stand for species.
{175} Between the lines occurs:--"one form be lost."
Now the Creationist believes these three Rhinoceroses were created{176}
with their deceptive appearance of true, not relationship;
as well can I believe the planets revolve in their present courses not
from one law of gravity but from distinct volition of Creator.
{176} The original sentence is here broken up by the insertion
of:--"out of the dust of Java, Sumatra, these allied to past
and present age and , with the stamp of inutility in
some of their organs and conversion in others."
If real species, sterile one with another, differently adapted, now
inhabiting different countries, with different structures and instincts,
are admitted to have common descent, we can only legitimately stop where
our facts stop. Look how far in some case a chain of species will lead
us.
May we not jump (considering how much extermination, and how imperfect
geological records) from one sub-genus to another sub-genus. Can genera
restrain us; many of the same arguments, which made us give up species,
inexorably demand genera and families and orders to fall, and classes
tottering. We ought to stop only when clear unity of type, independent
of use and adaptation, ceases.
Be it remembered no naturalist pretends to give test from external
characters of species; in many genera the distinction is quite
arbitrary{177}. But there remains one other way of comparing species
with races; it is to compare the effects of crossing them. Would it not
be wonderful, if the union of two organisms, produced by two separate
acts of Creation, blended their characters together when crossed
according to the same rules, as two races which have undoubtedly
descended from same parent stock; yet this can be shown to be the case.
For sterility, though a usual , is not an invariable concomitant, it
varies much in degree and has been shown to be probably dependent on
causes closely analogous with those which make domesticated organisms
sterile. Independent of sterility there is no difference between
mongrels and hybrids, as can be shown in a long series of facts. It is
strikingly seen in cases of instincts, when the minds of the two species
or races become blended together{178}. In both cases if the half-breed
be crossed with either parent for a few generations, all traces of the
one parent form is lost (as Kölreuter in two tobacco species almost
sterile together), so that the Creationist in the case of a species,
must believe that one act of creation is absorbed into another!
{177} Between the lines occur the words:--"Species vary according
to same general laws as varieties; they cross according to same
laws."
{178} "A cross with a bull-dog has affected for many generations
the courage and obstinacy of greyhounds," _Origin_, Ed. i. p. 214,
vi. p. 327.
{Illustration: Facsimile of the original manuscript of the paragraph on
p. 50.}
CONCLUSION.
Such are my reasons for believing that specific forms are not immutable.
The affinity of different groups, the unity of types of structure, the
representative forms through which foetus passes, the metamorphosis of
organs, the abortion of others cease to be metaphorical expressions and
become intelligible facts. We no longer look on animal as a savage does
at a ship{179}, or other great work of art, as a thing wholly beyond
comprehension, but we feel far more interest in examining it. How
interesting is every instinct, when we speculate on their origin as an
hereditary or congenital habit or produced by the selection of
individuals differing slightly from their parents. We must look at every
complicated mechanism and instinct, as the summary of a long history,
of{180} useful contrivances, much like a work of art.
How interesting does the distribution of all animals become, as throwing
light on ancient geography. [We see some seas bridged over.] Geology
loses in its glory from the imperfection of its archives{181}, but how
does it gain in the immensity of the periods of its formations and of
the gaps separating these formations. There is much grandeur in looking
at the existing animals either as the lineal descendants of the forms
buried under thousand feet of matter, or as the coheirs of some still
more ancient ancestor. It accords with what we know of the law impressed
on matter by the Creator, that the creation and extinction of forms,
like the birth and death of individuals should be the effect of
secondary [laws] means{182}. It is derogatory that the Creator of
countless systems of worlds should have created each of the myriads of
creeping parasites and [slimy] worms which have swarmed each day of life
on land and water [this] one globe. We cease being astonished, however
much we may deplore, that a group of animals should have been directly
created to lay their eggs in bowels and flesh of other,--that some
organisms should delight in cruelty,--that animals should be led away by
false instincts,--that annually there should be an incalculable waste
of eggs and pollen. From death, famine, rapine, and the concealed war of
nature we can see that the highest good, which we can conceive, the
creation of the higher animals has directly come. Doubtless it at first
transcends our humble powers, to conceive laws capable of creating
individual organisms, each characterised by the most exquisite
workmanship and widely-extended adaptations. It accords better with [our
modesty] the lowness of our faculties to suppose each must require the
fiat of a creator, but in the same proportion the existence of such laws
should exalt our notion of the power of the omniscient Creator{183}.
There is a simple grandeur in the view of life with its powers of
growth, assimilation and reproduction, being originally breathed into
matter under one or a few forms, and that whilst this our planet has
gone circling on according to fixed laws, and land and water, in a cycle
of change, have gone on replacing each other, that from so simple an
origin, through the process of gradual selection of infinitesimal
changes, endless forms most beautiful and most wonderful have been
evolved{184}.
{179} The simile of the savage and the ship occurs in the _Origin_,
Ed. i. p. 485, vi. p. 665.
{180} In the _Origin_, Ed. i. p. 486, vi. p. 665, the author speaks
of the "summing up of many contrivances": I have therefore
introduced the above words which make the passage clearer. In the
_Origin_ the comparison is with "a great mechanical
invention,"--not with a work of art.
{181} See a similar passage in the _Origin_, Ed. i. p. 487, vi. p.
667.
{182} See the _Origin_, Ed. i. p. 488, vi. p. 668.
{183} The following discussion, together with some memoranda are on
the last page of the MS. "The supposed creative spirit does not
create either number or kind which from analogy adapted to site
(viz. New Zealand): it does not keep them all permanently adapted
to any country,--it works on spots or areas of creation,--it is not
persistent for great periods,--it creates forms of same groups in
same regions, with no physical similarity,--it creates, on islands
or mountain summits, species allied to the neighbouring ones, and
not allied to alpine nature as shown in other mountain
summits--even different on different island of similarly
constituted archipelago, not created on two points: never mammifers
created on small isolated island; nor number of organisms adapted
to locality: its power seems influenced or related to the range of
other species wholly distinct of the same genus,--it does not
equally effect, in amount of difference, all the groups of the same
class."
{184} This passage is the ancestor of the concluding words in the
first edition of the _Origin of Species_ which have remained
substantially unchanged throughout subsequent editions, "There is
grandeur in this view of life, with its several powers, having been
originally breathed into a few forms or into one; and that whilst
this planet has gone cycling 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." In the 2nd
edition "by the Creator" is introduced after "originally breathed."
N.B.--There ought somewhere to be a discussion from Lyell to show that
external conditions do vary, or a note to Lyell's works .
Besides other difficulties in ii. Part, non-acclimatisation of plants.
Difficulty when asked _how_ did white and negro become altered from
common intermediate stock: no facts. We do NOT know that species are
immutable, on the contrary. What arguments against this theory, except
our not perceiving every step, like the erosion of valleys{185}.
{185} Compare the _Origin_, Ed. i. p. 481, vi. p. 659, "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 slow action of the
coast-waves."
THE ESSAY OF 1844 PART I
CHAPTER I
ON THE VARIATION OF ORGANIC BEINGS UNDER DOMESTICATION; AND ON THE
PRINCIPLES OF SELECTION
The most favourable conditions for variation seem to be when organic
beings are bred for many generations under domestication{186}: one may
infer this from the simple fact of the vast number of races and breeds
of almost every plant and animal, which has long been domesticated.
Under certain conditions organic beings even during their individual
lives become slightly altered from their usual form, size, or other
characters: and many of the peculiarities thus acquired are transmitted
to their offspring. Thus in animals, the size and vigour of body,
fatness, period of maturity, habits of body or consensual movements,
habits of mind and temper, are modified or acquired during the life of
the individual{187}, and become inherited. There is reason to believe
that when long exercise has given to certain muscles great development,
or disuse has lessened them, that such development is also inherited.
Food and climate will occasionally produce changes in the colour and
texture of the external coverings of animals; and certain unknown
conditions affect the horns of cattle in parts of Abyssinia; but whether
these peculiarities, thus acquired during individual lives, have been
inherited, I do not know. It appears certain that malconformation and
lameness in horses, produced by too much work on hard roads,--that
affections of the eyes in this animal probably caused by bad
ventilation,--that tendencies towards many diseases in man, such as
gout, caused by the course of life and ultimately producing changes of
structure, and that many other diseases produced by unknown agencies,
such as goitre, and the idiotcy resulting from it, all become
hereditary.
{186} The cumulative effect of domestication is insisted on in the
_Origin_, see _e.g. Origin_, Ed. i. p. 7, vi. p. 8.
{187} This type of variation passes into what he describes as the
direct effect of conditions. Since they are due to causes acting
during the adult life of the organism they might be called
individual variations, but he uses this term for congenital
variations, _e.g._ the differences discoverable in plants raised
from seeds of the same pod _(Origin_, Ed. i. p. 45, vi. p. 53).
It is very doubtful whether the flowers and leaf-buds, annually produced
from the same bulb, root, or tree, can properly be considered as parts
of the same individual, though in some respects they certainly seem to
be so. If they are parts of an individual, plants also are subject to
considerable changes during their _individual_ lives. Most
florist-flowers if neglected degenerate, that is, they lose some of
their characters; so common is this, that trueness is often stated, as
greatly enhancing the value of a variety{188}: tulips break their
colours only after some years' culture; some plants become double and
others single, by neglect or care: these characters can be transmitted
by cuttings or grafts, and in some cases by true or seminal propagation.
Occasionally a single bud on a plant assumes at once a new and widely
different character: thus it is certain that nectarines have been
produced on peach trees and moss roses on provence roses; white
currants on red currant bushes; flowers of a different colour from that
of the stock, in Chrysanthemums, Dahlias, sweet-williams, Azaleas, &c.,
&c.; variegated leaf-buds on many trees, and other similar cases. These
new characters appearing in single buds, can, like those lesser changes
affecting the whole plant, be multiplied not only by cuttings and such
means, but often likewise by true seminal generation.
{188} :
Case of Orchis,--most remarkable as not long cultivated by
seminal propagation. Case of varieties which soon acquire, like
_Ægilops_ and Carrot (and Maize) _a certain general character_ and
then go on varying.
The changes thus appearing during the lives of individual animals and
plants are extremely rare compared with those which are congenital or
which appear soon after birth. Slight differences thus arising are
infinitely numerous: the proportions and form of every part of the
frame, inside and outside, appear to vary in very slight degrees:
anatomists dispute what is the "beau ideal" of the bones, the liver and
kidneys, like painters do of the proportions of the face: the proverbial
expression that no two animals or plants are born absolutely alike, is
much truer when applied to those under domestication, than to those in a
state of nature{189}. Besides these slight differences, single
individuals are occasionally born considerably unlike in certain parts
or in their whole structure to their parents: these are called by
horticulturists and breeders "sports"; and are not uncommon except when
very strongly marked. Such sports are known in some cases to have been
parents of some of our domestic races; and such probably have been the
parents of many other races, especially of those which in some senses
may be called hereditary monsters; for instance where there is an
additional limb, or where all the limbs are stunted (as in the Ancon
sheep), or where a part is wanting, as in rumpless fowls and tailless
dogs or cats{190}. The effects of external conditions on the size,
colour and form, which can rarely and obscurely be detected during one
individual life, become apparent after several generations: the slight
differences, often hardly describable, which characterize the stock of
different countries, and even of districts in the same country, seem to
be due to such continued action.
{189} Here, as in the MS. of 1842, the author is inclined to
minimise the variation occurring in nature.
{190} This is more strongly stated than in the _Origin_, Ed. i. p.
30.
_On the hereditary tendency._
A volume might be filled with facts showing what a strong tendency there
is to inheritance, in almost every case of the most trifling, as well as
of the most remarkable congenital peculiarities{191}. The term
congenital peculiarity, I may remark, is a loose expression and can only
mean a peculiarity apparent when the part affected is nearly or fully
developed: in the Second Part, I shall have to discuss at what period of
the embryonic life connatal peculiarities probably first appear; and I
shall then be able to show from some evidence, that at whatever period
of life a new peculiarity first appears, it tends hereditarily to appear
at a corresponding period{192}. Numerous though slight changes, slowly
supervening in animals during mature life (often, though by no means
always, taking the form of disease), are, as stated in the first
paragraphs, very often hereditary. In plants, again, the buds which
assume a different character from their stock likewise tend to transmit
their new peculiarities. There is not sufficient reason to believe that
either mutilations{193} or changes of form produced by mechanical
pressure, even if continued for hundreds of generations, or that any
changes of structure quickly produced by disease, are inherited; it
would appear as if the tissue of the part affected must slowly and
freely grow into the new form, in order to be inheritable. There is a
very great difference in the hereditary tendency of different
peculiarities, and of the same peculiarity, in different individuals and
species; thus twenty thousand seeds of the weeping ash have been sown
and not one come up true;--out of seventeen seeds of the weeping yew,
nearly all came up true. The ill-formed and almost monstrous "Niata"
cattle of S. America and Ancon sheep, both when bred together and when
crossed with other breeds, seem to transmit their peculiarities to their
offspring as truly as the ordinary breeds. I can throw no light on these
differences in the power of hereditary transmission. Breeders believe,
and apparently with good cause, that a peculiarity generally becomes
more firmly implanted after having passed through several generations;
that is if one offspring out of twenty inherits a peculiarity from its
parents, then its descendants will tend to transmit this peculiarity to
a larger proportion than one in twenty; and so on in succeeding
generations. I have said nothing about mental peculiarities being
inheritable for I reserve this subject for a separate chapter.
{191} See _Origin_, Ed. i. p. 13.
{192} _Origin_, Ed. i. p. 86, vi. p. 105.
{193} It is interesting to find that though the author, like his
contemporaries, believed in the inheritance of acquired characters,
he excluded the case of mutilation.
_Causes of Variation._
Attention must here be drawn to an important distinction in the first
origin or appearance of varieties: when we see an animal highly kept
producing offspring with an hereditary tendency to early maturity and
fatness; when we see the wild-duck and Australian dog always becoming,
when bred for one or a few generations in confinement, mottled in their
colours; when we see people living in certain districts or circumstances
becoming subject to an hereditary taint to certain organic diseases, as
consumption or plica polonica,--we naturally attribute such changes to
the direct effect of known or unknown agencies acting for one or more
generations on the parents. It is probable that a multitude of
peculiarities may be thus directly caused by unknown external agencies.
But in breeds, characterized by an extra limb or claw, as in certain
fowls and dogs; by an extra joint in the vertebræ; by the loss of a
part, as the tail; by the substitution of a tuft of feathers for a comb
in certain poultry; and in a multitude of other cases, we can hardly
attribute these peculiarities directly to external influences, but
indirectly to the laws of embryonic growth and of reproduction. When we
see a multitude of varieties (as has often been the case, where a cross
has been carefully guarded against) produced from seeds matured in the
very same capsule{194}, with the male and female principle nourished
from the same roots and necessarily exposed to the same external
influences; we cannot believe that the endless slight differences
between seedling varieties thus produced, can be the effect of any
corresponding difference in their exposure. We are led (as Müller has
remarked) to the same conclusion, when we see in the same litter,
produced by the same act of conception, animals considerably different.
{194} This corresponds to _Origin_, Ed. i. p. 10, vi. p. 9.
As variation to the degree here alluded to has been observed only in
organic beings under domestication, and in plants amongst those most
highly and long cultivated, we must attribute, in such cases, the
varieties (although the difference between each variety cannot possibly
be attributed to any corresponding difference of exposure in the
parents) to the indirect effects of domestication on the action of the
reproductive system{195}. It would appear as if the reproductive powers
failed in their ordinary function of producing new organic beings
closely like their parents; and as if the entire organization of the
embryo, under domestication, became in a slight degree plastic{196}. We
shall hereafter have occasion to show, that in organic beings, a
considerable change from the natural conditions of life, affects,
independently of their general state of health, in another and
remarkable manner the reproductive system. I may add, judging from the
vast number of new varieties of plants which have been produced in the
same districts and under nearly the same routine of culture, that
probably the indirect effects of domestication in making the
organization plastic, is a much more efficient source of variation than
any direct effect which external causes may have on the colour, texture,
or form of each part. In the few instances in which, as in the
Dahlia{197}, the course of variation has been recorded, it appears that
domestication produces little effect for several generations in
rendering the organization plastic; but afterwards, as if by an
accumulated effect, the original character of the species suddenly gives
way or breaks.
{195} _Origin_, Ed. i. p. 8, vi. p. 10.
{196} For _plasticity_ see _Origin_, Ed. i. pp. 12, 132.
{197} _Var. under Dom._, Ed. ii. I. p. 393.
_On Selection._
We have hitherto only referred to the first appearance in individuals of
new peculiarities; but to make a race or breed, something more is
generally{198} requisite than such peculiarities (except in the case of
the peculiarities being the direct effect of constantly surrounding
conditions) should be inheritable,--namely the principle of selection,
implying separation. Even in the rare instances of sports, with the
hereditary tendency very strongly implanted, crossing must be prevented
with other breeds, or if not prevented the best characterized of the
half-bred offspring must be carefully selected. Where the external
conditions are constantly tending to give some character, a race
possessing this character will be formed with far greater ease by
selecting and breeding together the individuals most affected. In the
case of the endless slight variations produced by the indirect effects
of domestication on the action of the reproductive system, selection is
indispensable to form races; and when carefully applied, wonderfully
numerous and diverse races can be formed. Selection, though so simple in
theory, is and has been important to a degree which can hardly be
overrated. It requires extreme skill, the results of long practice, in
detecting the slightest difference in the forms of animals, and it
implies some distinct object in view; with these requisites and
patience, the breeder has simply to watch for every the smallest
approach to the desired end, to select such individuals and pair them
with the most suitable forms, and so continue with succeeding
generations. In most cases careful selection and the prevention of
accidental crosses will be necessary for several generations, for in new
breeds there is a strong tendency to vary and especially to revert to
ancestral forms: but in every succeeding generation less care will be
requisite for the breed will become truer; until ultimately only an
occasional individual will require to be separated or destroyed.
Horticulturalists in raising seeds regularly practise this, and call it
"roguing," or destroying the "rogues" or false varieties. There is
another and less efficient means of selection amongst animals: namely
repeatedly procuring males with some desirable qualities, and allowing
them and their offspring to breed freely together; and this in the
course of time will affect the whole lot. These principles of selection
have been _methodically_ followed for scarcely a century; but their
high importance is shown by the practical results, and is admitted
in the writings of the most celebrated agriculturalists and
horticulturalists;--I need only name Anderson, Marshall, Bakewell, Coke,
Western, Sebright and Knight.
{198} Selection is here used in the sense of isolation, rather than
as implying the summation of small differences. Professor Henslow
in his _Heredity of Acquired Characters in Plants_, 1908, p. 2,
quotes from Darwin's _Var. under Dom._, Ed. i. II. p. 271, a
passage in which the author, speaking of the direct action of
conditions, says:--"A new sub-variety would thus be produced
without the aid of selection." Darwin certainly did not mean to
imply that such varieties are freed from the action of natural
selection, but merely that a new form may appear without
_summation_ of new characters. Professor Henslow is apparently
unaware that the above passage is omitted in the second edition of
_Var. under Dom._, II. p. 260.
Even in well-established breeds the individuals of which to an
unpractised eye would appear absolutely similar, which would give, it
might have been thought, no scope to selection, the whole appearance of
the animal has been changed in a few years (as in the case of Lord
Western's sheep), so that practised agriculturalists could scarcely
credit that a change had not been effected by a cross with other breeds.
Breeders both of plants and animals frequently give their means of
selection greater scope, by crossing different breeds and selecting the
offspring; but we shall have to recur to this subject again.
The external conditions will doubtless influence and modify the results
of the most careful selection; it has been found impossible to prevent
certain breeds of cattle from degenerating on mountain pastures; it
would probably be impossible to keep the plumage of the wild-duck in the
domesticated race; in certain soils, no care has been sufficient to
raise cauliflower seed true to its character; and so in many other
cases. But with patience it is wonderful what man has effected. He has
selected and therefore in one sense made one breed of horses to race and
another to pull; he has made sheep with fleeces good for carpets and
other sheep good for broadcloth; he has, in the same sense, made one dog
to find game and give him notice when found, and another dog to fetch
him the game when killed; he has made by selection the fat to lie mixed
with the meat in one breed and in another to accumulate in the bowels
for the tallow-chandler{199}; he has made the legs of one breed of
pigeons long, and the beak of another so short, that it can hardly feed
itself; he has previously determined how the feathers on a bird's body
shall be coloured, and how the petals of many flowers shall be streaked
or fringed, and has given prizes for complete success;--by selection, he
has made the leaves of one variety and the flower-buds of another
variety of the cabbage good to eat, at different seasons of the year;
and thus has he acted on endless varieties. I do not wish to affirm that
the long-and short-wooled sheep, or that the pointer and retriever, or
that the cabbage and cauliflower have certainly descended from one and
the same aboriginal wild stock; if they have not so descended, though it
lessens what man has effected, a large result must be left unquestioned.
{199} See the Essay of 1842, p. 3.
In saying as I have done that man makes a breed, let it not be
confounded with saying that man makes the individuals, which are given
by nature with certain desirable qualities; man only adds together and
makes a permanent gift of nature's bounties. In several cases, indeed,
for instance in the "Ancon" sheep, valuable from not getting over
fences, and in the turnspit dog, man has probably only prevented
crossing; but in many cases we positively know that he has gone on
selecting, and taking advantage of successive small variations.
Selection{200} has been _methodically_ followed, as I have said, for
barely a century; but it cannot be doubted that occasionally it has been
practised from the remotest ages, in those animals completely under the
dominion of man. In the earliest chapters of the Bible there are rules
given for influencing the colours of breeds, and black and white sheep
are spoken of as separated. In the time of Pliny the barbarians of
Europe and Asia endeavoured by cross-breeding with a wild stock to
improve the races of their dogs and horses. The savages of Guyana now do
so with their dogs: such care shows at least that the characters of
individual animals were attended to. In the rudest times of English
history, there were laws to prevent the exportation of fine animals of
established breeds, and in the case of horses, in Henry VIII's time,
laws for the destruction of all horses under a certain size. In one of
the oldest numbers of the _Phil. Transactions_, there are rules for
selecting and improving the breeds of sheep. Sir H. Bunbury, in 1660,
has given rules for selecting the finest seedling plants, with as much
precision as the best recent horticulturalist could. Even in the most
savage and rude nations, in the wars and famines which so frequently
occur, the most useful of their animals would be preserved: the value
set upon animals by savages is shown by the inhabitants of Tierra del
Fuego devouring their old women before their dogs, which as they
asserted are useful in otter-hunting{201}: who can doubt but that in
every case of famine and war, the best otter-hunters would be preserved,
and therefore in fact selected for breeding. As the offspring so
obviously take after their parents, and as we have seen that savages
take pains in crossing their dogs and horses with wild stocks, we may
even conclude as probable that they would sometimes pair the most useful
of their animals and keep their offspring separate. As different races
of men require and admire different qualities in their domesticated
animals, each would thus slowly, though unconsciously, be selecting a
different breed. As Pallas has remarked, who can doubt but that the
ancient Russian would esteem and endeavour to preserve those sheep in
his flocks which had the thickest coats. This kind of insensible
selection by which new breeds are not selected and kept separate, but a
peculiar character is slowly given to the whole mass of the breed, by
often saving the life of animals with certain characteristics, we may
feel nearly sure, from what we see has been done by the more direct
method of separate selection within the last 50 years in England, would
in the course of some thousand years produce a marked effect.
{200} See _Origin_, Ed. i. p. 33, vi. p. 38. The evidence is given
in the present Essay rather more fully than in the _Origin_.
{201} _Journal of Researches_, Ed. 1860, p. 214. "Doggies catch
otters, old women no."
_Crossing Breeds._
When once two or more races are formed, or if more than one race, or
species fertile _inter se_, originally existed in a wild state, their
crossing becomes a most copious source of new races{202}. When two
well-marked races are crossed the offspring in the first generation take
more or less after either parent or are quite intermediate between them,
or rarely assume characters in some degree new. In the second and
several succeeding generations, the offspring are generally found to
vary exceedingly, one compared with another, and many revert nearly to
their ancestral forms. This greater variability in succeeding
generations seems analogous to the breaking or variability of organic
beings after having been bred for some generations under
domestication{203}. So marked is this variability in cross-bred
descendants, that Pallas and some other naturalists have supposed that
all variation is due to an original cross; but I conceive that the
history of the potato, Dahlia, Scotch Rose, the guinea-pig, and of many
trees in this country, where only one species of the genus exists,
clearly shows that a species may vary where there can have been no
crossing. Owing to this variability and tendency to reversion in
cross-bred beings, much careful selection is requisite to make
intermediate or new permanent races: nevertheless crossing has been a
most powerful engine, especially with plants, where means of propagation
exist by which the cross-bred varieties can be secured without incurring
the risk of fresh variation from seminal propagation: with animals the
most skilful agriculturalists now greatly prefer careful selection from
a well-established breed, rather than from uncertain cross-bred stocks.
{202} The effects of crossing is much more strongly stated here
than in the _Origin_. See Ed. i. p. 20, vi. p. 23, where indeed the
opposite point of view is given. His change of opinion may be due
to his work on pigeons. The whole of the discussion on crossing
corresponds to Chapter VIII of the _Origin_, Ed. i. rather than to
anything in the earlier part of the book.
{203} The parallelism between the effects of a cross and the
effects of conditions is given from a different point of view in
the _Origin_, Ed. i. p. 266, vi. p. 391. See the experimental
evidence for this important principle in the author's work on
_Cross and Self-Fertilisation_. Professor Bateson has suggested
that the experiments should be repeated with gametically pure
plants.
Although intermediate and new races may be formed by the mingling of
others, yet if the two races are allowed to mingle quite freely, so that
none of either parent race remain pure, then, especially if the parent
races are not widely different, they will slowly blend together, and the
two races will be destroyed, and one mongrel race left in its place.
This will of course happen in a shorter time, if one of the parent
races exists in greater number than the other. We see the effect of this
mingling, in the manner in which the aboriginal breeds of dogs and pigs
in the Oceanic Islands and the many breeds of our domestic animals
introduced into S. America, have all been lost and absorbed in a mongrel
race. It is probably owing to the freedom of crossing, that, in
uncivilised countries, where inclosures do not exist, we seldom meet
with more than one race of a species: it is only in enclosed countries,
where the inhabitants do not migrate, and have conveniences for
separating the several kinds of domestic animals, that we meet with a
multitude of races. Even in civilised countries, want of care for a few
years has been found to destroy the good results of far longer periods
of selection and separation.
This power of crossing will affect the races of all _terrestrial_
animals; for all terrestrial animals require for their reproduction the
union of two individuals. Amongst plants, races will not cross and blend
together with so much freedom as in terrestrial animals; but this
crossing takes place through various curious contrivances to a
surprising extent. In fact such contrivances exist in so very many
hermaphrodite flowers by which an occasional cross may take place, that
I cannot avoid suspecting (with Mr Knight) that the reproductive action
requires, at _intervals_, the concurrence of distinct individuals{204}.
Most breeders of plants and animals are firmly convinced that benefit is
derived from an occasional cross, not with another race, but with
another family of the same race; and that, on the other hand, injurious
consequences follow from long-continued close interbreeding in the same
family. Of marine animals, many more, than was till lately believed,
have their sexes on separate individuals; and where they are
hermaphrodite, there seems very generally to be means through the water
of one individual occasionally impregnating another: if individual
animals can singly propagate themselves for perpetuity, it is
unaccountable that no terrestrial animal, where the means of observation
are more obvious, should be in this predicament of singly perpetuating
its kind. I conclude, then, that races of most animals and plants, when
unconfined in the same country, would tend to blend together.
{204} The so-called Knight-Darwin Law is often misunderstood. See
Goebel in _Darwin and Modern Science_, 1909, p. 419; also F.
Darwin, _Nature_, Oct. 27, 1898.
_Whether our domestic races have descended from one or more wild
stocks._
Several naturalists, of whom Pallas{205} regarding animals, and Humboldt
regarding certain plants, were the first, believe that the breeds of
many of our domestic animals such as of the horse, pig, dog, sheep,
pigeon, and poultry, and of our plants have descended from more than one
aboriginal form. They leave it doubtful, whether such forms are to be
considered wild races, or true species, whose offspring are fertile when
crossed _inter se_. The main arguments for this view consist, firstly,
of the great difference between such breeds, as the Race-and Cart-Horse,
or the Greyhound and Bull-dog, and of our ignorance of the steps or
stages through which these could have passed from a common parent; and
secondly that in the most ancient historical periods, breeds resembling
some of those at present most different, existed in different countries.
The wolves of N. America and of Siberia are thought to be different
species; and it has been remarked that the dogs belonging to the
savages in these two countries resemble the wolves of the same country;
and therefore that they have probably descended from two different wild
stocks. In the same manner, these naturalists believe that the horse of
Arabia and of Europe have probably descended from two wild stocks both
apparently now extinct. I do not think the assumed fertility of these
wild stocks any very great difficulty on this view; for although in
animals the offspring of most cross-bred species are infertile, it is
not always remembered that the experiment is very seldom fairly tried,
except when two near species _both_ breed freely (which does not readily
happen, as we shall hereafter see) when under the dominion of man.
Moreover in the case of the China{206} and common goose, the canary and
siskin, the hybrids breed freely; in other cases the offspring from
hybrids crossed with either pure parent are fertile, as is practically
taken advantage of with the yak and cow; as far as the analogy of plants
serves, it is impossible to deny that some species are quite fertile
_inter se_; but to this subject we shall recur.
{205} Pallas' theory is discussed in the _Origin_, Ed. i. pp. 253,
254, vi. p. 374.
{206} See Darwin's paper on the fertility of hybrids from the
common and Chinese goose in _Nature_, Jan. 1, 1880.
On the other hand, the upholders of the view that the several breeds of
dogs, horses, &c., &c., have descended each from one stock, may aver
that their view removes all _difficulty about fertility_, and that the
main argument from the high antiquity of different breeds, somewhat
similar to the present breeds, is worth little without knowing the date
of the domestication of such animals, which is far from being the case.
They may also with more weight aver that, knowing that organic beings
under domestication do vary in some degree, the argument from the great
difference between certain breeds is worth nothing, without we know the
limits of variation during a long course of time, which is far from the
case. They may argue that almost every county in England, and in many
districts of other countries, for instance in India, there are slightly
different breeds of the domestic animals; and that it is opposed to all
that we know of the distribution of wild animals to suppose that these
have descended from so many different wild races or species: if so, they
may argue, is it not probable that countries quite separate and exposed
to different climates would have breeds not slightly, but considerably,
different? Taking the most favourable case, on both sides, namely that
of the dog; they might urge that such breeds as the bull-dog and
turnspit have been reared by man, from the ascertained fact that
strictly analogous breeds (namely the Niata ox and Ancon sheep) in other
quadrupeds have thus originated. Again they may say, seeing what
training and careful selection has effected for the greyhound, and
seeing how absolutely unfit the Italian greyhound is to maintain itself
in a state of nature, is it not probable that at least all
greyhounds,--from the rough deerhound, the smooth Persian, the common
English, to the Italian,--have descended from one stock{207}? If so, is
it so improbable that the deerhound and long-legged shepherd dog have so
descended? If we admit this, and give up the bull-dog, we can hardly
dispute the probable common descent of the other breeds.
{207} _Origin_, Ed. i. p. 19, vi. p. 22.
The evidence is so conjectural and balanced on both sides that at
present I conceive that no one can decide: for my own part, I lean to
the probability of most of our domestic animals having descended from
more than one wild stock; though from the arguments last advanced and
from reflecting on the slow though inevitable effect of different races
of mankind, under different circumstances, saving the lives of and
therefore selecting the individuals most useful to them, I cannot doubt
but that one class of naturalists have much overrated the probable
number of the aboriginal wild stocks. As far as we admit the difference
of our races due to the differences of their original stocks, so
much must we give up of the amount of variation produced under
domestication. But this appears to me unimportant, for we certainly know
in some few cases, for instance in the Dahlia, and potato, and rabbit,
that a great number of varieties have proceeded from one stock; and, in
many of our domestic races, we know that man, by slowly selecting and by
taking advantage of sudden sports, has considerably modified old races
and produced new ones. Whether we consider our races as the descendants
of one or several wild stocks, we are in far the greater number of cases
equally ignorant what these stocks were.
_Limits to Variation in degree and kind._
Man's power in making races deends, in the first instance, on the stock
on which he works being variable; but his labours are modified and
limited, as we have seen, by the direct effects of the external
conditions,--by the deficient or imperfect hereditariness of new
peculiarities,--and by the tendency to continual variation and
especially to reversion to ancestral forms. If the stock is not variable
under domestication, of course he can do nothing; and it appears that
species differ considerably in this tendency to variation, in the same
way as even sub-varieties from the same variety differ greatly in this
respect, and transmit to their offspring this difference in tendency.
Whether the absence of a tendency to vary is an unalterable quality in
certain species, or depends on some deficient condition of the
particular state of domestication to which they are exposed, there is no
evidence. When the organization is rendered variable, or plastic, as I
have expressed it, under domestication, different parts of the frame
vary more or less in different species: thus in the breeds of cattle it
has been remarked that the horns are the most constant or least variable
character, for these often remain constant, whilst the colour, size,
proportions of the body, tendency to fatten &c., vary; in sheep, I
believe, the horns are much more variable. As a general rule the less
important parts of the organization seem to vary most, but I think there
is sufficient evidence that every part occasionally varies in a slight
degree. Even when man has the primary requisite variability he is
necessarily checked by the health and life of the stock he is working
on: thus he has already made pigeons with such small beaks that they can
hardly eat and will not rear their own young; he has made families of
sheep with so strong a tendency to early maturity and to fatten, that in
certain pastures they cannot live from their extreme liability to
inflammation; he has made (_i.e._ selected) sub-varieties of plants with
a tendency to such early growth that they are frequently killed by the
spring frosts; he has made a breed of cows having calves with such large
hinder quarters that they are born with great difficulty, often to the
death of their mothers{208}; the breeders were compelled to remedy this
by the selection of a breeding stock with smaller hinder quarters; in
such a case, however, it is possible by long patience and great loss, a
remedy might have been found in selecting cows capable of giving birth
to calves with large hinder quarters, for in human kind there no
doubt hereditary bad and good confinements. Besides the limits already
specified, there can be little doubt that the variation of different
parts of the frame are connected together by many laws{209}: thus the
two sides of the body, in health and disease, seem almost always to vary
together: it has been asserted by breeders that if the head is much
elongated, the bones of the extremities will likewise be so; in
seedling-apples large leaves and fruit generally go together, and serve
the horticulturalist as some guide in his selection; we can here see the
reason, as the fruit is only a metamorphosed leaf. In animals the teeth
and hair seem connected, for the hairless Chinese dog is almost
toothless. Breeders believe that one part of the frame or function being
increased causes other parts to decrease: they dislike great horns and
great bones as so much flesh lost; in hornless breeds of cattle certain
bones of the head become more developed: it is said that fat
accumulating in one part checks its accumulation in another, and
likewise checks the action of the udder. The whole organization is so
connected that it is probable there are many conditions determining the
variation of each part, and causing other parts to vary with it; and man
in making new races must be limited and ruled by all such laws.
{208} _Var. under Dom._, Ed. ii. vol. II. p. 211.
{209} This discussion corresponds to the _Origin_, Ed. i. pp. 11
and 143, vi. pp. 13 and 177.
_In what consists Domestication._
In this chapter we have treated of variation under domestication, and it
now remains to consider in what does this power of domestication
consist{210}, a subject of considerable difficulty. Observing that
organic beings of almost every class, in all climates, countries, and
times, have varied when long bred under domestication, we must conclude
that the influence is of some very general nature{211}. Mr Knight alone,
as far as I know, has tried to define it; he believes it consists of an
excess of food, together with transport to a more genial climate, or
protection from its severities. I think we cannot admit this latter
proposition, for we know how many vegetable products, aborigines of this
country, here vary, when cultivated without any protection from the
weather; and some of our variable trees, as apricots, peaches, have
undoubtedly been derived from a more genial climate. There appears to be
much more truth in the doctrine of excess of food being the cause,
though I much doubt whether this is the sole cause, although it may well
be requisite for the kind of variation desired by man, namely increase
of size and vigour. No doubt horticulturalists, when they wish to raise
new seedlings, often pluck off all the flower-buds, except a few, or
remove the whole during one season, so that a great stock of nutriment
may be thrown into the flowers which are to seed. When plants are
transported from high-lands, forests, marshes, heaths, into our gardens
and greenhouses, there must be a considerable change of food, but it
would be hard to prove that there was in every case an excess of the
kind proper to the plant. If it be an excess of food, compared with that
which the being obtained in its natural state{212}, the effects continue
for an improbably long time; during how many ages has wheat been
cultivated, and cattle and sheep reclaimed, and we cannot suppose their
_amount_ of food has gone on increasing, nevertheless these are amongst
the most variable of our domestic productions. It has been remarked
(Marshall) that some of the most highly kept breeds of sheep and cattle
are truer or less variable than the straggling animals of the poor,
which subsist on commons, and pick up a bare subsistence{213}. In the
case of forest-trees raised in nurseries, which vary more than the same
trees do in their aboriginal forests, the cause would seem simply to lie
in their not having to struggle against other trees and weeds, which in
their natural state doubtless would limit the conditions of their
existence. It appears to me that the power of domestication resolves
itself into the accumulated effects of a change of all or some of the
natural conditions of the life of the species, often associated with
excess of food. These conditions moreover, I may add, can seldom remain,
owing to the mutability of the affairs, habits, migrations, and
knowledge of man, for very long periods the same. I am the more inclined
to come to this conclusion from finding, as we shall hereafter show,
that changes of the natural conditions of existence seem peculiarly to
affect the action of the reproductive system{214}. As we see that
hybrids and mongrels, after the first generation, are apt to vary much,
we may at least conclude that variability does not altogether depend on
excess of food.
{210} See _Origin_, Ed. i. p. 7, vi. p. 7.
{211} "Isidore G. St Hilaire insists that
breeding in captivity essential element. Schleiden on alkalies.
What is
it in domestication which causes variation?"
{212} "It appears that slight changes of
condition good for health; that more change affects the
generative system, so that variation results in the offspring;
that still more change checks or destroys fertility not of the
offspring." Compare the _Origin_, Ed. i. p. 9, vi. p. 11. What the
meaning of "not of the offspring" may be is not clear.
{213} In the _Origin_, Ed. i. p. 41, vi. p. 46 the question is
differently treated; it is pointed out that a large stock of
individuals gives a better chance of available variations
occurring. Darwin quotes from Marshall that sheep in small lots can
never be improved. This comes from Marshall's _Review of the
Reports to the Board of Agriculture_, 1808, p. 406. In this Essay
the name Marshall occurs in the margin. Probably this refers to
_loc. cit._ p. 200, where unshepherded sheep in many parts of
England are said to be similar owing to mixed breeding not being
avoided.
{214} See _Origin_, Ed. i. p. 8, vi. p. 8.
After these views, it may be asked how it comes that certain animals
and plants, which have been domesticated for a considerable length of
time, and transported from very different conditions of existence, have
not varied much, or scarcely at all; for instance, the ass, peacock,
guinea-fowl, asparagus, Jerusalem artichoke{215}. I have already said
that probably different species, like different sub-varieties, possess
different degrees of tendency to vary; but I am inclined to attribute in
these cases the want of numerous races less to want of variability than
to selection not having been practised on them. No one will take the
pains to select without some corresponding object, either of use or
amusement; the individuals raised must be tolerably numerous, and not so
precious, but that he may freely destroy those not answering to his
wishes. If guinea-fowls or peacocks{216} became "fancy" birds, I cannot
doubt that after some generations several breeds would be raised. Asses
have not been worked on from mere neglect; but they differ in _some_
degree in different countries. The insensible selection, due to
different races of mankind preserving those individuals most useful to
them in their different circumstances, will apply only to the oldest and
most widely domesticated animals. In the case of plants, we must put
entirely out of the case those exclusively (or almost so) propagated by
cuttings, layers or tubers, such as the Jerusalem artichoke and laurel;
and if we put on one side plants of little ornament or use, and those
which are used at so early a period of their growth that no especial
characters signify, as asparagus{217} and seakale, I can think of none
long cultivated which have not varied. In no case ought we to expect to
find as much variation in a race when it alone has been formed, as when
several have been formed, for their crossing and recrossing will
greatly increase their variability.
{215} See _Origin_, Ed. i. p. 42, vi. p. 48.
{216} There are white peacocks.
{217} There are varieties of asparagus.
_Summary of first Chapter._
To sum up this chapter. Races are made under domestication: 1st, by the
direct effects of the external conditions to which the species is
exposed: 2nd, by the indirect effects of the exposure to new conditions,
often aided by excess of food, rendering the organization plastic, and
by man's selecting and separately breeding certain individuals, or
introducing to his stock selected males, or often preserving with care
the life of the individuals best adapted to his purposes: 3rd, by
crossing and recrossing races already made, and selecting their
offspring. After some generations man may relax his care in selection:
for the tendency to vary and to revert to ancestral forms will decrease,
so that he will have only occasionally to remove or destroy one of the
yearly offspring which departs from its type. Ultimately, with a large
stock, the effects of free crossing would keep, even without this care,
his breed true. By these means man can produce infinitely numerous
races, curiously adapted to ends, both most important and most
frivolous; at the same time that the effects of the surrounding
conditions, the laws of inheritance, of growth, and of variation, will
modify and limit his labours.
CHAPTER II
ON THE VARIATION OF ORGANIC BEINGS IN A WILD STATE; ON THE NATURAL MEANS
OF SELECTION; AND ON THE COMPARISON OF DOMESTIC RACES AND TRUE SPECIES
Having treated of variation under domestication, we now come to it in a
_state of nature_.
Most organic beings in a state of nature vary exceedingly little{218}: I
put out of the case variations (as stunted plants &c., and sea-shells in
brackish water{219}) which are directly the effect of external agencies
and which we do not _know are in the breed_{220}, or are _hereditary_.
The amount of hereditary variation is very difficult to ascertain,
because naturalists (partly from the want of knowledge, and partly from
the inherent difficulty of the subject) do not all agree whether certain
forms are species or races{221}. Some strongly marked races of plants,
comparable with the decided sports of horticulturalists, undoubtedly
exist in a state of nature, as is actually known by experiment, for
instance in the primrose and cowslip{222}, in two so-called species of
dandelion, in two of foxglove{223}, and I believe in some pines. Lamarck
has observed that, as long as we confine our attention to one limited
country, there is seldom much difficulty in deciding what forms to call
species and what varieties; and that it is when collections flow in from
all parts of the world that naturalists often feel at a loss to decide
the limit of variation. Undoubtedly so it is, yet amongst British plants
(and I may add land shells), which are probably better known than any in
the world, the best naturalists differ very greatly in the relative
proportions of what they call species and what varieties. In many genera
of insects, and shells, and plants, it seems almost hopeless to
establish which are which. In the higher classes there are less doubts;
though we find considerable difficulty in ascertaining what deserve to
be called species amongst foxes and wolves, and in some birds, for
instance in the case of the white barn-owl. When specimens are brought
from different parts of the world, how often do naturalists dispute this
same question, as I found with respect to the birds brought from the
Galapagos islands. Yarrell has remarked that the individuals of the same
undoubted species of birds, from Europe and N. America, usually present
slight, indefinable though perceptible differences. The recognition
indeed of one animal by another of its kind seems to imply some
difference. The disposition of wild animals undoubtedly differs. The
variation, such as it is, chiefly affects the same parts in wild
organisms as in domestic breeds; for instance, the size, colour, and the
external and less important parts. In many species the variability of
certain organs or qualities is even stated as one of the specific
characters: thus, in plants, colour, size, hairiness, the number of the
stamens and pistils, and even their presence, the form of the leaves;
the size and form of the mandibles of the males of some insects; the
length and curvature of the beak in some birds (as in Opetiorynchus) are
variable characters in some species and quite fixed in others. I do not
perceive that any just distinction can be drawn between this recognised
variability of certain parts in many species and the more general
variability of the whole frame in domestic races.
{218} In Chapter II of the first edition of the _Origin_ Darwin
insists rather on the presence of variability in a state of nature;
see, for instance, p. 45, Ed. vi. p. 53, "I am convinced that the
most experienced naturalist would be surprised at the number of the
cases of variability ... which he could collect on good authority,
as I have collected, during a course of years."
{219} See _Origin_, Ed. i. p. 44, vi. p. 52.
{220} Here discuss _what is a species_,
sterility can most rarely be told when crossed.--Descent from common
stock.
{221} Give only rule: chain of intermediate
forms, and _analogy_; this important. Every Naturalist at first when
he gets hold of new variable type is _quite puzzled_ to know what to
think species and what variations.
{222} The author had not at this time the knowledge of the meaning
of dimorphism.
{223} Compare feathered heads in very different
birds with spines in Echidna and Hedgehog.
Plants under very different climate not varying. Digitalis shows
jumps in variation, like Laburnum and Orchis case--in fact hostile
cases. Variability of sexual characters alike in domestic and wild.
Although the amount of variation be exceedingly small in most organic
beings in a state of nature, and probably quite wanting (as far as our
senses serve) in the majority of cases; yet considering how many animals
and plants, taken by mankind from different quarters of the world for
the most diverse purposes, have varied under domestication in every
country and in every age, I think we may safely conclude that all
organic beings with few exceptions, if capable of being domesticated and
bred for long periods, would vary. Domestication seems to resolve itself
into a change from the natural conditions of the species [generally
perhaps including an increase of food]; if this be so, organisms in a
state of nature must _occasionally_, in the course of ages, be exposed
to analogous influences; for geology clearly shows that many places
must, in the course of time, become exposed to the widest range of
climatic and other influences; and if such places be isolated, so that
new and better adapted organic beings cannot freely emigrate, the old
inhabitants will be exposed to new influences, probably far more varied,
than man applies under the form of domestication. Although every species
no doubt will soon breed up to the full number which the country will
support, yet it is easy to conceive that, on an average, some species
may receive an increase of food; for the times of dearth may be short,
yet enough to kill, and recurrent only at long intervals. All such
changes of conditions from geological causes would be exceedingly slow;
what effect the slowness might have we are ignorant; under domestication
it appears that the effects of change of conditions accumulate, and then
break out. Whatever might be the result of these slow geological
changes, we may feel sure, from the means of dissemination common in a
lesser or greater degree to every organism taken conjointly with the
changes of geology, which are steadily (and sometimes suddenly, as when
an isthmus at last separates) in progress, that occasionally organisms
must suddenly be introduced into new regions, where, if the conditions
of existence are not so foreign as to cause its extermination, it will
often be propagated under circumstances still more closely analogous to
those of domestication; and therefore we expect will evince a tendency
to vary. It appears to me quite _inexplicable_ if this has never
happened; but it can happen very rarely. Let us then suppose that an
organism by some chance (which might be hardly repeated in 1000 years)
arrives at a modern volcanic island in process of formation and not
fully stocked with the most appropriate organisms; the new organism
might readily gain a footing, although the external conditions were
considerably different from its native ones. The effect of this we might
expect would influence in some small degree the size, colour, nature of
covering &c., and from inexplicable influences even special parts and
organs of the body. But we might further (and is far more important)
expect that the reproductive system would be affected, as under
domesticity, and the structure of the offspring rendered in some degree
plastic. Hence almost every part of the body would tend to vary from the
typical form in slight degrees, and in no determinate way, and therefore
_without selection_ the free crossing of these small variations
(together with the tendency to reversion to the original form) would
constantly be counteracting this unsettling effect of the extraneous
conditions on the reproductive system. Such, I conceive, would be the
unimportant result without selection. And here I must observe that the
foregoing remarks are equally applicable to that small and admitted
amount of variation which has been observed in some organisms in a state
of nature; as well as to the above hypothetical variation consequent on
changes of condition.
Let us now suppose a Being{224} with penetration sufficient to perceive
differences in the outer and innermost organization quite imperceptible
to man, and with forethought extending over future centuries to watch
with unerring care and select for any object the offspring of an
organism produced under the foregoing circumstances; I can see no
conceivable reason why he could not form a new race (or several were he
to separate the stock of the original organism and work on several
islands) adapted to new ends. As we assume his discrimination, and his
forethought, and his steadiness of object, to be incomparably greater
that those qualities in man, so we may suppose the beauty and
complications of the adaptations of the new races and their differences
from the original stock to be greater than in the domestic races
produced by man's agency: the ground-work of his labours we may aid by
supposing that the external conditions of the volcanic island, from its
continued emergence and the occasional introduction of new immigrants,
vary; and thus to act on the reproductive system of the organism, on
which he is at work, and so keep its organization somewhat plastic. With
time enough, such a Being might rationally (without some unknown law
opposed him) aim at almost any result.
{224} A corresponding passage occurs in _Origin_, Ed. i. p. 83, vi.
p. 101, where however Nature takes the place of the selecting
Being.
For instance, let this imaginary Being wish, from seeing a plant growing
on the decaying matter in a forest and choked by other plants, to give
it power of growing on the rotten stems of trees, he would commence
selecting every seedling whose berries were in the smallest degree more
attractive to tree-frequenting birds, so as to cause a proper
dissemination of the seeds, and at the same time he would select those
plants which had in the slightest degree more and more power of drawing
nutriment from rotten wood; and he would destroy all other seedlings
with less of this power. He might thus, in the course of century after
century, hope to make the plant by degrees grow on rotten wood, even
high up on trees, wherever birds dropped the non-digested seeds. He
might then, if the organization of the plant was plastic, attempt by
continued selection of chance seedlings to make it grow on less and less
rotten wood, till it would grow on sound wood{225}. Supposing again,
during these changes the plant failed to seed quite freely from
non-impregnation, he might begin selecting seedlings with a little
sweeter differently tasted honey or pollen, to tempt insects to visit
the flowers regularly: having effected this, he might wish, if it
profited the plant, to render abortive the stamens and pistils in
different flowers, which he could do by continued selection. By such
steps he might aim at making a plant as wonderfully related to other
organic beings as is the mistletoe, whose existence absolutely depends
on certain insects for impregnation, certain birds for transportal, and
certain trees for growth. Furthermore, if the insect which had been
induced regularly to visit this hypothetical plant profited much by it,
our same Being might wish by selection to modify by gradual selection
the insect's structure, so as to facilitate its obtaining the honey or
pollen: in this manner he might adapt the insect (always presupposing
its organization to be in some degree plastic) to the flower, and the
impregnation of the flower to the insect; as is the case with many bees
and many plants.
{225} The mistletoe is used as an illustration in _Origin_, Ed. i.
p. 3, vi. p. 3, but with less detail.
Seeing what blind capricious man has actually effected by selection
during the few last years, and what in a ruder state he has probably
effected without any systematic plan during the last few thousand years,
he will be a bold person who will positively put limits to what the
supposed Being could effect during whole geological periods. In
accordance with the plan by which this universe seems governed by the
Creator, let us consider whether there exists any _secondary_ means in
the economy of nature by which the process of selection could go on
adapting, nicely and wonderfully, organisms, if in ever so small a
degree plastic, to diverse ends. I believe such secondary means do
exist{226}.
{226} The selection, in cases where adult lives
only few hours as Ephemera, must fall on larva--curious speculation
of the effect changes in it would bring in parent.
_Natural means of Selection{227}._
{227} This section forms part of the joint paper by Darwin and
Wallace read before the Linnean Society on July 1, 1858.
De Candolle, in an eloquent passage, has declared that all nature is at
war, one organism with another, or with external nature. Seeing the
contented face of nature, this may at first be well doubted; but
reflection will inevitably prove it is too true. The war, however, is
not constant, but only recurrent in a slight degree at short periods and
more severely at occasional more distant periods; and hence its effects
are easily overlooked. It is the doctrine of Malthus applied in most
cases with ten-fold force. As in every climate there are seasons for
each of its inhabitants of greater and less abundance, so all annually
breed; and the moral restraint, which in some small degree checks the
increase of mankind, is entirely lost. Even slow-breeding mankind has
doubled in 25 years{228}, and if he could increase his food with greater
ease, he would double in less time. But for animals, without artificial
means, _on an average_ the amount of food for each species must be
constant; whereas the increase of all organisms tends to be geometrical,
and in a vast majority of cases at an enormous ratio. Suppose in a
certain spot there are eight pairs of [robins] birds, and that _only_
four pairs of them annually (including double hatches) rear only four
young; and that these go on rearing their young at the same rate: then
at the end of seven years (a short life, excluding violent deaths, for
any birds) there will be 2048 robins, instead of the original sixteen;
as this increase is quite impossible, so we must conclude either that
robins do not rear nearly half their young or that the average life of a
robin when reared is from accident not nearly seven years. Both checks
probably concur. The same kind of calculation applied to all vegetables
and animals produces results either more or less striking, but in
scarcely a single instance less striking than in man{229}.
{228} Occurs in _Origin_, Ed. i. p. 64, vi. p. 79.
{229} Corresponds approximately with _Origin_, Ed. i. pp. 64-65,
vi. p. 80.
Many practical illustrations of this rapid tendency to increase are on
record, namely during peculiar seasons, in the extraordinary increase of
certain animals, for instance during the years 1826 to 1828, in La
Plata, when from drought, some millions of cattle perished, the whole
country _swarmed_ with innumerable mice: now I think it cannot be
doubted that during the breeding season all the mice (with the exception
of a few males or females in excess) ordinarily pair; and therefore that
this astounding increase during three years must be attributed to a
greater than usual number surviving the first year, and then breeding,
and so on, till the third year, when their numbers were brought down to
their usual limits on the return of wet weather. Where man has
introduced plants and animals into a new country favourable to them,
there are many accounts in how surprisingly few years the whole country
has become stocked with them. This increase would necessarily stop as
soon as the country was fully stocked; and yet we have every reason to
believe from what is known of wild animals that _all_ would pair in the
spring. In the majority of cases it is most difficult to imagine where
the check falls, generally no doubt on the seeds, eggs, and young; but
when we remember how impossible even in mankind (so much better known
than any other animal) it is to infer from repeated casual observations
what the average of life is, or to discover how different the percentage
of deaths to the births in different countries, we ought to feel no
legitimate surprise at not seeing where the check falls in animals and
plants. It should always be remembered that in most cases the checks are
yearly recurrent in a small regular degree, and in an extreme degree
during occasionally unusually cold, hot, dry, or wet years, according to
the constitution of the being in question. Lighten any check in the
smallest degree, and the geometrical power of increase in every
organism will instantly increase the average numbers of the favoured
species. Nature may be compared to a surface, on which rest ten thousand
sharp wedges touching each other and driven inwards by incessant
blows{230}. Fully to realise these views much reflection is requisite;
Malthus on man should be studied; and all such cases as those of the
mice in La Plata, of the cattle and horses when first turned out in S.
America, of the robins by our calculation, &c., should be well
considered: reflect on the enormous multiplying power _inherent and
annually in action_ in all animals; reflect on the countless seeds
scattered by a hundred ingenious contrivances, year after year, over the
whole face of the land; and yet we have every reason to suppose that the
average percentage of every one of the inhabitants of a country will
_ordinarily_ remain constant. Finally, let it be borne in mind that this
average number of individuals (the external conditions remaining the
same) in each country is kept up by recurrent struggles against other
species or against external nature (as on the borders of the arctic
regions{231}, where the cold checks life); and that ordinarily each
individual of each species holds its place, either by its own struggle
and capacity of acquiring nourishment in some period (from the egg
upwards) of its life, or by the struggle of its parents (in short lived
organisms, when the main check occurs at long intervals) against and
compared with other individuals of the _same_ or _different_ species.
{230} This simile occurs in _Origin_, Ed. i. p. 67, not in the
later editions.
{231} In case like mistletoe, it may be
asked why not more species, no other species interferes; answer
almost sufficient, same causes which check the multiplication of
individuals.
But let the external conditions of a country change; if in a small
degree, the relative proportions of the inhabitants will in most cases
simply be slightly changed; but let the number of inhabitants be small,
as in an island{232}, and free access to it from other countries be
circumscribed; and let the change of condition continue progressing
(forming new stations); in such case the original inhabitants must cease
to be so perfectly adapted to the changed conditions as they originally
were. It has been shown that probably such changes of external
conditions would, from acting on the reproductive system, cause the
organization of the beings most affected to become, as under
domestication, plastic. Now can it be doubted from the struggle each
individual (or its parents) has to obtain subsistence that any minute
variation in structure, habits, or instincts, adapting that individual
better to the new conditions, would tell upon its vigour and health? In
the struggle it would have a better _chance_ of surviving, and those of
its offspring which inherited the variation, let it be ever so slight,
would have a better _chance_ to survive. Yearly more are bred than can
survive; the smallest grain in the balance, in the long run, must tell
on which death shall fall, and which shall survive{233}. Let this work
of selection, on the one hand, and death on the other, go on for a
thousand generations; who would pretend to affirm that it would produce
no effect, when we remember what in a few years Bakewell effected in
cattle and Western in sheep, by this identical principle of selection.
{232} See _Origin_, Ed. i. pp. 104, 292, vi. pp. 127, 429.
{233} Recognition of the importance of minute differences in the
struggle occurs in the Essay of 1842, p. 8 note 3.{Note 59}
To give an imaginary example, from changes in progress on an island, let
the organization{234} of a canine animal become slightly plastic, which
animal preyed chiefly on rabbits, but sometimes on hares; let these same
changes cause the number of rabbits very slowly to decrease and the
number of hares to increase; the effect of this would be that the fox or
dog would be driven to try to catch more hares, and his numbers would
tend to decrease; his organization, however, being slightly plastic,
those individuals with the lightest forms, longest limbs, and best
eye-sight (though perhaps with less cunning or scent) would be slightly
favoured, let the difference be ever so small, and would tend to live
longer and to survive during that time of the year when food was
shortest; they would also rear more young, which young would tend to
inherit these slight peculiarities. The less fleet ones would be rigidly
destroyed. I can see no more reason to doubt but that these causes in a
thousand generations would produce a marked effect, and adapt the form
of the fox to catching hares instead of rabbits, than that greyhounds
can be improved by selection and careful breeding. So would it be with
plants under similar circumstances; if the number of individuals of a
species with plumed seeds could be increased by greater powers of
dissemination within its own area (that is if the check to increase fell
chiefly on the seeds), those seeds which were provided with ever so
little more down, or with a plume placed so as to be slightly more acted
on by the winds, would in the long run tend to be most disseminated; and
hence a greater number of seeds thus formed would germinate, and would
tend to produce plants inheriting this slightly better adapted down.
{234} See _Origin_, Ed. i. p. 90, vi. p. 110.
Besides this natural means of selection, by which those individuals are
preserved, whether in their egg or seed or in their mature state, which
are best adapted to the place they fill in nature, there is a second
agency at work in most bisexual animals tending to produce the same
effect, namely the struggle of the males for the females. These
struggles are generally decided by the law of battle; but in the case
of birds, apparently, by the charms of their song{235}, by their beauty
or their power of courtship, as in the dancing rock-thrush of Guiana.
Even in the animals which pair there seems to be an excess of males
which would aid in causing a struggle: in the polygamous animals{236},
however, as in deer, oxen, poultry, we might expect there would be
severest struggle: is it not in the polygamous animals that the males
are best formed for mutual war? The most vigorous males, implying
perfect adaptation, must generally gain the victory in their several
contests. This kind of selection, however, is less rigorous than the
other; it does not require the death of the less successful, but gives
to them fewer descendants. This struggle falls, moreover, at a time of
year when food is generally abundant, and perhaps the effect chiefly
produced would be the alteration of sexual characters, and the selection
of individual forms, no way related to their power of obtaining food, or
of defending themselves from their natural enemies, but of fighting one
with another. This natural struggle amongst the males may be compared in
effect, but in a less degree, to that produced by those agriculturalists
who pay less attention to the careful selection of all the young animals
which they breed and more to the occasional use of a choice male{237}.
{235} These two forms of sexual selection are given in _Origin_,
Ed. i. p. 87, vi. p. 107. The Guiana rock-thrush is given as an
example of bloodless competition.
{236} Seals? Pennant about battles of seals.
{237} In the Linnean paper of July 1, 1858 the final word is
_mate_: but the context shows that it should be _male_; it is
moreover clearly so written in the MS.
_Differences between "Races" and "Species":--first, in their trueness or
variability._
Races{238} produced by these natural means of selection{239} we may
expect would differ in some respects from those produced by man. Man
selects chiefly by the eye, and is not able to perceive the course of
every vessel and nerve, or the form of the bones, or whether the
internal structure corresponds to the outside shape. He{240} is unable
to select shades of constitutional differences, and by the protection he
affords and his endeavours to keep his property alive, in whatever
country he lives, he checks, as much as lies in his power, the selecting
action of nature, which will, however, go on to a lesser degree with all
living things, even if their length of life is not determined by their
own powers of endurance. He has bad judgment, is capricious, he does
not, or his successors do not, wish to select for the same exact end for
hundreds of generations. He cannot always suit the selected form to the
properest conditions; nor does he keep those conditions uniform: he
selects that which is useful to him, not that best adapted to those
conditions in which each variety is placed by him: he selects a small
dog, but feeds it highly; he selects a long-backed dog, but does not
exercise it in any peculiar manner, at least not during every
generation. He seldom allows the most vigorous males to struggle for
themselves and propagate, but picks out such as he possesses, or such as
he prefers, and not necessarily those best adapted to the existing
conditions. Every agriculturalist and breeder knows how difficult it is
to prevent an occasional cross with another breed. He often grudges to
destroy an individual which departs considerably from the required type.
He often begins his selection by a form or sport considerably departing
from the parent form. Very differently does the natural law of selection
act; the varieties selected differ only slightly from the parent
forms{241}; the conditions are constant for long periods and change
slowly; rarely can there be a cross; the selection is rigid and
unfailing, and continued through many generations; a selection can
_never be made_ without the form be _better_ adapted to the conditions
than the parent form; the selecting power goes on without caprice, and
steadily for thousands of years adapting the form to these conditions.
The selecting power is not deceived by external appearances, it tries
the being during its whole life; and if less well adapted than its
_congeners_, without fail it is destroyed; every part of its structure
is thus scrutinised and proved good towards the place in nature which it
occupies.
{238} In the _Origin_ the author would here have used the word
_variety_.
{239} The whole of p. 94 and 15 lines of p. 95 are, in the MS.,
marked through in pencil with vertical lines, beginning at "Races
produced, &c." and ending with "to these conditions."
{240} See _Origin_, Ed. i. p. 83, vi. p. 102.
{241} In the present Essay there is some evidence that the author
attributed more to _sports_ than was afterwards the case: but the
above passage points the other way. It must always be remembered
that many of the minute differences, now considered small
mutations, are the small variations on which Darwin conceived
selection to act.
We have every reason to believe that in proportion to the number of
generations that a domestic race is kept free from crosses, and to the
care employed in continued steady selection with one end in view, and to
the care in not placing the variety in conditions unsuited to it; in
such proportion does the new race become "true" or subject to little
variation{242}. How incomparably "truer" then would a race produced by
the above rigid, steady, natural means of selection, excellently trained
and perfectly adapted to its conditions, free from stains of blood or
crosses, and continued during thousands of years, be compared with one
produced by the feeble, capricious, misdirected and ill-adapted
selection of man. Those races of domestic animals produced by savages,
partly by the inevitable conditions of their life, and partly
unintentionally by their greater care of the individuals most valuable
to them, would probably approach closest to the character of a species;
and I believe this is the case. Now the characteristic mark of a
species, next, if not equal in importance to its sterility when crossed
with another species, and indeed almost the only other character
(without we beg the question and affirm the essence of a species, is its
not having descended from a parent common to any other form), is the
similarity of the individuals composing the species, or in the language
of agriculturalists their "trueness."
{242} See _Var. under Dom._, Ed. ii. vol. II. p. 230.
_Difference between "Races" and "Species" in fertility when crossed._
The sterility of species, or of their offspring, when crossed has,
however, received more attention than the uniformity in character of the
individuals composing the species. It is exceedingly natural that such
sterility{243} should have been long thought the certain characteristic
of species. For it is obvious that if the allied different forms which
we meet with in the same country could cross together, instead of
finding a number of distinct species, we should have a confused and
blending series. The fact however of a perfect gradation in the degree
of sterility between species, and the circumstance of some species most
closely allied (for instance many species of crocus and European heaths)
refusing to breed together, whereas other species, widely different,
and even belonging to distinct genera, as the fowl and the peacock,
pheasant and grouse{244}, Azalea and Rhododendron, Thuja and Juniperus,
breeding together ought to have caused a doubt whether the sterility did
not depend on other causes, distinct from a law, coincident with their
creation. I may here remark that the fact whether one species will or
will not breed with another is far less important than the sterility of
the offspring when produced; for even some domestic races differ so
greatly in size (as the great stag-greyhound and lap-dog, or cart-horse
and Burmese ponies) that union is nearly impossible; and what is less
generally known is, that in plants Kölreuter has shown by hundreds of
experiments that the pollen of one species will fecundate the germen of
another species, whereas the pollen of this latter will never act on the
germen of the former; so that the simple fact of mutual impregnation
certainly has no relation whatever to the distinctness in creation of
the two forms. When two species are attempted to be crossed which are so
distantly allied that offspring are never produced, it has been observed
in some cases that the pollen commences its proper action by exserting
its tube, and the germen commences swelling, though soon afterwards it
decays. In the next stage in the series, hybrid offspring are produced
though only rarely and few in number, and these are absolutely sterile:
then we have hybrid offspring more numerous, and occasionally, though
very rarely, breeding with either parent, as is the case with the common
mule. Again, other hybrids, though infertile _inter se_, will breed
_quite_ freely with either parent, or with a third species, and will
yield offspring generally infertile, but sometimes fertile; and these
latter again will breed with either parent, or with a third or fourth
species: thus Kölreuter blended together many forms. Lastly it is now
admitted by those botanists who have longest contended against the
admission, that in certain families the hybrid offspring of many of the
species are sometimes perfectly fertile in the first generation when
bred together: indeed in some few cases Mr Herbert{245} found that the
hybrids were decidedly more fertile than either of their pure parents.
There is no way to escape from the admission that the hybrids from some
species of plants are fertile, except by declaring that no form shall be
considered as a species, if it produces with another species fertile
offspring: but this is begging the question{246}. It has often been
stated that different species of animals have a sexual repugnance
towards each other; I can find no evidence of this; it appears as if
they merely did not excite each others passions. I do not believe that
in this respect there is any essential distinction between animals and
plants; and in the latter there cannot be a feeling of repugnance.
{243} If domestic animals are descended from
several species and _become_ fertile _inter se_, then one can see
they gain fertility by becoming adapted to new conditions and
certainly domestic animals can withstand changes of climate without
loss of fertility in an astonishing manner.
{244} See Suchetet, _L'Hybridité dans la Nature_, Bruxelles, 1888,
p. 67. In _Var. under Dom._, Ed. ii. vol. II. hybrids between the
fowl and the pheasant are mentioned. I can give no information on
the other cases.
{245} _Origin_, Ed. i. p. 250, vi. p. 370.
{246} This was the position of Gärtner and of Kölreuter: see
_Origin_, Ed. i. pp. 246-7, vi. pp. 367-8.
_Causes of Sterility in Hybrids._
The difference in nature between species which causes the greater or
lesser degree of sterility in their offspring appears, according to
Herbert and Kölreuter, to be connected much less with external form,
size, or structure, than with constitutional peculiarities; by which is
meant their adaptation to different climates, food and situation, &c.:
these peculiarities of constitution probably affect the entire frame,
and no one part in particular{247}.
{247} Yet this seems introductory to the
case of the heaths and crocuses above mentioned.
From the foregoing facts I think we must admit that there exists a
perfect gradation in fertility between species which when crossed are
quite fertile (as in Rhododendron, Calceolaria, &c.), and indeed in an
extraordinary degree fertile (as in Crinum), and those species which
never produce offspring, but which by certain effects (as the exsertion
of the pollen-tube) evince their alliance. Hence, I conceive, we must
give up sterility, although undoubtedly in a lesser or greater degree of
very frequent occurrence, as an unfailing mark by which _species_ can be
distinguished from _races_, _i.e._ from those forms which have descended
from a common stock.
_Infertility from causes distinct from hybridisation._
Let us see whether there are any analogous facts which will throw any
light on this subject, and will tend to explain why the offspring of
certain species, when crossed, should be sterile, and not others,
without requiring a distinct law connected with their creation to that
effect. Great numbers, probably a large majority of animals when caught
by man and removed from their natural conditions, although taken very
young, rendered quite tame, living to a good old age, and apparently
quite healthy, seem incapable under these circumstances of
breeding{248}. I do not refer to animals kept in menageries, such as at
the Zoological Gardens, many of which, however, appear healthy and live
long and unite but do not produce; but to animals caught and left partly
at liberty in their native country. Rengger{249} enumerates several
caught young and rendered tame, which he kept in Paraguay, and which
would not breed: the hunting leopard or cheetah and elephant offer other
instances; as do bears in Europe, and the 25 species of hawks, belonging
to different genera, thousands of which have been kept for hawking and
have lived for long periods in perfect vigour. When the expense and
trouble of procuring a succession of young animals in a wild state be
borne in mind, one may feel sure that no trouble has been spared in
endeavours to make them breed. So clearly marked is this difference in
different kinds of animals, when captured by man, that St Hilaire makes
two great classes of animals useful to man:--the _tame_, which will not
breed, and the _domestic_ which will breed in domestication. From
certain singular facts we might have supposed that the non-breeding of
animals was owing to some perversion of instinct. But we meet with
exactly the same class of facts in plants: I do not refer to the large
number of cases where the climate does not permit the seed or fruit to
ripen, but where the flowers do not "set," owing to some imperfection of
the ovule or pollen. The latter, which alone can be distinctly examined,
is often manifestly imperfect, as any one with a microscope can observe
by comparing the pollen of the Persian and Chinese lilacs{250} with the
common lilac; the two former species (I may add) are equally sterile in
Italy as in this country. Many of the American bog plants here produce
little or no pollen, whilst the Indian species of the same genera freely
produce it. Lindley observes that sterility is the bane of the
horticulturist{251}: Linnæus has remarked on the sterility of nearly all
alpine flowers when cultivated in a lowland district{252}. Perhaps the
immense class of double flowers chiefly owe their structure to an excess
of food acting on parts rendered slightly sterile and less capable of
performing their true function, and therefore liable to be rendered
monstrous, which monstrosity, like any other disease, is inherited and
rendered common. So far from domestication being in itself unfavourable
to fertility, it is well known that when an organism is once capable of
submission to such conditions fertility is increased{253} beyond the
natural limit. According to agriculturists, slight changes of
conditions, that is of food or habitation, and likewise crosses with
races slightly different, increase the vigour and probably the fertility
of their offspring. It would appear also that even a great change of
condition, for instance, transportal from temperate countries to India,
in many cases does not in the least affect fertility, although it does
health and length of life and the period of maturity. When sterility is
induced by domestication it is of the same kind, and varies in degree,
exactly as with hybrids: for be it remembered that the most sterile
hybrid is no way monstrous; its organs are perfect, but they do not act,
and minute microscopical investigations show that they are in the same
state as those of pure species in the intervals of the breeding season.
The defective pollen in the cases above alluded to precisely resembles
that of hybrids. The occasional breeding of hybrids, as of the common
mule, may be aptly compared to the most rare but occasional reproduction
of elephants in captivity. The cause of many exotic Geraniums producing
(although in vigorous health) imperfect pollen seems to be connected
with the period when water is given them{254}; but in the far greater
majority of cases we cannot form any conjecture on what exact cause the
sterility of organisms taken from their natural conditions depends. Why,
for instance, the cheetah will not breed whilst the common cat and
ferret (the latter generally kept shut up in a small box) do,--why the
elephant will not whilst the pig will abundantly--why the partridge and
grouse in their own country will not, whilst several species of
pheasants, the guinea-fowl from the deserts of Africa and the peacock
from the jungles of India, will. We must, however, feel convinced that
it depends on some constitutional peculiarities in these beings not
suited to their new condition; though not necessarily causing an ill
state of health. Ought we then to wonder much that those hybrids which
have been produced by the crossing of species with different
constitutional tendencies (which tendencies we know to be eminently
inheritable) should be sterile: it does not seem improbable that the
cross from an alpine and lowland plant should have its constitutional
powers deranged, in nearly the same manner as when the parent alpine
plant is brought into a lowland district. Analogy, however, is a
deceitful guide, and it would be rash to affirm, although it may appear
probable, that the sterility of hybrids is due to the constitutional
peculiarities of one parent being disturbed by being blended with those
of the other parent in exactly the same manner as it is caused in some
organic beings when placed by man out of their natural conditions{255}.
Although this would be rash, it would, I think, be still rasher, seeing
that sterility is no more incidental to _all_ cross-bred productions
than it is to all organic beings when captured by man, to assert that
the sterility of certain hybrids proved a distinct creation of their
parents.
{248} Animals seem more often made sterile by
being taken out of their native condition than plants, and so are
more sterile when crossed.
We have one broad fact that sterility in hybrids is not closely
related to external difference, and these are what man alone gets
by selection.
{249} See _Var. under Dom._, Ed. ii. vol. II. p. 132; for the case
of the cheetah see _loc cit._ p. 133.
{250} _Var. under Dom._, Ed. ii. vol. II. p. 148.
{251} Quoted in the _Origin_, Ed. i. p. 9.
{252} See _Var. under Dom._, Ed. ii. vol. II. p. 147.
{253} _Var. under Dom._, Ed. ii. vol. II. p. 89.
{254} See _Var. under Dom._, Ed. ii. vol. II. p. 147.
{255} _Origin_, Ed. i. p. 267, vi. p. 392. This is the principle
experimentally investigated in the author's _Cross-and
Self-Fertilisation_.
But it may be objected{256} (however little the sterility of certain
hybrids is connected with the distinct creations of species), how comes
it, if species are only races produced by natural selection, that when
crossed they so frequently produce sterile offspring, whereas in the
offspring of those races confessedly produced by the arts of man there
is no one instance of sterility. There is not much difficulty in this,
for the races produced by the natural means above explained will be
slowly but steadily selected; will be adapted to various and diverse
conditions, and to these conditions they will be rigidly confined for
immense periods of time; hence we may suppose that they would acquire
different constitutional peculiarities adapted to the stations they
occupy; and on the constitutional differences between species their
sterility, according to the best authorities, depends. On the other hand
man selects by external appearance{257}; from his ignorance, and from
not having any test at least comparable in delicacy to the natural
struggle for food, continued at intervals through the life of each
individual, he cannot eliminate fine shades of constitution, dependent
on invisible differences in the fluids or solids of the body; again,
from the value which he attaches to each individual, he asserts his
utmost power in contravening the natural tendency of the most vigorous
to survive. Man, moreover, especially in the earlier ages, cannot have
kept his conditions of life constant, and in later ages his stock pure.
Until man selects two varieties from the same stock, adapted to two
climates or to other different external conditions, and confines each
rigidly for one or several thousand years to such conditions, always
selecting the individuals best adapted to them, he cannot be said to
have even commenced the experiment. Moreover, the organic beings which
man has longest had under domestication have been those which were of
the greatest use to him, and one chief element of their usefulness,
especially in the earlier ages, must have been their capacity to undergo
sudden transportals into various climates, and at the same time to
retain their fertility, which in itself implies that in such respects
their constitutional peculiarities were not closely limited. If the
opinion already mentioned be correct, that most of the domestic animals
in their present state have descended from the fertile commixture of
wild races or species, we have indeed little reason now to expect
infertility between any cross of stock thus descended.
{256} _Origin_, Ed. i. p. 268, vi. p. 398.
{257} Mere difference of structure no guide to
what will or will not cross. First step gained by races keeping
apart.
It is worthy of remark, that as many organic beings, when taken by man
out of their natural conditions, have their reproductive system
affected as to be incapable of propagation, so, we saw in the first
chapter, that although organic beings when taken by man do propagate
freely, their offspring after some generations vary or sport to a degree
which can only be explained by their reproductive system being some way
affected. Again, when species cross, their offspring are generally
sterile; but it was found by Kölreuter that when hybrids are capable of
breeding with either parent, or with other species, that their
offspring are subject after some generations to excessive
variation{258}. Agriculturists, also, affirm that the offspring from
mongrels, after the first generation, vary much. Hence we see that both
sterility and variation in the succeeding generations are consequent
both on the removal of individual species from their natural states and
on species crossing. The connection between these facts may be
accidental, but they certainly appear to elucidate and support each
other,--on the principle of the reproductive system of all organic
beings being eminently sensitive to any disturbance, whether from
removal or commixture, in their constitutional relations to the
conditions to which they are exposed.
{258} _Origin_, Ed. i. p. 272, vi. p. 404.
_Points of Resemblance between "Races" and "Species{259}."_
{259} This section seems not to correspond closely with any in the
_Origin_, Ed. i.; in some points it resembles pp. 15, 16, also the
section on analogous variation in distinct species, _Origin_, Ed.
i. p. 159, vi. p. 194.
Races and reputed species agree in some respects, although differing
from causes which, we have seen, we can in some degree understand, in
the fertility and "trueness" of their offspring. In the first place,
there is no clear sign by which to distinguish races from species, as is
evident from the great difficulty experienced by naturalists in
attempting to discriminate them. As far as external characters are
concerned, many of the races which are descended from the same stock
differ far more than true species of the same genus; look at the
willow-wrens, some of which skilful ornithologists can hardly
distinguish from each other except by their nests; look at the wild
swans, and compare the distinct species of these genera with the races
of domestic ducks, poultry, and pigeons; and so again with plants,
compare the cabbages, almonds, peaches and nectarines, &c. with the
species of many genera. St Hilaire has even remarked that there is a
greater difference in size between races, as in dogs (for he believes
all have descended from one stock), than between the species of any one
genus; nor is this surprising, considering that amount of food and
consequently of growth is the element of change over which man has most
power. I may refer to a former statement, that breeders believe the
growth of one part or strong action of one function causes a decrease in
other parts; for this seems in some degree analogous to the law of
"organic compensation{260}," which many naturalists believe holds good.
To give an instance of this law of compensation,--those species of
Carnivora which have the canine teeth greatly developed have certain
molar teeth deficient; or again, in that division of the Crustaceans in
which the tail is much developed, the thorax is little so, and the
converse. The points of difference between different races is often
strikingly analogous to that between species of the same genus: trifling
spots or marks of colour{261} (as the bars on pigeons' wings) are often
preserved in races of plants and animals, precisely in the same manner
as similar trifling characters often pervade all the species of a genus,
and even of a family. Flowers in varying their colours often become
veined and spotted and the leaves become divided like true species: it
is known that the varieties of the same plant never have red, blue and
yellow flowers, though the hyacinth makes a very near approach to an
exception{262}; and different species of the same genus seldom, though
sometimes they have flowers of these three colours. Dun-coloured horses
having a dark stripe down their backs, and certain domestic asses having
transverse bars on their legs, afford striking examples of a variation
analogous in character to the distinctive marks of other species of the
same genus.
{260} The law of compensation is discussed in the _Origin_, Ed. i.
p. 147, vi. p. 182.
{261} Boitard and Corbié on outer edging red in
tail of bird,--so bars on wing, white or black or brown, or white
edged with black or : analogous to marks running through
genera but with different colours. Tail coloured in pigeons.
{262} Oxalis and Gentian.
_External characters of Hybrids and Mongrels._
There is, however, as it appears to me, a more important method of
comparison between species and races, namely the character of the
offspring{263} when species are crossed and when races are crossed: I
believe, in no one respect, except in sterility, is there any
difference. It would, I think, be a marvellous fact, if species have
been formed by distinct acts of creation, that they should act upon each
other in uniting, like races descended from a common stock. In the first
place, by repeated crossing one species can absorb and wholly obliterate
the characters of another, or of several other species, in the same
manner as one race will absorb by crossing another race. Marvellous,
that one act of creation should absorb another or even several acts of
creation! The offspring of species, that is hybrids, and the offspring
of races, that is mongrels, resemble each other in being either
intermediate in character (as is most frequent in hybrids) or in
resembling sometimes closely one and sometimes the other parent; in both
the offspring produced by the same act of conception sometimes differ in
their degree of resemblance; both hybrids and mongrels sometimes retain
a certain part or organ very like that of either parent, both, as we
have seen, become in succeeding generations variable; and this tendency
to vary can be transmitted by both; in both for many generations there
is a strong tendency to reversion to their ancestral form. In the case
of a hybrid laburnum and of a supposed mongrel vine different parts of
the same plants took after each of their two parents. In the hybrids
from some species, and in the mongrel of some races, the offspring
differ according as which of the two species, or of the two races, is
the father (as in the common mule and hinny) and which the mother. Some
races will breed together, which differ so greatly in size, that the dam
often perishes in labour; so it is with some species when crossed; when
the dam of one species has borne offspring to the male of another
species, her succeeding offspring are sometimes stained (as in Lord
Morton's mare by the quagga, wonderful as the fact{264} is) by this
first cross; so agriculturists positively affirm is the case when a pig
or sheep of one breed has produced offspring by the sire of another
breed.
{263} This section corresponds roughly to that on _Hybrids and
Mongrels compared independently of their fertility_, _Origin_, Ed.
i. p. 272, vi. p. 403. The discussion on Gärtner's views, given in
the _Origin_, is here wanting. The brief mention of prepotency is
common to them both.
{264} See _Animals and Plants_, Ed. ii. vol. I. p. 435. The
phenomenon of _Telegony_, supposed to be established by this and
similar cases, is now generally discredited in consequence of
Ewart's experiments.
_Summary of second chapter_{265}.
{265} The section on p. 109 is an appendix to the summary.
Let us sum up this second chapter. If slight variations do occur in
organic beings in a state of nature; if changes of condition from
geological causes do produce in the course of ages effects analogous to
those of domestication on any, however few, organisms; and how can we
doubt it,--from what is actually known, and from what may be presumed,
since thousands of organisms taken by man for sundry uses, and placed
in new conditions, have varied. If such variations tend to be
hereditary; and how can we doubt it,--when we see shades of expression,
peculiar manners, monstrosities of the strangest kinds, diseases, and a
multitude of other peculiarities, which characterise and form, being
inherited, the endless races (there are 1200 kinds of cabbages{266}) of
our domestic plants and animals. If we admit that every organism
maintains its place by an almost periodically recurrent struggle; and
how can we doubt it,--when we know that all beings tend to increase in a
geometrical ratio (as is instantly seen when the conditions become for a
time more favourable); whereas on an average the amount of food must
remain constant, if so, there will be a natural means of selection,
tending to preserve those individuals with any slight deviations of
structure more favourable to the then existing conditions, and tending
to destroy any with deviations of an opposite nature. If the above
propositions be correct, and there be no law of nature limiting the
possible amount of variation, new races of beings will,--perhaps only
rarely, and only in some few districts,--be formed.
{266} I do not know the authority for this statement.
_Limits of Variation._
That a limit to variation does exist in nature is assumed by most
authors, though I am unable to discover a single fact on which this
belief is grounded{267}. One of the commonest statements is that plants
do not become acclimatised; and I have even observed that kinds not
raised by seed, but propagated by cuttings, &c., are instanced. A good
instance has, however, been advanced in the case of kidney beans, which
it is believed are now as tender as when first introduced. Even if we
overlook the frequent introduction of seed from warmer countries, let me
observe that as long as the seeds are gathered promiscuously from the
bed, without continual observation and _careful_ selection of those
plants which have stood the climate best during their whole growth, the
experiment of acclimatisation has hardly been begun. Are not all those
plants and animals, of which we have the greatest number of races, the
oldest domesticated? Considering the quite recent progress{268} of
systematic agriculture and horticulture, is it not opposed to every
fact, that we have exhausted the capacity of variation in our cattle and
in our corn,--even if we have done so in some trivial points, as their
fatness or kind of wool? Will any one say, that if horticulture
continues to flourish during the next few centuries, that we shall not
have numerous new kinds of the potato and Dahlia? But take two varieties
of each of these plants, and adapt them to certain fixed conditions and
prevent any cross for 5000 years, and then again vary their conditions;
try many climates and situations; and who{269} will predict the number
and degrees of difference which might arise from these stocks? I repeat
that we know nothing of any limit to the possible amount of variation,
and therefore to the number and differences of the races, which might be
produced by the natural means of selection, so infinitely more efficient
than the agency of man. Races thus produced would probably be very
"true"; and if from having been adapted to different conditions of
existence, they possessed different constitutions, if suddenly removed
to some new station, they would perhaps be sterile and their offspring
would perhaps be infertile. Such races would be undistinguishable from
species. But is there any evidence that the species, which surround us
on all sides, have been thus produced? This is a question which an
examination of the economy of nature we might expect would answer either
in the affirmative or negative{270}.
{267} In the _Origin_ no limit is placed to variation as far as I
know.
{268} History of pigeons shows increase of
peculiarities during last years.
{269} Compare an obscure passage in the Essay of 1842, p. 14.
{270} Certainly ought to
be here introduced, viz., difficulty in forming such organ, as eye,
by selection.
CHAPTER III
ON THE VARIATION OF INSTINCTS AND OTHER MENTAL ATTRIBUTES UNDER
DOMESTICATION AND IN STATE OF NATURE; ON THE DIFFICULTIES IN THIS
SUBJECT; AND ON ANALOGOUS DIFFICULTIES WITH RESPECT TO CORPOREAL
STRUCTURES
_Variation of mental attributes under domestication._
I have as yet only alluded to the mental qualities which differ greatly
in different species. Let me here premise that, as will be seen in the
Second Part, there is no evidence and consequently no attempt to show
that _all_ existing organisms have descended from any one common
parent-stock, but that only those have so descended which, in the
language of naturalists, are clearly related to each other. Hence the
facts and reasoning advanced in this chapter do not apply to the first
origin of the senses{271}, or of the chief mental attributes, such as of
memory, attention, reasoning, &c., &c., by which most or all of the
great related groups are characterised, any more than they apply to the
first origin of life, or growth, or the power of reproduction. The
application of such facts as I have collected is merely to the
differences of the primary mental qualities and of the instincts in the
species{272} of the several great groups. In domestic animals every
observer has remarked in how great a degree, in the individuals of the
same species, the dispositions, namely courage, pertinacity, suspicion,
restlessness, confidence, temper, pugnaciousness, affection, care of
their young, sagacity, &c., &c., vary. It would require a most able
metaphysician to explain how many primary qualities of the mind must be
changed to cause these diversities of complex dispositions. From these
dispositions being inherited, of which the testimony is unanimous,
families and breeds arise, varying in these respects. I may instance the
good and ill temper of different stocks of bees and of horses,--the
pugnacity and courage of game fowls,--the pertinacity of certain dogs,
as bull-dogs, and the sagacity of others,--for restlessness and
suspicion compare a wild rabbit reared with the greatest care from its
earliest age with the extreme tameness of the domestic breed of the same
animal. The offspring of the domestic dogs which have run wild in
Cuba{273}, though caught quite young, are most difficult to tame,
probably nearly as much so as the original parent-stock from which the
domestic dog descended. The habitual "_periods_" of different families
of the same species differ, for instance, in the time of year of
reproduction, and the period of life when the capacity is acquired, and
the hour of roosting (in Malay fowls), &c., &c. These periodical habits
are perhaps essentially corporeal, and may be compared to nearly similar
habits in plants, which are known to vary extremely. Consensual
movements (as called by Müller) vary and are inherited,--such as the
cantering and ambling paces in horses, the tumbling of pigeons, and
perhaps the handwriting, which is sometimes so similar between father
and sons, may be ranked in this class. _Manners_, and even tricks which
perhaps are only _peculiar_ manners, according to W. Hunter and my
father, are distinctly inherited in cases where children have lost their
parent in early infancy. The inheritance of expression, which often
reveals the finest shades of character, is familiar to everyone.
{271} A similar proviso occurs in the chapter on instinct in
_Origin_, Ed. i. p. 207, vi. p. 319.
{272} The discussion occurs later in Chapter VII of the _Origin_,
Ed. i. than in the present Essay, where moreover it is fuller in
some respects.
{273} In the margin occurs the name of Poeppig. In _Var. under
Dom._, Ed. ii. vol. I. p. 28, the reference to Poeppig on the Cuban
dogs contains no mention of the wildness of their offspring.
Again the tastes and pleasures of different breeds vary, thus the
shepherd-dog delights in chasing the sheep, but has no wish to kill
them,--the terrier (see Knight) delights in killing vermin, and the
spaniel in finding game. But it is impossible to separate their mental
peculiarities in the way I have done: the tumbling of pigeons, which I
have instanced as a consensual movement, might be called a trick and is
associated with a taste for flying in a close flock at a great height.
Certain breeds of fowls have a taste for roosting in trees. The
different actions of pointers and setters might have been adduced in the
same class, as might the peculiar _manner_ of hunting of the spaniel.
Even in the same breed of dogs, namely in fox-hounds, it is the fixed
opinion of those best able to judge that the different pups are born
with different tendencies; some are best to find their fox in the cover;
some are apt to run straggling, some are best to make casts and to
recover the lost scent, &c.; and that these peculiarities undoubtedly
are transmitted to their progeny. Or again the tendency to point might
be adduced as a distinct habit which has become inherited,--as might the
tendency of a true sheep dog (as I have been assured is the case) to run
round the flock instead of directly at them, as is the case with other
young dogs when attempted to be taught. The "transandantes" sheep{274}
in Spain, which for some centuries have been yearly taken a journey of
several hundred miles from one province to another, know when the time
comes, and show the greatest restlessness (like migratory birds in
confinement), and are prevented with difficulty from starting by
themselves, which they sometimes do, and find their own way. There is a
case on good evidence{275} of a sheep which, when she lambed, would
return across a mountainous country to her own birth-place, although at
other times of year not of a rambling disposition. Her lambs inherited
this same disposition, and would go to produce their young on the farm
whence their parent came; and so troublesome was this habit that the
whole family was destroyed.
{274} Several authors.
{275} In the margin "Hogg" occurs as authority for this fact. For
the reference, see p. 17, note 4.
These facts must lead to the conviction, justly wonderful as it is, that
almost infinitely numerous shades of disposition, of tastes, of peculiar
movements, and even of individual actions, can be modified or acquired
by one individual and transmitted to its offspring. One is forced to
admit that mental phenomena (no doubt through their intimate connection
with the brain) can be inherited, like infinitely numerous and fine
differences of corporeal structure. In the same manner as peculiarities
of corporeal structure slowly acquired or lost during mature life
(especially cognisant in disease), as well as congenital peculiarities,
are transmitted; so it appears to be with the mind. The inherited paces
in the horse have no doubt been acquired by compulsion during the lives
of the parents: and temper and tameness may be modified in a breed by
the treatment which the individuals receive. Knowing that a pig has been
taught to point, one would suppose that this quality in pointer-dogs was
the simple result of habit, but some facts, with respect to the
occasional appearance of a similar quality in other dogs, would make one
suspect that it originally appeared in a less perfect degree, "_by
chance_," that is from a congenital tendency{276} in the parent of the
breed of pointers. One cannot believe that the tumbling, and high flight
in a compact body, of one breed of pigeons has been taught; and in the
case of the slight differences in the manner of hunting in young
fox-hounds, they are doubtless congenital. The inheritance of the
foregoing and similar mental phenomena ought perhaps to create less
surprise, from the reflection that in no case do individual acts of
reasoning, or movements, or other phenomena connected with
consciousness, appear to be transmitted. An action, even a very
complicated one, when from long practice it is performed unconsciously
without any effort (and indeed in the case of many peculiarities of
manners opposed to the will) is said, according to a common expression,
to be performed "instinctively." Those cases of languages, and of songs,
learnt in early childhood and _quite_ forgotten, being _perfectly_
repeated during the unconsciousness of illness, appear to me only a few
degrees less wonderful than if they had been transmitted to a second
generation{277}.
{276} In the _Origin_, Ed. i., he speaks more decidedly against the
belief that instincts are hereditary habits, see for instance pp.
209, 214, Ed. vi. pp. 321, 327. He allows, however, something to
habit (p. 216).
{277} A suggestion of Hering's and S. Butler's views on memory and
inheritance. It is not, however, implied that Darwin was inclined
to accept these opinions.
_Hereditary habits compared with instincts._
The chief characteristics of true instincts appear to be their
invariability and non-improvement during the mature age of the
individual animal: the absence of knowledge of the end, for which the
action is performed, being associated, however, sometimes with a degree
of reason; being subject to mistakes and being associated with certain
states of the body or times of the year or day. In most of these
respects there is a resemblance in the above detailed cases of the
mental qualities acquired or modified during domestication. No doubt the
instincts of wild animals are more uniform than those habits or
qualities modified or recently acquired under domestication, in the same
manner and from the same causes that the corporeal structure in this
state is less uniform than in beings in their natural conditions. I have
seen a young pointer point as fixedly, the first day it was taken out,
as any old dog; Magendie says this was the case with a retriever which
he himself reared: the tumbling of pigeons is not probably improved by
age: we have seen that in the case above given that the young sheep
inherited the migratory tendency to their particular birth-place the
first time they lambed. This last fact offers an instance of a domestic
instinct being associated with a state of body; as do the
"transandantes" sheep with a time of year. Ordinarily the acquired
instincts of domestic animals seem to require a certain degree of
education (as generally in pointers and retrievers) to be perfectly
developed: perhaps this holds good amongst wild animals in rather a
greater degree than is generally supposed; for instance, in the singing
of birds, and in the knowledge of proper herbs in Ruminants. It seems
pretty clear that bees transmit knowledge from generation to generation.
Lord Brougham{278} insists strongly on ignorance of the end proposed
being eminently characteristic of true instincts; and this appears to me
to apply to many acquired hereditary habits; for instance, in the case
of the young pointer alluded to before, which pointed so steadfastly the
first day that we were obliged several times to carry him away{279}.
This puppy not only pointed at sheep, at large white stones, and at
every little bird, but likewise "backed" the other pointers: this young
dog must have been as unconscious for what end he was pointing, namely
to facilitate his master's killing game to eat, as is a butterfly which
lays her eggs on a cabbage, that her caterpillars would eat the leaves.
So a horse that ambles instinctively, manifestly is ignorant that he
performs that peculiar pace for the ease of man; and if man had never
existed, he would never have ambled. The young pointer pointing at white
stones appears to be as much a mistake of its acquired instinct, as in
the case of flesh-flies laying their eggs on certain flowers instead of
putrifying meat. However true the ignorance of the end may generally be,
one sees that instincts are associated with some degree of reason; for
instance, in the case of the tailor-bird, who spins threads with which
to make her nest will use artificial threads when she can procure
them{280}; so it has been known that an old pointer has broken his point
and gone round a hedge to drive out a bird towards his master{281}.
{278} Lord Brougham's _Dissertations on Subjects of Science_, etc.,
1839, p. 27.
{279} This case is more briefly given in the _Origin_, Ed. i. p.
213, vi. p. 326. The simile of the butterfly occurs there also.
{280} "A little dose, as Pierre Huber expresses it, of judgment or
reason, often comes into play." _Origin_, Ed. i. p. 208, vi. p.
320.
{281} In the margin is written "Retriever killing one bird." This
refers to the cases given in the _Descent of Man_, 2nd Ed. (in 1
vol.) p. 78, of a retriever being puzzled how to deal with a
wounded and a dead bird, killed the former and carried both at
once. This was the only known instance of her wilfully injuring
game.
There is one other quite distinct method by which the instincts or
habits acquired under domestication may be compared with those given by
nature, by a test of a fundamental kind; I mean the comparison of the
mental powers of mongrels and hybrids. Now the instincts, or habits,
tastes, and dispositions of one _breed_ of animals, when crossed with
another breed, for instance a shepherd-dog with a harrier, are blended
and appear in the same curiously mixed degree, both in the first and
succeeding generations, exactly as happens when one _species_ is crossed
with another{282}. This would hardly be the case if there was any
fundamental difference between the domestic and natural instinct{283};
if the former were, to use a metaphorical expression, merely
superficial.
{282} See _Origin_, Ed. i. p. 214, vi. p. 327.
{283} Give some definition of instinct, or at
least give chief attributes. The term instinct is often
used in sense which implies no more than that the animal does
the action in question. Faculties and instincts may I think be
imperfectly separated. The mole has the faculty of scratching
burrows, and the instinct to apply it. The bird of passage has the
faculty of finding its way and the instinct to put it in action at
certain periods. It can hardly be said to have the faculty of
knowing the time, for it can possess no means, without indeed it be
some consciousness of passing sensations. Think over all habitual
actions and see whether faculties and instincts can be separated.
We have faculty of waking in the night, if an instinct prompted us
to do something at certain hour of night or day. Savages finding
their way. Wrangel's account--probably a faculty inexplicable by
the possessor. There are besides faculties "_means_," as conversion
of larvæ into neuters and queens. I think all this generally
implied, anyhow useful.
_Variation in the mental attributes of wild animals._
With respect to the variation{284} of the mental powers of animals in a
wild state, we know that there is a considerable difference in the
disposition of different individuals of the same species, as is
recognised by all those who have had the charge of animals in a
menagerie. With respect to the wildness of animals, that is fear
directed particularly against man, which appears to be as true an
instinct as the dread of a young mouse of a cat, we have excellent
evidence that it is slowly acquired and becomes hereditary. It is also
certain that, in a natural state, individuals of the same species lose
or do not practice their migratory instincts--as woodcocks in Madeira.
With respect to any variation in the more complicated instincts, it is
obviously most difficult to detect, even more so than in the case of
corporeal structure, of which it has been admitted the variation is
exceedingly small, and perhaps scarcely any in the majority of species
at any one period. Yet, to take one excellent case of instinct, namely
the nests of birds, those who have paid most attention to the subject
maintain that not only certain individuals seem to be able
to build very imperfectly, but that a difference in skill may not
unfrequently be detected between individuals{285}. Certain birds,
moreover, adapt their nests to circumstances; the water-ouzel makes no
vault when she builds under cover of a rock--the sparrow builds very
differently when its nest is in a tree or in a hole, and the
golden-crested wren sometimes suspends its nest below and sometimes
places it _on_ the branches of trees.
{284} A short discussion of a similar kind occurs in the _Origin_,
Ed. i. p. 211, vi. p. 324.
{285} This sentence agrees with the MS., but is clearly in need of
correction.
_Principles of Selection applicable to instincts._
As the instincts of a species are fully as important to its preservation
and multiplication as its corporeal structure, it is evident that if
there be the slightest congenital differences in the instincts and
habits, or if certain individuals during their lives are induced or
compelled to vary their habits, and if such differences are in the
smallest degree more favourable, under slightly modified external
conditions, to their preservation, such individuals must in the long run
have a better _chance_ of being preserved and of multiplying{286}. If
this be admitted, a series of small changes may, as in the case of
corporeal structure, work great changes in the mental powers, habits and
instincts of any species.
{286} This corresponds to _Origin_, Ed. i. p. 212, vi. p. 325.
_Difficulties in the acquirement of complex instincts by Selection._
Every one will at first be inclined to explain (as I did for a long
time) that many of the more complicated and wonderful instincts could
not be acquired in the manner here supposed{287}. The Second Part of
this work is devoted to the general consideration of how far the general
economy of nature justifies or opposes the belief that related species
and genera are descended from common stocks; but we may here consider
whether the instincts of animals offer such a _primâ facie_ case of
impossibility of gradual acquirement, as to justify the rejection of any
such theory, however strongly it may be supported by other facts. I beg
to repeat that I wish here to consider not the _probability_ but the
_possibility_ of complicated instincts having been acquired by the slow
and long-continued selection of very slight (either congenital or
produced by habit) modifications of foregoing simpler instincts; each
modification being as useful and necessary, to the species practising
it, as the most complicated kind.
{287} This discussion is interesting in differing from the
corresponding section of the _Origin_, Ed. i. p. 216, vi. p. 330,
to the end of the chapter. In the present Essay the subjects dealt
with are nest-making instincts, including the egg-hatching habit of
the Australian bush-turkey. The power of "shamming death."
"Faculty" in relation to instinct. The instinct of lapse of time,
and of direction. Bees' cells very briefly given. Birds feeding
their young on food differing from their own natural food. In the
_Origin_, Ed. i., the cases discussed are the instinct of laying
eggs in other birds' nests; the slave-making instinct in ants; the
construction of the bee's comb, very fully discussed.
First, to take the case of birds'-nests; of existing species (almost
infinitely few in comparison with the multitude which must have existed,
since the period of the new Red Sandstone of N. America, of whose habits
we must always remain ignorant) a tolerably perfect series could be made
from eggs laid on the bare ground, to others with a few sticks just
laid round them, to a simple nest like the wood-pigeons, to others more
and more complicated: now if, as is asserted, there occasionally exist
slight differences in the building powers of an individual, and if,
which is at least probable, that such differences would tend to be
inherited, then we can see that it is at least _possible_ that the
nidificatory instincts may have been acquired by the gradual selection,
during thousands and thousands of generations, of the eggs and young of
those individuals, whose nests were in some degree better adapted to the
preservation of their young, under the then existing conditions. One of
the most surprising instincts on record is that of the Australian
bush-turkey, whose eggs are hatched by the heat generated from a huge
pile of fermenting materials, which it heaps together; but here the
habits of an allied species show how this instinct _might possibly_ have
been acquired. This second species inhabits a tropical district, where
the heat of the sun is sufficient to hatch its eggs; this bird, burying
its eggs, apparently for concealment, under a lesser heap of rubbish,
but of a dry nature, so as not to ferment. Now suppose this bird to
range slowly into a climate which was cooler, and where leaves were more
abundant, in that case, those individuals, which chanced to have their
collecting instinct strongest developed, would make a somewhat larger
pile, and the eggs, aided during some colder season, under the slightly
cooler climate by the heat of incipient fermentation, would in the long
run be more freely hatched and would probably produce young ones with
the same more highly developed collecting tendencies; of these again,
those with the best developed powers would again tend to rear most
young. Thus this strange instinct might _possibly_ be acquired, every
individual bird being as ignorant of the laws of fermentation, and the
consequent development of heat, as we know they must be.
Secondly, to take the case of animals feigning death (as it is commonly
expressed) to escape danger. In the case of insects, a perfect series
can be shown, from some insects, which momentarily stand still, to
others which for a second slightly contract their legs, to others which
will remain immovably drawn together for a quarter of an hour, and may
be torn asunder or roasted at a slow fire, without evincing the smallest
sign of sensation. No one will doubt that the length of time, during
which each remains immovable, is well adapted to
escape the dangers to which it is most exposed, and few will deny
the _possibility_ of the change from one degree to another, by the means
and at the rate already explained. Thinking it, however, wonderful
(though not impossible) that the attitude of death should have been
acquired by methods which imply no imitation, I compared several
species, when feigning, as is said, death, with others of the same
species really dead, and their attitudes were in no one case the same.
Thirdly, in considering many instincts it is useful to _endeavour_ to
separate the faculty{288} by which they perform it, and the mental power
which urges to the performance, which is more properly called an
instinct. We have an instinct to eat, we have jaws &c. to give us the
faculty to do so. These faculties are often unknown to us: bats, with
their eyes destroyed, can avoid strings suspended across a room, we know
not at present by what faculty they do this. Thus also, with migratory
birds, it is a wonderful instinct which urges them at certain times of
the year to direct their course in certain directions, but it is a
faculty by which they know the time and find their way. With respect to
time{289}, man without seeing the sun can judge to a certain extent of
the hour, as must those cattle which come down from the inland mountains
to feed on sea-weed left bare at the changing hour of low-water{290}. A
hawk (D'Orbigny) seems certainly to have acquired a knowledge of a
period of every 21 days. In the cases already given of the sheep which
travelled to their birth-place to cast their lambs, and the sheep in
Spain which know their time of march{291}, we may conjecture that the
tendency to move is associated, we may then call it instinctively, with
some corporeal sensations. With respect to direction we can easily
conceive how a tendency to travel in a certain course may possibly have
been acquired, although we must remain ignorant how birds are able to
preserve any direction whatever in a dark night over the wide ocean. I
may observe that the power of some savage races of mankind to find their
way, although perhaps wholly different from the faculty of birds, is
nearly as unintelligible to us. Bellinghausen, a skilful navigator,
describes with the utmost wonder the manner in which some Esquimaux
guided him to a certain point, by a course never straight, through newly
formed hummocks of ice, on a thick foggy day, when he with a compass
found it impossible, from having no landmarks, and from their course
being so extremely crooked, to preserve any sort of uniform direction:
so it is with Australian savages in thick forests. In North and South
America many birds slowly travel northward and southward, urged on by
the food they find, as the seasons change; let them continue to do this,
till, as in the case of the sheep in Spain, it has become an urgent
instinctive desire, and they will gradually accelerate their journey.
They would cross narrow rivers, and if these were converted by
subsidence into narrow estuaries, and gradually during centuries to arms
of the sea, still we may suppose their restless desire of travelling
onwards would impel them to cross such an arm, even if it had become of
great width beyond their span of vision. How they are able to preserve a
course in any direction, I have said, is a faculty unknown to us. To
give another illustration of the means by which I conceive it _possible_
that the direction of migrations have been determined. Elk and reindeer
in N. America annually cross, as if they could marvellously smell or see
at the distance of a hundred miles, a wide tract of absolute desert, to
arrive at certain islands where there is a scanty supply of food; the
changes of temperature, which geology proclaims, render it probable that
this desert tract formerly supported some vegetation, and thus these
quadrupeds might have been annually led on, till they reached the more
fertile spots, and so acquired, like the sheep of Spain, their migratory
powers.
{288} The distinction between _faculty_ and _instinct_ corresponds
in some degree to that between perception of a stimulus and a
specific reaction. I imagine that the author would have said that
the sensitiveness to light possessed by a plant is _faculty_, while
_instinct_ decides whether the plant curves to or from the source
of illumination.
{289} At the time
when corn was pitched in the market instead of sold by sample, the
geese in the town fields of Newcastle used to
know market day and come in to pick up the corn spilt.
{290} Macculloch and others.
{291} I can find no reference to the _transandantes_ sheep in
Darwin's published work. He was possibly led to doubt the accuracy
of the statement on which he relied. For the case of the sheep
returning to their birth-place see p. 17, note 4.{Note 91}
Fourthly, with respect to the combs of the hive-bee{292}; here again we
must look to some faculty or means by which they make their hexagonal
cells, without indeed we view these instincts as mere machines. At
present such a faculty is quite unknown: Mr Waterhouse supposes that
several bees are led by their instinct to excavate a mass of wax to a
certain thinness, and that the result of this is that hexagons
necessarily remain. Whether this or some other theory be true, some such
means they must possess. They abound, however, with true instincts,
which are the most wonderful that are known. If we examine the little
that is known concerning the habits of other species of bees, we find
much simpler instincts: the humble bee merely fills rude balls of wax
with honey and aggregates them together with little order in a rough
nest of grass. If we knew the instinct of all the bees, which ever had
existed, it is not improbable that we should have instincts of every
degree of complexity, from actions as simple as a bird making a nest,
and rearing her young, to the wonderful architecture and government of
the hive-bee; at least such is _possible_, which is all that I am here
considering.
{292} _Origin_, Ed. i. p. 224, vi. p. 342.
Finally, I will briefly consider under the same point of view one other
class of instincts, which have often been advanced as truly wonderful,
namely parents bringing food to their young which they themselves
neither like nor partake of{293};--for instance, the common sparrow, a
granivorous bird, feeding its young with caterpillars. We might of
course look into the case still earlier, and seek how an instinct in the
parent, of feeding its young at all, was first derived; but it is
useless to waste time in conjectures on a series of gradations from the
young feeding themselves and being slightly and occasionally assisted in
their search, to their entire food being brought to them. With respect
to the parent bringing a different kind of food from its own kind, we
may suppose either that the remote stock, whence the sparrow and other
congenerous birds have descended, was insectivorous, and that its own
habits and structure have been changed, whilst its ancient instincts
with respect to its young have remained unchanged; or we may suppose
that the parents have been induced to vary slightly the food of their
young, by a slight scarcity of the proper kind (or by the instincts of
some individuals not being so truly developed), and in this case those
young which were most capable of surviving were necessarily most often
preserved, and would themselves in time become parents, and would be
similarly compelled to alter their food for their young. In the case of
those animals, the young of which feed themselves, changes in their
instincts for food, and in their structure, might be selected from
slight variations, just as in mature animals. Again, where the food of
the young depends on where the mother places her eggs, as in the case of
the caterpillars of the cabbage-butterfly, we may suppose that the
parent stock of the species deposited her eggs sometimes on one kind and
sometimes on another of congenerous plants (as some species now do), and
if the cabbage suited the caterpillars better than any other plant, the
caterpillars of those butterflies, which had chosen the cabbage, would
be most plentifully reared, and would produce butterflies more apt to
lay their eggs on the cabbage than on the other congenerous plants.
{293} This is an expansion of an obscure passage in the Essay of
1842, p. 19.
However vague and unphilosophical these conjectures may appear, they
serve, I think, to show that one's first impulse utterly to reject any
theory whatever, implying a gradual acquirement of these instincts,
which for ages have excited man's admiration, may at least be delayed.
Once grant that dispositions, tastes, actions or habits can be slightly
modified, either by slight congenital differences (we must suppose in
the brain) or by the force of external circumstances, and that such
slight modifications can be rendered inheritable,--a proposition which
no one can reject,--and it will be difficult to put any limit to the
complexity and wonder of the tastes and habits which may _possibly_ be
thus acquired.
_Difficulties in the acquirement by Selection of complex corporeal
structures._
After the past discussion it will perhaps be convenient here to consider
whether any particular corporeal organs, or the entire structure of any
animals, are so wonderful as to justify the rejection _primâ facie_ of
our theory{294}. In the case of the eye, as with the more complicated
instincts, no doubt one's first impulse is to utterly reject every such
theory. But if the eye from its most complicated form can be shown to
graduate into an exceedingly simple state,--if selection can produce the
smallest change, and if such a series exists, then it is clear (for in
this work we have nothing to do with the first origin of organs in their
simplest forms{295}) that it may _possibly_ have been acquired by
gradual selection of slight, but in each case, useful deviations{296}.
Every naturalist, when he meets with any new and singular organ, always
expects to find, and looks for, other and simpler modifications of it in
other beings. In the case of the eye, we have a multitude of different
forms, more or less simple, not graduating into each other, but
separated by sudden gaps or intervals; but we must recollect how
incomparably greater would the multitude of visual structures be if we
had the eyes of every fossil which ever existed. We shall discuss the
probable vast proportion of the extinct to the recent in the succeeding
Part. Notwithstanding the large series of existing forms, it is most
difficult even to conjecture by what intermediate stages very many
simple organs could possibly have graduated into complex ones: but it
should be here borne in mind, that a part having originally a wholly
different function, may on the theory of gradual selection be slowly
worked into quite another use; the gradations of forms, from which
naturalists believe in the hypothetical metamorphosis of part of the ear
into the swimming bladder in fishes{297}, and in insects of legs into
jaws, show the manner in which this is possible. As under domestication,
modifications of structure take place, without any continued selection,
which man finds very useful, or valuable for curiosity (as the hooked
calyx of the teazle, or the ruff round some pigeons' necks), so in a
state of nature some small modifications, apparently beautifully adapted
to certain ends, may perhaps be produced from the accidents of the
reproductive system, and be at once propagated without long-continued
selection of small deviations towards that structure{298}. In
conjecturing by what stages any complicated organ in a species may have
arrived at its present state, although we may look to the analogous
organs in other existing species, we should do this merely to aid and
guide our imaginations; for to know the real stages we must look only
through one line of species, to one ancient stock, from which the
species in question has descended. In considering the eye of a
quadruped, for instance, though we may look at the eye of a molluscous
animal or of an insect, as a proof how simple an organ will serve some
of the ends of vision; and at the eye of a fish as a nearer guide of the
manner of simplification; we must remember that it is a mere chance
(assuming for a moment the truth of our theory) if any existing organic
being has preserved any one organ, in exactly the same condition, as it
existed in the ancient species at remote geological periods.
{294} The difficulties discussed in the _Origin_, Ed. i. p. 171,
vi. p. 207, are the rarity of transitional varieties, the origin of
the tail of the giraffe; the otter-like polecat (_Mustela vison_);
the flying habit of the bat; the penguin and the logger-headed
duck; flying fish; the whale-like habit of the bear; the
woodpecker; diving petrels; the eye; the swimming bladder;
Cirripedes; neuter insects; electric organs.
Of these, the polecat, the bat, the woodpecker, the eye, the
swimming bladder are discussed in the present Essay, and in
addition some botanical problems.
{295} In the _Origin_, Ed. vi. p. 275, the author replies to
Mivart's criticisms (_Genesis of Species_, 1871), referring
especially to that writer's objection "that natural selection is
incompetent to account for the incipient stages of useful
structures."
{296} "and that each eye throughout the animal kingdom is
not only most useful, but _perfect_ for its possessor."
{297} _Origin_, Ed. i. p. 190, vi. p. 230.
{298} This is one of the most definite statements in the present
Essay of the possible importance of _sports_ or what would now be
called _mutations_. As is well known the author afterwards doubted
whether species could arise in this way. See _Origin_, Ed. v. p.
103, vi. p. 110, also _Life and Letters_, vol. iii. p. 107.
The nature or condition of certain structures has been thought by some
naturalists to be of no use to the possessor{299}, but to have been
formed wholly for the good of other species; thus certain fruit and
seeds have been thought to have been made nutritious for certain
animals--numbers of insects, especially in their larval state, to exist
for the same end--certain fish to be bright coloured to aid certain
birds of prey in catching them, &c. Now could this be proved (which I am
far from admitting) the theory of natural selection would be quite
overthrown; for it is evident that selection depending on the advantage
over others of one individual with some slight deviation would never
produce a structure or quality profitable only to another species. No
doubt one being takes advantage of qualities in another, and may even
cause its extermination; but this is far from proving that this quality
was produced for such an end. It may be advantageous to a plant to have
its seeds attractive to animals, if one out of a hundred or a thousand
escapes being digested, and thus aids dissemination: the bright colours
of a fish may be of some advantage to it, or more probably may result
from exposure to certain conditions in favourable haunts for food,
_notwithstanding_ it becomes subject to be caught more easily by certain
birds.
{299} See _Origin_, Ed. i. p. 210, vi. p. 322, where the question
is discussed for the case of instincts with a proviso that the same
argument applies to structure. It is briefly stated in its general
bearing in _Origin_, Ed. i. p. 87, vi. p. 106.
If instead of looking, as above, at certain individual organs, in order
to speculate on the stages by which their parts have been matured and
selected, we consider an individual animal, we meet with the same or
greater difficulty, but which, I believe, as in the case of single
organs, rests entirely on our ignorance. It may be asked by what
intermediate forms could, for instance, a bat possibly have passed; but
the same question might have been asked with respect to the seal, if we
had not been familiar with the otter and other semi-aquatic carnivorous
quadrupeds. But in the case of the bat, who can say what might have been
the habits of some parent form with less developed wings, when we now
have insectivorous opossums and herbivorous squirrels fitted for merely
gliding through the air{300}. One species of bat is at present partly
aquatic in its habits{301}. Woodpeckers and tree-frogs are especially
adapted, as their names express, for climbing trees; yet we have species
of both inhabiting the open plains of La Plata, where a tree does not
exist{302}. I might argue from this circumstance that a structure
eminently fitted for climbing trees might descend from forms inhabiting
a country where a tree did not exist. Notwithstanding these and a
multitude of other well-known facts, it has been maintained by several
authors that one species, for instance of the carnivorous order, could
not pass into another, for instance into an otter, because in its
transitional state its habits would not be adapted to any proper
conditions of life; but the jaguar{303} is a thoroughly terrestrial
quadruped in its structure, yet it takes freely to the water and catches
many fish; will it be said that it is _impossible_ that the conditions
of its country might become such that the jaguar should be driven to
feed more on fish than they now do; and in that case is it impossible,
is it not probable, that any the slightest deviation in its instincts,
its form of body, in the width of its feet, and in the extension of the
skin (which already unites the base of its toes) would give such
individuals a better _chance_ of surviving and propagating young with
similar, barely perceptible (though thoroughly exercised),
deviations{304}? Who will say what could thus be effected in the course
of ten thousand generations? Who can answer the same question with
respect to instincts? If no one can, the _possibility_ (for we are not
in this chapter considering the _probability_) of simple organs or
organic beings being modified by natural selection and the effects of
external agencies into complicated ones ought not to be absolutely
rejected.
{300} No one will dispute that the gliding is
most useful, probably necessary for the species in question.
{301} Is this the Galeopithecus? I forget.
<_Galeopithecus_ "or the flying Lemur" is mentioned in the
corresponding discussion in the _Origin_, Ed. i. p. 181, vi. p. 217,
as formerly placed among the bats. I do not know why it is described
as partly aquatic in its habits.>
{302} In the _Origin_, Ed. vi. p. 221, the author modified the
statement that it _never_ climbs trees; he also inserted a sentence
quoting Mr Hudson to the effect that in other districts this
woodpecker climbs trees and bores holes. See Mr Darwin's paper,
_Zoolog. Soc. Proc._, 1870, and _Life and Letters_, iii. p. 153.
{303} Note by the late Alfred Newton. Richardson in _Fauna
Boreali-Americana_, i. p. 49.
{304} See Richardson a far better case of a
polecat animal <_Mustela vison_>, which half-year is aquatic.
PART II{305}
ON THE EVIDENCE FAVOURABLE AND OPPOSED TO THE VIEW THAT SPECIES ARE
NATURALLY FORMED RACES, DESCENDED FROM COMMON STOCKS
{305} In the _Origin_ the division of the work into Parts I and II
is omitted. In the MS. the chapters of Part II are numbered afresh,
the present being Ch. I of Pt. II. I have thought it best to call
it Ch. IV and there is evidence that Darwin had some thought of
doing the same. It corresponds to Ch. IX of _Origin_, Ed. i., Ch. X
in Ed. vi.
CHAPTER IV
ON THE NUMBER OF INTERMEDIATE FORMS REQUIRED ON THE THEORY OF COMMON
DESCENT; AND ON THEIR ABSENCE IN A FOSSIL STATE
I must here premise that, according to the view ordinarily received, the
myriads of organisms, which have during past and present times peopled
this world, have been created by so many distinct acts of creation. It
is impossible to reason concerning the will of the Creator, and
therefore, according to this view, we can see no cause why or why not
the individual organism should have been created on any fixed scheme.
That all the organisms of this world have been produced on a scheme is
certain from their general affinities; and if this scheme can be shown
to be the same with that which would result from allied organic beings
descending from common stocks, it becomes highly improbable that they
have been separately created by individual acts of the will of a
Creator. For as well might it be said that, although the planets move in
courses conformably to the law of gravity, yet we ought to attribute
the course of each planet to the individual act of the will of the
Creator{306}. It is in every case more conformable with what we know of
the government of this earth, that the Creator should have imposed only
general laws. As long as no method was known by which races could become
exquisitely adapted to various ends, whilst the existence of species was
thought to be proved by the sterility{307} of their offspring, it was
allowable to attribute each organism to an individual act of creation.
But in the two former chapters it has (I think) been shown that the
production, under existing conditions, of exquisitely adapted species,
is at least _possible_. Is there then any direct evidence in favour or
against this view? I believe that the geographical distribution of
organic beings in past and present times, the kind of affinity linking
them together, their so-called "metamorphic" and "abortive" organs,
appear in favour of this view. On the other hand, the imperfect evidence
of the continuousness of the organic series, which, we shall immediately
see, is required on our theory, is against it; and is the most weighty
objection{308}. The evidence, however, even on this point, as far as it
goes, is favourable; and considering the imperfection of our knowledge,
especially with respect to past ages, it would be surprising if evidence
drawn from such sources were not also imperfect.
{306} In the Essay of 1842 the author uses astronomy in the same
manner as an illustration. In the _Origin_ this does not occur; the
reference to the action of secondary causes is more general, _e.g._
Ed. i. p. 488, vi. p. 668.
{307} It is interesting to find the argument from sterility given
so prominent a place. In a corresponding passage in the _Origin_,
Ed. i. p. 480, vi. p. 659, it is more summarily treated. The author
gives, as the chief bar to the acceptance of evolution, the fact
that "we are always slow in admitting any great change of which we
do not see the intermediate steps"; and goes on to quote Lyell on
geological action. It will be remembered that the question of
sterility remained a difficulty for Huxley.
{308} Similar statements occur in the Essay of 1842, p. 24, note 1,
and in the _Origin_, Ed. i. p. 299.
As I suppose that species have been formed in an analogous manner with
the varieties of the domesticated animals and plants, so must there have
existed intermediate forms between all the species of the same group,
not differing more than recognised varieties differ. It must not be
supposed necessary that there should have existed forms exactly
intermediate in character between any two species of a genus, or even
between any two varieties of a species; but it is necessary that there
should have existed every intermediate form between the one species or
variety of the common parent, and likewise between the second species or
variety, and this same common parent. Thus it does not necessarily
follow that there ever has existed series of intermediate sub-varieties
(differing no more than the occasional seedlings from the same
seed-capsule,) between broccoli and common red cabbage; but it is
certain that there has existed, between broccoli and the wild parent
cabbage, a series of such intermediate seedlings, and again between red
cabbage and the wild parent cabbage: so that the broccoli and red
cabbage are linked together, but not _necessarily_ by directly
intermediate forms{309}. It is of course possible that there _may_ have
been directly intermediate forms, for the broccoli may have long since
descended from a common red cabbage, and this from the wild cabbage. So
on my theory, it must have been with species of the same genus. Still
more must the supposition be avoided that there has necessarily ever
existed (though one _may_ have descended from other) directly
intermediate forms between any two genera or families--for instance
between the genus _Sus_ and the Tapir{310}; although it is necessary
that intermediate forms (not differing more than the varieties of our
domestic animals) should have existed between Sus and some unknown
parent form, and Tapir with this same parent form. The latter may have
differed more from Sus and Tapir than these two genera now differ from
each other. In this sense, according to our theory, there has been a
gradual passage (the steps not being wider apart than our domestic
varieties) between the species of the same genus, between genera of the
same family, and between families of the same order, and so on, as far
as facts, hereafter to be given, lead us; and the number of forms which
must have at former periods existed, thus to make good this passage
between different species, genera, and families, must have been almost
infinitely great.
{309} In the _Origin_, Ed. i. p. 280, vi. p. 414 he uses his
newly-acquired knowledge of pigeons to illustrate this point.
{310} Compare the _Origin_, Ed. i. p. 281, vi. p. 414.
What evidence{311} is there of a number of intermediate forms having
existed, making a passage in the above sense, between the species of the
same groups? Some naturalists have supposed that if every fossil which
now lies entombed, together with all existing species, were collected
together, a perfect series in every great class would be formed.
Considering the enormous number of species requisite to effect this,
especially in the above sense of the forms not being _directly_
intermediate between the existing species and genera, but only
intermediate by being linked through a common but often widely different
ancestor, I think this supposition highly improbable. I am however far
from underrating the probable number of fossilised species: no one who
has attended to the wonderful progress of palæontology during the last
few years will doubt that we as yet have found only an exceedingly small
fraction of the species buried in the crust of the earth. Although the
almost infinitely numerous intermediate forms in no one class may have
been preserved, it does not follow that they have not existed. The
fossils which have been discovered, it is important to remark, do tend,
the little way they go, to make good the series; for as observed by
Buckland they all fall into or between existing groups{312}. Moreover,
those that fall between our existing groups, fall in, according to the
manner required by our theory, for they do not directly connect two
existing species of different groups, but they connect the groups
themselves: thus the Pachydermata and Ruminantia are now separated by
several characters, the Pachydermata{313} have both a
tibia and fibula, whilst Ruminantia have only a tibia; now the fossil
Macrauchenia has a leg bone exactly intermediate in this respect, and
likewise has some other intermediate characters. But the Macrauchenia
does not connect any one species of Pachydermata with some one other of
Ruminantia but it shows that these two groups have at one time been less
widely divided. So have fish and reptiles been at one time more closely
connected in some points than they now are. Generally in those groups in
which there has been most change, the more ancient the fossil, if not
identical with recent, the more often it falls between existing groups,
or into small existing groups which now lie between other large existing
groups. Cases like the foregoing, of which there are many, form steps,
though few and far between, in a series of the kind required by my
theory.
{311} _Origin_, Ed. i. p. 301, vi. p. 440.
{312} _Origin_, Ed. i. p. 329, vi. p. 471.
{313} The structure of the Pachyderm leg was a favourite with the
author. It is discussed in the Essay of 1842, p. 48. In the present
Essay the following sentence in the margin appears to refer to
Pachyderms and Ruminants: "There can be no doubt, if we banish all
fossils, existing groups stand more separate." The following occurs
between the lines "The earliest forms would be such as others could
radiate from."
As I have admitted the high improbability, that if every fossil were
disinterred, they would compose in each of the Divisions of Nature a
perfect series of the kind required; consequently I freely admit, that
if those geologists are in the right who consider the lowest known
formation as contemporaneous with the first appearances of life{314}; or
the several formations as at all closely consecutive; or any one
formation as containing a nearly perfect record of the organisms which
existed during the whole period of its deposition in that quarter of the
globe;--if such propositions are to be accepted, my theory must be
abandoned.
{314} _Origin_, Ed. i. p. 307, vi. p. 448.
If the Palæozoic system is really contemporaneous with the first
appearance of life, my theory must be abandoned, both inasmuch as it
limits _from shortness of time_ the total number of forms which can have
existed on this world, and because the organisms, as fish, mollusca{315}
and star-fish found in its lower beds, cannot be considered as the
parent forms of all the successive species in these classes. But no one
has yet overturned the arguments of Hutton and Lyell, that the lowest
formations known to us are only those which have escaped being
metamorphosed ; if we argued from some considerable districts,
we might have supposed that even the Cretaceous system was that in which
life first appeared. From the number of distant points, however, in
which the Silurian system has been found to be the lowest, and not
always metamorphosed, there are some objections to Hutton's and Lyell's
view; but we must not forget that the now existing land forms only 1/5
part of the superficies of the globe, and that this fraction is only
imperfectly known. With respect to the fewness of the organisms found in
the Silurian and other Palæozoic formations, there is less difficulty,
inasmuch as (besides their gradual obliteration) we can expect
formations of this vast antiquity to escape entire denudation, only when
they have been accumulated over a wide area, and have been subsequently
protected by vast superimposed deposits: now this could generally only
hold good with deposits accumulating in a wide and deep ocean, and
therefore unfavourable to the presence of many living things. A mere
narrow and not very thick strip of matter, deposited along a coast where
organisms most abound, would have no chance of escaping denudation and
being preserved to the present time from such immensely distant
ages{316}.
{315} The parent-forms of Mollusca
would probably differ greatly from all recent,--it is not directly
that any one division of Mollusca would descend from first time
unaltered, whilst others had become metamorphosed from it.
{316} _Origin_, Ed. i. p. 291, vi. p. 426.
If the several known formations are at all nearly consecutive in time,
and preserve a fair record of the organisms which have existed, my
theory must be abandoned. But when we consider the great changes in
mineralogical nature and texture between successive formations, what
vast and entire changes in the geography of the surrounding countries
must generally have been effected, thus wholly to have changed the
nature of the deposits on the same area. What time such changes must
have required! Moreover how often has it not been found, that between
two conformable and apparently immediately successive deposits a vast
pile of water-worn matter is interpolated in an adjoining district. We
have no means of conjecturing in many cases how long a period{317} has
elapsed between successive formations, for the species are often wholly
different: as remarked by Lyell, in some cases probably as long a period
has elapsed between two formations as the whole Tertiary system, itself
broken by wide gaps.
{317} Reflect on coming in of the Chalk,
extending from Iceland to the Crimea.
Consult the writings of any one who has particularly attended to any one
stage in the Tertiary system (and indeed of every system) and see how
deeply impressed he is with the time required for its accumulation{318}.
Reflect on the years elapsed in many cases, since the latest beds
containing only living species have been formed;--see what Jordan Smith
says of the 20,000 years since the last bed, which is above the boulder
formation in Scotland, has been upraised; or of the far longer period
since the recent beds of Sweden have been upraised 400 feet, what an
enormous period the boulder formation must have required, and yet how
insignificant are the records (although there has been plenty of
elevation to bring up submarine deposits) of the shells, which we know
existed at that time. Think, then, over the entire length of the
Tertiary epoch, and think over the probable length of the intervals,
separating the Secondary deposits. Of these deposits, moreover, those
consisting of sand and pebbles have seldom been favourable, either to
the embedment or to the preservation of fossils{319}.
{318} _Origin_, Ed. i. p. 282, vi. p. 416.
{319} _Origin_, Ed. i. pp. 288, 300, vi. pp. 422, 438.
Nor can it be admitted as probable that any one Secondary formation
contains a fair record even of those organisms which are most easily
preserved, namely hard marine bodies. In how many cases have we not
certain evidence that between the deposition of apparently closely
consecutive beds, the lower one existed for an unknown time as land,
covered with trees. Some of the Secondary formations which contain most
marine remains appear to have been formed in a wide and not deep sea,
and therefore only those marine animals which live in such situations
would be preserved{320}. In all cases, on indented rocky coasts, or any
other coast, where sediment is not accumulating, although often highly
favourable to marine animals, none can be embedded: where pure sand and
pebbles are accumulating few or none will be preserved. I may here
instance the great western line of the S. American coast{321}, tenanted
by many peculiar animals, of which none probably will be preserved to a
distant epoch. From these causes, and especially from such deposits as
are formed along a line of coast, steep above and below water, being
necessarily of little width, and therefore more likely to be
subsequently denuded and worn away, we can see why it is improbable that
our Secondary deposits contain a fair record of the Marine Fauna of any
one period. The East Indian Archipelago offers an area, as large as most
of our Secondary deposits, in which there are wide and shallow seas,
teeming with marine animals, and in which sediment is accumulating; now
supposing that all the hard marine animals, or rather those having hard
parts to preserve, were preserved to a future age, excepting those which
lived on rocky shores where no sediment or only sand and gravel were
accumulating, and excepting those embedded along the steeper coasts,
where only a narrow fringe of sediment was accumulating, supposing all
this, how poor a notion would a person at a future age have of the
Marine Fauna of the present day. Lyell{322} has compared the geological
series to a work of which only the few latter but not consecutive
chapters have been preserved; and out of which, it may be added, very
many leaves have been torn, the remaining ones only illustrating a
scanty portion of the Fauna of each period. On this view, the records
of anteceding ages confirm my theory; on any other they destroy it.
{320} Neither highest or lowest fish (_i.e._
Myxina or Lepidosiren) could be preserved in intelligible
condition in fossils.
{321} _Origin_, Ed. i. p. 290, vi. p. 425.
{322} See _Origin_, Ed. i. p. 310, vi. p. 452 for Lyell's metaphor.
I am indebted to Prof. Judd for pointing out that Darwin's version
of the metaphor is founded on the first edition of Lyell's
_Principles_, vol. I. and vol. III.; see the Essay of 1842, p. 27.
Finally, if we narrow the question into, why do we not find in some
instances every intermediate form between any two species? the answer
may well be that the average duration of each specific form (as we have
good reason to believe) is immense in years, and that the transition
could, according to my theory, be effected only by numberless small
gradations; and therefore that we should require for this end a most
perfect record, which the foregoing reasoning teaches us not to expect.
It might be thought that in a vertical section of great thickness in the
same formation some of the species ought to be found to vary in the
upper and lower parts{323}, but it may be doubted whether any formation
has gone on accumulating without any break for a period as long as the
duration of a species; and if it had done so, we should require a series
of specimens from every part. How rare must be the chance of sediment
accumulating for some 20 or 30 thousand years on the same spot{324},
with the bottom subsiding, so that a proper depth might be preserved for
any one species to continue living: what an amount of subsidence would
be thus required, and this subsidence must not destroy the source whence
the sediment continued to be derived. In the case of terrestrial
animals, what chance is there when the present time is become a
pleistocene formation (at an earlier period than this, sufficient
elevation to expose marine beds could not be expected), what chance is
there that future geologists will make out the innumerable transitional
sub-varieties, through which the short-horned and long-horned cattle
(so different in shape of body) have been derived from the same parent
stock{325}? Yet this transition has been effected in _the same country_,
and in a far _shorter time_, than would be probable in a wild state,
both contingencies highly favourable for the future hypothetical
geologists being enabled to trace the variation.
{323} See _More Letters_, vol. I. pp. 344-7, for Darwin's interest
in the celebrated observations of Hilgendorf and Hyatt.
{324} This corresponds partly to _Origin_, Ed. i. p. 294, vi. p.
431.
{325} _Origin_, Ed. i. p. 299, vi. p. 437.
CHAPTER V
GRADUAL APPEARANCE AND DISAPPEARANCE OF SPECIES{326}
{326} This chapter corresponds to ch. X of _Origin_, Ed. i., vi.
ch. XI, "On the geological succession of organic beings."
In the Tertiary system, in the last uplifted beds, we find all the
species recent and living in the immediate vicinity; in rather older
beds we find only recent species, but some not living in the immediate
vicinity{327}; we then find beds with two or three or a few more extinct
or very rare species; then considerably more extinct species, but with
gaps in the regular increase; and finally we have beds with only two or
three or not one living species. Most geologists believe that the gaps
in the percentage, that is the sudden increments, in the number of the
extinct species in the stages of the Tertiary system are due to the
imperfection of the geological record. Hence we are led to believe that
the species in the Tertiary system have been gradually introduced; and
from analogy to carry on the same view to the Secondary formations. In
these latter, however, entire groups of species generally come in
abruptly; but this would naturally result, if, as argued in the
foregoing chapter, these Secondary deposits are separated by wide
epochs. Moreover it is important to observe that, with our increase of
knowledge, the gaps between the older formations become fewer and
smaller; geologists of a few years standing remember how beautifully
has the Devonian system{328} come in between the Carboniferous and
Silurian formations. I need hardly observe that the slow and gradual
appearance of new forms follows from our theory, for to form a new
species, an old one must not only be plastic in its organization,
becoming so probably from changes in the conditions of its existence,
but a place in the natural economy of the district must [be made,] come
to exist, for the selection of some new modification of its structure,
better fitted to the surrounding conditions than are the other
individuals of the same or other species{329}.
{327} _Origin_, Ed. i. p. 312, vi. p. 453.
{328} In the margin the author has written "Lonsdale." This refers
to W. Lonsdale's paper "Notes on the age of the Limestone of South
Devonshire," _Geolog. Soc. Trans._, Series 2, vol. V. 1840, p. 721.
According to Mr H. B. Woodward (_History of the Geological Society
of London_, 1907, p. 107) "Lonsdale's 'important and original
suggestion of the existence of an intermediary type of Palæozoic
fossils, since called Devonian,' led to a change which was then
'the greatest ever made at one time in the classification of our
English formations'." Mr Woodward's quotations are from Murchison
and Buckland.
{329} Better begin with this. If species really,
after catastrophes, created in showers over world, my theory false.
In the Tertiary system the same facts, which make us admit as probable
that new species have slowly appeared, lead to the admission that old
ones have slowly disappeared, not several together, but one after
another; and by analogy one is induced to extend this belief to the
Secondary and Palæozoic epochs. In some cases, as the subsidence of a
flat country, or the breaking or the joining of an isthmus, and the
sudden inroad of many new and destructive species, extinction might be
locally sudden. The view entertained by many geologists, that each fauna
of each Secondary epoch has been suddenly destroyed over the whole
world, so that no succession could be left for the production of new
forms, is subversive of my theory, but I see no grounds whatever to
admit such a view. On the contrary, the law, which has been made out,
with reference to distinct epochs, by independent observers, namely,
that the wider the geographical range of a species the longer is its
duration in time, seems entirely opposed to any universal
extermination{330}. The fact of species of mammiferous animals and fish
being renewed at a quicker rate than mollusca, though both aquatic; and
of these the terrestrial genera being renewed quicker than the marine;
and the marine mollusca being again renewed quicker than the Infusorial
animalcula, all seem to show that the extinction and renewal of species
does not depend on general catastrophes, but on the particular relations
of the several classes to the conditions to which they are exposed{331}.
{330} Opposite to this passage the author has written "d'Archiac,
Forbes, Lyell."
{331} This passage, for which the author gives as authorities the
names of Lyell, Forbes and Ehrenberg, corresponds in part to the
discussion beginning on p. 313 of _Origin_, Ed. i., vi. p. 454.
Some authors seem to consider the fact of a few species having
survived{332} amidst a number of extinct forms (as is the case with a
tortoise and a crocodile out of the vast number of extinct sub-Himalayan
fossils) as strongly opposed to the view of species being mutable. No
doubt this would be the case, if it were presupposed with Lamarck that
there was some inherent tendency to change and development in all
species, for which supposition I see no evidence. As we see some species
at present adapted to a wide range of conditions, so we may suppose that
such species would survive unchanged and unexterminated for a long time;
time generally being from geological causes a correlative of changing
conditions. How at present one species becomes adapted to a wide range,
and another species to a restricted range of conditions, is of difficult
explanation.
{332} The author gives Falconer as his authority: see _Origin_, Ed.
i. p. 313, vi. p. 454.
_Extinction of species._
The extinction of the larger quadrupeds, of which we imagine we better
know the conditions of existence, has been thought little less wonderful
than the appearance of new species; and has, I think, chiefly led to the
belief of universal catastrophes. When considering the wonderful
disappearance within a late period, whilst recent shells were living, of
the numerous great and small mammifers of S. America, one is strongly
induced to join with the catastrophists. I believe, however, that very
erroneous views are held on this subject. As far as is historically
known, the disappearance of species from any one country has been
slow--the species becoming rarer and rarer, locally extinct, and finally
lost{333}. It may be objected that this has been effected by man's
direct agency, or by his indirect agency in altering the state of the
country; in this latter case, however, it would be difficult to draw any
just distinction between his agency and natural agencies. But we now
know in the later Tertiary deposits, that shells become rarer and rarer
in the successive beds, and finally disappear: it has happened, also,
that shells common in a fossil state, and thought to have been extinct,
have been found to be still living species, but very _rare_ ones{334}.
If the rule is that organisms become extinct by becoming rarer and
rarer, we ought not to view their extinction, even in the case of the
larger quadrupeds, as anything wonderful and out of the common course of
events. For no naturalist thinks it wonderful that one species of a
genus should be rare and another abundant, notwithstanding he be quite
incapable of explaining the causes of the comparative rareness{335}. Why
is one species of willow-wren or hawk or woodpecker common in England,
and another extremely rare: why at the Cape of Good Hope is one species
of rhinoceros or antelope far more abundant than other species? Why
again is the same species much more abundant in one district of a
country than in another district? No doubt there are in each case good
causes: but they are unknown and unperceived by us. May we not then
safely infer that as certain causes are acting _unperceived_ around us,
and are making one species to be common and another exceedingly rare,
that they might equally well cause the final extinction of some species
without being perceived by us? We should always bear in mind that there
is a recurrent struggle for life in every organism, and that in every
country a destroying agency is always counteracting the geometrical
tendency to increase in every species; and yet without our being able to
tell with certainty at what period of life, or at what period of the
year, the destruction falls the heaviest. Ought we then to expect to
trace the steps by which this destroying power, always at work and
scarcely perceived by us, becomes increased, and yet if it continues to
increase ever so slowly (without the fertility of the species in
question be likewise increased) the average number of the individuals of
that species must decrease, and become finally lost. I may give a single
instance of a check causing local extermination which might long have
escaped discovery{336}; the horse, though swarming in a wild state in La
Plata, and likewise under apparently the most unfavourable conditions in
the scorched and alternately flooded plains of Caraccas, will not in a
wild state extend beyond a certain degree of latitude into the
intermediate country of Paraguay; this is owing to a certain fly
depositing its eggs on the navels of the foals: as, however, man with a
_little_ care can rear horses in a tame state _abundantly_ in Paraguay,
the problem of its extinction is probably complicated by the greater
exposure of the wild horse to occasional famine from the droughts, to
the attacks of the jaguar and other such evils. In the Falkland Islands
the check to the _increase_ of the wild horse is said to be loss of the
sucking foals{337}, from the stallions compelling the mares to travel
across bogs and rocks in search of food: if the pasture on these islands
decreased a little, the horse, perhaps, would cease to exist in a wild
state, not from the absolute want of food, but from the impatience of
the stallions urging the mares to travel whilst the foals were too
young.
{333} This corresponds approximately to _Origin_, Ed. i. p. 317,
vi. p. 458.
{334} The case of _Trigonia_, a great Secondary genus of shells
surviving in a single species in the Australian seas, is given as
an example in the _Origin_, Ed. i. p. 321, vi. p. 463.
{335} This point, on which the author laid much stress, is
discussed in the _Origin_, Ed. i. p. 319, vi. p. 461.
{336} _Origin_, Ed. i. p. 72, vi. p. 89.
{337} This case does not occur in the _Origin_, Ed.
From our more intimate acquaintance with domestic animals, we cannot
conceive their extinction without some glaring agency; we forget that
they would undoubtedly in a state of nature (where other animals are
ready to fill up their place) be acted on in some part of their lives by
a destroying agency, keeping their numbers on an average constant. If
the common ox was known only as a wild S. African species, we should
feel no surprise at hearing that it was a very rare species; and this
rarity would be a stage towards its extinction. Even in man, so
infinitely better known than any other inhabitant of this world, how
impossible it has been found, without statistical calculations, to judge
of the proportions of births and deaths, of the duration of life, and of
the increase and decrease of population; and still less of the causes of
such changes: and yet, as has so often been repeated, decrease in
numbers or rarity seems to be the high-road to extinction. To marvel at
the extermination of a species appears to me to be the same thing as to
know that illness is the road to death,--to look at illness as an
ordinary event, nevertheless to conclude, when the sick man dies, that
his death has been caused by some unknown and violent agency{338}.
{338} An almost identical sentence occurs in the _Origin_, Ed. i.
p. 320, vi. p. 462.
In a future part of this work we shall show that, as a general rule,
groups of allied species{339} gradually appear and disappear, one after
the other, on the face of the earth, like the individuals of the same
species: and we shall then endeavour to show the probable cause of this
remarkable fact.
{339} _Origin_, Ed. i. p. 316, vi. p. 457.
CHAPTER VI
ON THE GEOGRAPHICAL DISTRIBUTION OF ORGANIC BEINGS IN PAST AND PRESENT
TIMES
For convenience sake I shall divide this chapter into three
sections{340}. In the first place I shall endeavour to state the laws of
the distribution of existing beings, as far as our present object is
concerned; in the second, that of extinct; and in the third section I
shall consider how far these laws accord with the theory of allied
species having a common descent.
{340} Chapters XI and XII in the _Origin_, Ed. i., vi. chs. XII and
XIII ("On geographical distribution") show signs of having been
originally one, in the fact that one summary serves for both. The
geological element is not separately treated there, nor is there a
separate section on "how far these laws accord with the theory,
&c."
In the MS. the author has here written in the margin "If same
species appear at two spot at once, fatal to my theory." See
_Origin_, Ed. i. p. 352, vi. p. 499
SECTION FIRST.
_Distribution of the inhabitants in the different continents._
In the following discussion I shall chiefly refer to terrestrial
mammifers, inasmuch as they are better known; their differences in
different countries, strongly marked; and especially as the necessary
means of their transport are more evident, and confusion, from the
accidental conveyance by man of a species from one district to another
district, is less likely to arise. It is known that all mammifers (as
well as all other organisms) are united in one great system; but that
the different species, genera, or families of the same order inhabit
different quarters of the globe. If we divide the land{341} into two
divisions, according to the amount of difference, and disregarding the
numbers of the terrestrial mammifers inhabiting them, we shall have
first Australia including New Guinea; and secondly the rest of the
world: if we make a three-fold division, we shall have Australia, S.
America, and the rest of the world; I must observe that North America is
in some respects neutral land, from possessing some S. American forms,
but I believe it is more closely allied (as it certainly is in its
birds, plants and shells) with Europe. If our division had been
four-fold, we should have had Australia, S. America, Madagascar (though
inhabited by few mammifers) and the remaining land: if five-fold,
Africa, especially the southern eastern parts, would have to be
separated from the remainder of the world. These differences in the
mammiferous inhabitants of the several main divisions of the globe
cannot, it is well known, be explained by corresponding differences in
their conditions{342}; how similar are parts of tropical America and
Africa; and accordingly we find some _analogous_ resemblances,--thus
both have monkeys, both large feline animals, both large Lepidoptera,
and large dung-feeding beetles; both have palms and epiphytes; and yet
the essential difference between their productions is as great as
between those of the arid plains of the Cape of Good Hope and the
grass-covered savannahs of La Plata{343}. Consider the distribution of
the Marsupialia, which are eminently characteristic of Australia, and in
a lesser degree of S. America; when we reflect that animals of this
division, feeding both on animal and vegetable matter, frequent the dry
open or wooded plains and mountains of Australia, the humid impenetrable
forests of New Guinea and Brazil; the dry rocky mountains of Chile, and
the grassy plains of Banda Oriental, we must look to some other cause,
than the nature of the country, for their absence in Africa and other
quarters of the world.
{341} This division of the land into regions does not occur in the
_Origin_, Ed. i.
{342} _Origin_, Ed. i. p. 346, vi. p. 493.
{343} Opposite this passage is written "_not botanically_," in Sir
J. D. Hooker's hand. The word _palms_ is underlined three times and
followed by three exclamation marks. An explanatory note is added
in the margin "singular paucity of palms and epiphytes in Trop.
Africa compared with Trop. America and Ind. Or." <=East Indies>.
Furthermore it may be observed that _all_ the organisms inhabiting any
country are not perfectly adapted to it{344}; I mean by not being
perfectly adapted, only that some few other organisms can generally be
found better adapted to the country than some of the aborigines. We must
admit this when we consider the enormous number of horses and cattle
which have run wild during the three last centuries in the uninhabited
parts of St Domingo, Cuba, and S. America; for these animals must have
supplanted some aboriginal ones. I might also adduce the same fact in
Australia, but perhaps it will be objected that 30 or 40 years has not
been a sufficient period to test this power of struggling and
overcoming the aborigines. We know the European mouse is driving before
it that of New Zealand, like the Norway rat has driven before it the old
English species in England. Scarcely an island can be named, where
casually introduced plants have not supplanted some of the native
species: in La Plata the Cardoon covers square leagues of country on
which some S. American plants must once have grown: the commonest weed
over the whole of India is an introduced Mexican poppy. The geologist
who knows that slow changes are in progress, replacing land and water,
will easily perceive that even if all the organisms of any country had
originally been the best adapted to it, this could hardly continue so
during succeeding ages without either extermination, or changes, first
in the relative proportional numbers of the inhabitants of the country,
and finally in their constitutions and structure.
{344} This partly corresponds to _Origin_, Ed. i. p. 337, vi. p.
483.
Inspection of a map of the world at once shows that the five divisions,
separated according to the greatest amount of difference in the
mammifers inhabiting them, are likewise those most widely separated from
each other by barriers{345} which mammifers cannot pass: thus Australia
is separated from New Guinea and some small adjoining islets only by a
narrow and shallow strait; whereas New Guinea and its adjoining islets
are cut off from the other East Indian islands by deep water. These
latter islands, I may remark, which fall into the great Asiatic group,
are separated from each other and the continent only by shallow water;
and where this is the case we may suppose, from geological oscillations
of level, that generally there has been recent union. South America,
including the southern part of Mexico, is cut off from North America by
the West Indies, and the great table-land of Mexico, except by a mere
fringe of tropical forests along the coast: it is owing, perhaps, to
this fringe that N. America possesses some S. American forms. Madagascar
is entirely isolated. Africa is also to a great extent isolated,
although it approaches, by many promontories and by lines of shallower
sea, to Europe and Asia: southern Africa, which is the most distinct in
its mammiferous inhabitants, is separated from the northern portion by
the Great Sahara Desert and the table-land of Abyssinia. That the
distribution of organisms is related to barriers, stopping their
progress, we clearly see by comparing the distribution of marine and
terrestrial productions. The marine animals being different on the two
sides of land tenanted by the same terrestrial animals, thus the shells
are wholly different on the opposite sides of the temperate parts of
South America{346}, as they are (?) in the Red Sea and the
Mediterranean. We can at once perceive that the destruction of a barrier
would permit two geographical groups of organisms to fuse and blend into
one. But the original cause of groups being different on opposite sides
of a barrier can only be understood on the hypothesis of each organism
having been created or produced on one spot or area, and afterwards
migrating as widely as its means of transport and subsistence permitted
it.
{345} On the general importance of barriers, see _Origin_, Ed. i.
p. 347, vi. p. 494.
{346} _Origin_, Ed. i. p. 348, vi. p. 495.
_Relation of range in genera and species._
It is generally{347} found, that where a genus or group ranges over
nearly the entire world, many of the species composing the group have
wide ranges: on the other hand, where a group is restricted to any one
country, the species composing it generally have restricted ranges in
that country{348}. Thus among mammifers the feline and canine genera are
widely distributed, and many of the individual species have enormous
ranges [the genus Mus I believe, however, is a strong exception to the
rule]. Mr Gould informs me that the rule holds with birds, as in the
owl genus, which is mundane, and many of the species range widely. The
rule holds also with land and fresh-water mollusca, with butterflies and
very generally with plants. As instances of the converse rule, I may
give that division of the monkeys which is confined to S. America, and
amongst plants, the Cacti, confined to the same continent, the species
of both of which have generally narrow ranges. On the ordinary theory of
the separate creation of each species, the cause of these relations is
not obvious; we can see no reason, because many allied species have been
created in the several main divisions of the world, that several of
these species should have wide ranges; and on the other hand, that
species of the same group should have narrow ranges if all have been
created in one main division of the world. As the result of such and
probably many other unknown relations, it is found that, even in the
same great classes of beings, the different divisions of the world are
characterised by either merely different species, or genera, or even
families: thus in cats, mice, foxes, S. America differs from Asia and
Africa only in species; in her pigs, camels and monkeys the difference
is generic or greater. Again, whilst southern Africa and Australia
differ more widely in their mammalia than do Africa and S. America, they
are more closely (though indeed very distantly) allied in their plants.
{347} The same laws seem to govern distribution
of species and genera, and individuals in time and space.
{348} _Origin_, Ed. i. p. 404, vi. p. 559.
_Distribution of the inhabitants in the same continent._
If we now look at the distribution of the organisms in any one of the
above main divisions of the world, we shall find it split up into many
regions, with all or nearly all their species distinct, but yet
partaking of one common character. This similarity of type in the
subdivisions of a great region is equally well-known with the
dissimilarity of the inhabitants of the several great regions; but it
has been less often insisted on, though more worthy of remark. Thus for
instance, if in Africa or S. America, we go from south to north{349}, or
from lowland to upland, or from a humid to a dryer part, we find wholly
different species of those genera or groups which characterise the
continent over which we are passing. In these subdivisions we may
clearly observe, as in the main divisions of the world, that
sub-barriers divide different groups of species, although the opposite
sides of such sub-barriers may possess nearly the same climate, and may
be in other respects nearly similar: thus it is on the opposite sides of
the Cordillera of Chile, and in a lesser degree on the opposite sides of
the Rocky mountains. Deserts, arms of the sea, and even rivers form the
barriers; mere preoccupied space seems sufficient in several cases: thus
Eastern and Western Australia, in the same latitude, with very similar
climate and soils, have scarcely a plant, and few animals or birds, in
common, although all belong to the peculiar genera characterising
Australia. It is in short impossible to explain the differences in the
inhabitants, either of the main divisions of the world, or of these
sub-divisions, by the differences in their physical conditions, and by
the adaptation of their inhabitants. Some other cause must intervene.
{349} _Origin_, Ed. i. p. 349, vi. p. 496.
We can see that the destruction of sub-barriers would cause (as before
remarked in the case of the main divisions) two sub-divisions to blend
into one; and we can only suppose that the original difference in the
species, on the opposite sides of sub-barriers, is due to the creation
or production of species in distinct areas, from which they have
wandered till arrested by such sub-barriers. Although thus far is pretty
clear, it may be asked, why, when species in the same main division of
the world were produced on opposite sides of a sub-barrier, both when
exposed to similar conditions and when exposed to widely different
influences (as on alpine and lowland tracts, as on arid and humid soils,
as in cold and hot climates), have they invariably been formed on a
similar type, and that type confined to this one division of the world?
Why when an ostrich{350} was produced in the southern parts of America,
was it formed on the American type, instead of on the African or on
Australian types? Why when hare-like and rabbit-like animals were formed
to live on the Savannahs of La Plata, were they produced on the peculiar
Rodent type of S. America, instead of on the true{351} hare-type of
North America, Asia and Africa? Why when borrowing Rodents, and
camel-like animals were formed to tenant the Cordillera, were they
formed on the same type{352} with their representatives on the plains?
Why were the mice, and many birds of different species on the opposite
sides of the Cordillera, but exposed to a very similar climate and soil,
created on the same peculiar S. American type? Why were the plants in
Eastern and Western Australia, though wholly different as species,
formed on the same peculiar Australian types? The generality of the
rule, in so many places and under such different circumstances, makes it
highly remarkable and seems to demand some explanation.
{350} The case of the ostrich (_Rhea_) occurs in the _Origin_, Ed.
i. p. 349, vi. p. 496.
{351} There is a hare in S. America,--so bad
example.
{352} See _Origin_, Ed. i. p. 349, vi. p. 497.
_Insular Faunas._
If we now look to the character of the inhabitants of small
islands{353}, we shall find that those situated close to other land have
a similar fauna with that land{354}, whilst those at a considerable
distance from other land often possess an almost entirely peculiar
fauna. The Galapagos Archipelago{355} is a remarkable instance of this
latter fact; here almost every bird, its one mammifer, its reptiles,
land and sea shells, and even fish, are almost all peculiar and distinct
species, not found in any other quarter of the world: so are the
majority of its plants. But although situated at the distance of between
500 and 600 miles from the S. American coast, it is impossible to even
glance at a large part of its fauna, especially at the birds, without at
once seeing that they belong to the American type{356}. Hence, in fact,
groups of islands thus circumstanced form merely small but well-defined
sub-divisions of the larger geographical divisions. But the fact is in
such cases far more striking: for taking the Galapagos Archipelago as an
instance; in the first place we must feel convinced, seeing that every
island is wholly volcanic and bristles with craters, that in a
geological sense the whole is of recent origin comparatively with a
continent; and as the species are nearly all peculiar, we must conclude
that they have in the same sense recently been produced on this very
spot; and although in the nature of the soil, and in a lesser degree in
the climate, there is a wide difference with the nearer part of the S.
American coast, we see that the inhabitants have been formed on the same
closely allied type. On the other hand, these islands, as far as their
physical conditions are concerned, resemble closely the Cape de Verde
volcanic group, and yet how wholly unlike are the productions of these
two archipelagoes. The Cape de Verde{357} group, to which may be added
the Canary Islands, are allied in their inhabitants (of which many are
peculiar species) to the coast of Africa and southern Europe, in
precisely the same manner as the Galapagos Archipelago is allied to
America. We here clearly see that mere geographical proximity affects,
more than any relation of adaptation, the character of species. How many
islands in the Pacific exist far more like in their physical conditions
to Juan Fernandez than this island is to the coast of Chile, distant 300
miles; why then, except from mere proximity, should this island alone be
tenanted by two very peculiar species of humming-birds--that form of
birds which is so exclusively American? Innumerable other similar cases
might be adduced.
{353} For the general problem of Oceanic Islands, see _Origin_, Ed.
i. p. 388, vi. p. 541.
{354} This is an illustration of the general theory of barriers
(_Origin_, Ed. i. p. 347, vi. p. 494). At i. p. 391, vi. p. 544 the
question is discussed from the point of view of means of transport.
Between the lines, above the words "with that land," the author
wrote "Cause, formerly joined, no one doubts after Lyell."
{355} _Origin_, Ed. i. p. 390, vi. p. 543.
{356} See _Origin_, Ed. i. p. 397, vi. p. 552.
{357} The Cape de Verde and Galapagos Archipelagoes are compared in
the _Origin_, Ed. i. p. 398, vi. p. 553. See also _Journal of
Researches_, 1860, p. 393.
The Galapagos Archipelago offers another, even more remarkable, example
of the class of facts we are here considering. Most of its genera are,
as we have said, American, many of them are mundane, or found
everywhere, and some are quite or nearly confined to this archipelago.
The islands are of absolutely similar composition, and exposed to the
same climate; most of them are in sight of each other; and yet several
of the islands are inhabited, each by peculiar species (or in some cases
perhaps only varieties) of some of the genera characterising the
archipelago. So that the small group of the Galapagos Islands typifies,
and follows exactly the same laws in the distribution of its
inhabitants, as a great continent. How wonderful it is that two or three
closely similar but distinct species of a mocking-thrush{358} should
have been produced on three neighbouring and absolutely similar islands;
and that these three species of mocking-thrush should be closely related
to the other species inhabiting wholly different climates and different
districts of America, and only in America. No similar case so striking
as this of the Galapagos Archipelago has hitherto been observed; and
this difference of the productions in the different islands may perhaps
be partly explained by the depth of the sea between them (showing that
they could not have been united within recent geological periods), and
by the currents of the sea sweeping _straight_ between them,--and by
storms of wind being rare, through which means seeds and birds could be
blown, or drifted, from one island to another. There are however some
similar facts: it is said that the different, though neighbouring
islands of the East Indian Archipelago are inhabited by some different
species of the same genera; and at the Sandwich group some of the
islands have each their peculiar species of the same genera of plants.
{358} In the _Origin_, Ed. i. p. 390, a strong point is made of
birds which immigrated "with facility and in a body" not having
been modified. Thus the author accounts for the small percentage of
peculiar "marine birds."
Islands standing quite isolated within the intra-tropical oceans have
generally very peculiar floras, related, though feebly (as in the case
of St Helena{359} where almost every species is distinct), with the
nearest continent: Tristan d'Acunha is feebly related, I believe, in its
plants, both to Africa and S. America, not by having species in common,
but by the genera to which they belong{360}. The floras of the numerous
scattered islands of the Pacific are related to each other and to all
the surrounding continents; but it has been said, that they have more of
an Indo-Asiatic than American character{361}. This is somewhat
remarkable, as America is nearer to all the Eastern islands, and lies in
the direction of the trade-wind and prevailing currents; on the other
hand, all the heaviest gales come from the Asiatic side. But even with
the aid of these gales, it is not obvious on the ordinary theory of
creation how the possibility of migration (without we suppose, with
extreme improbability, that each species with an Indo-Asiatic character
has actually travelled from the Asiatic shores, where such species do
not now exist) explains this Asiatic character in the plants of the
Pacific. This is no more obvious than that (as before remarked) there
should exist a relation between the creation of closely allied species
in several regions of the world, and the fact of many such species
having wide ranges; and on the other hand, of allied species confined to
one region of the world having in that region narrow ranges.
{359} "The affinities of the St Helena flora are strongly South
African." Hooker's _Lecture on Insular Floras_ in the _Gardeners'
Chronicle_, Jan. 1867.
{360} It is impossible to make out the precise form which the
author intended to give to this sentence, but the meaning is clear.
{361} This is no doubt true, the flora of the Sandwich group
however has marked American affinities.
_Alpine Floras._
We will now turn to the floras of mountain-summits which are well known
to differ from the floras of the neighbouring lowlands. In certain
characters, such as dwarfness of stature, hairiness, &c., the species
from the most distant mountains frequently resemble each other,--a kind
of analogy like that for instance of the succulency of most desert
plants. Besides this analogy, Alpine plants present some eminently
curious facts in their distribution. In some cases the summits of
mountains, although immensely distant from each other, are clothed by
the same identical species{362} which are likewise the same with those
growing on the likewise very distant Arctic shores. In other cases,
although few or none of the species may be actually identical, they are
closely related; whilst the plants of the lowland districts surrounding
the two mountains in question will be wholly dissimilar. As
mountain-summits, as far as their plants are concerned, are islands
rising out of an ocean of land in which the Alpine species cannot live,
nor across which is there any known means of transport, this fact
appears directly opposed to the conclusion which we have come to from
considering the general distribution of organisms both on continents and
on islands--namely, that the degree of relationship between the
inhabitants of two points depends on the completeness and nature of the
barriers between those points{363}. I believe, however, this anomalous
case admits, as we shall presently see, of some explanation. We might
have expected that the flora of a mountain summit would have presented
the same relation to the flora of the surrounding lowland country, which
any isolated part of a continent does to the whole, or an island does to
the mainland, from which it is separated by a rather wide space of sea.
This in fact is the case with the plants clothing the summits of _some_
mountains, which mountains it may be observed are particularly isolated;
for instance, all the species are peculiar, but they belong to the forms
characteristic of the surrounding continent, on the mountains of
Caraccas, of Van Dieman's Land and of the Cape of Good Hope{364}. On
some other mountains, for instance Tierra del Fuego and in Brazil,
some of the plants though distinct species are S. American forms; whilst
others are allied to or are identical with the Alpine species of Europe.
In islands of which the lowland flora is distinct but allied to
that of the nearest continent, the Alpine plants are sometimes (or
perhaps mostly) eminently peculiar and distinct{365}; this is the case
on Teneriffe, and in a lesser degree even on some of the Mediterranean
islands.
{362} See _Origin_, Ed. i. p. 365, vi. p. 515. The present
discussion was written before the publication of Forbes' celebrated
paper on the same subject; see _Life and Letters_, vol. I. p. 88.
{363} The apparent breakdown of the doctrine of barriers is
slightly touched on in the _Origin_, Ed. i. p. 365, vi. p. 515.
{364} In the _Origin_, Ed. i. p. 375, vi. p. 526, the author points
out that on the mountains at the Cape of Good Hope "some few
representative European forms are found, which have not been
discovered in the inter-tropical parts of Africa."
{365} See Hooker's _Lecture on Insular Floras_ in the _Gardeners'
Chronicle_, Jan. 1867.
If all Alpine floras had been characterised like that of the mountain of
Caraccas, or of Van Dieman's Land, &c., whatever explanation is possible
of the general laws of geographical distribution would have applied to
them. But the apparently anomalous case just given, namely of the
mountains of Europe, of some mountains in the United States (Dr Boott)
and of the summits of the Himalaya (Royle), having many identical
species in common conjointly with the Arctic regions, and many species,
though not identical, closely allied, require a separate explanation.
The fact likewise of several of the species on the mountains of Tierra
del Fuego (and in a lesser degree on the mountains of Brazil) not
belonging to American forms, but to those of Europe, though so immensely
remote, requires also a separate explanation.
_Cause of the similarity in the floras of some distant mountains._
Now we may with confidence affirm, from the number of the then floating
icebergs and low descent of the glaciers, that within a period so near
that species of shells have remained the same, the whole of Central
Europe and of North America (and perhaps of Eastern Asia) possessed a
very cold climate; and therefore it is probable that the floras of these
districts were the same as the present Arctic one,--as is known to have
been to some degree the case with then existing sea-shells, and those
now living on the Arctic shores. At this period the mountains must have
been covered with ice of which we have evidence in the surfaces polished
and scored by glaciers. What then would be the natural and almost
inevitable effects of the gradual change into the present more temperate
climate{366}? The ice and snow would disappear from the mountains, and
as new plants from the more temperate regions of the south migrated
northward, replacing the Arctic plants, these latter would crawl{367} up
the now uncovered mountains, and likewise be driven northward to the
present Arctic shores. If the Arctic flora of that period was a nearly
uniform one, as the present one is, then we should have the same plants
on these mountain-summits and on the present Arctic shores. On this view
the Arctic flora of that period must have been a widely extended one,
more so than even the present one; but considering how similar the
physical conditions must always be of land bordering on perpetual frost,
this does not appear a great difficulty; and may we not venture to
suppose that the almost infinitely numerous icebergs, charged with
great masses of rocks, soil and _brushwood_{368} and often driven high
up on distant beaches, might have been the means of widely distributing
the seeds of the same species?
{366} In the margin the author has written "(Forbes)." This may
have been inserted at a date later than 1844, or it may refer to a
work by Forbes earlier than his Alpine paper.
{367} See _Origin_, Ed. i. p. 367, vi. p. 517.
{368} Perhaps vitality checked by cold and so
prevented germinating.
I will only hazard one other observation, namely that during the change
from an extremely cold climate to a more temperate one the conditions,
both on lowland and mountain, would be singularly favourable for the
diffusion of any existing plants, which could live on land, just freed
from the rigour of eternal winter; for it would possess no inhabitants;
and we cannot doubt that _preoccupation_{369} is the chief bar to the
diffusion of plants. For amongst many other facts, how otherwise can we
explain the circumstance that the plants on the opposite, though
similarly constituted sides of a wide river in Eastern Europe (as I was
informed by Humboldt) should be widely different; across which river
birds, swimming quadrupeds and the wind must often transport seeds; we
can only suppose that plants already occupying the soil and freely
seeding check the germination of occasionally transported seeds.
{369} A note by the author gives "many authors" apparently as
authority for this statement.
At about the same period when icebergs were transporting boulders in N.
America as far as 36° south, where the cotton tree now grows in South
America, in latitude 42° (where the land is now clothed with forests
having an almost tropical aspect with the trees bearing epiphytes and
intertwined with canes), the same ice action was going on; is it not
then in some degree probable that at this period the whole tropical
parts of the two Americas possessed{370} (as Falconer asserts that
India did) a more temperate climate? In this case the Alpine plants of
the long chain of the Cordillera would have descended much lower and
there would have been a broad high-road{371} connecting those parts of
North and South America which were then frigid. As the present climate
supervened, the plants occupying the districts which now are become in
both hemispheres temperate and even semi-tropical must have been driven
to the Arctic and Antarctic{372} regions; and only a few of the loftiest
points of the Cordillera can have retained their former connecting
flora. The transverse chain of Chiquitos might perhaps in a similar
manner during the ice-action period have served as a connecting road
(though a broken one) for Alpine plants to become dispersed from the
Cordillera to the highlands of Brazil. It may be observed that some
(though not strong) reasons can be assigned for believing that at about
this same period the two Americas were not so thoroughly divided as they
now are by the West Indies and tableland of Mexico. I will only further
remark that the present most singularly close similarity in the
vegetation of the lowlands of Kerguelen's Land{373} and of Tierra del
Fuego (Hooker), though so far apart, may perhaps be explained by the
dissemination of seeds during this same cold period, by means of
icebergs, as before alluded to{374}.
{370} Opposite to this passage, in the margin, the author has
written:--"too hypothetical."
{371} The Cordillera is described as supplying a great line of
invasion in the _Origin_, Ed. i. p. 378.
{372} This is an approximation to the author's views on
trans-tropical migration (_Origin_, Ed. i. pp. 376-8). See
Thiselton-Dyer's interesting discussion in _Darwin and Modern
Science_, p. 304.
{373} See Hooker's _Lecture on Insular Floras_ in the _Gardeners'
Chronicle_, Jan. 1867.
{374} Similarity of flora of coral islands
easily explained.
Finally, I think we may safely grant from the foregoing facts and
reasoning that the anomalous similarity in the vegetation of certain
very distant mountain-summits is not in truth opposed to the conclusion
of the intimate relation subsisting between proximity in space (in
accordance with the means of transport in each class) and the degree of
affinity of the inhabitants of any two countries. In the case of several
quite isolated mountains, we have seen that the general law holds good.
_Whether the same species has been created more than once._
As the fact of the same species of plants having been found on
mountain-summits immensely remote has been one chief cause of the belief
of some species having been contemporaneously produced or created at two
different points{375}, I will here briefly discuss this subject. On the
ordinary theory of creation, we can see no reason why on two similar
mountain-summits two similar species may not have been created; but the
opposite view, independently of its simplicity, has been generally
received from the analogy of the general distribution of all organisms,
in which (as shown in this chapter) we almost always find that great and
continuous barriers separate distinct series; and we are naturally led
to suppose that the two series have been separately created. When taking
a more limited view we see a river, with a quite similar country on both
sides, with one side well stocked with a certain animal and on the other
side not one (as is the case with the Bizcacha{376} on the opposite
sides of the Plata), we are at once led to conclude that the Bizcacha
was produced on some one point or area on the western side of the
river. Considering our ignorance of the many strange chances of
diffusion by birds (which occasionally wander to immense distances) and
quadrupeds swallowing seeds and ova (as in the case of the flying
water-beetle which disgorged the eggs of a fish), and of whirlwinds
carrying seeds and animals into strong upper currents (as in the case of
volcanic ashes and showers of hay, grain and fish{377}), and of the
possibility of species having survived for short periods at intermediate
spots and afterwards becoming extinct there{378}; and considering our
knowledge of the great changes which _have_ taken place from subsidence
and elevation in the surface of the earth, and of our ignorance of the
greater changes which _may have_ taken place, we ought to be very slow
in admitting the probability of double creations. In the case of plants
on mountain-summits, I think I have shown how almost necessarily they
would, under the past conditions of the northern hemisphere, be as
similar as are the plants on the present Arctic shores; and this ought
to teach us a lesson of caution.
{375} On centres of creation see _Origin_, Ed. i. p. 352, vi. p.
499.
{376} In the _Journal of Researches_, Ed. 1860, p. 124, the
distribution of the Bizcacha is described as limited by the river
Uruguay. The case is not I think given in the _Origin_.
{377} In the _Origin_, Ed. i. a special section (p. 356, vi. p.
504) is devoted to _Means of Dispersal_. The much greater
prominence given to this subject in the _Origin_ is partly
accounted for by the author's experiments being of later date,
_i.e._ 1855 (_Life and Letters_, vol. II. p. 53). The carriage of
fish by whirlwinds is given in the _Origin_, Ed. i. p. 384, vi. p.
536.
{378} The case of islands serving as halting places is given in the
_Origin_, Ed. i. p. 357, vi. p. 505. But here the evidence of this
having occurred is supposed to be lost by the subsidence of the
islands, not merely by the extinction of the species.
But the strongest argument against double creations may be drawn from
considering the case of mammifers{379} in which, from their nature and
from the size of their offspring, the means of distribution are more in
view. There are no cases where the same species is found in _very
remote_ localities, except where there is a continuous belt of land:
the Arctic region perhaps offers the strongest exception, and here we
know that animals are transported on icebergs{380}. The cases of lesser
difficulty may all receive a more or less simple explanation; I will
give only one instance; the nutria{381}, I believe, on the eastern coast
of S. America live exclusively in fresh-water rivers, and I was much
surprised how they could have got into rivulets, widely apart, on the
coast of Patagonia; but on the opposite coast I found these quadrupeds
living exclusively in the sea, and hence their migration along the
Patagonian coast is not surprising. There is no case of the same
mammifer being found on an island far from the coast, and on the
mainland, as happens with plants{382}. On the idea of double creations
it would be strange if the same species of several plants should have
been created in Australia and Europe; and no one instance of the same
species of mammifer having been created, or aboriginally existing, in
two as nearly remote and equally isolated points. It is more
philosophical, in such cases, as that of some plants being found in
Australia and Europe, to admit that we are ignorant of the means of
transport. I will allude only to one other case, namely, that of the
Mydas{383}, an Alpine animal, found only on the distant peaks of the
mountains of Java: who will pretend to deny that during the ice period
of the northern and southern hemispheres, and when India is believed to
have been colder, the climate might not have permitted this animal to
haunt a lower country, and thus to have passed along the ridges from
summit to summit? Mr Lyell has further observed that, _as in space, so
in time_, there is no reason to believe that after the extinction of a
species, the self-same form has ever reappeared{384}. I think, then, we
may, notwithstanding the many cases of difficulty, conclude with some
confidence that every species has been created or produced on a single
point or area.
{379} "We find no inexplicable cases of the same mammal inhabiting
distant points of the world." _Origin_, Ed. i. p. 352, vi. p. 500.
See also _Origin_, Ed. i. p. 393, vi. p. 547.
{380} Many authors.
{381} _Nutria_ is the Spanish for otter, and is now a synonym for
_Lutra_. The otter on the Atlantic coast is distinguished by minute
differences from the Pacific species. Both forms are said to take
to the sea. In fact the case presents no especial difficulties.
{382} In _Origin_, Ed. i. p. 394, vi. p. 548, bats are mentioned as
an explicable exception to this statement.
{383} This reference is doubtless to _Mydaus_, a badger-like animal
from the mountains of Java and Sumatra (Wallace, _Geographical
Distribution_, ii. p. 199). The instance does not occur in the
_Origin_ but the author remarks (_Origin_, Ed. i. p. 376, vi. p.
527) that cases, strictly analogous to the distribution of plants,
occur among terrestrial mammals.
{384} See _Origin_, Ed. i. p. 313, vi. p. 454.
_On the number of species, and of the classes to which they belong in
different regions._
The last fact in geographical distribution, which, as far as I can see,
in any way concerns the origin of species, relates to the absolute
number and nature of the organic beings inhabiting different tracts of
land. Although every species is admirably adapted (but not necessarily
better adapted than every other species, as we have seen in the great
increase of introduced species) to the country and station it frequents;
yet it has been shown that the entire difference between the species in
distant countries cannot possibly be explained by the difference of the
physical conditions of these countries. In the same manner, I believe,
neither the number of the species, nor the nature of the great classes
to which they belong, can possibly in all cases be explained by the
conditions of their country. New Zealand{385}, a linear island
stretching over about 700 miles of latitude, with forests, marshes,
plains and mountains reaching to the limits of eternal snow, has far
more diversified habitats than an equal area at the Cape of Good Hope;
and yet, I believe, at the Cape of Good Hope there are, of phanerogamic
plants, from five to ten times the number of species as in all New
Zealand. Why on the theory of absolute creations should this large and
diversified island only have from 400 to 500 (? Dieffenbach)
phanerogamic plants? and why should the Cape of Good Hope, characterised
by the uniformity of its scenery, swarm with more species of plants than
probably any other quarter of the world? Why on the ordinary theory
should the Galapagos Islands abound with terrestrial reptiles? and why
should many equal-sized islands in the Pacific be without a single
one{386} or with only one or two species? Why should the great island of
New Zealand be without one mammiferous quadruped except the mouse, and
that was probably introduced with the aborigines? Why should not one
island (it can be shown, I think, that the mammifers of Mauritius and St
Iago have all been introduced) in the open ocean possess a mammiferous
quadruped? Let it not be said that quadrupeds cannot live in islands,
for we know that cattle, horses and pigs during a long period have run
wild in the West Indian and Falkland Islands; pigs at St Helena; goats
at Tahiti; asses in the Canary Islands; dogs in Cuba; cats at Ascension;
rabbits at Madeira and the Falklands; monkeys at St Iago and the
Mauritius; even elephants during a long time in one of the very small
Sooloo Islands; and European mice on very many of the smallest islands
far from the habitations of man{387}. Nor let it be assumed that
quadrupeds are more slowly created and hence that the oceanic islands,
which generally are of volcanic formation, are of too recent origin to
possess them; for we know (Lyell) that new forms of quadrupeds succeed
each other quicker than Mollusca or Reptilia. Nor let it be assumed
(though such an assumption would be no explanation) that quadrupeds
cannot be created on small islands; for islands not lying in mid-ocean
do possess their peculiar quadrupeds; thus many of the smaller islands
of the East Indian Archipelago possess quadrupeds; as does Fernando Po
on the West Coast of Africa; as the Falkland Islands possess a peculiar
wolf-like fox{388}; so do the Galapagos Islands a peculiar mouse of the
S. American type. These two last are the most remarkable cases with
which I am acquainted; inasmuch as the islands lie further from other
land. It is possible that the Galapagos mouse may have been introduced
in some ship from the S. American coast (though the species is at
present unknown there), for the aboriginal species soon haunts the goods
of man, as I noticed in the roof of a newly erected shed in a desert
country south of the Plata. The Falkland Islands, though between 200 and
300 miles from the S. American coast, may in one sense be considered as
intimately connected with it; for it is certain that formerly many
icebergs loaded with boulders were stranded on its southern coast, and
the old canoes which are occasionally now stranded, show that the
currents still set from Tierra del Fuego. This fact, however, does not
explain the presence of the _Canis antarcticus_ on the Falkland Islands,
unless we suppose that it formerly lived on the mainland and became
extinct there, whilst it survived on these islands, to which it was
borne (as happens with its northern congener, the common wolf) on an
iceberg, but this fact removes the anomaly of an island, in appearance
effectually separated from other land, having its own species of
quadruped, and makes the case like that of Java and Sumatra, each having
their own rhinoceros.
{385} The comparison between New Zealand and the Cape is given in
the _Origin_, Ed. i. p. 389, vi. p. 542.
{386} In a corresponding discussion in the _Origin_, Ed. i. p. 393,
vi. p. 546, stress is laid on the distribution of Batrachians not
of reptiles.
{387} The whole argument is given--more briefly than here--in the
_Origin_, Ed. i. p. 394, vi. p. 547.
{388} See _Origin_, Ed i. p. 393, vi. p. 547. The discussion is
much fuller in the present Essay.
Before summing up all the facts given in this section on the present
condition of organic beings, and endeavouring to see how far they admit
of explanation, it will be convenient to state all such facts in the
past geographical distribution of extinct beings as seem anyway to
concern the theory of descent.
SECTION SECOND.
_Geographical distribution of extinct organisms._
I have stated that if the land of the entire world be divided into (we
will say) three sections, according to the amount of difference of the
terrestrial mammifers inhabiting them, we shall have three unequal
divisions of (1st) Australia and its dependent islands, (2nd) South
America, (3rd) Europe, Asia and Africa. If we now look to the mammifers
which inhabited these three divisions during the later Tertiary periods,
we shall find them almost as distinct as at the present day, and
intimately related in each division to the existing forms in that
division{389}. This is wonderfully the case with the several fossil
Marsupial genera in the caverns of New South Wales and even more
wonderfully so in South America, where we have the same peculiar group
of monkeys, of a guanaco-like animal, of many rodents, of the Marsupial
Didelphys, of Armadilloes and other Edentata. This last family is at
present very characteristic of S. America, and in a late Tertiary epoch
it was even more so, as is shown by the numerous enormous animals of the
Megatheroid family, some of which were protected by an osseous armour
like that, but on a gigantic scale, of the recent Armadillo. Lastly,
over Europe the remains of the several deer, oxen, bears, foxes,
beavers, field-mice, show a relation to the present inhabitants of this
region; and the contemporaneous remains of the elephant, rhinoceros,
hippopotamus, hyæna, show a relation with the grand Africo-Asiatic
division of the world. In Asia the fossil mammifers of the Himalaya
(though mingled with forms long extinct in Europe) are equally related
to the existing forms of the Africo-Asiatic division; but especially to
those of India itself. As the gigantic and now extinct quadrupeds of
Europe have naturally excited more attention than the other and smaller
remains, the relation between the past and the present mammiferous
inhabitants of Europe has not been sufficiently attended to. But in fact
the mammifers of Europe are at present nearly as much Africo-Asiatic as
they were formerly when Europe had its elephants and rhinoceroses, etc.;
Europe neither now nor then possessed peculiar groups as does Australia
and S. America. The extinction of certain peculiar forms in one quarter
does not make the remaining mammifers of that quarter less related to
its own great division of the world: though Tierra del Fuego possesses
only a fox, three rodents, and the guanaco, no one (as these all belong
to S. American types, but not to the most characteristic forms) would
doubt for one minute classifying this district with S. America;
and if fossil Edentata, Marsupials and monkeys were to be found in
Tierra del Fuego, it would not make this district more truly S. American
than it now is. So it is with Europe{390}, and so far as is known with
Asia, for the lately past and present mammifers all belong to the
Africo-Asiatic division of the world. In every case, I may add, the
forms which a country has is of more importance in geographical
arrangement than what it has not.
{389} See _Origin_, Ed. i. p. 339, vi. p. 485.
{390} In the _Origin_, Ed. i. p. 339, vi. p. 485, which corresponds
to this part of the present Essay, the author does not make a
separate section for such cases as the occurrence of fossil
Marsupials in Europe (_Origin_, Ed. i. p. 340, vi. p. 486) as he
does in the present Essay; see the section on _Changes in
geographical distribution_, p. 177.
We find some evidence of the same general fact in a relation between the
recent and the Tertiary sea-shells, in the different main divisions of
the marine world.
This general and most remarkable relation between the lately past and
present mammiferous inhabitants of the three main divisions of the world
is precisely the same kind of fact as the relation between the different
species of the several sub-regions of any one of the main divisions. As
we usually associate great physical changes with the total extinction of
one series of beings, and its succession by another series, this
identity of relation between the past and the present races of beings in
the same quarters of the globe is more striking than the same relation
between existing beings in different sub-regions: but in truth we have
no reason for supposing that a change in the conditions has in any of
these cases supervened, greater than that now existing between the
temperate and tropical, or between the highlands and lowlands of the
same main divisions, now tenanted by related beings. Finally, then, we
clearly see that in each main division of the world the same relation
holds good between its inhabitants in time as over space{391}.
{391} "We can understand how it is that all the forms of life,
ancient and recent, make together one grand system; for all are
connected by generation." _Origin_, Ed. i. p. 344, vi. p. 491.
_Changes in geographical distribution._
If, however, we look closer, we shall find that even Australia, in
possessing a terrestrial Pachyderm, was so far less distinct from the
rest of the world than it now is; so was S. America in possessing the
Mastodon, horse, [hyæna,]{392} and antelope. N. America, as I have
remarked, is now, in its mammifers, in some respects neutral ground
between S. America and the great Africo-Asiatic division; formerly, in
possessing the horse, Mastodon and three Megatheroid animals, it was
more nearly related to S. America; but in the horse and Mastodon, and
likewise in having the elephant, oxen, sheep, and pigs, it was as much,
if not more, related to the Africo-Asiatic division. Again, northern
India was much more closely related (in having the giraffe,
hippopotamus, and certain musk-deer) to southern Africa than it now is;
for southern and eastern Africa deserve, if we divide the world into
five parts, to make one division by itself. Turning to the dawn of the
Tertiary period, we must, from our ignorance of other portions of the
world, confine ourselves to Europe; and at that period, in the presence
of Marsupials{393} and Edentata, we behold an _entire_ blending of those
mammiferous forms which now eminently characterise Australia and S.
America{394}.
{392} The word _hyæna_ is erased. There appear to be no fossil
Hyænidæ in S. America.
{393} See note 1{390}, p. 175, also _Origin_, Ed. i. p. 340, vi. p. 486.
{394} And see Eocene European mammals in
N. America.
If we now look at the distribution of sea-shells, we find the same
changes in distribution. The Red Sea and the Mediterranean were more
nearly related in these shells than they now are. In different parts of
Europe, on the other hand, during the Miocene period, the sea-shells
seem to have been more different than at present. In{395} the Tertiary
period, according to Lyell, the shells of N. America and Europe were
less related than at present, and during the Cretaceous still less like;
whereas, during this same Cretaceous period, the shells of India and
Europe were more like than at present. But going further back to the
Carbonaceous period, in N. America and Europe, the productions were much
more like than they now are{396}. These facts harmonise with the
conclusions drawn from the present distribution of organic beings, for
we have seen, that from species being created in different points or
areas, the formation of a barrier would cause or make two distinct
geographical areas; and the destruction of a barrier would permit their
diffusion{397}. And as long-continued geological changes must both
destroy and make barriers, we might expect, the further we looked
backwards, the more changed should we find the present distribution.
This conclusion is worthy of attention; because, finding in widely
different parts of the same main division of the world, and in volcanic
islands near them, groups of distinct, but related, species;--and
finding that a singularly analogous relation holds good with respect to
the beings of past times, when none of the present species were living,
a person might be tempted to believe in some mystical relation between
certain areas of the world, and the production of certain organic forms;
but we now see that such an assumption would have to be complicated by
the admission that such a relation, though holding good for long
revolutions of years, is not truly persistent.
{395} All this requires much verification.
{396} This point seems to be less insisted on in the _Origin_.
{397} _Origin_, Ed. i. p. 356, vi. p. 504.
I will only add one more observation to this section. Geologists
finding in the most remote period with which we are acquainted, namely
in the Silurian period, that the shells and other marine
productions{398} in North and South America, in Europe, Southern Africa,
and Western Asia, are much more similar than they now are at these
distant points, appear to have imagined that in these ancient times the
laws of geographical distribution were quite different than what they
now are: but we have only to suppose that great continents were extended
east and west, and thus did not divide the inhabitants of the temperate
and tropical seas, as the continents now do; and it would then become
probable that the inhabitants of the seas would be much more similar
than they now are. In the immense space of ocean extending from the east
coast of Africa to the eastern islands of the Pacific, which space is
connected either by lines of tropical coast or by islands not very
distant from each other, we know (Cuming) that many shells, perhaps even
as many as 200, are common to the Zanzibar coast, the Philippines, and
the eastern islands of the Low or Dangerous Archipelago in the Pacific.
This space equals that from the Arctic to the Antarctic pole! Pass over
the space of quite open ocean, from the Dangerous Archipelago to the
west coast of S. America, and every shell is different: pass over the
narrow space of S. America, to its eastern shores, and again every shell
is different! Many fish, I may add, are also common to the Pacific and
Indian Oceans.
{398} D'Orbigny shows that this is not so.
_Summary on the distribution of living and extinct organic beings._
Let us sum up the several facts now given with respect to the past and
present geographical distribution of organic beings. In a previous
chapter it was shown that species are not exterminated by universal
catastrophes, and that they are slowly produced: we have also seen that
each species is probably only once produced, on one point or area once
in time; and that each diffuses itself, as far as barriers and its
conditions of life permit. If we look at any one main division of the
land, we find in the different parts, whether exposed to different
conditions or to the same conditions, many groups of species wholly or
nearly distinct as species, nevertheless intimately related. We find the
inhabitants of islands, though distinct as species, similarly related to
the inhabitants of the nearest continent; we find in some cases, that
even the different islands of one such group are inhabited by species
distinct, though intimately related to one another and to those of the
nearest continent:--thus typifying the distribution of organic beings
over the whole world. We find the floras of distant mountain-summits
either very similar (which seems to admit, as shown, of a simple
explanation) or very distinct but related to the floras of the
surrounding region; and hence, in this latter case, the floras of two
mountain-summits, although exposed to closely similar conditions, will
be very different. On the mountain-summits of islands, characterised by
peculiar faunas and floras, the plants are often eminently peculiar. The
dissimilarity of the organic beings inhabiting nearly similar countries
is best seen by comparing the main divisions of the world; in each of
which some districts may be found very similarly exposed, yet the
inhabitants are wholly unlike;--far more unlike than those in very
dissimilar districts in the same main division. We see this strikingly
in comparing two volcanic archipelagoes, with nearly the same climate,
but situated not very far from two different continents; in which case
their inhabitants are totally unlike. In the different main divisions of
the world, the amount of difference between the organisms, even in the
same class, is widely different, each main division having only the
species distinct in some families, in other families having the genera
distinct. The distribution of aquatic organisms is very different from
that of the terrestrial organisms; and necessarily so, from the barriers
to their progress being quite unlike. The nature of the conditions in an
isolated district will not explain the number of species inhabiting it;
nor the absence of one class or the presence of another class. We find
that terrestrial mammifers are not present on islands far removed from
other land. We see in two regions, that the species though distinct are
more or less related, according to the greater or less _possibility_ of
the transportal in past and present times of species from one to the
other region; although we can hardly admit that all the species in such
cases have been transported from the first to the second region, and
since have become extinct in the first: we see this law in the presence
of the fox on the Falkland Islands; in the European character of some of
the plants of Tierra del Fuego; in the Indo-Asiatic character of the
plants of the Pacific; and in the circumstance of those genera which
range widest having many species with wide ranges; and those genera with
restricted ranges having species with restricted ranges. Finally, we
find in each of the main divisions of the land, and probably of the sea,
that the existing organisms are related to those lately extinct.
Looking further backwards we see that the past geographical distribution
of organic beings was different from the present; and indeed,
considering that geology shows that all our land was once under water,
and that where water now extends land is forming, the reverse could
hardly have been possible.
Now these several facts, though evidently all more or less connected
together, must by the creationist (though the geologist may explain some
of the anomalies) be considered as so many ultimate facts. He can only
say, that it so pleased the Creator that the organic beings of the
plains, deserts, mountains, tropical and temperature forests, of S.
America, should all have some affinity together; that the inhabitants of
the Galapagos Archipelago should be related to those of Chile; and that
some of the species on the similarly constituted islands of this
archipelago, though most closely related, should be distinct; that all
its inhabitants should be totally unlike those of the similarly volcanic
and arid Cape de Verde and Canary Islands; that the plants on the summit
of Teneriffe should be eminently peculiar; that the diversified island
of New Zealand should have not many plants, and not one, or only one,
mammifer; that the mammifers of S. America, Australia and Europe should
be clearly related to their ancient and exterminated prototypes; and so
on with other facts. But it is absolutely opposed to every analogy,
drawn from the laws imposed by the Creator on inorganic matter, that
facts, when connected, should be considered as ultimate and not the
direct consequences of more general laws.
SECTION THIRD.
_An attempt to explain the foregoing laws of geographical distribution,
on the theory of allied species having a common descent._
First let us recall the circumstances most favourable for variation
under domestication, as given in the first chapter--viz. 1st, a change,
or repeated changes, in the conditions to which the organism has been
exposed, continued through several seminal (_i.e._ not by buds or
divisions) generations: 2nd, steady selection of the slight varieties
thus generated with a fixed end in view: 3rd, isolation as perfect as
possible of such selected varieties; that is, the preventing their
crossing with other forms; this latter condition applies to all
terrestrial animals, to most if not all plants and perhaps even to most
(or all) aquatic organisms. It will be convenient here to show the
advantage of isolation in the formation of a new breed, by comparing the
progress of two persons (to neither of whom let time be of any
consequence) endeavouring to select and form some very peculiar new
breed. Let one of these persons work on the vast herds of cattle in the
plains of La Plata{399}, and the other on a small stock of 20 or 30
animals in an island. The latter might have to wait centuries (by the
hypothesis of no importance){400} before he obtained a "sport"
approaching to what he wanted; but when he did and saved the greater
number of its offspring and their offspring again, he might hope that
his whole little stock would be in some degree affected, so that by
continued selection he might gain his end. But on the Pampas, though
the man might get his first approach to his desired form sooner, how
hopeless would it be to attempt, by saving its offspring amongst so many
of the common kind, to affect the whole herd: the effect of this one
peculiar "sport{401}" would be quite lost before he could obtain a
second original sport of the same kind. If, however, he could separate a
small number of cattle, including the offspring of the desirable
"sport," he might hope, like the man on the island, to effect his end.
If there be organic beings of which two individuals _never_ unite, then
simple selection whether on a continent or island would be equally
serviceable to make a new and desirable breed; and this new breed might
be made in surprisingly few years from the great and geometrical powers
of propagation to beat out the old breed; as has happened
(notwithstanding crossing) where good breeds of dogs and pigs have been
introduced into a limited country,--for instance, into the islands of
the Pacific.
{399} This instance occurs in the Essay of 1842, p. 32, but not in
the _Origin_; though the importance of isolation is discussed
(_Origin_, Ed. i. p. 104, vi. p. 127).
{400} The meaning of the words within parenthesis is obscure.
{401} It is unusual to find the author speaking of the selection of
_sports_ rather than small variations.
Let us now take the simplest natural case of an islet upheaved by the
volcanic or subterranean forces in a deep sea, at such a distance from
other land that only a few organic beings at rare intervals were
transported to it, whether borne by the sea{402} (like the seeds of
plants to coral-reefs), or by hurricanes, or by floods, or on rafts, or
in roots of large trees, or the germs of one plant or animal attached to
or in the stomach of some other animal, or by the intervention (in most
cases the most probable means) of other islands since sunk or destroyed.
It may be remarked that when one part of the earth's crust is raised it
is probably the general rule that another part sinks. Let this island
go on slowly, century after century, rising foot by foot; and in the
course of time we shall have instead a small mass of rock{403},
lowland and highland, moist woods and dry sandy spots, various soils,
marshes, streams and pools: under water on the sea shore, instead of a
rocky steeply shelving coast, we shall have in some parts bays with mud,
sandy beaches and rocky shoals. The formation of the island by itself
must often slightly affect the surrounding climate. It is impossible
that the first few transported organisms could be perfectly adapted to
all these stations; and it will be a chance if those successively
transported will be so adapted. The greater number would probably come
from the lowlands of the nearest country; and not even all these would
be perfectly adapted to the new islet whilst it continued low and
exposed to coast influences. Moreover, as it is certain that all
organisms are nearly as much adapted in their structure to the other
inhabitants of their country as they are to its physical conditions, so
the mere fact that a _few_ beings (and these taken in great degree by
chance) were in the first case transported to the islet, would in itself
greatly modify their conditions{404}. As the island continued rising we
might also expect an occasional new visitant; and I repeat that even one
new being must often affect beyond our calculation by occupying the room
and taking part of the subsistence of another (and this again from
another and so on), several or many other organisms. Now as the first
transported and any occasional successive visitants spread or tended to
spread over the growing island, they would undoubtedly be exposed
through several generations to new and varying conditions: it might also
easily happen that some of the species _on an average_ might obtain an
increase of food, or food of a more nourishing quality{405}. According
then to every analogy with what we have seen takes place in every
country, with nearly every organic being under domestication, we might
expect that some of the inhabitants of the island would "sport," or have
their organization rendered in some degree plastic. As the number of the
inhabitants are supposed to be few and as all these cannot be so well
adapted to their new and varying conditions as they were in their native
country and habitat, we cannot believe that every place or office in the
economy of the island would be as well filled as on a continent where
the number of aboriginal species is far greater and where they
consequently hold a more strictly limited place. We might therefore
expect on our island that although very many slight variations were of
no use to the plastic individuals, yet that occasionally in the course
of a century an individual might be born{406} of which the structure or
constitution in some slight degree would allow it better to fill up some
office in the insular economy and to struggle against other species. If
such were the case the individual and its offspring would have a better
_chance_ of surviving and of beating out its parent form; and if (as is
probable) it and its offspring crossed with the unvaried parent form,
yet the number of the individuals being not very great, there would be a
chance of the new and more serviceable form being nevertheless in some
slight degree preserved. The struggle for existence would go on annually
selecting such individuals until a new race or species was formed.
Either few or all the first visitants to the island might become
modified, according as the physical conditions of the island and those
resulting from the kind and number of other transported species were
different from those of the parent country--according to the
difficulties offered to fresh immigration--and according to the length
of time since the first inhabitants were introduced. It is obvious that
whatever was the country, generally the nearest from which the first
tenants were transported, they would show an affinity, even if all had
become modified, to the natives of that country and even if the
inhabitants of the same source (?) had been modified. On this view we
can at once understand the cause and meaning of the affinity of the
fauna and flora of the Galapagos Islands with that of the coast of S.
America; and consequently why the inhabitants of these islands show not
the smallest affinity with those inhabiting other volcanic islands, with
a very similar climate and soil, near the coast of Africa{407}.
{402} This brief discussion is represented in the _Origin_, Ed. i.
by a much fuller one (pp. 356, 383, vi. pp. 504, 535). See,
however, the section in the present Essay, p. 168.
{403} On the formation of new stations, see _Origin_, Ed. i. p.
292, vi. p. 429.
{404} _Origin_, Ed. i. pp. 390, 400, vi. pp. 543, 554.
{405} In the MS. _some of the species ... nourishing quality_ is
doubtfully erased. It seems clear that he doubted whether such a
problematical supply of food would be likely to cause variation.
{406} At this time the author clearly put more faith in the
importance of sport-like variation than in later years.
{407} _Origin_, Ed. i. p. 398, vi. p. 553.
To return once again to our island, if by the continued action of the
subterranean forces other neighbouring islands were formed, these would
generally be stocked by the inhabitants of the first island, or by a few
immigrants from the neighbouring mainland; but if considerable obstacles
were interposed to any communication between the terrestrial productions
of these islands, and their conditions were different (perhaps only by
the number of different species on each island), a form transported from
one island to another might become altered in the same manner as one
from the continent; and we should have several of the islands tenanted
by representative races or species, as is so wonderfully the case with
the different islands of the Galapagos Archipelago. As the islands
become mountainous, if mountain-species were not introduced, as could
rarely happen, a greater amount of variation and selection would be
requisite to adapt the species, which originally came from the lowlands
of the nearest continent, to the mountain-summits than to the lower
districts of our islands. For the lowland species from the continent
would have first to struggle against other species and other conditions
on the coast-land of the island, and so probably become modified by the
selection of its best fitted varieties, then to undergo the same process
when the land had attained a moderate elevation; and then lastly when it
had become Alpine. Hence we can understand why the faunas of insular
mountain-summits are, as in the case of Teneriffe, eminently peculiar.
Putting on one side the case of a widely extended flora being driven up
the mountain-summits, during a change of climate from cold to temperate,
we can see why in other cases the floras of mountain-summits (or as I
have called them islands in a sea of land) should be tenanted by
peculiar species, but related to those of the surrounding lowlands, as
are the inhabitants of a real island in the sea to those of the nearest
continent{408}.
{408} See _Origin_, Ed. i. p. 403, vi. p. 558, where the author
speaks of Alpine humming birds, rodents, plants, &c. in S. America,
all of strictly American forms. In the MS. the author has added
between the lines "As world has been getting hotter, there has been
radiation from high-lands,--old view?--curious; I presume Diluvian
in origin."
Let us now consider the effect of a change of climate or of other
conditions on the inhabitants of a continent and of an isolated island
without any great change of level. On a continent the chief effects
would be changes in the numerical proportion of the individuals of the
different species; for whether the climate became warmer or colder,
drier or damper, more uniform or extreme, some species are at present
adapted to its diversified districts; if for instance it became cooler,
species would migrate from its more temperate parts and from its higher
land; if damper, from its damper regions, &c. On a small and isolated
island, however, with few species, and these not adapted to much
diversified conditions, such changes instead of merely increasing the
number of certain species already adapted to such conditions, and
decreasing the number of other species, would be apt to affect the
constitutions of some of the insular species: thus if the island became
damper it might well happen that there were no species living in any
part of it adapted to the consequences resulting from more moisture. In
this case therefore, and still more (as we have seen) during the
production of new stations from the elevation of the land, an island
would be a far more fertile source, as far as we can judge, of new
specific forms than a continent. The new forms thus generated on an
island, we might expect, would occasionally be transported by accident,
or through long-continued geographical changes be enabled to emigrate
and thus become slowly diffused.
But if we look to the origin of a continent; almost every geologist will
admit that in most cases it will have first existed as separate islands
which gradually increased in size{409}; and therefore all that which has
been said concerning the probable changes of the forms tenanting a small
archipelago is applicable to a continent in its early state.
Furthermore, a geologist who reflects on the geological history of
Europe (the only region well known) will admit that it has been many
times depressed, raised and left stationary. During the sinking of a
continent and the probable generally accompanying changes of climate the
effect would be little, _except_ on the numerical proportions and in the
extinction (from the lessening of rivers, the drying of marshes and the
conversion of high-lands into low &c.) of some or of many of the
species. As soon however as the continent became divided into many
isolated portions or islands, preventing free immigration from one part
to another, the effect of climatic and other changes on the species
would be greater. But let the now broken continent, forming isolated
islands, begin to rise and new stations thus to be formed, exactly as in
the first case of the upheaved volcanic islet, and we shall have equally
favourable conditions for the modification of old forms, that is the
formation of new races or species. Let the islands become reunited into
a continent; and then the new and old forms would all spread, as far as
barriers, the means of transportal, and the preoccupation of the land by
other species, would permit. Some of the new species or races would
probably become extinct, and some perhaps would cross and blend
together. We should thus have a multitude of forms, adapted to all kinds
of slightly different stations, and to diverse groups of either
antagonist or food-serving species. The oftener these oscillations of
level had taken place (and therefore generally the older the land) the
greater the number of species would tend to be formed. The
inhabitants of a continent being thus derived in the first stage from
the same original parents, and subsequently from the inhabitants of one
wide area, since often broken up and reunited, all would be obviously
related together and the inhabitants of the most _dissimilar_ stations
on the same continent would be more closely allied than the inhabitants
of two very _similar_ stations on two of the main divisions of the
world{410}.
{409} See the comparison between the Malay Archipelago and the
probable former state of Europe, _Origin_, Ed. i. p. 299, vi. p.
438, also _Origin_, Ed. i. p. 292, vi. p. 429.
{410} _Origin_, Ed. i. p. 349, vi. p. 496. The arrangement of the
argument in the present Essay leads to repetition of statements
made in the earlier part of the book: in the _Origin_ this is
avoided.
I need hardly point out that we now can obviously see why the number of
species in two districts, independently of the number of stations in
such districts, should be in some cases as widely different as in New
Zealand and the Cape of Good Hope{411}. We can see, knowing the
difficulty in the transport of terrestrial mammals, why islands far from
mainlands do not possess them{412}; we see the general reason, namely
accidental transport (though not the precise reason), why certain
islands should, and others should not, possess members of the class of
reptiles. We can see why an ancient channel of communication between two
distant points, as the Cordillera probably was between southern Chile
and the United States during the former cold periods; and icebergs
between the Falkland Islands and Tierra del Fuego; and gales, at a
former or present time, between the Asiatic shores of the Pacific and
eastern islands in this ocean; is connected with (or we may now say
causes) an affinity between the species, though distinct, in two such
districts. We can see how the better chance of diffusion, from several
of the species of any genus having wide ranges in their own countries,
explains the presence of other species of the same genus in other
countries{413}; and on the other hand, of species of restricted powers
of ranging, forming genera with restricted ranges.
{411} _Origin_, Ed. i. p. 389, vi. p. 542.
{412} _Origin_, Ed. i. p. 393, vi. p. 547.
{413} _Origin_, Ed. i. pp. 350, 404, vi. pp. 498, 559.
As every one would be surprised if two exactly similar but peculiar
varieties{414} of any species were raised by man by long continued
selection, in two different countries, or at two very different periods,
so we ought not to expect that an exactly similar form would be produced
from the modification of an old one in two distinct countries or at two
distinct periods. For in such places and times they would probably be
exposed to somewhat different climates and almost certainly to different
associates. Hence we can see why each species appears to have been
produced singly, in space and in time. I need hardly remark that,
according to this theory of descent, there is no necessity of
modification in a species, when it reaches a new and isolated country.
If it be able to survive and if slight variations better adapted to the
new conditions are not selected, it might retain (as far as we can see)
its old form for an indefinite time. As we see that some sub-varieties
produced under domestication are more variable than others, so in
nature, perhaps, some species and genera are more variable than others.
The same precise form, however, would probably be seldom preserved
through successive geological periods, or in widely and differently
conditioned countries{415}.
{414} _Origin_, Ed. i. p. 352, vi. p. 500.
{415} _Origin_, Ed. i. p. 313, vi. p. 454.
Finally, during the long periods of time and probably of oscillations of
level, necessary for the formation of a continent, we may conclude (as
above explained) that many forms would become extinct. These extinct
forms, and those surviving (whether or not modified and changed in
structure), will all be related in each continent in the same manner and
degree, as are the inhabitants of any two different sub-regions in that
same continent. I do not mean to say that, for instance, the present
Marsupials of Australia or Edentata and rodents of S. America have
descended from any one of the few fossils of the same orders which have
been discovered in these countries. It is possible that, in a very few
instances, this may be the case; but generally they must be considered
as merely codescendants of common stocks{416}. I believe in this, from
the improbability, considering the vast number of species, which (as
explained in the last chapter) must by our theory have existed, that
the _comparatively_ few fossils which have been found should chance to
be the immediate and linear progenitors of those now existing. Recent as
the yet discovered fossil mammifers of S. America are, who will pretend
to say that very many intermediate forms may not have existed? Moreover,
we shall see in the ensuing chapter that the very existence of genera
and species can be explained only by a few species of each epoch leaving
modified successors or new species to a future period; and the more
distant that future period, the fewer will be the _linear_ heirs of the
former epoch. As by our theory, all mammifers must have descended from
the same parent stock, so is it necessary that each land now possessing
terrestrial mammifers shall at some time have been so far united to
other land as to permit the passage of mammifers{417}; and it accords
with this necessity, that in looking far back into the earth's history
we find, first changes in the geographical distribution, and secondly a
period when the mammiferous forms most distinctive of two of the present
main divisions of the world were living together{418}.
{416} _Origin_, Ed. i. p. 341, vi. p. 487.
{417} _Origin_, Ed. i. p. 396, vi. p. 549.
{418} _Origin_, Ed. i. p. 340, vi. p. 486.
I think then I am justified in asserting that most of the above
enumerated and often trivial points in the geographical distribution of
past and present organisms (which points must be viewed by the
creationists as so many ultimate facts) follow as a simple consequence
of specific forms being mutable and of their being adapted by natural
selection to diverse ends, conjoined with their powers of dispersal, and
the geologico-geographical changes now in slow progress and which
undoubtedly have taken place. This large class of facts being thus
explained, far more than counterbalances many separate difficulties and
apparent objections in convincing my mind of the truth of this theory of
common descent.
_Improbability of finding fossil forms intermediate between existing
species._
There is one observation of considerable importance that may be here
introduced, with regard to the improbability of the chief transitional
forms between any two species being found fossil. With respect to the
finer shades of transition, I have before remarked that no one has any
cause to expect to trace them in a fossil state, without he be bold
enough to imagine that geologists at a future epoch will be able to
trace from fossil bones the gradations between the Short-Horns,
Herefordshire, and Alderney breeds of cattle{419}. I have attempted to
show that rising islands, in process of formation, must be the best
nurseries of new specific forms, and these points are the least
favourable for the embedment of fossils{420}: I appeal, as evidence, to
the state of the _numerous_ scattered islands in the several great
oceans: how rarely do any sedimentary deposits occur on them; and when
present they are mere narrow fringes of no great antiquity, which the
sea is generally wearing away and destroying. The cause of this lies in
isolated islands being generally volcanic and rising points; and the
effects of subterranean elevation is to bring up the surrounding
newly-deposited strata within the destroying action of the coast-waves:
the strata, deposited at greater distances, and therefore in the depths
of the ocean, will be almost barren of organic remains. These remarks
may be generalised:--periods of subsidence will always be most
favourable to an accumulation of great thicknesses of strata, and
consequently to their long preservation; for without one formation be
protected by successive strata, it will seldom be preserved to a distant
age, owing to the enormous amount of denudation, which seems to be a
general contingent of time{421}. I may refer, as evidence of this
remark, to the vast amount of subsidence evident in the great pile of
the European formations, from the Silurian epoch to the end of the
Secondary, and perhaps to even a later period. Periods of elevation on
the other hand cannot be favourable to the accumulation of strata and
their preservation to distant ages, from the circumstance just alluded
to, viz. of elevation tending to bring to the surface the
circum-littoral strata (always abounding most in fossils) and destroying
them. The bottom of tracts of deep water (little favourable, however, to
life) must be excepted from this unfavourable influence of elevation. In
the quite open ocean, probably no sediment{422} is accumulating, or at a
rate so slow as not to preserve fossil remains, which will always be
subject to disintegration. Caverns, no doubt, will be equally likely to
preserve terrestrial fossils in periods of elevation and of subsidence;
but whether it be owing to the enormous amount of denudation, which all
land seems to have undergone, no cavern with fossil bones has been found
belonging to the Secondary period{423}.
{419} _Origin_, Ed. i. p. 299, vi. p. 437.
{420} "Nature may almost be said to have guarded against the
frequent discovery of her transitional or linking forms," _Origin_,
Ed. i. p. 292. A similar but not identical passage occurs in
_Origin_, Ed. vi. p. 428.
{421} _Origin_, Ed. i. p. 291, vi. p. 426.
{422} _Origin_, Ed. i. p. 288, vi. p. 422.
{423} _Origin_, Ed. i. p. 289, vi. p. 423.
Hence many more remains will be preserved to a distant age, in any
region of the world, during periods of its subsidence{424}, than of its
elevation.
{424} _Origin_, Ed. i. p. 300, vi. p. 439.
But during the subsidence of a tract of land, its inhabitants (as before
shown) will from the decrease of space and of the diversity of its
stations, and from the land being fully preoccupied by species fitted to
diversified means of subsistence, be little liable to modification from
selection, although many may, or rather must, become extinct. With
respect to its circum-marine inhabitants, although during a change from
a continent to a _great_ archipelago, the number of stations fitted for
marine beings will be increased, their means of diffusion (an important
check to change of form) will be greatly improved; for a continent
stretching north and south, or a quite open space of ocean, seems to be
to them the only barrier. On the other hand, during the elevation of a
small archipelago and its conversion into a continent, we have, whilst
the number of stations are increasing, both for aquatic and terrestrial
productions, and whilst these stations are not fully preoccupied by
perfectly adapted species, the most favourable conditions for the
selection of new specific forms; but few of them in their early
transitional states will be preserved to a distant epoch. We must wait
during an enormous lapse of time, until long-continued subsidence shall
have taken the place in this quarter of the world of the elevatory
process, for the best conditions of the embedment and the preservation
of its inhabitants. Generally the great mass of the strata in every
country, from having been chiefly accumulated during subsidence, will be
the tomb, not of transitional forms, but of those either becoming
extinct or remaining unmodified.
The state of our knowledge, and the slowness of the changes of level, do
not permit us to test the truth of these remarks, by observing whether
there are more transitional or "fine" (as naturalists would term them)
species, on a rising and enlarging tract of land, than on an area of
subsidence. Nor do I know whether there are more "fine" species on
isolated volcanic islands in process of formation, than on a continent;
but I may remark, that at the Galapagos Archipelago the number of forms,
which according to some naturalists are true species, and according to
others are mere races, is considerable: this particularly applies to the
different species or races of the same genera inhabiting the different
islands of this archipelago. Furthermore it may be added (as bearing on
the great facts discussed in this chapter) that when naturalists confine
their attention to any one country, they have comparatively little
difficulty in determining what forms to call species and what to call
varieties; that is, those which can or cannot be traced or shown to be
probably descendants of some other form: but the difficulty increases,
as species are brought from many stations, countries and islands. It was
this increasing (but I believe in few cases insuperable) difficulty
which seems chiefly to have urged Lamarck to the conclusion that species
are mutable.
CHAPTER VII
ON THE NATURE OF THE AFFINITIES AND CLASSIFICATION OF ORGANIC
BEINGS{425}
{425} Ch. XIII of the _Origin_, Ed. i., Ch. XIV Ed. vi. begins with
a similar statement. In the present Essay the author adds a
note:--"The obviousness of the fact (_i.e._ the natural grouping of
organisms) alone prevents it being remarkable. It is scarcely
explicable by creationist: groups of aquatic, of vegetable feeders
and carnivorous, &c., might resemble each other; but why as it is.
So with plants,--analogical resemblance thus accounted for. Must
not here enter into details." This argument is incorporated with
the text in the _Origin_, Ed. i.
_Gradual appearance and disappearance of groups._
It has been observed from the earliest times that organic beings fall
into groups{426}, and these groups into others of several values, such
as species into genera, and then into sub-families, into families,
orders, &c. The same fact holds with those beings which no longer exist.
Groups of species seem to follow the same laws in their appearance and
extinction{427}, as do the individuals of any one species: we have
reason to believe that, first, a few species appear, that their numbers
increase; and that, when tending to extinction, the numbers of the
species decrease, till finally the group becomes extinct, in the same
way as a species becomes extinct, by the individuals becoming rarer and
rarer. Moreover, groups, like the individuals of a species, appear to
become extinct at different times in different countries. The
Palæotherium was extinct much sooner in Europe than in India: the
Trigonia{428} was extinct in early ages in Europe, but now lives in the
seas of Australia. As it happens that one species of a family will
endure for a much longer period than another species, so we find that
some whole groups, such as Mollusca, tend to retain their forms, or to
remain persistent, for longer periods than other groups, for instance
than the Mammalia. Groups therefore, in their appearance, extinction,
and rate of change or succession, seem to follow nearly the same laws
with the individuals of a species{429}.
{426} _Origin_, Ed. i. p. 411, vi. p. 566.
{427} _Origin_, Ed. i. p. 316, vi. p. 457.
{428} _Origin_, Ed. i. p. 321, vi. p. 463.
{429} In the _Origin_, Ed. i. this preliminary matter is replaced
(pp. 411, 412, vi. pp. 566, 567) by a discussion in which
extinction is also treated, but chiefly from the point of view of
the theory of divergence.
_What is the Natural System?_
The proper arrangement of species into groups, according to the natural
system, is the object of all naturalists; but scarcely two naturalists
will give the same answer to the question, What is the natural system
and how are we to recognise it? The most important characters{430} it
might be thought (as it was by the earliest classifiers) ought to be
drawn from those parts of the structure which determine its habits and
place in the economy of nature, which we may call the final end of its
existence. But nothing is further from the truth than this; how much
external resemblance there is between the little otter (Chironectes) of
Guiana and the common otter; or again between the common swallow and the
swift; and who can doubt that the means and ends of their existence are
closely similar, yet how grossly wrong would be the classification,
which put close to each other a Marsupial and Placental animal, and two
birds with widely different skeletons. Relations, such as in the two
latter cases, or as that between the whale and fishes, are denominated
"analogical{431}," or are sometimes described as "relations of
adaption." They are infinitely numerous and often very singular; but are
of no use in the classification of the higher groups. How it comes, that
certain parts of the structure, by which the habits and functions of the
species are settled, are of no use in classification, whilst other
parts, formed at the same time, are of the greatest, it would be
difficult to say, on the theory of separate creations.
{430} _Origin_, Ed. i. p. 414, vi. p. 570.
{431} _Origin_, Ed. i. p. 414, vi. p. 570.
Some authors as Lamarck, Whewell &c., believe that the degree of
affinity on the natural system depends on the degrees of resemblance in
organs more or less physiologically important for the preservation of
life. This scale of importance in the organs is admitted to be of
difficult discovery. But quite independent of this, the proposition, as
a general rule, must be rejected as false; though it may be partially
true. For it is universally admitted that the same part or organ, which
is of the highest service in classification in one group, is of very
little use in another group, though in both groups, as far as we can
see, the part or organ is of equal physiological importance: moreover,
characters quite unimportant physiologically, such as whether the
covering of the body consists of hair or feathers, whether the nostrils
communicated with the mouth{432} &c., &c., are of the highest generality
in classification; even colour, which is so inconstant in many species,
will sometimes well characterise even a whole group of species. Lastly,
the fact, that no one character is of so much importance in determining
to what great group an organism belongs, as the forms through which the
embryo{433} passes from the germ upwards to maturity, cannot be
reconciled with the idea that natural classification follows according
to the degrees of resemblance in the parts of most physiological
importance. The affinity of the common rock-barnacle with the
Crustaceans can hardly be perceived in more than a single character in
its mature state, but whilst young, locomotive, and furnished with eyes,
its affinity cannot be mistaken{434}. The cause of the greater value of
characters, drawn from the early stages of life, can, as we shall in a
succeeding chapter see, be in a considerable degree explained, on the
theory of descent, although inexplicable on the views of the
creationist.
{432} These instances occur with others in the _Origin_, Ed. i. p.
416, vi. p. 572.
{433} _Origin_, Ed. i. p. 418, vi. p. 574.
{434} _Origin_, Ed. i. pp. 419, 440, vi. pp. 575, 606.
Practically, naturalists seem to classify according to the resemblance
of those parts or organs which in related groups are most uniform, or
vary least{435}: thus the æstivation, or manner in which the petals etc.
are folded over each other, is found to afford an unvarying character in
most families of plants, and accordingly any difference in this respect
would be sufficient to cause the rejection of a species from many
families; but in the Rubiaceæ the æstivation is a varying character, and
a botanist would not lay much stress on it, in deciding whether or not
to class a new species in this family. But this rule is obviously so
arbitrary a formula, that most naturalists seem to be convinced that
something ulterior is represented by the natural system; they appear to
think that we only discover by such similarities what the arrangement of
the system is, not that such similarities make the system. We can only
thus understand Linnæus'{436} well-known saying, that the characters do
not make the genus; but that the genus gives the characters: for a
classification, independent of characters, is here presupposed. Hence
many naturalists have said that the natural system reveals the plan of
the Creator: but without it be specified whether order in time or place,
or what else is meant by the plan of the Creator, such expressions
appear to me to leave the question exactly where it was.
{435} _Origin_, Ed. i. pp. 418, 425, vi. pp. 574, 581.
{436} _Origin_, Ed. i. p. 413, vi. p. 569.
Some naturalists consider that the geographical position{437} of a
species may enter into the consideration of the group into which it
should be placed; and most naturalists (either tacitly or openly) give
value to the different groups, not solely by their relative differences
in structure, but by the number of forms included in them. Thus a genus
containing a few species might be, and has often been, raised into a
family on the discovery of several other species. Many natural families
are retained, although most closely related to other families, from
including a great number of closely similar species. The more logical
naturalist would perhaps, if he could, reject these two contingents in
classification. From these circumstances, and especially from the
undefined objects and criterions of the natural system, the number of
divisions, such as genera, sub-families, families, &c., &c., has been
quite arbitrary{438}; without the clearest definition, how can it be
possible to decide whether two groups of species are of equal value, and
of what value? whether they should both be called genera or families; or
whether one should be a genus, and the other a family{439}?
{437} _Origin_, Ed. i. pp. 419, 427, vi. pp. 575, 582.
{438} This is discussed from the point of view of divergence in the
_Origin_, Ed. i. pp. 420, 421, vi. pp. 576, 577.
{439}