{i}

THE FOUNDATIONS OF THE
ORIGIN OF SPECIES

{ii}

CAMBRIDGE UNIVERSITY PRESS
London: FETTER LANE, E.C.
C. F. CLAY, Manager

Edinburgh: 100, PRINCES STREET
ALSO
London: H. K. LEWIS, 136, GOWER STREET, W.C.

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Leipzig: F. A. BROCKHAUS

New York: G. P. PUTNAM’S SONS

Bombay and Calcutta: MACMILLAN AND Co., Ltd.

All rights reserved

{iii}

From a photograph by Maull & Fox in 1854

{iv}

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

{v}

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.

{vi}

TO THE MASTER AND FELLOWS
OF CHRIST’S COLLEGE, THIS
BOOK IS DEDICATED BY THE
EDITOR IN TOKEN OF RESPECT
AND GRATITUDE

{vii}

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

{viii}

ESSAY OF 1844

PART I

CHAPTER I
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 57–80

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.

• 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 81–111

CHAPTER III
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 112–132

{ix}

PART II
ON THE EVIDENCE FAVOURABLE AND OPPOSED TO THE VIEW
THAT SPECIES ARE NATURALLY FORMED RACES, DESCENDED
FROM COMMON STOCKS.

CHAPTER IV
ON THE NUMBER OF INTERMEDIATE FORMS REQUIRED ON THE
THEORY OF COMMON DESCENT; AND ON THEIR ABSENCE
IN A FOSSIL STATE 133–143

CHAPTER V
GRADUAL APPEARANCE AND DISAPPEARANCE OF SPECIES. 144–150

• 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
ON THE NATURE OF THE AFFINITIES AND CLASSIFICATION
OF ORGANIC BEINGS. 198–213

• 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

{x}

CHAPTER VIII
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 214–230

CHAPTER IX
ABORTIVE OR RUDIMENTARY ORGANS.

• The abortive organs of Naturalists
• The abortive organs of Physiologists
• Abortion from gradual disuse 231–238

CHAPTER X
RECAPITULATION AND CONCLUSION.

• Recapitulation
• Why do we wish to reject the Theory of Common Descent?
• Conclusion 239–255
• Index 257
• Portrait frontispiece
• Facsimile to face p. 50

{xi}

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?

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.{xii}
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.”

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.”

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 {xiii}
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.

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.”

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 {xiv}
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.

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 {xv}
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.

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, {xvi}
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.”

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«d» 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.”

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.

{xvii}
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 {xviii}
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,—fœtal
state,—abortive organs.”

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 {xix}
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.

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.

{xx}
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.

When a word cannot be deciphered, it is replaced by:—«illegible», 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 «?».
{xxi}
Lastly, words inserted by the editor, of which the appropriateness is
doubtful, are printed thus «variation?».

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 «illegible»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
{xxii}
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
{xxiii}
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 {xxiv}
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 «the» 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.”

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.

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.
{xxv}
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.

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.{xxvi}

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 «to» 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 {xxvii}
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.

“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.

“My remaining collections in Natural History may be given to any
one or any museum where «they» would be accepted….”

«The following note seems to have formed part of the original
letter, but may have been of later date:»

“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, {xxviii}
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.”

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.

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 {xxix}
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.

{xxx}

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.

{1}

PART I.

§ I. «On Variation under Domestication, and on the Principles of Selection.»

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.

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 {2}
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] «causes» 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.

[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 {3}
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}.

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
«illegible» 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 «if» 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{4}
[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
«the» form «?» lives, but those most useful to
him. This might all be otherwise.

§ II. «On Variation in a State of Nature and on the Natural Means of Selection.»

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.

Our experience would lead us to expect that any and every one of these
organisms would vary if «the organism were» 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 «illegible» how far the
slowness «?» would produce tendency to vary. But
Geolog«ists» 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.{5}
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.

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 «at» 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 {6}
climate adapting woodpecker{50}
to crawl «?» up trees, «illegible» miseltoe,
«sentence incomplete». But if every part of a plant or
animal was to vary «illegible», 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 «animal would need» 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 «illegible» rotten
trees or [gradually select plants which «he» 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 {7}
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.

Before considering whether «there» 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 «things» 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
«countries» 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
«occur» here «?», how astoundingly some tribes
«?» increase, also introduced animals{56},
the {8}
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 œconomy of nature. This requires much
reflection; study Malthus and calculate rates of increase and remember
the resistance,—only periodical.

The unavoidable effect of this «is» 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., «it» 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.

Let hares{61}
increase very slowly from change of climate affecting peculiar plants,
and some other «illegible» rabbit decrease in same
proportion [let this unsettle organisation of], a canine animal, who
{9}
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.

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 «and» 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}.

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 «an» 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
{10}
nerves, muscles, arteries, are developed in proportion to the change of
external form.

Besides selection by death, in bisexual animals «illegible»
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, «whose» instincts «are»
best developed, will rear more young, probably possessing her good
qualities, and a greater number will thus «be» 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}.

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 {11}
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 {12}
on the fact of the supposed races of nature being sterile, though none
of the domestic ones are? Mr Herbert «and» 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 «do not?» 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 «it» 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 «an» effect on their mind and a special case.

But turning to plants we find same class of facts. I do not refer to
seeds not ripening, perhaps the commonest {13}
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 «in» 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.

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
«with» 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 {14}
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
«has» 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
«illegible» has been «illegible» 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}.

{15}
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 «as» 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}.

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 «the» end appears difficulty. But
think of gradation, even now manifest, (Tibia and Fibula). Everyone will
allow if every fossil preserved, gradation {16}
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}.

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.

{17}

§ III. «On Variation in instincts and other mental attributes.»

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 «the» 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.{18}
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.

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 {19}
whole theory ought not at once to be rejected on this score.

Every instinct must, by my theory, have been acquired gradually by
slight changes «illegible» 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.

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 «illegible», 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.

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.

Last case of parent feeding young with different food (take case of
Galapagos birds, gradation from{20}
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.

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 «of» 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 «remember» 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 {21}
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 «would» think that horses or corn could be
produced? Take dahlia and potato, who will pretend in 5000 years{103}
«that great changes might not be effected»: 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,
«I conclude» that it is impossible to say we know the limit
of races, which would be true «to their» 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
«that» species «have» been thus produced, this
is a question wholly independent of all previous points, and which on
examination of the kingdom of nature «we» ought to answer
one way or another.

{22}

PART II{104}.

§§ IV. & V. «On the evidence from Geology.»

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
«illegible» 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
«not» 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 {23}
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.

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«s» 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], {24}
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«to», 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 «by» 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
«go» they tend towards such gradation{110}.
Illustrate it with net. Toxodon,—tibia and fibula,—dog and
otter,—but so utterly improbable is «it», in ex. gr.
Pachydermata, to compose series as perfect as cattle, that if, as many
geologists seem to {25}
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.]

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,
«illegible» littoral deposits: for otherwise denudation
«will destroy them»,—they must live in a shallow space
which sediment will tend to fill up,—as movement is
«in?» 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}.

I believe safely inferred «that» groups of marine
«?» fossils only preserved for future ages where sediment
goes on long «and» continuous«ly»
and with rapid but not too rapid deposition in «an» area of
subsidence. In how few places in any one region like Europe will
«?» these contingencies be going on? Hence «?»
in {26}
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 «illegible» at age «illegible»
as far back as Miocene{115}?
We know then cattle existed. Compare number of living,—immense
duration of each period,—fewness of fossils.

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 «of intermediate beds», 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.

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, {27}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 «? we» 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.

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
«be» viewed as objection.] If geology present us with mere
pages in chapters, towards end of «a» 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}.

{28}
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 «illegible» tiger of India so
rare? Curious and general sources of error, the place of an organism is
instantly filled up.

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.

{29}
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.

«Geographical Distribution.»

§ 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 {30}
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 «of» difference in the organisms bears a certain,
but not invariable relation to the amount of physical difficulties to
transit{123}.

There are some curious exceptions, namely, similarity of fauna of
mountains of Europe and N. America and Lapland. Other cases just
«the» 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}.]

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 {31}
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 «would» 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 «that» 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 «illegible» 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.

{32}
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 «that the» 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
«of» 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
{33}
occupy an island{131}.
Now we can at once see that «if» 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.

The detection of transitional forms would be rendered more difficult on
rising point of land.

The distribution therefore in the above enumerated
{34}
points, even the trivial ones, which on any other «theory?»
can be viewed as so many ultimate facts, all follow «in»
a simple manner on the theory of the occurrence of species by «illegible»
and being adapted by selection to «illegible»,
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}.

{35}

§ VII. «Affinities and Classification.»

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 «that we have an»
undefined instinct of the importance of organs{135},
we have no means in lower {36}
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 «one»; 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
«illegible» 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
{37}
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
«an» 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 {38}
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 «air»{144},
to water, and to these in «illegible» and then these great
divisions would show numerical relations in their classification.

§ 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 «?»
«of» 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 «illegible» or walking animals, becoming
through infinite number of small {39}
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.

[We know the number of similar parts, as vertebræ and ribs can
vary, hence this also we might expect.] Also «if» 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.

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 «? referring»
to a unity of type of different organs in the same individual,
denominated the science of “Morphology.” The «?
this» 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 «limbs» 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 {40}
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 «the» 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.

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 «that?» 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.{41}
But we can see that if this carried to extreme, unity
lost,—Plesiosaurus. Here we have seen the same organ is formed
«?» «for» different purposes «ten words
illegible»: and if, in several orders of vertebrata, we could
trace origin «of» 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.

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 «and instead of being»
utterly unintelligible becomes simple matter of fact{155}.

{42}
«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
fœtus passes{156}.
In early stage, the wing of bat, hoof, hand, paddle are not to be
distinguished. At a still earlier «stage» there is no
difference between fish, bird, &c. &c. and mammal. It is not
that they cannot be distinguished, but the arteries{157}
«illegible». It is not true that one passes through the form
of a lower group, though no doubt fish more nearly related to
fœtal state{158}.

This similarity at the earliest stage is remarkably shown in the course
of the arteries which become greatly altered, as fœtus 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.

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 {43}
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
fœtus is effected, it tends to appear at same period. When we
«see» 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 fœtal 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 {44}
object gained in varying form &c. of fœtus (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.

Thus there is no power to change the course of {45}
the arteries, as long as they nourish the fœtus; it is the
selection of slight changes which supervene at any time during
«illegible» of life.

The less differences of fœtus,—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 fœtus, retaining traces of the
ancestral form, is of the highest value in classification.

§ IX. «Abortive organs.»

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 «to bite», and yet we find these
organs perfect in every detail in situations where they cannot possibly
be of their normal use{166}.

The term abortive organ has been thus applied{46}
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, «and of» 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 {47}
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. «We can» 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.

Our theory, I may remark would permit an organ «to» 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}.

«The following passage was possibly intended to be inserted
here.» 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.

{48}

§ X. Recapitulation and conclusion.

Let us recapitulate the whole «?»
«of» 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
«illegible» 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 fœtal
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, {49}
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 «from» their aboriginal forms; might be selected
to serve different ends.

Now the Creationist believes these three Rhinoceroses were created{176}
with their deceptive appearance of true, not «illegible»
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.

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. «This probably refers to the Crustacea, where the two ends of
the series have “hardly a character in common.” Origin,
Ed. i. p. 419.» 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 {50}
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!

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 fœtus passes, the metamorphosis
of organs, the abortion of others cease to be metaphorical expressions
and become intelligible facts. We no longer look «an»
on animal as a savage does at a ship{179},
or other great work of art, as a thing wholly beyond comprehension, but
we {51}
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, «as the summing
up» 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 «on»
[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 {52}
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}.

{53}
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 «work?».

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}.

{55}

THE ESSAY OF 1844

{57}

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.{58}
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.

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 {59}
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.

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 {60}
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.

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 {61}
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.

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, {62}
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.

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
{63}
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.

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 {64}
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 {65}
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.

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 {66}
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.

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 {67}
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 {68}
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.

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 {69}
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.

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 {70}
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
{71}
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.

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 {72}
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.

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 {73}
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.

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 {74}
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 «to be» 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 {75}
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 «are» no doubt
hereditary bad and {76}
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.

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 {77}
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 {78}
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.

After these views, it may be asked how it comes {79}
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, {80}
for their crossing and recrossing will greatly increase their
variability.

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.

{81}

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, {82}
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 {83}
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.

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
{84}
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 {85}
even special parts and organs of the body. But we might further (and
«this» 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 {86}
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.

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 «or» 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 {87}
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.

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}.

Natural means of Selection{227}.

De Candolle, in an eloquent passage, has declared that all nature is at
war, one organism with another, {88}
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}.

Many practical illustrations of this rapid tendency {89}
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 {90}
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.

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 {91}
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.

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 {92}
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.

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; {93}
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}.

{94}

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.{95}
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.

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, {96}
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.”

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
{97}
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 {98}
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.

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 {99}
peculiarities of constitution probably affect the entire frame, and no
one part in particular{247}.

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 {100}
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 {101}
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 «its»
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
{102}
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 {103}
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.

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 {104}
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.

It is worthy of remark, that as many organic beings, when taken by man
out of their natural conditions, have their reproductive system
«so» 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 «in» 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 {105}
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.

Points of Resemblance between “Races” and “Species{259}.”

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 {106}
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
{107}
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.

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
{108}
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.

Summary of second chapter{265}.

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 {109}
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.

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 {110}
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.
{111}
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}.

{112}

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 {113}
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 {114}
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.

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 {115}
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.

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 {116}
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}.

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 {117}
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 {118}
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
«yet» 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}.

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 {119}
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.

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
{120}
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 «?
species» 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.

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.

{121}

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.

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 {122}
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 {123}
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 «favour the
insect’s» escape «from» 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 {124}
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 {125}
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.

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{126}
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.

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 {127}
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.

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 {128}
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 {129}
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 {130}
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.

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 {131}
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.

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 {132}
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.

{133}

PART II{305}
ON THE EVIDENCE FAVOURABLE AND OPPOSED TO THE VIEW THAT SPECIES ARE
NATURALLY FORMED RACES, DESCENDED FROM COMMON STOCKS

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 {134}
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 «of» 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.

As I suppose that species have been formed in {135}
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 «a»
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 «the» 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 {136}
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.

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 {137}
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, «for instance» 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.

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 {138}
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.

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 «illegible»; 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{139}
(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}.

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.

Consult the writings of any one who has particularly attended to any one
stage in the Tertiary {140}
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}.

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 {141}
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
{142}
this view, the records of anteceding ages confirm my theory; on any
other they destroy it.

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 {143}
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.

{144}

CHAPTER V
GRADUAL APPEARANCE AND DISAPPEARANCE OF SPECIES{326}

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
{145}
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}.

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 {146}
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}.

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.

{147}

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
{148}
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 {149}
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.

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
{150}
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}.

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.

{151}

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.

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
{152}
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 {153}
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.

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 «with» 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 {154}
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.

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 {155}
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.

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].{156}
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.

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{157}
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.

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 {158}
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.

{159}

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 {160}
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.

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{161}
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.

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
{162}
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.

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 {163}
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{164}
Land and of the Cape of Good Hope{364}.
On some other mountains, for instance «in» 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 «from» 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.

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.

{165}

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 {166}
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?

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.

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 {167}
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}.

Finally, I think we may safely grant from the foregoing facts and
reasoning that the anomalous {168}
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 {169}
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.

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, {170}
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{171}
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.

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 {172}
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 {173}
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 {174}
from other land, having its own species of quadruped, and makes the
case like that of Java and Sumatra, each having their own rhinoceros.

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 {175}
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 «as to» 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 {176}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.

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}.

{177}

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}.

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{178}
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.

I will only add one more observation to this {179}
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.

{180}

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 {181}
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.

{182}
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.

{183}

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 {184}
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.

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 {185}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
«of» 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
{186}
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 {187}
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}.

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 {188}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}.

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 {189}
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 {190}
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 «which» 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}.

I need hardly point out that we now can obviously {191}
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.

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
{192}
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}.

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 {193}
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}.

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, {194}
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 {195}
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}.

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.

{196}
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 {197}
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.

{198}

CHAPTER VII
ON THE NATURE OF THE AFFINITIES AND CLASSIFICATION OF ORGANIC
BEINGS{425}

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 {199}
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}.

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 {200}
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.

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 {201}
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.

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.{202}
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.

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}?

{203}

On the kind of relation between distinct groups.

I have only one other remark on the affinities of organic beings; that
is, when two quite distinct groups approach each other, the approach is
generally generic{440}
and not special; I can explain this most easily by an example: of all
Rodents the Bizcacha, by certain peculiarities in its reproductive
system, approaches nearest to the Marsupials; of all Marsupials the
Phascolomys, on the other hand, appears to approach in the form of its
teeth and intestines nearest to the Rodents; but there is no special
relation between these two genera{441};
the Bizcacha is no nearer related to the Phascolomys than to any other
Marsupial in the points in which it approaches this division; nor again
is the Phascolomys, in the points of structure in which it approaches
the Rodents, any nearer related to the Bizcacha than to any other
Rodent. Other examples might have been chosen, but I have given (from
Waterhouse) this example as it illustrates another point, namely, the
difficulty of determining what are analogical or adaptive and what real
affinities; it seems that the teeth of the Phascolomys though appearing
closely to resemble those of a Rodent are found to be built on the
Marsupial type; and it is thought that these teeth and consequently the
intestines may have been adapted to the peculiar life of this animal and
therefore may not show any real relation. The structure in the Bizcacha
that connects it with the Marsupials does not seem a peculiarity related
to its manner of life, and I imagine that no one would doubt that this
shows a real affinity, though not more with any one Marsupial {204}
species than with another. The difficulty of determining what relations
are real and what analogical is far from surprising when no one pretends
to define the meaning of the term relation or the ulterior object of all
classification. We shall immediately see on the theory of descent how it
comes that there should be “real” and
“analogical” affinities; and why the former alone should be
of value in classification—difficulties which it would be I
believe impossible to explain on the ordinary theory of separate
creations.

Classification of Races or Varieties.

Let us now for a few moments turn to the classification of the generally
acknowledged varieties and subdivisions of our domestic beings{442};
we shall find them systematically arranged in groups of higher and
higher value. De Candolle has treated the varieties of the cabbage
exactly as he would have done a natural family with various divisions
and subdivisions. In dogs again we have one main division which may be
called the family of hounds; of these, there are several (we will call
them) genera, such as blood-hounds, fox-hounds, and harriers; and of
each of these we have different species, as the blood-hound of Cuba
and that of England; and of the latter again we have breeds truly
producing their own kind, which may be called races or varieties. Here
we see a classification practically used which typifies on a lesser
scale that which holds good in nature. But amongst true species in the
natural system and amongst domestic races the number of divisions or
groups, instituted between those most alike and those most unlike, seems
to be quite {205}
arbitrary. The number of the forms in both cases seems practically,
whether or not it ought theoretically, to influence the denomination of
groups including them. In both, geographical distribution has sometimes
been used as an aid to classification{443};
amongst varieties, I may instance, the cattle of India or the sheep of
Siberia, which from possessing some characters in common permit a
classification of Indian and European cattle, or Siberian and European
sheep. Amongst domestic varieties we have even something very like the
relations of “analogy” or “adaptation{444}”;
thus the common and Swedish turnip are both artificial varieties which
strikingly resemble each other, and they fill nearly the same end in the
economy of the farm-yard; but although the swede so much more resembles
a turnip than its presumed parent the field cabbage, no one thinks of
putting it out of the cabbages into the turnips. Thus the greyhound and
racehorse, having been selected and trained for extreme fleetness for
short distances, present an analogical resemblance of the same kind, but
less striking as that between the little otter (Marsupial) of Guiana and
the common otter; though these two otters are really less related than
«are» the horse and dog. We are even cautioned by authors
treating on varieties, to follow the natural in contradistinction of
an artificial system and not, for instance, to class two varieties of
the pine-apple{445}
near each other, because their fruits accidentally resemble each other
closely (though the fruit may be called the final end of this plant in
the economy of its world, the hothouse), but to judge from the general
resemblance of the entire plants. Lastly, varieties often become
extinct; sometimes from unexplained causes, sometimes {206}
from accident, but more often from the production of more useful
varieties, and the less useful ones being destroyed or bred out.

I think it cannot be doubted that the main cause of all the varieties
which have descended from the aboriginal dog or dogs, or from the
aboriginal wild cabbage, not being equally like or unlike—but on
the contrary, obviously falling into groups and sub-groups—must in
chief part be attributed to different degrees of true relationship; for
instance, that the different kinds of blood-hound have descended from
one stock, whilst the harriers have descended from another stock, and
that both these have descended from a different stock from that which
has been the parent of the several kinds of greyhound. We often hear of
a florist having some choice variety and breeding from it a whole group
of sub-varieties more or less characterised by the peculiarities of the
parent. The case of the peach and nectarine, each with their many
varieties, might have been introduced. No doubt the relationship of our
different domestic breeds has been obscured in an extreme degree by
their crossing; and likewise from the slight difference between many
breeds it has probably often happened that a “sport” from
one breed has less closely resembled its parent breed than some other
breed, and has therefore been classed with the latter. Moreover the
effects of a similar climate{446}
may in some cases have more than counterbalanced the similarity,
consequent on a common descent, though I should think the similarity of
the breeds of cattle of India or sheep of Siberia was far more probably
due to the community of their descent than to the effects of climate on
animals descended from different stocks.

Notwithstanding these great sources of difficulty,{207}
I apprehend every one would admit, that if it were possible, a
genealogical classification of our domestic varieties would be the most
satisfactory one; and as far as varieties were concerned would be the
natural system: in some cases it has been followed. In attempting to
follow out this object a person would have to class a variety, whose
parentage he did not know, by its external characters; but he would have
a distinct ulterior object in view, namely, its descent in the same
manner as a regular systematist seems also to have an ulterior but
undefined end in all his classifications. Like the regular systematist
he would not care whether his characters were drawn from more or less
important organs as long as he found in the tribe which he was examining
that the characters from such parts were persistent; thus amongst cattle
he does value a character drawn from the form of the horns more than
from the proportions of the limbs and whole body, for he finds that the
shape of the horns is to a considerable degree persistent amongst
cattle{447},
whilst the bones of the limbs and body vary. No doubt as a frequent rule
the more important the organ, as being less related to external
influences, the less liable it is to variation; but he would expect that
according to the object for which the races had been selected, parts
more or less important might differ; so that characters drawn from parts
generally most liable to vary, as colour, might in some instances be
highly serviceable—as is the case. He would admit that general
resemblances scarcely definable by language might sometimes serve to
allocate a species by its nearest relation. He would be able to assign a
clear reason why the close similarity of the fruit in two varieties of
pine-apple, and of the so-called root in the common and Swedish turnips,
and why the {208}
similar gracefulness of form in the greyhound and racehorse, are
characters of little value in classification; namely, because they are
the result, not of community of descent, but either of selection for a
common end, or of the effects of similar external conditions.

Classification of “races” and species similar.

Thus seeing that both the classifiers of species and of varieties{448}
work by the same means, make similar distinctions in the value of the
characters, and meet with similar difficulties, and that both seem to
have in their classification an ulterior object in view; I cannot avoid
strongly suspecting that the same cause, which has made amongst our
domestic varieties groups and sub-groups, has made similar groups (but
of higher values) amongst species; and that this cause is the greater or
less propinquity of actual descent. The simple fact of species, both
those long since extinct and those now living, being divisible into
genera, families, orders &c.—divisions analogous to those into
which varieties are divisible—is otherwise an inexplicable fact,
and only not remarkable from its familiarity.

Origin of genera and families.

Let us suppose{449}
for example that a species spreads and arrives at six or more different
regions, or being already diffused over one wide area, let this area be
divided into six distinct regions, exposed to different conditions, and
with stations slightly different, not fully occupied with other species,
so {209}
that six different races or species were formed by selection, each best
fitted to its new habits and station. I must remark that in every case,
if a species becomes modified in any one sub-region, it is probable that
it will become modified in some other of the sub-regions over which it
is diffused, for its organization is shown to be capable of being
rendered plastic; its diffusion proves that it is able to struggle with
the other inhabitants of the several sub-regions; and as the organic
beings of every great region are in some degree allied, and as even the
physical conditions are often in some respects alike, we might expect
that a modification in structure, which gave our species some advantage
over antagonist species in one sub-region, would be followed by other
modifications in other of the sub-regions. The races or new species
supposed to be formed would be closely related to each other; and would
either form a new genus or sub-genus, or would rank (probably forming a
slightly different section) in the genus to which the parent species
belonged. In the course of ages, and during the contingent physical
changes, it is probable that some of the six new species would be
destroyed; but the same advantage, whatever it may have been (whether
mere tendency to vary, or some peculiarity of organization, power of
mind, or means of distribution), which in the parent-species and in its
six selected and changed species-offspring, caused them to prevail over
other antagonist species, would generally tend to preserve some or many
of them for a long period. If then, two or three of the six species were
preserved, they in their turn would, during continued changes, give rise
to as many small groups of species: if the parents of these small groups
were closely similar, the new species would form one great genus, barely
perhaps divisible into two or three sections: but if the {210}
parents were considerably unlike, their species-offspring would, from
inheriting most of the peculiarities of their parent-stocks, form either
two or more sub-genera or (if the course of selection tended in
different ways) genera. And lastly species descending from different
species of the newly formed genera would form new genera, and such
genera collectively would form a family.

The extermination of species follows from changes in the external
conditions, and from the increase or immigration of more favoured
species: and as those species which are undergoing modification in any
one great region (or indeed over the world) will very often be allied
ones from (as just explained) partaking of many characters, and
therefore advantages in common, so the species, whose place the new or
more favoured ones are seizing, from partaking of a common inferiority
(whether in any particular point of structure, or of general powers of
mind, of means of distribution, of capacity for variation, &c., &c.),
will be apt to be allied. Consequently species of the same genus will
slowly, one after the other, tend to become rarer and rarer in
numbers, and finally extinct; and as each last species of several allied
genera fails, even the family will become extinct. There may of course
be occasional exceptions to the entire destruction of any genus or
family. From what has gone before, we have seen that the slow and
successive formation of several new species from the same stock will
make a new genus, and the slow and successive formation of several other
new species from another stock will make another genus; and if these two
stocks were allied, such genera will make a new family. Now, as far as
our knowledge serves, it is in this slow and gradual manner that groups
of species appear on, and disappear from, the face of the earth.

{211}
The manner in which, according to our theory, the arrangement of species
in groups is due to partial extinction, will perhaps be rendered clearer
in the following way. Let us suppose in any one great class, for
instance in the Mammalia, that every species and every variety, during
each successive age, had sent down one unaltered descendant (either
fossil or living) to the present time; we should then have had one
enormous series, including by small gradations every known mammiferous
form; and consequently the existence of groups{450},
or chasms in the series, which in some parts are in greater width, and
in some of less, is solely due to former species, and whole groups of
species, not having thus sent down descendants to the present time.

With respect to the “analogical” or “adaptive”
resemblances between organic beings which are not really related{451},
I will only add, that probably the isolation of different groups of
species is an important element in the production of such characters:
thus we can easily see, in a large increasing island, or even a
continent like Australia, stocked with only certain orders of the main
classes, that the conditions would be highly favourable for species from
these orders to become adapted to play parts in the economy of nature,
which in other countries were performed by tribes especially adapted to
such parts. We can understand how it might happen that an otter-like
animal might have been formed in Australia by slow selection from the
more carnivorous Marsupial types; thus we can understand that curious
case in the southern hemisphere, where there are no auks (but many
petrels), of a petrel{452}
having been modified into the {212}
external general form so as to play the same office in nature with the
auks of the northern hemisphere; although the habits and form of the
petrels and auks are normally so wholly different. It follows, from our
theory, that two orders must have descended from one common stock at an
immensely remote epoch; and we can perceive when a species in either
order, or in both, shows some affinity to the other order, why the
affinity is usually generic and not particular—that is why the
Bizcacha amongst Rodents, in the points in which it is related to the
Marsupial, is related to the whole group{453},
and not particularly to the Phascolomys, which of all Marsupialia is
related most to the Rodents. For the Bizcacha is related to the present
Marsupialia, only from being related to their common parent-stock; and
not to any one species in particular. And generally, it may be observed
in the writings of most naturalists, that when an organism is described
as intermediate between two great groups, its relations are not to
particular species of either group, but to both groups, as wholes. A
little reflection will show how exceptions (as that of the Lepidosiren,
a fish closely related to particular reptiles) might occur, namely
from a few descendants of those species, which at a very early period
branched out from a common parent-stock and so formed the two orders or
groups, having survived, in nearly their original state, to the present
time.

Finally, then, we see that all the leading facts in the affinities and
classification of organic beings can be explained on the theory of the
natural system being simply a genealogical one. The similarity of the
principles in classifying domestic varieties and true species, both
those living and extinct, is at once {213}
explained; the rules followed and difficulties met with being the same.
The existence of genera, families, orders, &c., and their mutual
relations, naturally ensues from extinction going on at all periods
amongst the diverging descendants of a common stock. These terms of
affinity, relations, families, adaptive characters, &c., which
naturalists cannot avoid using, though metaphorically, cease being so,
and are full of plain signification.

{214}

CHAPTER VIII
UNITY OF TYPE IN THE GREAT CLASSES; AND MORPHOLOGICAL STRUCTURES

Unity of Type{454}.

Scarcely anything is more wonderful or has been oftener insisted on than
that the organic beings in each great class, though living in the most
distant climes and at periods immensely remote, though fitted to widely
different ends in the economy of nature, yet all in their internal
structure evince an obvious uniformity. What, for instance, is more
wonderful than that the hand to clasp, the foot or hoof to walk, the
bat’s wing to fly, the porpoise’s fin{455}
to swim, should all be built on the same plan? and that the bones in
their position and number should be so similar that they can all be
classed and called by the same names. Occasionally some of the bones are
merely represented by an apparently useless, smooth style, or are
soldered closely to other bones, but the unity of type is not by this
destroyed, and hardly rendered less clear. We see in this fact some deep
bond of union between the organic beings of the same great
classes—to illustrate which is the object and foundation of the
natural {215}
system. The perception of this bond, I may add, is the evident cause
that naturalists make an ill-defined distinction between true and
adaptive affinities.

Morphology.

There is another allied or rather almost identical class of facts
admitted by the least visionary naturalists and included under the name
of Morphology. These facts show that in an individual organic being,
several of its organs consist of some other organ metamorphosed{456}:
thus the sepals, petals, stamens, pistils, &c. of every plant can be
shown to be metamorphosed leaves; and thus not only can the number,
position and transitional states of these several organs, but likewise
their monstrous changes, be most lucidly explained. It is believed that
the same laws hold good with the gemmiferous vesicles of Zoophytes. In
the same manner the number and position of the extraordinarily
complicated jaws and palpi of Crustacea and of insects, and likewise
their differences in the different groups, all become simple, on the
view of these parts, or rather legs and all metamorphosed appendages,
being metamorphosed legs. The skulls, again, of the Vertebrata are
composed of three metamorphosed vertebræ, and thus we can see a
meaning in the number and strange complication of the bony case of the
brain. In this latter instance, and in that of the jaws of the
Crustacea, it is only necessary to see a series taken from the different
groups of each class to admit the truth of these views. It is evident
that when in each species of a group its organs consist of some other
part metamorphosed, that there must also be a “unity of
type” in such a group. And {216}
in the cases as that above given in which the foot, hand, wing and
paddle are said to be constructed on a uniform type, if we could
perceive in such parts or organs traces of an apparent change from some
other use or function, we should strictly include such parts or organs
in the department of morphology: thus if we could trace in the limbs of
the Vertebrata, as we can in their ribs, traces of an apparent change
from being processes of the vertebræ, it would be said that in
each species of the Vertebrata the limbs were “metamorphosed
spinal processes,” and that in all the species throughout the
class the limbs displayed a “unity of type{457}.”