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 facts seemed to me to throw
some light on the origin of species--that mystery of mysteries, as it has been
called by one of our greatest philosophers. On my return home, it occurred to
me, in 1837, that something might perhaps be made out on this question by
patiently accumulating and reflecting on all sorts of facts which could
possibly have any bearing on it. After five years' work I allowed myself to
speculate on the subject, and drew up some short notes; these I enlarged in
1844 into a sketch of the conclusions, which then seemed to me probable: from
that period to the present day I have steadily pursued the same object. I hope
that I may be excused for entering on these personal details, as I give them
to show that I have not been hasty in coming to a decision.
My work is now nearly finished; but as it
will take me two or three more years to complete it, and as my health is far
from strong, I have been urged to publish this Abstract. I have more
especially been induced to do this, as Mr. Wallace, who is now studying the
natural history of the Malay archipelago, has arrived at almost exactly the
same general conclusions that I have on the origin of species. Last year he
sent to me a memoir on this subject, with a request that I would forward it to
Sir Charles Lyell, who sent it to the Linnean Society, and it is published in
the third volume of the Journal of that Society. Sir C. Lyell and Dr. Hooker,
who both knew of my work--the latter having read my sketch of 1844--honoured
me by thinking it advisable to publish, with Mr. Wallace's excellent memoir,
some brief extracts from my manuscripts.
This Abstract, which I now publish, must
necessarily be imperfect. I cannot here give references and authorities for my
several statements; and I must trust to the reader reposing some confidence in
my accuracy. No doubt errors will have crept in, though I hope I have always
been cautious in trusting to good authorities alone. I can here give only the
general conclusions at which I have arrived, with a few facts in illustration,
but which, I hope, in most cases will suffice. No one can feel more sensible
than I do of the necessity of hereafter publishing in detail all the facts,
with references, on which my conclusions have been grounded; and I hope in a
future work to do this. For I am well aware that scarcely a single point is
discussed in this volume on which facts cannot be adduced, often apparently
leading to conclusions directly opposite to those at which I have arrived. A
fair result can be obtained only by fully stating and balancing the facts and
arguments on both sides of each question; and this cannot possibly be here
done.
I much regret that want of space prevents my
having the satisfaction of acknowledging the generous assistance which I have
received from very many naturalists, some of them personally unknown to me. I
cannot, however, let this opportunity pass without expressing my deep
obligations to Dr. Hooker, who for the last fifteen years has aided me in
every possible way by his large stores of knowledge and his excellent
judgment.
In considering the Origin of Species, it is
quite conceivable that a naturalist, reflecting on the mutual affinities of
organic beings, on their embryological relations, their geographical
distribution, geological succession, and other such facts, might come to the
conclusion that each species had not been independently created, but had
descended, like varieties, from other species. Nevertheless, such a
conclusion, even if well founded, would be unsatisfactory, until it could be
shown how the innumerable species inhabiting this world have been modified, so
as to acquire that perfection of structure and coadaptation which most justly
excites our admiration. Naturalists continually refer to external conditions,
such as climate, food, &c., as the only possible cause of variation. In
one very limited sense, as we shall hereafter see, this may be true; but it is
preposterous to attribute to mere external conditions, the structure, for
instance, of the woodpecker, with its feet, tail, beak, and tongue, so
admirably adapted to catch insects under the bark of trees. In the case of the
misseltoe, which draws its nourishment from certain trees, which has seeds
that must be transported by certain birds, and which has flowers with separate
sexes absolutely requiring the agency of certain insects to bring pollen from
one flower to the other, it is equally preposterous to account for the
structure of this parasite, with its relations to several distinct organic
beings, by the effects of external conditions, or of habit, or of the volition
of the plant itself.
The author of the 'Vestiges of Creation'
would, I presume, say that, after a certain unknown number of generations,
some bird had given birth to a woodpecker, and some plant to the misseltoe,
and that these had been produced perfect as we now see them; but this
assumption seems to me to be no explanation, for it leaves the case of the
coadaptations of organic beings to each other and to their physical conditions
of life, untouched and unexplained.
It is, therefore, of the highest importance
to gain a clear insight into the means of modification and coadaptation. At
the commencement of my observations it seemed to me probable that a careful
study of domesticated animals and of cultivated plants would offer the best
chance of making out this obscure problem. Nor have I been disappointed; in
this and in all other perplexing cases I have invariably found that our
knowledge, imperfect though it be, of variation under domestication, afforded
the best and safest clue. I may venture to express my conviction of the high
value of such studies, although they have been very commonly neglected by
naturalists.
From these considerations, I shall devote
the first chapter of this Abstract to Variation under Domestication. We shall
thus see that a large amount of hereditary modification is at least possible,
and, what is equally or more important, we shall see how great is the power of
man in accumulating by his Selection successive slight variations. I will then
pass on to the variability of species in a state of nature; but I shall,
unfortunately, be compelled to treat this subject far too briefly, as it can
be treated properly only by giving long catalogues of facts. We shall,
however, be enabled to discuss what circumstances are most favourable to
variation. In the next chapter the Struggle for Existence amongst all organic
beings throughout the world, which inevitably follows from their high
geometrical powers of increase, will be treated of. This is the doctrine of
Malthus, applied to the whole animal and vegetable kingdoms. As many more
individuals of each species are born than can possibly survive; and as,
consequently, there is a frequently recurring struggle for existence, it
follows that any being, if it vary however slightly in any manner profitable
to itself, under the complex and sometimes varying conditions of life, will
have a better chance of surviving, and thus be naturally selected. From the
strong principle of inheritance, any selected variety will tend to propagate
its new and modified form.
This fundamental subject of Natural
Selection will be treated at some length in the fourth chapter; and we shall
then see how Natural Selection almost inevitably causes much Extinction of the
less improved forms of life and induces what I have called Divergence of
Character. In the next chapter I shall discuss the complex and little known
laws of variation and of correlation of growth. In the four succeeding
chapters, the most apparent and gravest difficulties on the theory will be
given: namely, first, the difficulties of transitions, or in understanding how
a simple being or a simple organ can be changed and perfected into a highly
developed being or elaborately constructed organ; secondly the subject of
Instinct, or the mental powers of animals, thirdly, Hybridism, or the
infertility of species and the fertility of varieties when intercrossed; and
fourthly, the imperfection of the Geological Record. In the next chapter I
shall consider the geological succession of organic beings throughout time; in
the eleventh and twelfth, their geographical distribution throughout space; in
the thirteenth, their classification or mutual affinities, both when mature
and in an embryonic condition. In the last chapter I shall give a brief
recapitulation of the whole work, and a few concluding remarks.
No one ought to feel surprise at much
remaining as yet unexplained in regard to the origin of species and varieties,
if he makes due allowance for our profound ignorance in regard to the mutual
relations of all the beings which live around us. Who can explain why one
species ranges widely and is very numerous, and why another allied species has
a narrow range and is rare? Yet these relations are of the highest importance,
for they determine the present welfare, and, as I believe, the future success
and modification of every inhabitant of this world. Still less do we know of
the mutual relations of the innumerable inhabitants of the world during the
many past geological epochs in its history. Although much remains obscure, and
will long remain obscure, I can entertain no doubt, after the most deliberate
study and dispassionate judgment of which I am capable, that the view which
most naturalists entertain, and which I formerly entertained--namely, that
each species has been independently created--is erroneous. I am fully
convinced that species are not immutable; but that those belonging to what are
called the same genera are lineal descendants of some other and generally
extinct species, in the same manner as the acknowledged varieties of any one
species are the descendants of that species. Furthermore, I am convinced that
Natural Selection has been the main but not exclusive means of modification.