 Introduction
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 judgement.
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 co-adaptation 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 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 judgement 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.
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