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, etc.,
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.