On the Origin of Species by Means of Natural Selection (1859)
by Charles Darwin
ON THE ORIGIN OF SPECIES.
INTRODUCTION.
HEN 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 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. In 1858 he sent 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.
[ Charles Darwin, "Introduction" to
On the Origin of Species; Reprinted in Ernst Mayr, ed.,
On
the Origin Of Species: A Facsimile of the First Edition,
Cambridge, Massachusetts: Harvard University Press, 1964, pp. 1-6. ]
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