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 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.