On the Origin of Species

Introduction

When on board H.M.S. Beagle, as naturalist, I was much struck withcertain facts in the distribution of the inhabitants of South America,and in the geological relations of the present to the past inhabitantsof that continent. These facts seemed to me to throw some light on theorigin of species -- that mystery of mysteries, as it has been calledby one of our greatest philosophers. On my return home, it occurred tome, in 1837, that something might perhaps be made out on this questionby patiently accumulating and reflecting on all sorts of facts whichcould possibly have any bearing on it. After five years work I allowedmyself to speculate on the subject, and drew up some short notes; theseI enlarged in 1844 into a sketch of the conclusions, which then seemedto me probable; from that period to the present day I have steadilypursued the same object. I hope that I may be excused for entering onthese personal details, as I give them to show that I have not beenhasty in coming to a decision.

My work is now nearly finished; but as it will take me two or threemore years to complete it, and as my health is far from strong, I havebeen urged to publish this Abstract. I have more especially been inducedto do this, as Mr. Wallace, who is now studying the natural history ofthe Malay archipelago, has arrived at almost exactly the same generalconclusions that I have on the origin of species. Last year he sent tome a memoir on this subject, with a request that I would forward it toSir Charles Lyell, who sent it to the Linnean Society, and it is publishedin 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 of1844 -- honoured me by thinking it advisable to publish, with Mr. Wallace'sexcellent memoir, some brief extracts from my manuscripts.

In considering the Origin of Species, it is quite conceivable that anaturalist, reflecting on the mutual affinities of organic beings, ontheir embryological relations, their geographical distribution, geologicalsuccession, and other such facts, might come to the conclusion that eachspecies had not been independently created, but had descended, likevarieties, from other species. Nevertheless, such a conclusion, evenif well founded, would be unsatisfactory, until it could be shown howthe innumerable species inhabiting this world have been modified, so asto acquire that perfection of structure and coadaptation which mostjustly excites our admiration. Naturalists continually refer to externalconditions, such as climate, food, etc., as the only possible cause ofvariation. In one very limited sense, as we shall hereafter see, this maybe 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 admirable adapted to catch insects under the bark of trees.In the case of the misseltoe, which draws its nourishment from certaintrees, which has seeds that must be transported by certain birds, andwhich has flowers with separate sexes absolutely requiring the agencyof certain insects to bring pollen from one flower to the other, it isequally preposterous to account for the structure of this parasite, withits relations to several distinct organic beings, by the effects ofexternal 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 birthto a woodpecker, and some plant to the misseltoe, and that these had beenproduced perfect as we now see them; but this assumption seems to me tobe no explanation, for it leaves the case of the coadaptations of organicbeings to each other and to their physical condition of life, untouchedand unexplained.

It is, therefore, of the highest importance to gain a clear insightinto the means of modification and coadaptation. At the commencement ofmy observations it seemed to me probable that a careful study ofdomesticated animals and of cultivated plants would offer the bestchance of making out this obscure problem. Nor have I been disappointed;in this and in all other perplexing cases I have invariable found thatour knowledge, imperfect though it be, of variation under domestication,afforded the best and safest clue. I may venture to express my convictionof the high value of such studies, although they have been very commonlyneglected by naturalists.

No one ought to feel surprise at much remaining as yet unexplained inregard to the origin of species and varieties, if he makes due allowancefor our profound ignorance in regard to the mutual relations of all thebeings which live around us. Who can explain why one species rangeswidely and is very numerous, and why another allied species has a narrowrange and is rare? Yet these relations are of the highest importance, forthey determine the present welfare, and, as I believe, the future successand modification of every inhabitant of this world. Still less do we knowof the mutual relations of the innumerable inhabitants of the world duringthe many past geological epochs in its history. Although much remainsobscure, and will long remain obscure, I can entertain no doubt, afterthe most deliberate study and dispassionate judgment of which I am capable,that the view which most naturalists entertain, and which I formerlyentertained -- namely, that each species has been independently created --is erroneous. I am fully convinced that species are not immutable; but thatthose belonging to what are called the same genera are lineal descendantsof some other and generally extinct species, in the same manner as theacknowledged varieties of any one species are the descendants of thatspecies. Furthermore, I am convinced that Natural Selection has been themain but not exclusive means of modification.

On the Origin of Species by Means of Natural Selection.

London. 1859.

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