When on board H.M.S. Beagle, as naturalist, I was much struck with certainfacts in the distribution of the organic beings inhabiting South America,and in the geological relations of the present to the past inhabitants ofthat continent. These facts, as will be seen in the latter chapters ofthis volume, seemed to throw some light on the origin of species--thatmystery of mysteries, as it has been called by one of our greatestphilosophers. On my return home, it occurred to me, in 1837, thatsomething might perhaps be made out on this question by patientlyaccumulating and reflecting on all sorts of facts which could possibly haveany bearing on it. After five years' work I allowed myself to speculate onthe subject, and drew up some short notes; these I enlarged in 1844 into asketch of the conclusions, which then seemed to me probable: from thatperiod to the present day I have steadily pursued the same object. I hopethat I may be excused for entering on these personal details, as I givethem to show that I have not been hasty in coming to a decision.

My work is now (1859) nearly finished; but as it will take me many moreyears to complete it, and as my health is far from strong, I have beenurged to publish this abstract. I have more especially been induced to dothis, as Mr. Wallace, who is now studying the natural history of the MalayArchipelago, has arrived at almost exactly the same general conclusionsthat I have on the origin of species. In 1858 he sent me a memoir on thissubject, with a request that I would forward it to Sir Charles Lyell, whosent it to the Linnean Society, and it is published in the third volume ofthe Journal of that Society. Sir C. Lyell and Dr. Hooker, who both knew ofmy work--the latter having read my sketch of 1844--honoured me by thinkingit advisable to publish, with Mr. Wallace's excellent memoir, some briefextracts from my manuscripts.

This abstract, which I now publish, must necessarily be imperfect. Icannot here give references and authorities for my several statements; andI must trust to the reader reposing some confidence in my accuracy. Nodoubt errors may have crept in, though I hope I have always been cautiousin trusting to good authorities alone. I can here give only the generalconclusions at which I have arrived, with a few facts in illustration, butwhich, I hope, in most cases will suffice. No one can feel more sensiblethan 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 ina future work to do this. For I am well aware that scarcely a single pointis discussed in this volume on which facts cannot be adduced, oftenapparently leading to conclusions directly opposite to those at which Ihave arrived. A fair result can be obtained only by fully stating andbalancing the facts and arguments on both sides of each question; and thisis here impossible.

I much regret that want of space prevents my having the satisfaction ofacknowledging the generous assistance which I have received from very manynaturalists, some of them personally unknown to me. I cannot, however, letthis opportunity pass without expressing my deep obligations to Dr. Hooker,who, for the last fifteen years, has aided me in every possible way by hislarge stores of knowledge and his excellent judgment.

In considering the origin of species, it is quite conceivable that anaturalist, reflecting on the mutual affinities of organic beings, on theirembryological relations, their geographical distribution, geologicalsuccession, and other such facts, might come to the conclusion that specieshad not been independently created, but had descended, like varieties, fromother species. Nevertheless, such a conclusion, even if well founded,would be unsatisfactory, until it could be shown how the innumerablespecies, inhabiting this world have been modified, so as to acquire thatperfection of structure and coadaptation which justly excites ouradmiration. Naturalists continually refer to external conditions, such asclimate, food, etc., as the only possible cause of variation. In onelimited sense, as we shall hereafter see, this may be true; but it ispreposterous to attribute to mere external conditions, the structure, forinstance, of the woodpecker, with its feet, tail, beak, and tongue, soadmirably adapted to catch insects under the bark of trees. In the case ofthe mistletoe, which draws its nourishment from certain trees, which hasseeds that must be transported by certain birds, and which has flowers withseparate sexes absolutely requiring the agency of certain insects to bringpollen from one flower to the other, it is equally preposterous to accountfor the structure of this parasite, with its relations to several distinctorganic beings, by the effects of external conditions, or of habit, or ofthe volition of the plant itself.

It is, therefore, of the highest importance to gain a clear insight intothe means of modification and coadaptation. At the commencement of myobservations it seemed to me probable that a careful study of domesticatedanimals and of cultivated plants would offer the best chance of making outthis obscure problem. Nor have I been disappointed; in this and in allother perplexing cases I have invariably found that our knowledge,imperfect though it be, of variation under domestication, afforded the bestand safest clue. I may venture to express my conviction of the high valueof such studies, although they have been very commonly neglected bynaturalists.

>From these considerations, I shall devote the first chapter of thisabstract to variation under domestication. We shall thus see that a largeamount of hereditary modification is at least possible; and, what isequally or more important, we shall see how great is the power of man inaccumulating by his selection successive slight variations. I will thenpass 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 itcan be treated properly only by giving long catalogues of facts. We shall,however, be enabled to discuss what circumstances are most favourable tovariation. In the next chapter the struggle for existence among allorganic beings throughout the world, which inevitably follows from the highgeometrical ratio of their increase, will be considered. This is thedoctrine of Malthus, applied to the whole animal and vegetable kingdoms. As many more individuals of each species are born than can possiblysurvive; and as, consequently, there is a frequently recurring struggle forexistence, it follows that any being, if it vary however slightly in anymanner profitable to itself, under the complex and sometimes varyingconditions of life, will have a better chance of surviving, and thus beNATURALLY SELECTED. From the strong principle of inheritance, any selectedvariety will tend to propagate its new and modified form.

This fundamental subject of natural selection will be treated at somelength in the fourth chapter; and we shall then see how natural selectionalmost inevitably causes much extinction of the less improved forms oflife, and leads to what I have called divergence of character. In the nextchapter I shall discuss the complex and little known laws of variation. Inthe five succeeding chapters, the most apparent and gravest difficulties inaccepting the theory will be given: namely, first, the difficulties oftransitions, or how a simple being or a simple organ can be changed andperfected into a highly developed being or into an elaborately constructedorgan; secondly the subject of instinct, or the mental powers of animals;thirdly, hybridism, or the infertility of species and the fertility ofvarieties when intercrossed; and fourthly, the imperfection of thegeological record. In the next chapter I shall consider the geologicalsuccession of organic beings throughout time; in the twelfth andthirteenth, their geographical distribution throughout space; in thefourteenth, their classification or mutual affinities, both when mature andin an embryonic condition. In the last chapter I shall give a briefrecapitulation of the whole work, and a few concluding remarks.

No one ought to feel surprise at much remaining as yet unexplained inregard to the origin of species and varieties, if he make due allowance forour profound ignorance in regard to the mutual relations of the many beingswhich live around us. Who can explain why one species ranges widely and isvery numerous, and why another allied species has a narrow range and israre? Yet these relations are of the highest importance, for theydetermine the present welfare and, as I believe, the future success andmodification of every inhabitant of this world. Still less do we know ofthe mutual relations of the innumerable inhabitants of the world during themany past geological epochs in its history. Although much remains obscure,and will long remain obscure, I can entertain no doubt, after the mostdeliberate study and dispassionate judgment of which I am capable, that theview which most naturalists until recently entertained, and which Iformerly entertained--namely, that each species has been independentlycreated--is erroneous. I am fully convinced that species are notimmutable; but that those belonging to what are called the same genera arelineal descendants of some other and generally extinct species, in the samemanner as the acknowledged varieties of any one species are the descendantsof that species. Furthermore, I am convinced that natural selection hasbeen the most important, but not the exclusive, means of modification.