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Show 12 INTRODUCTION. conviction of the high value of such studies, although they have been very c01nmonly 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, w~ shall se~ how gr~at is the powe~ of man in accumul~ting by his Selection succes~I v~ . shght variations. I will then pass on to the vanabihty 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 hl~h 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 con d:itions of life, will have a better chance of surviving, ana thus be naturally selected. From the strong principle of inheritance, any selected variety will tend to propagatr its new and modified form. This fundamental subject of Natural Selection will b~ treated at some leng!h 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 co1nplex 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 : nam~ly, 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 con- INTRODUCTION. 13 structed 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 w·ork, 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 ran~es wid~ly and is very numerous, and why another alhed species has a narrow range and is rare? Yet th~se relations are of the highest importance, for they determine the present welfare, and, as I believe the future su?cess and modification of every inhabitant of this world. Still less do we know of the mutual relations of the innumer~ ble inhabit.an~s of.the world during the many past geological epoc~s 1n Its hist~ry. Although much remains obscure, and w1lllong remain obscure, I can entertain no ~oubt, after the ~ost deliberate study and dispassionate JUdgment of which I am capable, that the view which m?st naturalists entertain, and which I formerly enteP.. tained-n.amely, .that each species has been independently created-:-Is erroneQus. I am fully convinced that speciec. 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 t~at Natural Selection has been the main' but not excluSIVe means of modification. |
