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Show 4 INTRODUCTION. generations, some bird had given birth to a woodpecker, and some plant to the misseltoe, and that these ha~ been produced perfect as we now see them ~ but th~s assumption seems to me to be no explana.tion,. for It leaves the case of the coadaptations of organic bmngs to each other and to their physical conditions of life, un-touched and unexplained. . It is therefore, of the highest importance to gain a clear i~sight into the means of modification and. coadaptation. At the commencement of my obse:vatwns 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 in~ariably fou~d . that our knowledge, imperfect though It be, of vanation 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 Domestica~ion. 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, unfo.rtunatel~, be compelled to treat this subject far too bnefly, as It ean 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 am_ong~t all organic beings throughout the world, which Inevitably follows from their high geometrical powers of INTRODUCTION. 5 Increase, will be treated of. This is the doctrine of ~~althus, applied to the whole animal and vegetable kingdoms. As many more individuals of each species are born than can possibly survive; and as, consequ. ently, tl~ere is a frequently recurring struggle for e~Istence; 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 |
