We thus see, that the evidence as to variation afforded by animals and plants under domestication strikingly accords with that which we have proved to exist in a state of nature. And it is not at all surprising that it should be so, since all the species were in a state of nature when first domesticated or cultivated by man, and whatever variations occur must be due to purely natural causes. Moreover, on comparing the variations which occur in any one generation of domesticated animals with those which we know to occur in wild animals, we find no evidence of greater individual variation in the former than in the latter. The results of man's selection are more striking to us because we have always considered the varieties of each domestic animal to be essentially identical, while those which we observe in a wild state are held to be essentially diverse. The greyhound and the spaniel seem wonderful, as varieties of one animal produced by man's selection; while we think little of the diversities of the fox and the wolf, or the horse and the zebra, because we have been accustomed to look upon them as radically distinct animals, not as the results of nature's selection of the varieties of a common ancestor. FOOTNOTES: [Footnote 31: Darwin, _Animals and Plants under Domestication_, vol. i. p. 322.] [Footnote 32: These facts are taken from Darwin's _Domesticated Animals and Cultivated Plants_, vol. i. pp. 359, 360, 392-401; vol. ii. pp. 231, 275, 330.] [Footnote 33: See Darwin's _Animals and Plants under Domestication_, vol. i. pp. 40-42.] [Footnote 34: Mr. Brent in _Journal of Horticulture_, 1861, p. 76; quoted by Darwin, _Animals and Plants under Domestication_, vol. i. p. 151.] [Footnote 35: This account of domestic pigeons is greatly condensed from Mr. Darwin's work already referred to.] [Footnote 36: _Animals and Plants under Domestication_, vol. ii. pp. 307-311.] CHAPTER V NATURAL SELECTION BY VARIATION AND SURVIVAL OF THE FITTEST Effect of struggle for existence under unchanged conditions--The effect under change of conditions--Divergence of character--In insects--In birds--In mammalia--Divergence leads to a maximum of life in each area--Closely allied species inhabit distinct areas--Adaptation to conditions at various periods of life--The continued existence of low forms of life--Extinction of low types among the higher animals--Circumstances favourable to the origin of new species--Probable origin of the dippers--The importance of isolation--On the advance of organisation by natural selection--Summary of the first five chapters.