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CHAPTER IV.
NATURAL SELECTION.
Natural Selection— its power compared with man's selection— its power on characters of trifling importance— its power at all ages and on both sexes— Sexual Selection— On the generality of intercrosses between individuals of the same species— Circumstances favourable and unfavourable to Natural Selection, namely, intercrossing, isolation, number of individuals— Slow action— Extinction caused by Natural Selection— Divergence of Character, related to the diversity of inhabitants of any small area, and to naturalisation— Action of Natural Selection, through Divergence of Character and Extinction, on the descendants from a common parent— Explains the Grouping of all organic beings.
HOW will the struggle for existence, discussed too briefly in the last chapter, act in regard to variation? Can the principle of selection, which we have seen is so potent in the hands of man, apply in nature? I think we shall see that it can act most effectually. Let it be borne in mind in what an endless number of strange peculiarities our domestic productions, and, in a lesser degree, those under nature, vary; and how strong the hereditary tendency is. Under domestication, it may be truly said that the whole organisation becomes in some degree plastic.
Text in this page (from paragraph 100, sentence 510 to paragraph 100, sentence 510, word 47) is not present in 1859
CHAPTER IV.
NATURAL SELECTION.
Natural Selection— its power compared with man's selection— its power on characters of trifling importance— its power at all ages and on both sexes— Sexual Selection— On the generality of intercrosses between individuals of the same species— Circumstances favourable and unfavourable to Natural Selection, namely, intercrossing, isolation, number of individuals— Slow action— Extinction caused by Natural Selection— Divergence of Character, related to the diversity of inhabitants of any small area, and to naturalisation— Action of Natural Selection, through Divergence of Character and Extinction, on the descendants from a common parent— Explains the Grouping of all organic beings— Advance in organisation— Low forms preserved— Objections considered— Indefinite multiplication of species— Summary.
HOW will the struggle for existence, discussed too briefly in the last chapter, act in regard to variation? Can the principle of selection, which we have seen is so potent in the hands of man, apply in nature? I think we shall see that it can act most effectually. Let it be borne in mind in what an endless number of strange peculiarities our domestic productions, and, in a lesser degree, those under nature, vary; and how strong the hereditary tendency is. Under domestication, it may be truly said that the whole organisation becomes in some degree plastic. But the variability, which we almost universally meet with in our domestic productions, is not directly produced, as Hooker and Asa Gray have well remarked, by man; he can neither originate varieties, nor prevent their occurrence; he can only preserve and accumulate such as do occur; unintentionally