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 inter- 

 crosses between individuals of the same species — Circumstance? 

 favourable and unfavourable to Natural Selection, namely, inter- 

 crossing, isolation, number of individuals — Slow action — Extinc- 

 tion 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 ? 1 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. Let it be borne in mind how 

 infinitely complex and close-fitting are the mutual 

 relations of all organic beings to each other and to 

 their physical conditions of life. Can it, then, be 

 thought improbable, seeing that variations useful to 

 man have undoubtedly occurred, that other variations 

 useful in some way to each being in the great and com- 

 plex battle of life, should sometimes occur in the course 

 of thousands of generations ? If such do occur, can we 



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