NATURAL SELECTION 115 



descendants, yet at the most remote geological period, 

 the earth may have been as well peopled with many 

 species of many genera, families, orders, and classes, 

 as at the present day. 



Summary of Chapter. — If during the long course of 

 ages and under varying conditions of life, organic 

 beings vary at all in the several parts of their organisa- 

 tion, and I think this cannot be disputed ; if there be, 

 owing to the high geometrical ratio of increase of each 

 species, a severe struggle for life at some age, season, 

 or year, and this certainly cannot be disputed ; then, 

 considering the infinite complexity of the relations of 

 all organic beings to each other and to their conditions 

 of existence, causing an infinite diversity in structure, 

 constitution, and habits, to be advantageous to them, 

 I think it would be a most extraordinary fact if no 

 variation ever had occurred useful to each being's own 

 welfare, in the same manner as so many variations 

 have occurred useful to man. But if variations useful 

 to any organic being do occur, assuredly individuals 

 thus characterised will have the best chance of being 

 preserved in the struggle for life ; and from the strong 

 principle of inheritance they will tend to produce 

 offspring similarly characterised. This principle of 

 preservation, I have called, for the sake of brevity, 

 Natural Selection ; and it leads to the improvement of 

 each creature in relation to its organic and inorganic 

 conditions of life. 



Natural selection, on the principle of qualities being 

 inherited at corresponding ages, can modify the egg, 

 seed, or young, as easily as the adult. Amongst many 

 animals, sexual selection will give its aid to ordinary 

 selection, by assuring to the most vigorous and best 

 adapted males the greatest number of offspring. Sexual 

 selection will also give characters useful to the males 

 alone, in their struggles with other males. 



Whether natural selection has really thus acted in 

 nature, in modifying and adapting the various forms 

 of life to their several conditions and stations, must be 



