38 CLASSIFICATION AND ADAPTATION 



tion applies to these also, since we find that these 

 characters consist often of weapons such as horns, 

 antlers, and spurs, used in sexual combat, of 

 copulatory or clasping organs such as the pads on 

 a frog's forefeet, of ornamental plumage like the 

 peacock's tail serving to charm the female, or of 

 special pouches as in species of pipe-fish and frog 

 for holding the eggs or young. Darwin attempted 

 to explain sexual adaptation by sexual selection. 

 The selective process in this case was supposed to 

 be, not the survival of individuals best adapted to 

 secure food or shelter or to escape from enemies, but 

 the success of those males which were victorious in 

 combat, or which were most attractive to the 

 females, and therefore left the greater number of 

 offspring which inherited their variations. But, as 

 Darwin himself admitted, this theory of selection 

 does not in any way explain the differences between 

 the sexes — in other words, the limitation of the 

 characters or organs to one sex — since there is no 

 reason in the process of selection itself why the 

 peculiarity of a successful male should not be in- 

 herited by his female offspring as well as by his 

 male offspring. The real problem, then, is the sex- 

 limited heredity, and we shall consider later whether 

 in this kind of heredity also there are characters 

 of internal as well as external origin, blastogenic 

 as well as somatogenic. 



