220 Evolution and Adaptation 



affect the external beauty. Yet if these colors were more 

 extensive and on the exterior, there can be little doubt that 

 they would have been explained as due to sexual selection. 



19. When the females in certain species of birds differ 

 more from each other than they do from their respective 

 males, the case is compared to "those inexplicable ones, 

 which occur independently of man's selection in certain sub- 

 breeds of the game-fowl, in which the females are very dif- 

 ferent, whilst the males can hardly be distinguished." Here 

 then is a case of difference in color associated with sex, but 

 not the outcome of sexual selection. 



20. The long hairs on the throat of the stag are said possi- 

 bly to be of use to him when hunted, since the dogs generally 

 seize him by the throat, "but it is not probable that the hairs 

 were specially developed for this purpose ; otherwise the 

 young and the females would have been equally protected." 

 Here also is a sexual difference that can scarcely be ascribed 

 to selection. 



Some cases of differences in color between the sexes 

 " may be the result of variations confined to one sex, and 

 transmitted to the same sex without any good being gained, 

 and, therefore, without the aid of selection. We have 

 instances of this with our domesticated animals, as in the 

 males of certain cats being rusty-red while the females are 

 tortoise-shell colored. Analogous cases occur in nature : 

 Mr. Bartlett has seen many black varieties of the jaguar, 

 leopard, vulpine phalanger, and wombat ; and he is certain 

 that all or nearly all of these animals were males." If 

 changes of this sort occur, associated with one sex, why is 

 there any need of a special explanation in other cases of 

 difference ? 



In the light of the many difficulties that the theory of 

 sexual selection meets with, I think we shall be justified in 

 rejecting it as an explanation of the secondary sexual differ- 



