NATURAL SELECTION 133 



to his bantams, according to his standard of beauty, I 

 can see no good reason to doubt that female birds, bj 

 selecting, during thousands of generations, the most me- 

 lodious or beautiful males, according to their standard 

 of beauty, might produce a marked effect. Some well- 

 known laws, with respect to the plumage of male and 

 female birds, in comparison with the plumage of the 

 young, can partly be explained through the action of 

 sexual selection on variations occurring at different ages, 

 and transmitted to the males alone or to both sexes at 

 corresponding ages; but I have not space here to enter 

 on this subject. 



Thus it is, as I believe, that when the males and 

 females of any animal have the same general habits of 

 life, but differ in structure, color, or ornament, such dif- 

 ferences have been mainly caused by sexual selection: 

 that is, by individual males having had, in successive 

 generations, some slight advantage over other males, in 

 tbeir weapons, means of defence, or charms, which they 

 have transmitted to their male offspring alone. Yet, I 

 would not wish to attribute all sexual differences to this 

 agency: for we see in our domestic animals peculiarities 

 arising and Itecoming attached to tiie male sex, which 

 apparently have not been augmented through selection by 

 man. The tuft of hair on the breast of the wild turkey- 

 cock cannot be of any use, and it is doubtful whether it 

 can be ornamental in the eyes of the female bird; — 

 indeed, had the tuft appeared under domestication, it 

 would' have been called a monstrosity. 



