364 THE DESCENT OF MAN. 



besides sexual selection. Thus the males and females of the 

 same species of butterfly are in several cases known* to 

 inhabit different stations, the former commonly basking in 

 the sunshine, the latter haunting gloomy forests. It is 

 therefore possible that different conditions of life may have 

 acted directly on the two sexes; but this is not probable, f as 

 in the adult state they are exposed to different conditions 

 during a very short period ; and the larvae of both are 

 exposed to the same conditions. Mr. Wallace believes that 

 the difference between the sexes is due not so much to the 

 males having been modified, as to the females having in all 

 or almost all cases acquired dull colors for the sake 

 of protection. It seems to me, on the contrary, far 

 more probable that it is the males which have been 

 chiefly modified through sexual selection, the females having 

 been comparatively little changed. We can thus under- 

 stand how it is that the females of allied species generally 

 resemble one another so much more closely than do the 

 males. They thus show us approximately the primordial 

 coloring of the parent-species of the group to which they 

 belong. They have, however, almost always been somewhat 

 modified by the transfer to them of some of the successive 

 variations, through the accumulation of which the males 

 were rendered beautiful. But I do not wish to deny that 

 the females alone of some species may have been specially 

 modified for protection. In most cases the males and 

 females of distinct species will have been exposed during 

 their prolonged larval state to different conditions, and 

 may have been thus affected ; though with the males any 

 slight change of color thus caused will generally have been 

 masked by the brilliant tints gained through sexual selec- 

 tion. When we treat of birds, I shall have to discuss the 

 whole question, as to how far the differences in color 

 between the sexes are due to the males having been modi- 

 fied through sexual selection for ornamental purposes, or 

 to the females having been modified through natural selec- 

 tion for the sake of protection, so that I will here say but 

 little on the subject. 



In all the cases in which the more common form of equal 



*H. W. Bates, "The Naturalist on the Amazons," vol. ii, 1863, p. 

 228. A. R. Wallace, in " Transact. Linn. Soc.," vol. xxv, 1865, p. 10. 



f On this whole subject see " The Variation of Animals and Plants 

 under Domestication," 1868, vol. ii, chap, xxiii. 



