410 SEXUAL SELECTION. Part II. 



known laws or conditions, that they seem to us to be 

 most capricious in their action ; 23 and we can so far 

 understand how it is that with closely-allied species the 

 sexes of some differ to an astonishing degree, whilst 

 the sexes of others are identical in colour. As the 

 successive steps in the process of variation are neces- 

 sarily all transmitted through the female, a greater 

 or less number of such steps might readily become 

 developed in her; and thus we can understand the 

 frequent gradations from an extreme difference to no 

 difference at all between the sexes of the species within 

 the same group. These cases of gradation are much 

 too common to favour the supposition that we here see 

 females actually undergoing the process of transition 

 and losing their brightness for the sake of protection ; 

 for we have every reason to conclude that at any 

 one time the greater number of species are in a fixed 

 condition. With respect to the differences between the 

 females of the species in the same genus or family, we 

 can perceive that they depend, at least in part, on the 

 females partaking of the colours of their respective 

 males. This is well illustrated in those groups in which 

 the males are ornamented to an extraordinary degree ; 

 for the females in these groups generally partake to a 

 certain extent of the splendour of their male partners. 

 Lastly, we continually find, as already remarked, that 

 the females of almost all the species in the same genus, 

 or even family, resemble each other much more closely 

 in colour than do the males ; and this indicates that 

 the males have undergone a greater amount of modifi- 

 cation than the females. 



23 < The Variation of Animals and Plants under Domestication, 

 vol. ii. chap. xii. p. 17. 



