410 
SEXUAL SELECTION. 
Part IL 
known laws or conditions, that they seem to ns 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 w T e 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. 
