408 
SEXUAL SELECTION. 
Part II. 
in comparison with the species having brightly-coloured 
males. On the other hand, as bright colours are sup- 
posed to be highly serviceable to the males in their 
love-struggles, the brighter males (as w T e shall see 
in the chapter on Birds) although exposed to rather 
greater danger, would on an average procreate a greater 
number of offspring than the duller males. In this 
case, if the variations were limited in their transmission 
to the male sex, the males alone would be rendered 
more brilliantly coloured ; but if the variations were 
not thus limited, the preservation and augmentation of 
such variations would depend on whether more evil was 
caused to the species by the females being rendered 
conspicuous, than good to the males by certain indivi- 
duals being successful over their rivals. 
As there can hardly be a doubt that both sexes of 
many butterflies and moths have been rendered dull- 
coloured for the sake of protection, so it may have 
been with the females alone of some species in which 
successive variations towards dullness first appeared 
in the female sex and were from the first limited in 
their transmission to the same sex. If not thus limited, 
both sexes would become dull-coloured. We shall 
immediately see, when we treat of mimickry, that 
the females alone of certain butterflies have been ren- 
dered extremely beautiful for the sake of protection, 
without any of the successive protective variations 
having been transferred to the male, to whom they 
could not possibly have been in the least degree injuri- 
ous, and therefore could not have been eliminated 
through natural selection. Whether in each particular 
species, in which the sexes differ in colour, it is the 
female which has been specially modified for the sake 
of protection ; or whether it is the male which has been 
specially modified for the sake of sexual attraction, the 
