INSECTS 247 



But on this view the brilliance of the non-protective colora- 

 tion has to be explained. It can scarcely be suggested that 

 it is a warning coloration, for warning and protective 

 coloration cannot well exist in the same individual. On the 

 selection view it must be maintained that, on the one hand, 

 those individual butterflies were being selected in which the 

 coloration of the lower surface afforded the most protective 

 resemblance, while on the other those whose upper surfaces 

 were most brilliant and conspicuous were being chosen by 

 the females. But this raises the question Why did the 

 upper and lower surfaces of the wings vary independently ? 

 If the different exposures which undoubtedly exist determined 

 the modifications, we have an answer to this question, while 

 on the other view no attempt is made to consider the laws or 

 causes of variation. Or, to put the matter in another way, 

 the facts point with the utmost clearness to the conclusion 

 that the coloration has been influenced and determined by 

 the different exposures. 



On the theory of sexual selection it must be held that 

 selection by the female has been exercised in those cases in 

 which the male is specially adorned, and not in those in 

 which the se*xes are equally without adornment. Now 

 in birds this contention may be supported by evidence from 

 the different sexual habits of the various species and 

 families, some being promiscuous, some pairing for life, or 

 for a season, and some being polygamous. But in butterflies 

 and moths the sexual relations do not vary in this way in 

 different species or families. There is no permanent associa- 

 tion of male and female, but all the species are equally 

 promiscuous. Other things being equal, therefore, there 

 ought to be the same amount of competition between males, 

 and the same amount of selection in all species. Other things, 

 however, are not necessarily equal, and even if the degree 

 of competition were the same, the method of competition 



