Chap. YL] BEAUTY, HOW ACQUIEED. 253 



beautiful for beauty's sake; but this has been effected 

 through sexual selection, that is, by the more beautiful 

 males having been continually preferred by the females, 

 and not for the delight of man. So it is with the music 

 of birds. We may infer from all this that a nearly 

 similar taste for beautiful colours and for musical 

 sounds runs through a large part of the animal kingdom. 

 When the female is as beautifully coloured as the male, 

 which is not rarely the case with birds and butterflies, 

 the cause apparently lies in the colours acquired 

 through sexual selection having been transmitted to 

 both sexes, instead of to the males alone. How the 

 sense of beauty in its simplest form — that is, the 

 reception of a peculiar kind of pleasure from certain 

 colours, forms, and sounds — was first developed in the 

 mind of man and of the lower animals, is a very 

 obscure subject. The same sort of difficulty is pre- 

 sented, if we enquire how it is that certain flavours and 

 odours give pleasure, and others displeasure. Habit in 

 all these cases appears to have come to a certain extent 

 into play ; but there must be some fundamental cause 

 in the constitution of the nervous system in each 

 species. 



Natural selection cannot possibly produce any modi- 

 fication in a species exclusively for the good of another 

 species ; though throughout nature one species in- 

 cessantly takes advantage of, and profits by, the 

 structures of others. But natural selection can and 

 does often produce structures for the direct injury of 

 other animals, as we see in the fang of the adder, and 

 in the ovipositor of the ichneumon, by which its eggs 

 are deposited in the living bodies of other insects. If 



