DIFFICULTIES OF THE THEORY 165 



are always thus disseminated when embedded within a fruit of 

 any kind (that is within a fleshy or pulpy envelope), if it be col- 

 ored of any brilliant tint, or rendered conspicuous by being white 

 or black. 



On the other hand, I willingly admit that a great number of 

 male animals, as all our most gorgeous birds, some fishes, reptiles, 

 and mammals, and a host of magnificently colored butterflies, have 

 been rendered beautiful for beauty's sake. But this has been ef- 

 fected 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 colors 

 and for musical sounds runs through a large part of the animal 

 kingdom. When the female is as beautifully colored as the male, 

 which is not rarely the case with birds and butterflies, the cause 

 apparently lies in the colors acquired through sexual selection hav- 

 ing been transmitted to both sexes, instead of to the males alone. 

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

 tion of a peculiar kind of pleasure from certain colors, 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 

 presented if we inquire how it is that certain flavors and odors 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 modification in a 

 species exclusively for the good of another species, though through- 

 out nature one species incessantly 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 ich- 

 neumon, by which its eggs are deposited in the living bodies of 

 other insects. If it could be proved that any part of the structure 

 of any one species had been formed for the exclusive good of 

 another species, it would annihilate my theory, for such could not 

 have been produced through natural selection. Although many 

 statements may be found in works on natural history to this effect, 

 I cannot find even one which seems to me of any weight. It is ad- 

 mitted that the rattlesnake has a poison fang for its own defence 

 and for the destruction of its prey; but some authors suppose that 

 at the same time it is furnished with a rattle for its own injury, 



