EELATING TO SECONDARY SEXUAL CHARACTERS. 45 



cover also the case of birds and mammals. In answer to this criti- 

 cism it may be argued that it is also possible that the other explana- 

 tion when found need not necessarily apply to the higher animals, 

 where the laws of combat may still give the true explanation. On the 

 whole, I think that, for our present purpose, it will suffice to state 

 it is consistent with the theory of natural selection to accept provision- 

 ally this part of Darwin's theory for those species hi the higher groups 

 in which polygamy holds, conceding, however, that even here it may 

 have to be altered when fuller knowledge is gained. 



We are more concerned with that special feature of Darwin's theory 

 of sexual selection that is applied to those cases where the characters 

 are supposed to owe their special development to selection by the 

 individuals of the opposite sex. It is assumed that the female chooses 

 the better endowed males, because of the strong appeal he makes to 

 her sense-organs. Here we must employ perforce or for brevity's sake 

 the terms used in human psychology, and run the risk at every turn of 

 imputing to other animals the emotions and acquired associations 

 which man himself utilizes. Even granting that other animals pos- 

 sess somewhat similar emotions to ours, there still remains always the 

 danger, in the absence of real evidence, of imputing to them the par- 

 ticular emotion that we call ' 'feeling for beauty"; and the greater 

 danger of imputing an esthetic sense so highly developed that the choice 

 falls in the long run on the suitor better ornamented than his rivals. 



OTHER THEORIES TO ACCOUNT FOR SECONDARY SEXUAL 

 CHARACTERS. 



Wallace has always been an opponent of Darwin's theory of sexual 

 selection in so far as it is based on female choice. As already stated, 

 he believes that the difference between the plumage of the male and 

 female in birds is due to natural selection keeping down the ornamen- 

 tation and high coloration in the female, because these would be 

 expected to expose the female while sitting on the nest to the attacks 

 of enemies, more especially of hawks. In support of this view he 

 points to a long series of species which build exposed nests and in them 

 the female is plainly and inconspicuously colored, while he also points 

 out that in such birds as parrots, toucans, woodpeckers, hangnests, 

 and starlings, which nest in holes or have covered nests, the female 

 is often as highly colored as the male. It can not be denied that 

 he makes out rather a strong case in support of this view, despite the 

 fact that there are other birds, like the Baltimore oriole, that have 

 covered nests and in which the sexes are very markedly different. 



Wallace tries to meet cases like the last one by assuming that the 

 covering keeps off the rain; but, if so, why are the sexes still so different? 

 In the case of other highly colored birds, such as jays, magpies, hawks, 

 and crows, Wallace believes that these birds are all aggressive, hence 



