lO THE EVOLUTION OF SEX. 



must, however, be added. " I would not wish," he says in 

 the "Origin of Species,"' "to attribute all such sexual differences 

 to this agency ; for we see peculiarities arising and becoming 

 attached to the male sex in our domestic animals, which we 

 cannot believe to be either useful to the males in battle or 

 attractive to the females.'"' Had Darwin seen another inter- 

 pretation of the facts, he would thus doubtless have given it 

 frank recognition. 



§ 4. Criticisms of Darivins Explanation. — The above 

 explanation may be summed up in a single sentence, — a casual 

 variation, advantageous to its possessor (usually a male) in 

 courtship and reproduction, becomes established and perfected 

 by the success it entails. Sexual selection is thus only a 

 special case of the more general process of natural selection, 

 with this difference, that the female for the most part takes the 

 place of the general environment in the picking and choosing 

 which is supposed to work out the perfection of the species. 



The more serious objections which have been hitherto urged 

 against this hypothesis, apart altogether from criticism of special 

 cases, may be grouped in four grades : — (i) Some, who allow great 

 importance to both natural and sexual selection, are dissatisfied 

 with the adequacy of Darwin's analysis, and seek some deeper 

 basis for the variations so largely confined to the male sex. 

 The position occupied by Brooks will be sketched below. (2) 

 Others would explain the facts on the more general theory of 

 natural selection, allowing comparatively little import to the 

 alleged sexual selection exercised by the female. Wallace has 

 on this basis criticised Darwin's theory. (3) Different from 

 either of the above is the position occupied by St George 

 Mivart, who attaches comparatively little importance to either 

 natural or sexual selection. (4) "We have to recognise contri- 

 butions, such as those of ]\Iantegazza, which suggest the organic 

 or constitutional origin of the variations in question. It is this 

 constructive rather than destructive line of criticism which we 

 shall ourselves seek to develop. 



{a) Wallace^ s Objection. — It is more convenient to begin with 

 Wallace's criticism, which precedes that of Brooks's in chrono- 

 logical order. This is the more helpful in clearing the ground, 

 since the two theories of Wallace and Darwin are strikingly 

 and, at first sight, irreconcilably opposed. According to Darwin, 

 the gayness of male birds is due to selection on the part of the 

 females ; according to Wallace, the soberness of female birds is 



