THE SEXES AND SEXUAL SELECTION. 9 



IV. Criticisms of Darwin's Explanation. — The above expla- 

 nation may be summed up in a single sentence, — a casual variation, 

 advantageous to its possesser (usually a male) in courtship and repro- 

 duction, becomes established and perfected by the success it entails. 

 Sexual selection is thus only a special case of the more general pro- 

 cess 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 import- 

 ance 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 com- 

 paratively 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 recognize contri- 

 butions, such as those of Mantegazza, which suggest the organic or 

 constitutional origin of the variations in question. It is this con- 

 structive rather than destructive line of criticism whick we shall our- 

 selves seek to develop. 



(a) Wallace's Objection. — It is more convenient to begin with 

 Wallace's criticism, which precedes that of Brooks's in chronological 

 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 due to natural selection, 

 which has eliminated those which persisted to the death in being gay. 

 He points out that conspicuousness during incubation would be dan- 

 gerous and fatal; the more conspicuous have, he thinks, been picked 

 off their nests by hawks, foxes, and the like, and hence only the 

 sober-colored females now remain. Darwin starts from inconspicuous 

 forms, arid derives gorgeous males by sexual selection ; Wallace starts 

 from conspicuous forms, and derives the sober females by natural 

 selection; the former trusts to the preservation of beauty, the latter to 

 its extinction. In 1773, the Hon. Daines Barrington, a naturalist still 

 remembered as the correspondent of Gilbert White, suggested that 



