IO THE EVOLUTION OF SEX. 



singing-birds were small, and hen-birds mute for safety's sake. This 

 suggestion Wallace has repeated and elaborated in reference especially 

 to birds and insects. The female butterfly, exposed to danger during 

 egg-laying, is frequently dull and inconspicuous compared with her 

 mate. The original brightness has been forfeited by the sex as a 

 ransom for life. Female birds in open nests are similarly, in many 

 cases, colored like their surroundings; while in those of birds where 

 the nests are domed or covered, the plumage is gay in both sexes. 

 At the same time, Wallace allows original importance to sexual selec- 

 tion on both sides in evolving bright colors and the like. We need 

 not repeat Darwin's reply to Wallace's objections, as the reader will 

 at once recognize considerable force in each position.* 



(b) Brooks has called attention to the sexual differences in lizards, 

 where the females do not incubate; or in fishes, where the females are 

 even less exposed to danger than the males; or in domesticated birds, 

 where, though all danger is removed, the males are still the more 

 conspicuous and diversified sex. " The fact, too, that many structures, 

 which are not at all conspicuous, are confined, like gay plumage, to 

 male birds, also indicates the existence of an explanation more 

 fundamental than the one proposed by Wallace, and the latter 

 explanation gives no reason why the females of allied species- should 

 often be exactly alike when the males are very different." To the 

 explanation which Brooks proposes we must therefore pass. 



According to Darwin, Brooks says, the greater modification of the 

 males is due to their struggling with rivals, and to their selection by 

 the females, but " I do not believe that this goes to the root of the 

 matter." The study of domesticated pigeons, for instance, shows 

 that ' ' something within the animal determines that the male should 

 lead and the female follow in the evolution of new breeds. The same 

 is true in other domesticated animals, where, from the nature of the 

 circumstances, it is inadmissible to explain this with Darwin, by 



* Since the above was written, Mr. Wallace's book on "Darwinism" [No. 

 115 and No. 116 of The Humboldt Library] has been published, in which the 

 author proceeds yet further in his destructive criticism of Darwin's sexual selec- 

 tion. The phenomena of male ornament are discussed, and summed up as 

 being "due to the general laws of growth and development," and such that 

 it is "unnecessary to call to our aid so hypothetical a cause as the cumulative 

 action of female preference." Or again, "if ornament is the natural product 

 and direct outcome of superabundant health and vigor, then no other mode 

 of selection is needed to account for the presence of such ornament." These 

 conclusions are not only important in relation to Darwin's theory, but obviously 

 open up the possibility of interpreting not only these as the "natural product 

 and direct outcome of constitutional conditions" (see chap, xxi.), but many 

 other features also. This consideration, however, is fraught with serious con- 

 sequences to Mr. Wallace's main thesis. 



