8'2 CALIFORNIA ACADiOtY OF SCIENCES. 



to his bantams, according to liis standard of beauty, I 

 can see no good reason to doubt that female birds, by 

 selecting, during thousands of generations, the most 

 melodious or beautiful males, according to their standard 

 of beauty, might produce a marked effect." 



Darwin's theory of sexual selection with regard to the 

 colors of birds is simply this, that both sexes were orig- 

 inally dull colored and alike, but the females, in se- 

 lecting those males for mates which were more brightly 

 colored than their fellows, have gradually brought about 

 the brilliant and diversified plumage of the male birds 

 of to-day. Wallace takes a directly opposite view, as 

 expressed in the following passage: * "I have long 

 held this portion of Mr. Darwin's theory to be erroneous, 

 and have argued that the primary cause of sexual diver- 

 sity of color was the need of protection, repressing in 

 the female those bright colors which were normally 

 produced in both sexes by general laws; and I have 

 attempted to explain many of the more difficult cases on 

 this principle ('A Theory of Birds' Nests,' chap. VI. 

 ante)." 



Mr. Wallace then proceeds to elaborate his views, 

 explaining how the- colors of male birds have become 

 more brilliant without reference to sexual selection. He 

 makes the valuable suggestion that brilliant colors are 

 concomitants of a healthy organization, dull hues of a 

 diseased system. The vitality of the male he considers 

 to be greater than of the female, especially during the 

 breeding season, and the brilliant colors and long plumes 

 which are donned at that time are due to the necessity 

 for this vital energy to find some outlet. " The greater 

 intensity of coloration in the male " he says, f "which 

 may be termed the normal sexual difference, would be 



* Natural Selection 1891, pp. 364-365. 

 tl. u., p. 366. 



