Greater Value of Females 



tion will cause the species to become extinct, 

 by the elimination of all the males. Or, let us 

 suppose that the mutation in the direction of 

 showy plumage affects both sexes, then in such 

 a case the species will almost certainly become 

 extinct. If, however, the hypothetical species 

 nested in holes in trees, it is quite possible that 

 it might survive notwithstanding its showy 

 plumage. 



Whether, as Wallace suggests, the hen does 

 most of the incubating, and is exposed to special 

 danger when sitting on her eggs in an open nest, 

 or, as Stolzmann urges, it is of advantage to the 

 species that there should not be too many males, 

 the result is the same, that the species can afford 

 to allow the cock to be more gaily attired than 

 the hen. In either case the colouration of the 

 cock becomes a matter of comparatively little 

 importance to the species, and this, coupled with 

 the fact that the male tends to mutate more 

 readily than the female, will explain why, in 

 most species which exhibit sexual dimorphism, 

 it is the cocks that are the more conspicuous. 

 In certain species the cocks alone incubate, and 

 these then become more important than the 

 females to the race, so that they have not been 

 permitted to become showy, while the hens have 

 been allowed more freedom in this respect. 

 The extreme variability of the Ruff (Pavon- 

 cella pugnax] in breeding plumage points to the 



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