2i6 Habit and Instinct. 



contends that, given the variations, sexual selection will 

 guide them to special developments. 



Those, of whom Mr. Alfred Kussell Wallace is chief, 

 who are not prepared to admit sexual selection by prefer- 

 ential mating as a factor in organic evolution, assert that 

 there is no sufficient evidence of choice on the part of the 

 female bird. Mr. Wallace attributes the origin of plumes, 

 brilliance, and specialized activities to exuberant vitality : 

 he regards their suppression in the hen * as due to natural 

 selection through the elimination of conspicuous hens 

 during the important period of incubation ; and he 

 develops a theory suggested by Mr. Alfred Tylor,f that 

 the diversified coloration follows the chief lines of 

 structure, and changes at points, such as the joints, 

 where function changes. " Why, in allied species, the 

 development of accessory plumes has taken different 

 forms," he admits, J " we are unable to say, except that 

 it may be due to individual variability, which has served 

 as the starting-point for so much of what seems to us 

 strange in form or fantastic in colour, both in the 

 animal and vegetable world." 



So far as coloration and special adornments are con- 

 cerned, it would seem that, on Mr. Wallace's view, they 

 are of utilitarian value for the end of recognition. 

 " Each ornament," he says, " is a recognition mark, and 

 therefore essential to both the first production and 

 subsequent well-being of every species." But recognition 

 marks are, if we grant their utilitarian value, of essential 

 importance in connection with mating. The sight of 

 such ornaments would therefore become associated with 



* Generally in the hen. When the female is brightly coloured and the 

 male dull in hue, he is said to undertake the duties of incubation, 

 f ".Coloration in Animals and Plants." 

 % " Darwinism," p. 293. 



