CHAP. X.] SEXUAL SELECTION. 313 



existence of &quot; extreme contrast in colour between the sexes &quot; 

 (vol. ii. p. 79) the male being pure white while the female 

 is dusky-green with remarkable vocal powers, for its note 

 &quot; can be distinguished at the distance of nearly three miles, 

 and astonishes every one who first hears it.&quot; But why may 

 not both the song of birds and their display, be phenomena 

 analogous to the voice of the stag or the lion, the develop 

 ment of which Mr. Darwin does not by any means consider 

 due to sexual selection ? He says : 



&quot; The loud voice of the stag does not seem to be of any special 

 service to him, either during his courtship or battles, or in any other 

 way. But may we not believe that the frequent use of the voice, 

 under the strong excitement of love, jealousy, and rage, continued 

 during many generations, may at last have produced an inherited 

 effect on the vocal organs ?&quot; Vol. ii. p. 276. 



But if this may be the case in the stag, an extension of 

 the same principle would sufficiently account for the song of 

 birds. In a parallel way we may conceive that the male 

 pheasants instinctively display themselves at the breeding 

 season, without any necessity of attributing their success in 

 wooing to their plumage, when we have seen how often it 

 must rather be due to their strength and prowess. Indeed, 

 Mr. Darwin himself somewhat singularly remarks (vol. ii. 

 p. 95) : &quot; We must, however, be cautious in concluding that 

 the wings are spread out solely for display, as some birds act 

 thus whose wings are not beautiful ;&quot; and he adds, &quot; All male 

 birds of the same species display themselves exactly in the 

 same manner.&quot; So again the Howling monkeys have been 

 considered to perform their sonorous if not melodious concert 

 for its own sake, apart from any intention of female captiva- 

 tion. Mr. Darwin says : &quot; An excellent observer, Rengger, 

 could not perceive that they were excited to begin their con 

 cert by any special cause ; he thinks that, like many birds, 

 they delight in their own music, and try to excel each other &quot; 

 (vol. ii. p. 277). 



From the fact of &quot; display &quot; Mr. Darwin concludes that &quot; it 

 is obviously probable that the females appreciate the beauty 



