SEXUAL SELECTION. 209 



remarkable fact of the display by the male of each 

 species of its peculiar beauties of plumage and colour, 

 a display which Mr. Darwin evidently considers his 

 strongest argument in favour of conscious selection by 

 the female. This display is, no doubt, a very interesting 

 and important phenomenon ; but it may, 1 believe, be 

 satisfactorily explained on the general principles here laid 

 down, without calling to our aid a purely hypothetical 

 choice exerted by the female bird. 



At pairing-time, the male is in a state of excitement, and 

 full of exuberant energy. Even unornamental birds flutter 

 their wings or spread them out, erect their tails or crests, 

 and thus give vent to the nervous excitability with which 

 they are overcharged. It is not improbable that crests 

 and other erectile feathers may be primarily of use in 

 frightening away enemies, since they are generally 

 erected when angry or during combat. Those indi- 

 viduals who were most pugnacious and defiant, and who 

 brought these erectile plumes most frequently and most 

 powerfully into action, would tend to increase them by 

 use, and to leave them further developed in some of 

 their descendants. If, in the course of this development, 

 colour appeared and we have already shown that such 

 developments of plumage are a very probable cause 

 of colour we have every reason to believe it would 

 be most vivid in these most pugnacious and energetic 

 individuals ; and as these would always have the advan- 

 tage in the rivalry for mates (to which advantage the 

 excess of colour and plumage might sometimes conduce), 

 there seems nothing to prevent a progressive develop- 

 ment of these ornaments in all dominant races ; that is, 

 wherever there was such a surplus of vitality, and such 



p 



