PDF - Wallace Online

v COLOURS OF ANIMALS 377Darwin evidently considers to be the strongest argument infavour of conscious selection by the female. This display is,no doubt, a very interesting and important phenomenon ;butitmay, I believe, be satisfactorily explained on the generalprinciples here laid down, without calling to our aid a purelyhypothetical choice exerted by the female bird.At pairing-time the male is in a state of excitement, andfull of exuberant energy. Even unornamental birds fluttertheir wings or spread them out, erect their tails or crests,and thus give vent to the nervous excitability with whichthey are overcharged. It is not improbable that crests andother erectile feathers may be primarily of use in frighteningaway enemies, since they are generally erected when angryor during combat. Those individuals who were most pugnaciousand defiant, and who brought these erectile plumesmost frequently and most powerfully into action, wouldtend to leave them further developed in some of theirdescendants. If, in the course of this development, colourappeared and we have already shown that such developmentsof plumage are a very probable cause of colourwe have every reason to believe it would be most vivid inthese most pugnacious and energetic individuals; and asthese would always have the advantage in the rivalryfor mates (to which advantage the excess of colour andplumage might sometimes conduce), there seems nothing toprevent a progressive development of these ornaments in alldominant races ; that is, wherever there was such a surplus ofvitality, and such complete adaptation to conditions, that theinconvenience or danger produced by such ornaments was socomparatively small as not to affect the superiority of therace over its nearest allies.But if those portions of the plumage which were originallyerected under the influence of anger or fear became largelydeveloped and brightly coloured, the actual display underthe influence of jealousy or sexual excitement becomes quiteintelligible.The males, in their rivalry with each other,would endeavour to excel their enemies as far as voluntaryexertion would enable them to do so, just as they endeavourto rival each other in song, even sometimes to the point ofcausing their own destruction.