v COLOURS OF ANIMALS 369 



by natural selection, according to the needs of the animal. 

 In birds, too, we have the wonderful clothing of plumage 

 the most highly organised, the most varied, and the most 

 expanded of all dermal appendages. The endless processes of 

 growth and change during the development of feathers, and 

 the enormous extent of this delicately-organised surface, must 

 have been highly favourable to the production of varied 

 colour-effects, which, when not injurious, have been merely 

 fixed for purposes of specific identification, but have often 

 been modified or suppressed whenever different tints were 

 needed for purposes of protection. 



Selection by Females not a cause of Colour 

 To conscious sexual selection that is, the actual choice by 

 the females of the more brilliantly -coloured males or the 

 rejection of those less gaily coloured I believe very little if 

 any effect is directly due. It is undoubtedly proved that in 

 birds the females do sometimes exert a choice; but the 

 evidence of this fact, collected by Mr. Darwin (Descent of Man, 

 chap, xiv.), does not prove that colour determines that choice, 

 while much of the strongest evidence is directly opposed to 

 this view. All the facts appear to be consistent with the 

 choice depending on a variety of male characteristics, with 

 some of which colour is often correlated. Thus it is the 

 opinion of some of the best observers that vigour and liveli- 

 ness are most attractive, and these are no doubt usually 

 associated with intensity of colour. Again, the display of the 

 various ornamental appendages of the male during courtship 

 may be attractive ; but these appendages, with their bright 

 colours or shaded patterns, are due probably to general laws 

 of growth, and to that superabundant vitality which we have 

 seen to be a cause of colour. But there are many considera- 

 tions which seem to show that the possession of these orna- 

 mental appendages and bright colours in the male is not an 

 important character functionally, and that it has not been 

 produced by the action of conscious sexual selection. Amid 

 the copious mass of facts and opinions collected by Mr. 

 Darwin as to the display of colour and ornaments by the male 

 birds, there is a total absence of any evidence that the females, 

 as a rule, admire or even notice this display. The hen, the 

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