PDF - Wallace Online

v COLOURS OF ANIMALS 369by natural selection, according to the needs of the animal.In birds, too, we have the wonderful clothing of plumagethe most highly organised, the most varied, and the mostexpanded of all dermal appendages. The endless processes ofgrowth and change during the development of feathers, andthe enormous extent of this delicately-organised surface, musthave been highly favourable to the production of variedcolour-effects, which, when not injurious, have been merelyfixed for purposes of specific identification, but have oftenbeen modified or suppressed whenever different tints wereneeded for purposes of protection.Selection by Females not a cause of ColourTo conscious sexual selection that is, the actual choice bythe females of the more brilliantly -coloured males or therejection of those less gaily coloured I believe very little ifany effect is directly due. It is undoubtedly proved that inbirds the females do sometimes exert a choice; but theevidence 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 tothis view. All the facts appear to be consistent with thechoice depending on a variety of male characteristics, withsome of which colour is often correlated. Thus it is theopinion of some of the best observers that vigour and livelinessare most attractive, and these are no doubt usuallyassociated with intensity of colour. Again, the display of thevarious ornamental appendages of the male during courtshipmay be attractive ;but these appendages, with their brightcolours or shaded patterns, are due probably to general lawsof growth, and to that superabundant vitality which we haveseen to be a cause of colour. But there are many considerationswhich seem to show that the possession of these ornamentalappendages and bright colours in the male is not animportant character functionally, and that it has not beenproduced by the action of conscious sexual selection. Amidthe copious mass of facts and opinions collected by Mr.Darwin as to the display of colour and ornaments by the malebirds, there is a total absence of any evidence that the females,as a rule, admire or even notice this display. The hen, the2B