PDF - Wallace Online

TROPICAL NATUREment are much more numerous than the internal changes as;seen in the varied character of the integuments and appendagesof animals hair, horns, scales, feathers, etc., etc. andin plants,the leaves, bark, flowers, and fruit, with theirvarious modifications as compared with the great uniformityin the texture and composition of their internal tissues ;andthis accords with the uniformity of the tints of blood, muscle,nerve, and bone throughout extensive groups, as comparedwith the great diversity of colour of their external organs..It seems a fair conclusion that colour per se may be consideredto be normal, and to need no special accounting for ;whilethe absence of colour (that is, either white or black}, or theprevalence of certain colours to the constant exclusion ofothers, must be traced, like other modifications in theeconomy of living things, to the needs of the species. Or,that amid thelooking at it in another aspect, we may sayconstant variations of animals and plants colour is ever tendingto vary and to appear where it is absent and that natural;selection is constantly eliminating such tints as are injuriousto the species, or preserving and intensifying such as areuseful.This view is in accordance with the well-known fact ofcolours which rarely or never appear in the species in astate of nature, continually occurring among domesticatedanimals and cultivated plants ; showing us that the capacityto develop colour is ever present, so that almost any requiredtint can be produced which may, under changed conditions,be useful, in however small a degree.Let us now see how these principles will enable us tounderstand and explain the varied phenomena of colour innature, taking them in the order of our functional classificationof colours.Theory of Protective ColoursWe have seen that obscure or protective tints in theirinfinitely varied degrees are present in every part of theanimal kingdom ;whole families or genera being often thuscoloured. Now the various brown, earthy, ashy, and otherneutral tints are those which would be most readily produced,because they are due to an irregular mixture of many kinds