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PDF - Wallace Online

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36 NATURAL SELECTION inThis great principle gives us a clue which we can follow outin the study of many recondite phenomena, and leads us toseek a meaning and a purpose of some definite character inminutiae which we should otherwise be almost sure to passover as insignificant or unimportant.Popular Theories of Colour in AnimalsThe adaptation of the external colouring of animals totheir conditions of life has long been recognised, and has beenimputed either to an originally created specific peculiarity,or to the direct action of climate, soil, or food. Where theformer explanation has been accepted it has completelychecked inquiry, since we could never get any further thanthe fact of the adaptation. There was nothing more to beknown about the matter. The second explanation was soonfound to be quite inadequate to deal with all the variedphases of the phenomena, and to be contradicted by manywell known facts. For example, wild rabbits are always ofgray or brown tints well suited for concealment among grassand fern. But when these rabbits are domesticated, withoutany change of climate or food, they vary into white or black,and these varieties may be multiplied to any extent, formingwhite or black races. Exactly the same thing has occurredwith pigeons ;and in the case of rats and mice, the whitevariety has not been shown to be at all dependent on alterationof climate, food, or other external conditions. In manycases the wings of an insect not only assume the exact tint ofthe bark or leaf it is accustomed to rest on, but the form andveining of the leaf or the exact rugosity of the bark isimitated ;and these detailed modifications cannot be reasonablyimputed to climate or to food, since in many cases thespecies does not feed on the substance it resembles, and whenit does, no reasonable connection can be shown to existbetween the supposed cause and the effect produced. It wasreserved for the theory of Natural Selection to solve all theseproblems, and many others which were not at first supposedto be directly connected with them. To make these latterintelligible, it will be necessary to give a sketch of the wholeseries of phenomena which may be classed under the head ofuseful or protective resemblances.

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