CREATION BY EVOLUTION
conspicuous. But as the naturalist passes from one district to another he sees that the pattern of the groups becomes different, “as if at the touch of an enchanter’s wand,” to use the words by which Bates describes the change that sweeps over all the diverse members of a group. In Central America and Venezuela the chief group is made conspicuous by a tawny and black-barred pattern; in the Guianas the members of the corresponding group have much darker hind wings—the wings of some are almost entirely black; across the Amazon, in eastern Brazil, the hind wings change in the opposite direction, gaining a bright yellow stripe; high up the Amazon, at Ega (now Teffé), Bates’ headquarters for many years, the general colour of both wings changes from tawny to deep chestnut.
How shall we explain the advantages of these local colours and patterns, which run through many distantly related species? Let us see.
The insect-eating animals of each district, especially the birds, learn by experience that insects having certain conspicuous colours and patterns have an unpleasant taste or smell or are indigestible. So if a number of different noxious species bear the same pattern the birds easily learn to avoid them, with little waste of insect life in experimental tasting. Those so marked survive. Hence the great advantage to the butterflies of a combined advertisement or announcement that they are unpalatable, instead of each distasteful species having its own warning pattern, requiring to be tested separately. It is probable, too, that among the members of a large group there are many degrees of distastefulness and some also that are not distasteful at all, but that flaunt a false advertisement and live on the reputation (or rather the disreputation) of the others. This false advertisement was interpreted by H. W. Bates and is spoken of as
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