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Page:Popular Science Monthly Volume 72.djvu/308

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304
POPULAR SCIENCE MONTHLY

ACCIDENTAL RESEMBLANCES AMONG ANIMALS. A CHAPTER IN UN-NATURAL HISTORY
By Professor BASHFORD DEAN

COLUMBIA UNIVERSITY

THE naturalist of to-day is perhaps unduly saturated with the belief that animals and plants adapt themselves to their surroundings. He has seen so many and such admirable examples of this, and in every field of his work, that he is apt to conclude that the principle of adaptation can be called upon to explain phenomena which when critically considered may prove to be not adaptive at all. In the familiar case of an insect whose colors suggest lichen-covered bark, or a dead leaf, or a flower, we have come to conclude, since we have seen many examples of demonstrated utility, that the resemblance is significant, that it protects the insect against its enemies and that it has been the outcome of a series of evolutional changes which have made the protective coloration more and more complete. We have even reached a point, some of us at least, where we neglect to scrutinize the evidence that the creature in question frequented the kind of bark, leaf or flower which it resembles, or that, if it did, it was thereby protected so completely as to ensure its survival. We have reached the point, to make this attitude clear, when we hold up before our students a butterfly mounted on a twig and point out the marvelous "protective" resemblance between the butterfly and the neighboring pressed leaves, without suspecting that the leaves belonged to a beech tree "made in Germany," and that the butterfly came from the East Indies!

So also is our attitude a lax one in the case of animals which resemble other animals and are thereby protected, like moths which resemble wasps, flies which can be mistaken for bees, butterflies which are similar to butterflies known to be rejected by birds, etc. For we have seen so many instances of undoubted mimicry that we are apt to accept resemblances as of this type, even if they have not been experimentally demonstrated. That such accurate resemblances, on the other hand, could occur even in animals which live side by side and yet mean nothing, would be something of a heresy to many evolutionists. Yet I am inclined to believe that this is a fact—although to prove this in concrete instances would be at the moment difficult. However, it can, I think, be established indirectly and by striking analogies. For if there occur among animals numerous resemblances which mean nothing, we may justly be skeptical of other resemblances—unless their value can be experimentally proven.