304 POPULAR SCIENCE MONTHLY 



ACCIDENTAL RESEMBLANCES AMONG ANIMALS. 

 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 sur- 

 roundings. 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 prin- 

 ciple 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 sig- 

 nificant, 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 re- 

 semble other animals and are thereby protected, like moths which re- 

 semble 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 experi- 

 mentally 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 noth- 

 ing, we may justly be skeptical of other resemblances — unless their 

 value can be experimentally proven. 



