2IO EVOLUTION, GENETICS, AND EUGENICS 



sudden disappearance is most startling and confusing, greatly increas- 

 ing the difficulty of observing their resting-place." According to this 

 idea of "confusing coloration," a butterfly is supposed to mystify or 

 confuse its enemies by first attracting their attention and then suddenly 

 becoming invisible. One is reminded of the prestidigitator of his 

 favorite remark: "Now you see it and now you don't." But why 

 attract attention in the first place, when continued inconspicuousness 

 would be much less risky? The best answer to this question is to use 

 Thayer's interpretation, namely, that what looks like a conspicuous 

 coloration when observed in the stationary insect held against an alien 

 background is probably almost invisible when the animal is moving 

 its wings and flying through the air in the bright sunlight. 



The case of Kallima is probably more or less typical of the some- 

 what uncritical tendency on the part of naturalists to invent adaptive 

 explanations for every striking color or pattern seen among animals. 

 Let us examine the situation a httle further. Much has been said 

 about the minute details of resemblance to a dead and decaying leaf 

 on the part of this butterfly, yet, if its habits are at all like those of 

 other members of its order, it is hardly likely that its most active period 

 would coincide with that in which the leaves of trees would be decayed 

 and mildewed or even brown. Butterflies are active when flowers, 

 whose nectar forms their chief food, are numerous, and are usually in 

 their pupa cases when the leaves have died on the trees. It has also 

 been stated by critical observers that Kallimas do not frequently light 

 on trees whose leaves are very similar in shape to the folded wings of 

 a butterfly. Furthermore, there are many kinds of butterflies that 

 are more or less like leaves; in fact, it would be difficult for a butterfly 

 not to look somewhat like a leaf, since the wings are shaped like leaves. 

 Again, many species of butterflies have the swallowtails on the lower 

 wings without in other ways much resembling a leaf; others have spots 

 that might be interpreted as resembling decay and mildew without in 

 other ways being more than in general leaflike; and there are many 

 other species that show all degrees of leaf resemblance, some very im- 

 perfect and others almost as perfect as that of Kallima, yet they all 

 seem to be essentially successful in the life-struggle in spite of their less 

 perfect protective resemblance. 



Alleged cases of mimicry have failed also to meet critical examina- 

 tion. When a poisonous butterfly is mimicked by an edible species 

 several conditions must be met in order that the deception be effec- 

 tive. The model and the mimic must both occupy the same range, 



