MODERN BIOLOGY 487 



himself. He manifestly never felt so deeply moved by the actual doctrine of 

 the creation as Darwin had been, and, further, he has by no means the same 

 interest as Darwin in domestic-animal varieties, with which he himself had 

 never experimented; rather, having studied in the richest tropical regions, 

 he had gained a far stronger impression of the wealth of life-forms and their 

 adaptation to environment. This especially comes out in the mimicry theory 

 that he and his friend Bates created. 



Theory of protective resemblance 

 After a ten years' sojourn in the tropics of South America Bates returned 

 home with rich collections and eventually became secretary to the British 

 Geographical Society. He wrote an essay in which he propounded the idea 

 of protective resemblance in the animal kingdom — an idea that was after- 

 wards taken up and further developed by Wallace. It is known that a large 

 number of animals possess external characteristics that correspond to con- 

 ditions in the natural surroundings in which they live; the white fur of 

 polar animals, the sandy yellow of desert beasts, the likeness of many in- 

 sects to the bark of the trees on which they live, are all examples of this. In 

 the more abundant plant-life of the tropics there appear still more remark- 

 able instances of this similarity, especially among the insects; well-known 

 examples are the "wandering leaves" and "wandering sticks," which, 

 owing to their likeness to the undergrowth, often elude the observation 

 of even the most experienced collectors. Wallace believes that all these forms 

 have arisen through the circumstance that natural selection in the struggle 

 for existence has favoured those individuals that, owing to variations in 

 the direction of greatest likeness to their surroundings, have been better pro- 

 tected than others and have thereby had a better chance to propagate. But 

 Wallace considers that even the obvious exceptions from the rule which quite 

 often occur — animals with strikingly brilliant colours — only still fur- 

 ther confirm the law, seeing that they really possess some other character- 

 istic which acts as a powerful protection against their enemies and which 

 thus converts their splendid colours into a kind of warning signal to the 

 latter; as, for instance, an offensive odour, as in the skunk of America, the 

 natterjack, and the salamander, as well as a large number of insects, in- 

 cluding our common lady-bird, with its magnificent red-and-black spotted 

 wings; or, again, a hard shell, as in many brilliantly coloured tortoises; or 

 poison, as in many of the vividly marked snakes in the tropics. The most 

 remarkable application of this law Wallace sees, however, in the mimicry 

 or disguise whereby certain animals protect themselves against their enemies 

 by resembling other more dangerous animals in their outward appearance; 

 there are flies that in form and manner of flying resemble bumble-bees, butter- 

 flies that resemble wasps; and this disguise is demonstrated still more in the 

 tropics, where non-poisonous snakes are often misleadingly like the poisonous 



