SENSATION. 97 



opponent of evolution has pointed to the fact. For it might 

 he argued that here "\ve have a complicated piece of special 

 organic machinery constructed in ohvious anticipation of the 

 advent of cookery and warm baths. But I think the matter 

 may be explained on evolutionary principles, if we remember 

 that the only use of a sense of temperature is not that of 

 examining food. We know that differences of temperature 

 on the surface of the body (whether local or general) greatly 

 modify the conditions of the circulation in the part or parts 

 affected, and therefore it must always have been of use for 

 animals to be provided with a sensory apparatus upon the 

 surface of their bodies to give them immediate information 

 of such differences. Its development along special lines (so 

 that some parts of the body should be more sensitive to 

 changes of temperature than other parts) is easily to be 

 explained by the effects of habit or use. Thus, for example, 

 the fact that the lips of man, although provided with a skin 

 so delicate and so sensitive to tactile impressions, are never- 

 theless able to endure a sudden rise of temperature which 

 would be painful to the skin of the face, must be taken to 

 mean that habit has adapted the nerves in the lips to with- 

 stand a sudden rise of temperature — and this certainly within 

 the period since the invention of cookery. 



Mr. Grant Allen takes a more general view of this sub- 

 ject, and says: "To an animal, cold is death, and warmth is 

 life. Hence it is not astonishing that animals should very 

 early have developed a sense which informed them of 

 changes of temperature taking place in their vicinity; and 

 that this sense should have been equally diffused over the 

 whole organism. .... As soon as moving creatures 

 began to feel at all, they probably began to feel heat and 

 cold."* The truth of such a general statement of this must 

 be obvious, and the step between a sense of temperature 

 equally diffused over the whole organism, and the specializa- 

 tion of superficial nerve-endings to minister to this sens" 



alone, is not a large step. Moreover, the step between this 

 and the development of a rudimentary visual organ is like- 

 wise not a large one. fur the deposition of dark-coloured 

 pigment in particularly exposed parts of the skin must have 

 been <>r benefit to animals by enabling fin virtue of the 

 increased absorption of heat thus seemed) the nerve-endings 



• Colour Sense, p. 13. 



