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THE AMERICAN NATURALIST 



[Vol. L 



dous development throughout the same period which 

 brought in highly specialized language. No one has ever 

 suggested, however, because it develops along with highly 

 specialized language, that this muscle is concerned in 

 speech. I should say that the proper method is to see 

 whether there is any general tendency which would pro- 



duce chins in the course of evolution, a tendency which 

 would operate in the case of other animals, and also in 

 the case of man and his forerunners. I think there is 

 such a general principle, and a very simple one. I should 

 be inclined to explain the chin, not as a by-product of 

 speech, but as a result of a general reduction in the size of 

 the jaw. 



The man-like apes have very heavy chin-less jaws, 

 which, in point of absence of chin, compare with the jaws 

 of the great dogs or cats. Fossil man, too, exhibits, in 

 the more ancient types, enormously large jaws. One 

 general fact, then, in the evolution of modern man, has 

 been a reduction in the size of this part of the body struc- 

 ture. This reduction went along with wider intelligence 

 in the selection of food, and has perhaps been accelerated 

 in man's case by the invention of cooking and other ar- 

 tificial treatment of foodrsubstances. It is, then, a gen- 

 eral tendency in the evolution of the human and related 

 types. If we can not explain it, we may at least recognize 



