DIMINUTION OF THE JA WS. 7 



brought about by inheritance of the effects of 

 lessened use. But if English jaws are lighter 

 and thinner than those of Australians and 

 Negroes, so too is the rest of the skull. As 

 the diminution in the weight and thickness of 

 the walls of the cranium cannot well be ascribed 

 to disuse, it must be attributed to some other 

 cause ; and this cause may have affected the jaw 

 also. Cessation of the process by which natural 

 selection 1 favoured strong thick bones during 

 ages of brutal violence might bring about a 

 change in this direction. /Lightness of structure, 

 facilitating agility and being economical of 

 material, would also be favoured by natural 

 selection so far as strength was not too 



seriously diminished, j 



I 



1 Romanes, Galton, and Weismann have made great use of this 

 principle in explaining the diminution of disused organs. Weis- 

 mann has given it the name of Panmixia^ all individuals being 

 equally free to survive and commingle their variations, and not 

 merely selected or favoured individuals. See his Essays on Here- 

 dity, &c., p. 90 (Clarendon Press). 



