144 THE DESCENT OF MAN. Part I. 



habitual use, this shews that certain actions are 

 habitually performed and must be serviceable. Hence 

 the individuals which performed them best, would tend 

 to survive in greater numbers. 



The free use of the arms and hands, partly the cause 

 and partly the result of man's erect position, appears to 

 have led in an indirect manner to other modifications of 

 structure. The early male progenitors of man were, as 

 previously stated, probably furnished with great canine 

 teeth ; but as they gradually acquired the habit of using 

 stones, clubs, or other weapons, for fighting with their 

 enemies, they would have used their jaws and teeth less 

 and less. In this case, the jaws, together with the 

 teeth, would have become reduced in size, as we may 

 feel sure from innumerable analogous cases. In a future 

 chapter we shall meet with a closely-parallel case, in 

 the reduction or complete disappearance of the canine 

 teeth in male ruminants, apparently in relation with the 

 development of their horns ; and in horses, in relation 

 with their habit of fighting with their incisor teeth and 

 hoofs. 



In the adult male anthropomorphous apes, as Riiti- 

 meyer, 68 and others have insisted, it is precisely the effect 

 which the jaw-muscles by their great development have 

 produced on the skull, that causes it to differ so greatly 

 in many respects from that of man, and has given to 

 it " a truly frightful physiognomy." Therefore as the 

 jaws and teeth in the progenitors of man gradually 

 become reduced in size, the adult skull would have 

 presented nearly the same characters which it offers in 

 the young of the anthropomorphous apes, and would 

 thus have come to resemble more nearly that of existing 



68 



'Die Grenzen der Thierwelt, eine Betrachtung zu Darwin's 



Lehre,' 1868, s. 51. 



