ohap. II. Manner of Development. 5 3 



biped ; but, as an unprejudiced judge 75 insists, the anthropomor- 

 phous apes approach in structure more nearly to the bipedal 

 than to the quadrupedal type. 



As the progenitors of man became more and more erect, with 

 their hands and arms more and more modified for prehension 

 and other purposes, with their feet and legs at the same timo 

 transformed for firm support and progression, endless other 

 changes of structure would have become necessary. The pelvis 

 would have to be broadened, the spine peculiarly curved, and the 

 head fixed in an altered position, all which changes have been 

 attained by man. Prof. Schaaff hausen 7U maintains that "the 

 " powerful mastoid processes of the human skull are the result of 

 " his erect position ;" and these processes are absent in the orang, 

 chimpanzee, &c, and are smaller in the gorilla than in man. 

 Various other structures, which appear connected with man's 

 erect position, might here have been added. It is very difficult 

 to decide how far these correlated modifications are the result of 

 natural selection, and how far of the inherited effects of the 

 increased use of certain parts, or of the action of one part on 

 another. No doubt these means of change often co-operate : thus 

 when certain muscles, and the crests of bone to which they are 

 attached, become enlarged by 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 forefathers 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 or rivals, they would use their jaws 

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

 teeth, would become reduced in size, as we may feel almost sure 

 from innumerable analogous cases. In a future chapter we 

 shall meet with a closely parallel case, in the reduction or com- 

 plete disappearance of the canine teeth in male ruminants, 

 apparently in relation with the development of their horns ; and 

 in horses, in relation to then habit of fighting with their incisor 

 ieeth and hoofs. 



15 Prof, Broca, La Constitution the Skull,' translated in ' Anthro- 



les Vertebres caudales; 'La Revue pological Review,' Oct. 1868, p. 



1' Anthropologies 1872, p. 26, 428. Owen (' Anatomy of Verte- 



(separate copy). brates,' vol. ii. 1866, p. 551) on the 



76 ' Od the Primitive Form of mastoid processes in the higher ape* 



