MANNER OP DEVELOPMENT. 51 



commonly progresses by resting on its bent hands. The long- 

 armed apes occasionally use their arms like crutches, swinging 

 their bodies forward between them, and some kinds of Hylobates, 

 without having been taught, can walk or run upright with tolerable 

 quickness; yet they move awkwardly, and much less securely than 

 man. We see, in short, in existing monkeys a manner of progres- 

 sion intermediate between that of a quadruped and a biped; but, 

 as an unprejudiced judge'^ insists, the anthropomorphous apes 

 approach in structure more nearly to the bipedal than to the quad- 

 rupedal 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 time trans- 

 formed for firm support and progression, endless other changes of 

 structure would have become necessary. The pelvis would have 

 to be broadened, the spine peculiarly curbed, and the head fixed ir. 

 an altered position, all which changes have been attained by man. 

 Prof. Schaaffhausen™ maintains that "the powerful mastoid proc- 

 "esses 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 cor- 

 related 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 a,nother. No doubt these means of 

 change often co-operate: thus v/hen certain muscles, and the 

 crests of bone to which they are attached, become enlarged by ha- 

 bitual use, this shows that certain actions are habitually per- 

 formed 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 in- 

 direct 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, v/ould be- 

 come reduced in size, as we may feel almost sure from innumerable 

 analogous cases. In a future chapter we shall meet with a closely 



■"= Prof. Broca, La Constitution des Vertebres caudales; 'La Revue 

 d'AnthropoIog-ie,' 1872, p. 26 (separate copy). 



" 'On the Primitive Form of the Skull,' translated in 'Anthropolog- 

 fcal Review,' Oct. 1868, p. 428. Owen ('Anatomy of Vertebrates,' vol. ii. 

 1866, p. 551) on the mastoid processes in the higher apes. 



