68 ORGANIC EVOLUTION 



handed animals, the Quodrumana ; or, to use the 

 more familiar terms, man is a biped, not a 

 quadruped. 



Every one has seen pictures of the gorilla, striding 

 along on its hind-legs, but balancing its body on 

 the knuckles of its hands. Only by a muscular 

 effort, not long to be sustained, can any mammal 

 other than man dispense with the aid of the fore- 

 limbs in standing and in progression. 



So profoundly important has been the liberation 

 of man's fore-limbs from the performance of any 

 balancing or locomotory function, that we must 

 inquire into the anatomical circumstances which 

 permit of this liberation. Consider the hip-joint of 

 a dog or an ape, or a human baby. In each case, a 

 vertical line dropped from the centre of gravity of 

 the animal's body will reach the ground at a point 

 in front of the point reached by a vertical line 

 dropped from the hip-joints. This being so, none 

 of these animals, save by a great muscular effort, 

 can stand upright. As the baby grows, however, 

 the curvature of its spinal column — which at birth 

 and for some months thereafter is a simple curve 

 concave forwards — undergoes an important series of 

 modifications, the result of which is so to alter the 

 relation of the centre of gravity to the hip- joint 

 that the vertical from the former falls behind the 

 vertical from the latter. Thus the adult human 

 body tends to roll backwards at the hip-joints, 

 whilst the body of the infant (true to the history of 

 the race) tends to fall, and indeed does fall, for- 

 wards. This is why a baby crawls ere it can stand 

 or walk. In consequence of the change in equili- 



