THE EVOLUTION OF MAN 193 



The Effects of Brachiation. Two important changes may re- 

 sult from the use of such appendages. Physically, the ability to 

 hang from a limb by one or more appendages, makes possible the 

 type of locomotion, known as ])rachiation, i.e., swinging from 

 branch to branch by the fore-limbs, as is done by the arboreal 

 primates. The effect of gravity would then be felt by the body as 

 a straightening pull, while the hind-limbs would be resolved 

 functionally into supports for the body while resting upon branches 

 or moving about on the ground. Such division of locomotion 

 would be functional specialization of great importance to arboreal 

 animals. Jones writes, "As arboreal life becomes more complete, 

 the search for a new foothold will become a far more exacting 

 business than it is in the mere clambering we have pictured (of 

 quadrupedal animals). The more exacting the search becomes, 

 the more will there tend to be developed that most important 

 factor — the specialization of the functions of the fore- and hind-limbs. 

 While the animal reaches about with its fore-limb, the hind-limb 

 becomes the supporting organ. With the evolution of this process 

 there comes about a final liberation of the fore-liml) from any such 

 servile function as supporting the weight of the body; it becomes a 

 free organ full of possibilities, and already capable of many things. 

 This process I am terming the emancipation of the fore-limb, and its 

 importance as an evolutionary factor appears to me to be enor- 

 mous." Restriction of the supporting function to the hind-limb 

 and the straightening of the extended l^ody alike would tend to 

 develop the erect posture from the quadrupedal. The transition 

 is, of course, not a slight one, but in the peculiar locomotion of 

 the apes we see that such transitional development may exist. 



Brachiation and Mind. The "emancipation of the fore-limb" 

 could not fail to be an active stimulus to nervous development. 

 Swinging from branch to branch high above the ground would 

 require keenness of the senses, especially of vision, nice coordina- 

 tion, and exactness of judgment of contributing physical factors, 

 such as wind. We can best understand these things by consider- 

 ing the feats of acrobats. Since the penalty of inaccuracy would be 

 death or serious injury in most cases, there would be no question 

 of perpetuation of the unfit. In this way and through the freedom 

 of the fore-limbs for handling and examining any object within 

 reach the development would react upon the senses. Not only 

 would inherent keenness of the mind and senses be emphasized; a 



