MAN'S ARBOREAL APPRENTICESHIP 



what a door was opened by the division of labor 

 that made the foot the supporting and branch- 

 gripping member, and set the hand free to reach 

 upward, to hang on by, to seize the fruit, to hug 

 the young one close to the breast ! 



On that tack of evolution, everything we value 

 depended on setting the hand free from the sup- 

 porting function and yet keeping it generalized and 

 plastic. For the human hand, so often misunder- 

 stood, remains a generalized structure, able for 

 anything. " In bones and in muscles," Dr. Wood 

 Jones says, "the human fore limb is far more like 

 that of a tortoise than it is like that of a horse or a 

 dog." There is some sense, indeed, in the adage: 

 " Good for everything is good for nothing," but the 

 other side of it is seen in the plasticity of the un- 

 specialized human hand. The opposite extreme 

 is seen in the bat's hind leg, which was also freed 

 from the supporting function, but became specialized 

 into a mere hook by which the creature hangs itself 

 up to sleep. For us the important event was the 

 emancipation of the hand, and the fact that the 

 hand thus set free was plastic and generalized 

 open to adventure. 



The arboreal life, with an emancipated hand, led 

 on to an increased freedom of movement of the thigh 

 on the hip joint, to an adjustment of the backbone 

 as a supple yet stable pillar with a characteristic 

 curve in the region of the loins, to an adaptation of 

 musculature for balancing the body on the leg, to 

 a well-developed collar-bone, to a specialization of 



