MAN’S ARBOREAL APPRENTICESHIP 289 
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 
