The Arm We Brought Down From the Trees Summary and Analysis

Anatomically, ape and human hands have been, until recently, considered functionally equivalent by anthropologists. The prehuman arm, however, was considered functionally and anatomically different metaphorically by analysis to a construction crane and its operator. The operator must anticipate load weight and wind changes in addition to boom placement to avoid risks of tipping his crane over. The arm and shoulder may be viewed like a boom with the hand comparable to the bucket or lifting device. While the novice operator must make conscious adjustments until skilled to move his boom, the arm owner, whether quadruped or biped, moves through the unconscious control of a neuromuscular system that became "hardwired" over evolutionary time and inheritance.

The arm is suspended away from the body unlike the leg that is...