Babies posture to learn

A 9-month-old infant placed on a wooden platform spies a brightly colored ball and crawls awkwardly but relentlessly toward the toy. He reaches the platform’s edge and vainly thrusts an arm in the air. The ball lies beyond his reach on another platform, across a sheer drop of more than 2 feet. Unperturbed, he keeps right on going, as if to crawl through thin air.