When a slack-mouthed chimpanzee lets loose a husky guffaw, you know he's having a good time. Homo sapiens isn't always so transparent—sometimes when we laugh, we're just being polite—but it turns out ...

Compared to children, adults don't play as much, but social play into adulthood is considered a universal human trait. Play has a role in building tolerance, cohesion, bonding, and cooperation. By ...