As demonstrated in experiments by biologists and anthropologists, chimpanzees behave in a manner consistent with two key assumptions of economics--selfish behavior and independent decision-making. In contrast, human behavior is sometimes inconsistent with the assumptions: humans are inclined to share the rewards of collaboration, and sometimes imitate others rather than making independent decisions. Chimpanzees out-perform humans in the zero-sum matching- pennies game, while humans out-perform chimpanzees in a positive-sum puzzle-solving game where cooperation and imitation promote success