Studies have shown that during WWII, psychiatric patients had a decrease in symptoms when asked to help others in meaningful ways. Studies in ethology (the study of animal behavior) have demonstrated reciprocal altruism: Animals who share during good times receive more during bad times.  Brain imaging studies show increased activity in the dopamine-nucleus accumbens reward system. Cooperation, from a neurobiological standpoint, appears to be rewarding (Southwick, 2007).