Evolutionary theory predicts rigorous competition in nature and selfish behavior is thus seen as its inevitable consequence. Evidence of altruistic and cooperative behavior therefore appears at odds with evolutionary theory. However, evolutionary psychology suggests that past environments may be different from the current environments that humans inhabit. Here it is hypothesized that competition in two past environments might have led to strategies that favored altruism and cooperation toward nonkin. First, the expansion of the human brain is seen as requiring long-term, quality parental investment to sustain it. Altruistic displays could well have signaled an ability and willingness to provide such parental investment in a potential mate and been favored as a result. Second, the development of extra-somatic weapons is seen as leading to competition within hominin groups becoming more costly as disputes would have become lethal. A cooperative strategy could have achieved greater net fitness if the benefits of reduced involvement in such lethal disputes exceeded the costs of cooperation. Genes associated with human altruism and cooperation toward nonkin could thus have increased infrequency and come to be expressed in modern human populations despite the environments in which they evolved no longer being fully evident in the modern world.