Group 1: The Role of Cognition and Emotion in Cooperation

Altruism, behavior which reduces the individual fitness of the actor while increasing the fitness 7 of another organism, has attracted much attention from both biologists and economists because it 8 seems to defy the logic of both natural selection and standard preferences. In biology, kin 9 selection (Hamilton 1964) is the best-established explanation of the evolution and maintenance 10 of altruistic behavior. However, many examples of apparent altruism defy explanation by kin 11 selection, since they occur among unrelated individuals. The second best-established theory, 12 reciprocal altruism (Trivers 1971), offers to explain substantial portions of this remainder. 13 However, outside of humans, little good evidence exists, so its status is still undetermined. In 14 addition, many examples of putative altruism in humans, particular those of greatest interest to 15 economists, defy explanation by reciprocal altruism, either because they occur within very large 16 groups of individuals or occur without the possibility of reciprocation. Thus the challenge before 17 us is to understand better the range of mechanisms that support cooperation, particularly outside 18 kin selection. 19