Abstract
This paper reviews recent studies of reciprocal altruistic behaviours in non-human primates. Although altruistic behaviours such as alliances in agonistic interactions and social grooming are explained by the theories of kin selection or reciprocal altruism, evidence of reciprocity is scarce. Recent development of methods, however, may allow us to investigate reciprocity in quantitative and systematic ways. Model-based comparison of matrices of social interactions in a group are a powerful tool to investigate reciprocity at group level. Sequential analyses of social interactions reveal how monkeys do decision-making during the interactions with different partners in terms of reciprocity. Some computer simulations may give us an insight into false reciprocity in the case that human observers may assume the existence of reciprocity. It is also discussed whether reciprocal altruism could develop into true altruism which is reported exclusively in humans.
