A model is presented to account for the natural selection of what is termed reciprocally altruistic behavior. The model shows how selection can operate -against the cheater (non-reciprocator) in the system. Three instances of altruistic behavior are discussed, the evolution of which the model can explain: (1) behavior involved in cleaning symbioses; (2) warning cries in birds: and (3) human reciprocal altruism. Regarding human reciprocal altruism, it is shown that the details of the psychological system that regulates this altruism can (...) be explained by the model. Specifically, friendship,d islike, moralistic aggression, gratitude, sympathy, trust, suspicion, trustworthiness, aspects of guilt, and some forms of dishonesty and hypocrisy can be explained as important adaptations to regulate the altruistic system. Each individual human is seen as possessing altruistic and cheating tendencies, the expression of which is sensitive to developmental variables that were selected to set the tendencies at a balance appropriate to the local social and ecological environment. (shrink)

Humans rely heavily on their prosocial relationships. We propose that the experience and display of prosocial emotions evolved to regulate such relationships through inhibiting individual selfishness in service of others. Two emotions in particular serve to meet two central requirements for upholding prosociality: gratitude motivates maintenance of ongoing prosocial interactions, and guilt motivates repair of ruptured prosocial interactions. We further propose, and review developmental evidence, that nascent forms of these two emotions serve their respective functions from early in ontogeny. The (...) remarkably early emergence of these prosocial emotions allows even very young children to participate in and benefit from prosociality. We discuss the implications of and challenges to this conclusion and identify pressing future directions for this work. (shrink)