This paper surveys the evolutionary game theoretic literature on reciprocity in human interactions, dealing both with long-term relationships and with sporadic interactions. Four basic themes, repetition, commitment, assortation, and parochialism, appear repeatedly throughout the literature....

Strong reciprocity refers to the willingness to sacrifice one's own material self-interest to punish others for opportunistic actions. This propensity provides a decentralized mechanism for the enforcement of social norms, but its extent and persistence poses a theoretical puzzle. Since...

This paper provides an evolutionary theory of reciprocity as an aspect of preference interdependence. It is shown that reciprocal preferences, which place negative weight on the payoffs of materialists and positive weight on the payoffs of sufficiently altruistic individuals can invade a...