 Models of “reciprocal altruism” (Trivers 1971, 1985), on the other hand, tell us that cooperative behavior has no chance of evolving in random pairings, but will evolve in a social framework in which individuals can benefit from building reputations for being nice guys. Reciprocal altruism, however, does not require an evolutionary argument; a simple model of learning in ongoing close-knit groups will do, and has the further advantage of explaining why certain types of cooperative behavior are more likely to emerge than others. All that matters in these models is that agents can properly identify other agents, such that they can maintain a record of their past behavior. This allows for the possibility of reputations: people who have the reputation of being cooperative will be treated cooperatively, and those who have a reputation of being unfair will be treated unfairly.