Variation, Consistency, and Reputation

Abstract

There is typically considerable between-individual variation in trait values in natural populations. Game theory has often ignored this, treating individuals as the same. However, the existence and amount of variation is central to many predictions in biological game theory, as this chapter illustrates. Variation is central to signalling systems and stabilizes these systems as well as extensive-form games. Variation leads to individuals taking a chance that a partner is better than average; for example, promoting cooperation in a finitely repeated Prisoner’s Dilemma game. When there is both variation and within-individual consistency, so that past behaviour is predictive of current behaviour, reputation is important. As is demonstrated, once population members respond to reputation, this then selects for all to modify their behaviour so as to change their reputation and so change how others interact with them in the future, with consequences for the level of cooperation in the population. Furthermore, as a game of trust shows, the extent to which reputation matters can depend on whether individuals are prepared to pay the cost of being socially sensitive, which depends on the amount of variation. Variation selects for individuals to be choosy about their partner, and choosiness can lead to assortative pairing in a population, again promoting cooperation. The importance of choosiness in a market situation is demonstrated by a model in which partners have to decide how much to commit to one another, with factors that enhance choosiness leading to higher levels of commitment.