Evolution of norms for judging social behavior

Abstract

Reputations provide a powerful mechanism to sustain cooperation, as individuals cooperate with those of good social standing. But how should someone’s reputation be updated as we observe their social behavior, and when will a population converge on a shared norm for judging behavior? Here, we develop a mathematical model of cooperation conditioned on reputations, for a population that is stratified into groups. Each group may subscribe to a different social norm for assessing reputations and so norms compete as individuals choose to move from one group to another. We show that a group initially comprising a minority of the population may nonetheless overtake the entire population—especially if it adopts the Stern Judging norm, which assigns a bad reputation to individuals who cooperate with those of bad standing. When individuals do not change group membership, stratifying reputation information into groups tends to destabilize cooperation, unless individuals are strongly insular and favor in-group social interactions. We discuss the implications of our results for the structure of information flow in a population and for the evolution of social norms of judgment.

When do stereotypes undermine indirect reciprocity?

“…We describe the dynamics of competing strategies using replicator differential equations [30]. As is common in the literature on indirect reciprocity [14,15,27,29], we assume that the timescale of reputation updates is faster than that of strategy dynamics, so that reputations (individual or stereotyped) equilibrate before individuals consider updating their strategies: Every individual interacts pairwise with every other individual in each round of social interactions, acting once as a donor and once as a recipient. After all pairwise games are completed, reputations are updated according to a monitoring system and a social norm, described below.…”

“…We define monitoring systems for reputations that specify how reputations are shared within the population. Aside from the commonly studied cases of public [2,11,14,28] or private [16,18,19,27] monitoring systems, we also study a group-wise monitoring system [15,25] in which members within a group agree on their views of others, but there might be disagreement between groups. Altogether, we consider three scales of information sharing, summarized in To study the effects of stereotyping on cooperation, we consider two types of reputations (Fig 1D).…”

“…Theoretical models of indirect reciprocity have found that cooperation depends on the extent to which individuals share the same views of one another. When reputations are shared, public knowledge [9][10][11]-facilitated by gossip [2,12,13] or by institutions that broadcast information [14,15]-everyone agrees about each other's reputation, and cooperation thrives as individuals choose to cooperate with those of good social standing. However, when individuals hold private and thus possibly different opinions about the moral standings of others, disagreements about reputations can lead to the perception of unjustified behavior, a decay of reputations, and the eventual collapse of cooperation [16][17][18][19].…”

“…For instance, members within a group may agree on their opinions of others, but different groups may hold different views. Both of these effects remain understudied, with a few notable exceptions [15,25,26]. In this context, we can break down our main question into three interrelated questions.…”

“…To study these questions, we extend a game-theoretic model of indirect reciprocity in populations with group structure [15] in two ways. First, we introduce the possibility of stereotyped reputations-that is, reputations assigned to groups as opposed to individuals.…”