A persistent puzzle in the social and biological sciences is the existence of prosocial behavior, actions that benefit others, often at a cost to oneself. Recent theoretical models and empirical studies of indirect reciprocity show that actors behave prosocially in order to develop an altruistic reputation and receive future benefits from third parties. Accordingly, individuals should stop investing in reputations via prosocial behavior when a future benefit (via indirect reciprocity) is unlikely. The conclusion that the absence of reputational incentives necessarily leads to egoistic behavior contrasts sharply with models of heterogeneous social preferences. Such models demonstrate the theoretical plausibility of populations composed of egoists and altruists. Results of Study One show that actors classified a priori as egoists respond strategically to reputational incentives, whereas those classified a priori as altruists are less affected by these incentives. Egoists act prosocially when reputational incentives are at stake but not when opportunities for indirect reciprocity are absent, while altruists tend to act prosocially regardless of whether reputational incentives are present. These results suggest that altruistic behavior can result from non-strategic altruism or reputation-building egoism. Study Two replicates these results and explores indirect reciprocation of others' prosocial acts. We found that altruists indirectly reciprocate at higher levels than egoists, and individuals tend to discount others' prosocial behaviors when they occur in the presence of reputational incentives. As a result, public prosocial behaviors are indirectly reciprocated less than private prosocial behaviors. In line with our argument that altruists pay less attention to reputational incentives, egoists showed a greater tendency than altruists to discount others' public prosocial behaviors. The results support the growing focus on heterogeneity of individuals'social preferences in models of altruism and indirect reciprocity.

In explaining the sources of cooperation and prosocial behavior, psychologists, behavioral economists, and biologists often focus on factors internal to the individual, such as altruistic motivations, other-regarding preferences, and prosocial emotions. By contrast, sociologists typically emphasize social forces external to the individual, including norms, reputation systems, and social networks. Here we review evidence for these rules, reputations, and relations, showing that they have powerful and pervasive effects on cooperation and prosocial behavior. Our discussion highlights two emergent themes of the reviewed literature. First, although these classes of sociological mechanisms typically promote cooperation, their presence can also create ambiguity for individuals regarding the reasons for their own and others' prosocial acts, and that ambiguity can undermine future prosociality in subsequent settings where the mechanisms are absent. Second, altruistic preferences and social mechanisms often interact, such that the causal significance of altruism is attenuated where these mechanisms are present.

This article presents a refined explanation of why minimal group identities affect cooperation in social dilemmas. The refined approach builds on key tenets of social identity theory to argue that identity affects cooperation by leadings actors to maximize ingroup outcomes and minimize ingroup inequalities. A key implication of the argument is that social identity is predicted to reduce actors' responses to the ‘greed component’ in social dilemmas (the incentive to ‘free-ride’ on others' cooperation), but that it will not affect actors' responses to the ‘fear component’ (the motivation to avoid being ‘suckered’). These predictions stand in contrast to those of two existing explanations of social identity and cooperation. The three arguments are tested against the results of two new experiments. Overall, the results support the refined approach.

Norm enforcement may be important for resolving conflicts and promoting cooperation. However, little is known about how preferred responses to norm violations vary across cultures and across domains. In a preregistered study of 57 countries (using convenience samples of 22,863 students and non-students), we measured perceptions of the appropriateness of various responses to a violation of a cooperative norm and to atypical social behaviors. Our findings highlight both cultural universals and cultural variation. We find a universal negative relation between appropriateness ratings of norm violations and appropriateness ratings of responses in the form of confrontation, social ostracism and gossip. Moreover, we find the country variation in the appropriateness of sanctions to be consistent across different norm violations but not across different sanctions. Specifically, in those countries where use of physical confrontation and social ostracism is rated as less appropriate, gossip is rated as more appropriate.

How do people respond to violent political protest? The authors present a theory proposing that the use of violence leads the general public to view a protest group as less reasonable, a perception that reduces identification with the group. This reduced identification in turn reduces public support for the violent group. Furthermore, the authors argue that violence also leads to more support for groups that are perceived as opposing the violent group. The authors test this theory using a large ( n = 800) Internet-based survey experiment with a politically diverse sample. Participants responded to an experimental scenario based on recent violent confrontations between white nationalist protesters and antiracist counter-protesters, allowing the authors to study whether violent protest would reduce public support even when used against a widely reviled group. The authors found that the use of violence by an antiracist group against white nationalists led to decreased support for the antiracist group and increased support for the white nationalist group. Furthermore, the results were consistent with the theorized causal process: violence led to perceptions of unreasonableness, which reduced identification with and support for the protest group. Importantly, the results revealed a striking asymmetry: although acts of violence eroded support for an antiracist group, support for white nationalist groups was not reduced by the use of violence, perhaps because the public already perceives these groups as very unreasonable and identifies with them at low levels. Consistent with this interpretation, the authors found that self-identified Republicans, a subset of the sample that reported less extremely negative views of white nationalists, showed reduced support for white nationalists when they engaged in violence.