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The conflict between social groups is widespread, often imposing significant costs across multiple groups. The social insects make an ideal system for investigating inter-group relationships, because their interaction types span the full harming–helping continuum, from aggressive conflict, to mutual tolerance, to cooperation between spatially separate groups. Here we review inter-group conflict in the social insects and the various means by which they reduce the costs of conflict, including individual or colony-level avoidance, ritualistic behaviours and even group fusion. At the opposite extreme of the harming–helping continuum, social insect groups may peacefully exchange resources and thus cooperate between groups in a manner rare outside human societies. We discuss the role of population viscosity in favouring inter-group cooperation. We present a model encompassing intra- and inter-group interactions, and local and long-distance dispersal. We show that in this multi-level population structure, the increased likelihood of cooperative partners being kin is balanced by increased kin competition, such that neither cooperation (helping) nor conflict (harming) is favoured. This model provides a baseline context in which other intra- and inter-group processes act, tipping the balance toward or away from conflict. We discuss future directions for research into the ecological factors shaping the evolution of inter-group interactions. This article is part of the theme issue 'Intergroup conflict across taxa'.

Can intergroup cooperation over resources help prevent resource exhaustion and mitigate effects of climate change? How does resource uncertainty affect inter- and intra- group cooperation over resources in the common-pool resource dilemmas? I present experimental evidence from a mixed design experiment with two-between-groups factors: (1) the availability of intergroup sharing in which subjects can decide whether to give up some of their harvests to augment the resource stock of another group; (2) the presence (or absence) of shocks that can destroy a part of resources; and with one within-groups factor (41 replications). We present the evidence that random shocks encourage resource conservation. In addition, we find that intergroup cooperation is frequent. Many groups establish reciprocal exchanges of resources, which reduces the probability of resource exhaustion. The possible explanation of the high frequency of intergroup sharing in my sample is inequality aversion and reciprocity. Such reciprocal exchanges turned out to be successful in preventing resource collapse in the absence of shocks. However, the data I present show the dark sides of intergroup sharing. Subjects, who shared resources with the outgroup, harvested more for themselves following the donation. Moreover, under uncertainty, a combination of shocks and sharing made subjects overharvest resources.

Ingroup favoritism and intergroup discrimination can be mutually reinforcing during social interaction, threatening intergroup cooperation and the sustainability of societies. In two studies (N = 880), we investigated whether promoting prosocial outgroup altruism would weaken the ingroup favoritism cycle of influence. Using novel methods of human-agent interaction via a computer-mediated experimental platform, we introduced outgroup altruism by (i) nonadaptive artificial agents with preprogrammed outgroup altruistic behavior (Study 1; N = 400) and (ii) adaptive artificial agents whose altruistic behavior was informed by the prediction of a machine learning algorithm (Study 2; N = 480). A rating task ensured that the observed behavior did not result from the participant’s awareness of the artificial agents. In Study 1, nonadaptive agents prompted ingroup members to withhold cooperation from ingroup agents and reinforced ingroup favoritism among humans. In Study 2, adaptive agents were able to weaken ingroup favoritism over time by maintaining a good reputation with both the ingroup and outgroup members, who perceived agents as being fairer than humans and rated agents as more human than humans. We conclude that a good reputation of the individual exhibiting outgroup altruism is necessary to weaken ingroup favoritism and improve intergroup cooperation. Thus, reputation is important for designing nudge agents.

Indirect reciprocity is a reputation-based mechanism proposed to explain the evolution of human cooperation. Theoretical models demonstrated that the use of both first-order information (i.e., whether an evaluation target cooperated) and second-order information (i.e., the reputation of an interaction partner of the evaluation target) is critical for the evolution of cooperation. However, empirical findings on the use of second-order information have been mixed. Drawing upon the literature on group-bounded indirect reciprocity, we tested the hypothesis that individuals would be more sensitive to second-order information when evaluating in-group interactions, compared to when evaluating out-group interactions. We conducted a preregistered online experiment ( N  = 604), where we independently manipulated group membership (in-group vs. out-group), target behaviour (cooperation vs. defection), and recipient reputation (good vs. bad). We found that donors who defected against good recipients were rated more negatively than those who defected against bad recipients, indicating the use of second-order information. Partly consistently with our hypothesis, when individuals evaluated coopering donors, second-order information influenced reputation for in-group donor–recipient interactions more than for out-group donor–recipient interactions. Nevertheless, individuals readily used second-order information, whether or not they evaluated in-group or out-group donor–recipient interactions.

Political scientists have shown increased research interests in Asian Americans’ political behavior. Nevertheless, considerable skepticism remains over more fundamental questions about Asians, such as the capacity for pan-Asian cooperation and political solidarity in the US. To advance research in this area, the current study examines how a diverse, “pan-ethnic” Asian group can function as a cohesive collective using evidence from a behavioral game, an innovation in this area of research. I show that an inclusive common ingroup can be forged and cohesion attained when shared threats of exclusion that cut across subgroup distinctions are made salient. I demonstrate this using original experimental data that allow me to examine behavioral measures of group cohesion, as well as policy support for different subgroups. Results show the existence of co-ethnic bias among Asians in the US towards those who share their ethnic background. They also show the power of salient shared exclusionary discrimination to overcome this bias by increasing ingroup cohesion in a one-shot economic game and enhancing support for policies that benefit Asians as a group. Taken together, this study highlights unique conditions of group-based threats under which Asians in the US achieve political cooperation—particularly across South and East Asian lines—due to substantial heterogeneity within the group category.

In the International Relations (IR) literature, inequality has been identified as a major inf luence on climate policy cooperation and implementation. Identities formed by the multiple inequalities in the global order have become key organizing principles for climate negotiation and significantly affect whether policies are seen as fair. We focus on these inequality-related identities (IRIs) and present an analytical framework that translates concepts from Social Identity Theory for use in IR to systematically examine how IRIs affect perceptions of policy fairness and implementation. We contend that this framework is cross-scalar in character; that is, given the social basis of climate politics, the dynamics can be understood as social processes regardless of whether they are undertaken by states, international organizations, or individuals. We offer this framework as a tool for mobilizing insights from social psychology into IR research and understanding the ways social identities affect collective climate action.

Three experiments tested the hypothesis that implicit preferences for racial ingroup members are reduced when external mechanisms are available to incentivize cooperation between individuals. Study 1 varied the presence (vs. absence) of a third-party punisher in a series of upcoming cross-group trust games. Studies 2 and 3 held the presence of a punisher constant, but varied the punisher's likely effectiveness at incentivizing cooperation by manipulating the punisher's group membership or whether the punisher's presence was common knowledge. The results of S1 and S2 showed that anticipating an effective third party punisher reduced racial bias on an intervening evaluative priming measure. S3 was more equivocal, but overall (and as indexed by a multilevel meta-analysis) the findings across studies provide evidence for situational tuning of rapid evaluative responses as a function of contextually variable cooperative affordances.

We report the results of an ethnographic study of a natural food cooperative in which we found an inherent tension in its mission between idealism and pragmatism, and we explore the dynamics through which that tension was managed and engaged in day-to-day governance and activities. Insights from participant observation, archival data, semi-structured interviews, and surveys provide a detailed and holistic account of the intergroup and intragroup processes through which the co-op negotiated its dualistic nature, as embodied in its hybrid organizational identity. The findings suggest that the value of each side of the duality was recognized at both the individual and organizational levels. Members' discomfort with the duality, however, led them to split the mission in two and identify with one part, while projecting their less-favored part on others, creating an identity foil (an antithesis). This splitting resulted in ingroups and outgroups and heated intergroup conflict over realizing cooperative ideals vs. running a viable business. Ingroup members favoring one part of the mission nonetheless identified with the outgroup favoring the other because it embodied a side of themselves they continued to value. Individuals who exemplified their ingroup's most extreme attributes were seen by the outgroup as prototypical, thus serving as \"lightning rods\" for intergroup conflict; this dynamic paradoxically enabled other ingroup members to work more effectively with moderate members of the outgroup. The idealist-pragmatist duality was kept continually in play over time through oscillating decisions and actions that shifted power from one group to the other, coupled with ongoing rituals to repair and maintain relationships disrupted by the messiness of the process. Thus ostensible dysfunctionality at the group level fostered functionality at the organizational level.