Modelling behaviour in intergroup conflicts: a review of microeconomic approaches

Although uniquely destructive and wasteful, intergroup conflict and warfare are not confined to humans. They are seen across a range of group-living species, from social insects, fishes and birds to mammals, including nonhuman primates. With its unique collection of theory, research and review contributions from biology, anthropology and economics, this theme issue provides novel insights into intergroup conflict across taxa. Here, we introduce and organize this theme issue on the origins and consequences of intergroup conflict. We provide a coherent framework by modelling intergroup conflicts as multi-level games of strategy in which individuals within groups cooperate to compete with (individuals in) other groups for scarce resources, such as territory, food, mating opportunities, power and influence. Within this framework, we identify cross-species mechanisms and consequences of (participating in) intergroup conflict. We conclude by highlighting crosscutting innovations in the study of intergroup conflict set forth by individual contributions. These include, among others, insights on how within-group heterogeneities and leadership relate to group conflict, how intergroup conflict shapes social organization and how climate change and environmental degradation transition intergroup relations from peaceful coexistence to violent conflict. This article is part of the theme issue ‘Intergroup conflict across taxa’.

Section: (A) Individual Participation In Group Conflictmentioning

confidence: 99%

“…Borrowing from standard economic theory, we assume that choosing a conflictual path of action becomes more attractive for individuals, relative to less conflictual options, with increases in several characteristics of the decision situation [ 51 , 52 ] (also see [ 84 , 85 ]). Adding to past literature, several contributions to this theme issue converge on five key arguments that determine what we can call the ‘conflict participation function’ p for individual i :

Section: Initiating and Escalating Intergroup Conflictmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Intergroup conflict: origins, dynamics and consequences across taxa

Dreu

Triki

2022

“…The most active contributors in intergroup conflict typically should be those with greater capability or those who are likely to either pay lower costs or reap higher benefits [30]. Accordingly, having such variation in a group can catalyse collective action in intergroup conflict by asymmetrically advantaged individuals-even when it is high cost to them [49].…”

Section: Key Individuals In Intergroup Violencementioning

confidence: 99%

Key individuals catalyse intergroup violence

Glowacki

McDermott

2022

Intergroup violence is challenging to understand: why do individuals cooperate to harm members of other groups when they themselves may be killed or injured? Despite progress in understanding the evolutionary and proximate mechanisms that underlie violence, we still have little insight into the processes that lead to the emergence of coalitionary aggression. We argue that an overlooked component is the presence of individuals who have a crucial role in initiating violence. In instigating intergroup violence, these key individuals may expect to face lower costs, receive greater benefits, or garner benefits that have a greater value to them than others. Alternatively, key individuals may be motivated by individual traits such as increased boldness, propensity for aggression or exploratory behaviour. Key individuals catalyse the emergence of coalitionary violence through one of several processes including altering the costs and benefits that accrue to others, paying a greater share of the startup costs, signalling privileged knowledge, or providing coordination, among other factors. Here we integrate diverse lines of empirical research from humans and non-human animals demonstrating that inter-individual variation is an important factor in the emergence of intergroup violence. Focusing on the role of key individuals provides new insights into how and why violence emerges. This article is part of the theme issue ‘Intergroup conflict across taxa’.

“…This approach therefore assumes that individuals choose their behaviours freely with the goal of maximizing their payoff or other preferences (e.g. [15]), i.e. the rational actor model, while the material nature of the resources over which groups contest means that warfare can be regarded as a type of subsistence strategy in these formalizations.…”

Section: Introductionmentioning

confidence: 99%

Evolution of warfare by resource raiding favours polymorphism in belligerence and bravery

Mullon

Lehmann

2022

From protists to primates, intergroup aggression and warfare over resources have been observed in several taxa whose populations typically consist of groups connected by limited genetic mixing. Here, we model the coevolution between four traits relevant to this setting: (i) investment into common-pool resource production within groups (helping); (ii) proclivity to raid other groups to appropriate their resources (belligerence); and investments into (iii) defense and (iv) offense of group contests (defensive and offensive bravery). We show that when traits coevolve, the population often experiences disruptive selection favouring two morphs: ‘Hawks’, who express high levels of both belligerence and offensive bravery; and ‘Doves’, who express neither. This social polymorphism involves further among-traits associations when the fitness costs of helping and bravery interact. In particular, if helping is antagonistic with both forms of bravery, coevolution leads to the coexistence of individuals that either: (i) do not participate into common-pool resource production but only in its defense and appropriation (Scrounger Hawks) or (ii) only invest into common pool resource production (Producer Doves). Provided groups are not randomly mixed, these findings are robust to several modelling assumptions. This suggests that inter-group aggression is a potent mechanism in favouring within-group social diversity and behavioural syndromes. This article is part of the theme issue ‘Intergroup conflict across taxa’.