Leaders of war: modelling the evolution of conflict among heterogeneous groups

Abstract

War, in human and animal societies, can be extremely costly but can also offer significant benefits to the victorious group. We might expect groups to go into battle when the potential benefits of victory ( V ) outweigh the costs of escalated conflict ( C ); however, V and C are unlikely to be distributed evenly in heterogeneous groups. For example, some leaders who make the decision to go to war may monopolize the benefits at little cost to themselves (‘exploitative’ leaders). By contrast, other leaders may willingly pay increased costs, above and beyond their share of V (‘heroic’ leaders). We investigated conflict initiation and conflict participation in an ecological model where single-leader–multiple-follower groups came into conflict over natural resources. We found that small group size, low migration rate and frequent interaction between groups increased intergroup competition and the evolution of ‘exploitative’ leadership, while converse patterns favoured increased intragroup competition and the emergence of ‘heroic’ leaders. We also found evidence of an alternative leader/follower ‘shared effort’ outcome. Parameters that favoured high contributing ‘heroic’ leaders, and low contributing followers, facilitated transitions to more peaceful outcomes. We outline and discuss the key testable predictions of our model for empiricists studying intergroup conflict in humans and animals. This article is part of the theme issue ‘Intergroup conflict across taxa’.

Intergroup conflict: origins, dynamics and consequences across taxa

“…Sometimes, key group members, such as group leaders, may reap larger benefits than the rest of the group members or are at relatively low risk during the fighting [86,87]. Sankey et al [24] show evidence for this in banded mongooses where 'exploitative' leaders initiate group conflict and benefit disproportionately relative to the rest of the group. In addition to these material benefits, conflict participation may increase status-ranking (∂p i /∂γ > 0) (i.e.…”

“…Task specialization can also be vertical, carving up the group into leaders and followers (see [17,24]). Vertical specialization centralizes decision-making and can make collective action more efficient and effective [127][128][129].…”

“…B 377: 20210134 can coexist and coevolve within groups in the context of recurrent intergroup conflict. Also, grounded in field observations of intergroup conflicts in banded mongoose, Sankey et al [24] provide evolutionary agent-based modelling of how intergroup competition contributes to the emergence of 'exploitative' leaders.…”

“…R. Soc. B 377: 20210134 Sankey et al [24] show how different forms of leadership can survive in and emerge from intergroup conflict. Their analysis distinguishes 'exploitative' leaders who initiate intergroup conflict and monopolize the benefits at little cost to themselves and 'heroic' leaders who willingly pay increased costs of conflict participation above and beyond their share of the spoils.…”

“…It provides, for the first time, to our knowledge, a side-by-side treatment of intergroup conflict across taxa, detailing the origins and consequences of intergroup conflict. Each in their own way, the contributions provide insight on intergroup conflict for social insects [32,33], social fishes [40], group-living birds [26,27], non-primate mammals such as banded mongoose [24], lions and wolves [17], several monkey species [41][42][43], chimpanzees [18,44] and humans [45][46][47].…”