Theoretical model of exploitative leadership in collective violence in animal societies

Our model extends the classic hawk-dove model to consider pairwise encounters between groups of size n. In each encounter, an individuals is randomly selected as leader and the rest of the group assigned as followers. The leader decides whether the group collectively adopts either aggressive (hawk) or peaceful (dove) tactics, via their disproportionate influence on group behaviour. Total fitness payoffs to groups are identical to that of individuals in the classic model, except that we also allow for unequal sharing. Each follower’s share of the benefit obtained from fighting is reduced compared to that of their leader, while the leader’s share of any costs incurred is reduced compared to that of a follower. Our model predicts that extreme levels of intergroup aggression will evolve when a subset of group members can initiate conflicts that involve the whole group and when initiators gain a disproportionate benefit (or suffer lower costs) than others. It suggests that destructive warfare can result from the decoupling of leaders from the costs that they incite.