Collective conflicts among humans are widespread, though often highly destructive. A
classic explanation for the prevalence of such warfare is leadership by self-serving
individuals that reap the benefits of conflict while other members of society pay the
costs. Here, we show that leadership of this kind can also explain the evolution ...
Collective conflicts among humans are widespread, though often highly destructive. A
classic explanation for the prevalence of such warfare is leadership by self-serving
individuals that reap the benefits of conflict while other members of society pay the
costs. Here, we show that leadership of this kind can also explain the evolution of
collective violence in certain animal societies. We first extend the classic Hawk-Dove
model of the evolution of animal aggression to consider cases in which a subset of
individuals within each group may initiate fights in which all group members become
involved. We show that leadership of this kind, when combined with inequalities in the
payoffs of fighting, can lead to the evolution of severe intergroup aggression, with
negative consequences for population mean fitness. We test our model using long-term
data from wild banded mongooses, a species characterised by frequent intergroup
conflicts that have very different fitness consequences for male and female group
members. The data show that aggressive encounters between groups are initiated by
females, who gain fitness benefits from mating with extra-group males in the midst of
battle, whereas the costs of fighting are borne chiefly by males. In line with the model
predictions, the result is unusually severe levels of intergroup violence. Our findings
suggest that the decoupling of leaders from the costs that they incite amplifies the
destructive nature of intergroup conflict.