Exploitative leaders incite intergroup warfare in a social mammal

Rufus A. Johnstone, Michael A. Cant, Dominic Cram, Faye J. Thompson

Research output: Contribution to journalArticlepeer-review

Abstract

Collective conflicts among humans are widespread, although often highly destructive. A classic explanation for the prevalence of such warfare in some human societies 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 characterized 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 extragroup 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.
Original languageEnglish
Pages (from-to)29759-29766
Number of pages8
JournalProceedings of the National Academy of Sciences of the United States of America
Volume117
Issue number47
DOIs
Publication statusPublished - 9 Nov 2020

Keywords

  • Aggression
  • Animal behavior
  • Collective violence
  • Human evolution
  • Social evolution

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