The ecology and evolution of intergroup conflict in animal societies: theory and tests

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The history of life on earth has been dominated by a series of cooperative transitions in biological organisation, in which lower-level entities have banded together to form higher-level cooperative groups. The evolution of cooperation creates opportunities for productive coordination and teamwork within groups, but also the potential for destructive conflict and violence between groups. Humans, for example, are capable of astonishing feats of altruism and cooperation, but are at once among the most murderous and violent animals we know. In other animals there is great variation in the intensity and form of intergroup conflict, but we have a very poor understanding of the causes of this variation. The link between intergroup conflict and cooperation is also unclear: in some species intergroup conflict leads to greater social cohesion, whereas in other species it leads to greater within-group aggression. Our project combines new theory and empirical testing to explain these conflicting observations and to advance conceptual understanding of the biological roots of intergroup conflict. Our theoretical models will predict the ecological and social factors that promote or inhibit intergroup aggression, and how individuals and groups should respond to changes in levels of intergroup conflict. We will carry out the first tests of these models on an ideally suited wild mammal system, the banded mongoose Mungos mungo, which we have studied for 20 years at site in Uganda. Banded mongooses live in highly cooperative, territorial groups which engage in frequent intergroup fights. Intergroup aggression is more severe in banded mongooses than in meerkats, chimpanzees, or any other non-human mammal. Yet there is also great individual and group variation in levels of intergroup aggression, providing an opportunity to test our theoretical predictions using experiments and long-term observations. The research will provide a better understanding of patterns of competition in nature, and clarify the link between intergroup conflict and cooperation. We will leave a testable theoretical framework that can be applied to a very wide range of species, from microbes to humans. The project will be of much interdisciplinary interest, with the potential to influence future research in evolution, psychology, economics and political science.