Whether they are proposing to build a wall or to exit an international coalition, populist politicians like to pitch themselves as keeping ‘outsiders’ at bay, and it clearly strikes a chord with their home crowd.
One evolutionary hypothesis for our tendency toward ingroup loyalty is that it would have been advantageous to our tribal hunter-gatherer ancestors in their competition with rival tribes (as groups with more loyal and devoted members would have been more likely to survive and reproduce). The warring behaviour seen in our chimpanzee cousins, who form coalitions to steal the territory of rival groups, is cited as evidence that supports this theory.
Yet chimps might not be the most apposite species comparison for understanding humans, and there is a more optimistic perspective on human intergroup behaviour, one that has been largely neglected by scientists to date. In a recent issue of Evolutionary Anthropology, Anne Pisor, assistant professor of Anthropology at Washington State University and Martin Surbeck at Harvard University explain that, among primates, humans are an “outlier.”
In fact, Pisor and Surbeck believe that we have evolved to be uniquely tolerant among fission-fusion species, and that the roots of this lie in part in our unusually large brains and relatively high reproductive rates, compared with other primates. Together these characteristics make us extremely dependent on high-quality, high-risk (i.e., unpredictable across time and location) food and tool supplies.