4.4 Coalitions, groups, and warfare

Humans are intensely group-living. We form alliances, mark group boundaries, and sometimes wage coordinated violence against other groups. The psychology behind coalitions is some of the most consequential — and dangerous — of our evolved equipment.

Coalitional psychology

Ancestral life made coalitions — cooperative alliances — a route to resources, defense, and status. Selection therefore built a psychology for detecting alliances, tracking who is on whose side, and signaling group membership. We are exquisitely sensitive to coalitional cues, sometimes to a fault.

Ingroup and outgroup

Coalitional psychology generates the ingroup/outgroup distinction: cooperation and trust extended to "us," suspicion and competition directed at "them." Importantly, the categories that define groups are flexible — selection did not build us to track any particular marker but to detect whatever currently predicts alliance.

The intergroup-conflict logic

Coordinated intergroup violence appears in chimpanzees and across human societies. Models suggest it can pay when an aggressor coalition can attack with low risk to itself — the "imbalance of power" condition, where overwhelming numerical advantage makes lethal raiding cheap. Much human warfare psychology, including in-group loyalty and out-group dehumanization, can be read through this lens.

A grounding example

Robert Kurzban, John Tooby, and Leda Cosmides tested whether race is a fixed category in the mind or a stand-in for coalition. Participants watched members of two mixed-race teams argue; the experimenters measured whether observers automatically encoded each speaker's race or their team. When clothing and context made team membership salient, observers' tendency to categorize by race dropped sharply — they tracked coalition instead. The finding suggests the mind does not have a dedicated "race module"; rather, it has a coalition-detector that latches onto race only when race happens to predict alliance, and lets go when something better does.