Human adaptation to war: Evidence from 30+ studies

Was small-scale war a recurrent feature of life during human evolution, and—consequently—have humans adapted to war? This question has generated major scholarly debate, primarily informed by archaeology, ethnography, and primatology. We examine adaptation to war in contemporary humans via cognitive psychology experiments. If war recurred during evolution, then our minds are likely equipped with efficient, complex, and specialized mechanisms for effective navigation of intergroup coalitional aggression. Fourteen hypotheses were derived positing the existence of rapid and accurate coalition detection, enumeration, and formidability assessment mechanisms. Twenty-five exploratory experiments (ca. 5000 participants) custom-fitted established attentional bias, enumeration, and rating paradigms for large-scale online administration, and preliminary tested the hypotheses. Seven preregistered studies with probability samples totaling ca. 12,000 participants supported 11 of the hypotheses. Participants automatically attended to, efficiently enumerated, and made nuanced assessments of rapidly presented schematic coalitions. Male participants enumerated the coalitions more rapidly and accurately, female participants perceived them as more formidable, and female and less formidable participants overestimated their numerical size. Combined with multiple tests of alternative explanations, the evidence suggests the existence of specialized adaptations to intergroup coalitional aggression, consistent with the broader hypothesis that human prehistory was characterized by war.