Humans have an evolved propensity to think categorically about social groups. This propensity is manifest in cognitive processes that have broad implications for public and political endorsement of multicultural policy. Drawing on these principles, we postulate a cognitive-evolutionary account of human adaptation to social diversity. This account explains broad social trends marking a resistance to multiculturalism, while providing an important reorienting call for scholars and policy-makers seeking intervention-based solutions to the problem of prejudice.