Why is evolutionary theory controversial among members of the American public? We propose a novel explanation: allegiance to different criteria for belief. In one interview study, two online surveys, and one nationally representative phone poll, we found that evolutionists and creationists take different justifications for belief as legitimate. Those who accept evolution emphasize empirical evidence and scientific consensus. Creationists emphasize not only the Bible and religious authority, but also knowledge of the heart. These criteria for belief remain predictive of views about evolution even when taking into account other related factors like religion, political affiliation, and education. Each view is supported by its own internally specified criteria for what constitutes a justified belief. Changing minds may thus require changing epistemic norms.