Early liberal theories about the feasibility of moral progress were premised on empirically ungrounded assumptions about human psychology and society. In this article, we develop a richer naturalistic account of the conditions under which one important form of moral progress–the emergence of more “inclusive” moralities– is likely to arise and be sustained. Drawing upon work in evolutionary psychology and social moral epistemology, we argue that “exclusivist” morality is the result of an adaptively plastic response that is sensitive to cues of out-group threat that are detected during development. We conclude with a blueprint for reinforcing and extending inclusivist progress.