The proposed research focuses on the evolution and development of normative disagreement and its relation to the emergence of large-scale cooperation and cultural complexity. Normative disagreement is an understudied cause of cultural complexity via norm diversification. It leads to both opposing norms that govern the same aspects of our lives as well as norms that govern different aspects of it such as moral, religious, political, and epistemic norms. Human norm-psychology is often seen as a key driver of large-scale cooperation in our lineage. But large-scale cooperation is constantly threatened by normative disagreement, whether moral, religious, political, or epistemic. In this project, I aim to understand the evolutionary and developmental roots of these kinds of disagreement, the proximal mechanisms responsible for handling them, and the consequences that the underlying psychology of moral disagreement had for the expansion of cooperation in large, culturally complex societies.