Cultural evolutionary theory, like other evolutionary theories, links individual-level and population or society-level phenomena. It provides numerous bridges between social psychology and other disciplines and sub-disciplines. The theory uses mathematical models to understand the population-level consequences of the individual-level processes of individual and social learning. The theory has been used to explain group-level behavior such as cooperation, altruism, and the cross-cultural variation associated with social institutions. The empirical study of social psychological assumptions of such models and experimental tests of cultural-evolutionary hypotheses are in their infancy.