In recent work, Atran, Henrich, Norenzayan and colleagues developed an account of religion that reconciles insights from the ‘by-product’ accounts and the adaptive accounts. According to their synthesis, the process of cultural group selection driven by group competition has recruited our proclivity to adopt and spread religious beliefs and engage in religious practices to increase within group solidarity, harmony and cooperation. While their account has much merit, I believe it only tells us half the story of how institutional religions have (...) evolved. Their cultural evolutionary account of religion only looks at the cultural dynamics arising from competition between groups, not at the dynamics arising from within the group. Drawing from game-theoretic analyses of the emergence and cultural evolution of social institutions, I outline two sets of important ‘within-group’ dynamics that shape institutional religions. The first follow from the necessity to keep the interaction of the participants in an equilibrium state in order to maintain the social institution. The second arise from the competition of institutional features for traction within the group. Bringing these dynamics into account enables us to explain prominent features of institutional religions that cannot be satisfactorily explained by the current model of the cultural evolution of religions. (shrink)