Social norm dynamics and cooperation in changing groups.

Social norms promote cooperation in human groups. How are these norms and cooperation affected when groups change due to new members arriving and old members leaving? In this review we highlight the scant literature that researches the effects of group changes on social norms and cooperation. Thus far evidence suggests that newcomers cooperate less than incumbents but adjust their cooperation levels over time. However, this adjustment is not necessarily accompanied by adjustments in terms of group identification and norms. We also point to the data limitations that ensue when researching phenomena at the group level and outline future research directions.