constraints on in-group bias in prosocial behaviors – cooperation, norm enforcement, and sharing – among low-income rice farmers … in-group or out-group partners at village level. We find that in-group bias in cooperation and norm enforcement exist …

We investigate how group boundaries, and the economic environment surrounding groups, affect altruistic cooperation and … harm those who defect, encouraging a norm of cooperation towards the group. Adding competition between groups causes even … stronger in-group cooperation, but also a qualitative change in punishment: punishment becomes anti-social, harming cooperative …