In experiments, people behave more cooperatively when they are aware of an external threat, while in the field, we observe surprisingly high levels of within - group cooperation in conflict situations such as civil wars. We provide an explanation for these phenomena. We introduce a model in...

In experiments, people behave more cooperatively when they are aware of an external threat, while in the field, we observe surprisingly high levels of cooperation and altruism within groups in conflict situations such as civil wars. We provide an explanation for these phenomena. We introduce a...

Costly signaling of commitment to a group has been proposed as an explanation forparticipation in religion and ritual. But if the signal’s cost is too small, freeriders willsend the signal and behave selfishly later. Effective signaling may then be prohibitivelycostly. If the average level of...