Previous work has found that in social dilemmas, the selfish always free-ride, while others will cooperate if they expect their peers to do so as well. Outcomes may thus depend on conditional cooperators’ beliefs about the number of selfish types. An early round of the game may be played...

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...