Costly signalling of commitment to a group has been proposed as an explanation for participation in religion and ritual. But if the signal’s cost is too small, freeriders will send the signal and behave selfishly later. Effective signalling may then be prohibitively costly. If the average...

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...

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

Several papers have documented that when subjects play with standard laboratory endowmentsʺ they make less self-interested choices then when they use money they have either earned through a laboratory task or brought from outside the lab. In the context of a charitable giving experiment we...

People exhibit group reciprocity when they retaliate, not against the person who harmed them, but against somebody else in that person's group. Group reciprocity may be a key motivation behind intergroup conflict. We investigated group reciprocity in a laboratory experiment. After a group...

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...