Date Added: Sep 2010
The authors investigate how group boundaries, and the economic environment surrounding groups, affect altruistic cooperation and punishment behavior. Their paper uses experiments conducted with 525 officers in the Swiss Army, and exploits random assignment to platoons. They find that, without competition between groups, individuals are more prone to cooperate altruistically in a prisoner's dilemma game with in-group as opposed to out-group members. They also use a costly punishment option to selectively harm those who defect, encouraging a norm of cooperation towards the group.