Is punishment a destructive force that breaks societies or part of the very glue that holds them together? Last year, I blogged about two studies that tried to answer this question using similar psychological games. In both, volunteers played with tokens that were eventually exchanged for money. They had the option to either cooperate with each other so that the group as a whole reaped the greatest benefits, or cheat and freeload off the efforts of their peers.

In both studies, giving the players the option to punish each other soon put a relative end to cheating. Faced with the threat of retaliation, most players behaved themselves and levels of cooperation kept stable. But this collaboration came at a