Research reveals that cooperation has the best chance to spread in a community if there are many possibilities for productive interactions, if there are repeated encounters between the same people, and if people know each other and value their reputation. In this case, we can draw on the mechanisms of direct reciprocity—I scratch your back and you scratch mine—and indirect reciprocity, which means I scratch your back and I believe that somebody else will scratch mine down the road.
Costly punishment, in which one person punishes another at a cost to himself, rarely pays off. In cooperation games, those who engage in costly punishment do not benefit from their behavior individually, and the use of punitive behavior bestow no benefit on the group as a whole. In an extremely competitive setting, the winners are those who resist the temptation to escalate conflicts, while the losers punish and perish. These results demonstrate that costly punishment is not an effective force for promoting cooperation, and our tendency to engage in acts of spiteful punishment must have evolved for other reasons, such as establishing a dominance hierarchy or defending ownership.
