Data from: Evidence for strategic cooperation in humans

Humans may cooperate strategically, cooperating at higher levels than expected from their short-term interests, to try and stimulate others to cooperate. To test this, we experimentally manipulated the extent an individual’s behavior is known to others, and hence whether or not strategic cooperation is possible. In contrast to many previous studies, we avoided confounding factors by preventing individuals from learning during the game about either payoffs or about how other individuals behave. We found clear evidence for strategic cooperators – just telling some individuals that their groupmates would be informed about their behavior led to them tripling their initial level of cooperation, from 17 to 50 percent. We also found that many players play as if they do not understand the game, and their presence obscures the detection of strategic cooperation. Identifying such players allowed us to detect and study strategic motives for cooperation in novel, more powerful, ways.