Learning the lessons of tit-for-tat: Even competitors can get the message.

The tit-for-tat strategy is known for its ability to train cooperation during an iterated 2-person prisoner's dilemma. In this research, a repeated measures design was used to assess the nature and long-term persistence of such training. One month after playing against a programmed tit-for-tat strategy, participants returned to the lab to play a randomly matched other participant. Participants increased their levels of cooperative behavior, both during the 1st sequence and in the 2nd sequence compared with the first. Dispositional competitors increased the most from the 1st to the 2nd sequence and also gained the most new respect for opponents' self-interestedness following the 1st sequence. This suggests that competitors may be individualists at heart and that the punitive feature of tit-for-tat (R. Axelrod, 1984) is important for eliciting enhanced cooperation from such opponents.