When in Doubt . . . : Cooperation in a Noisy Prisoner's Dilemma

In the last decade, there has been a resurgence of interest in problems of cooperation, stimulated largely by Axelrod’s work. Using an innovative tournament approach, Axelrod found that a simple strategy, Tit-for-Tat (TFT), was most successful in playing the repeated Prisoner’s Dilemma (PD). However, recent analytic work has shown that monitoring problems caused by noise significantly impair TFT’s effectiveness. The primary purpose of the present research is to discover whether there exist alternative strategies that perform well in a noisy PD. To investigate this question, we conducted a computer tournament. In general, effective strategies were generous (i.e., cooperated more than their partners did). TFT, which uses strict reciprocity, performed rather poorly in our tournament, in sharp contrast to Axelrod’s original results.