Entered by Anatol Rapoport in Robert Axelrod's computer tournament (1980) and analyzed by Axelrod (The Evolution of Cooperation, 1984).
Cooperates on the first move and then copies the other side's last move, a clear and forgiving rule that sustains cooperation in repeated dealings.
When to reach for it
When dealing repeatedly with the same partner, supplier, or rival, and the question is how to sustain cooperation without being exploited.
How it runs
- Cooperate on the first interaction.
- Then match whatever the other side did last.
- Forgive an occasional defection to avoid a spiral.
- Make the rule visible so the other side can read it.
Where it sits in SOLVE eX
Go to the source
- Effective Choice in the Prisoner's Dilemma, Journal of Conflict Resolution 24(1), 1980
- The Evolution of Cooperation, 1984