Repeated Games & Axelrod's Tournaments
Robert Axelrod · 1984
"Axelrod invited game theorists to submit programs for iterated prisoner's dilemma and the simplest — Tit for Tat, cooperate first then copy the opponent — won, showing cooperation can evolve without central authority when the shadow of the future is long enough."
Axelrod ran a computer Olympics for prisoner's dilemmas in 1980: every submitted strategy played every other for 200 rounds. The winner was four lines long.
Tit for Tat's four properties — nice (starts cooperatively), retaliatory (punishes defection immediately), forgiving (returns to cooperation after the opponent does), and clear — make its intentions legible. In a repeated game, the expected value of future cooperation outweighs the one-shot gain from defection, so 'live and let live' equilibria emerge even among egoists. Extensions (generosity, contrition) handle noise, but the core lesson stands: design the repetition, not just the single move.
Why did Tit for Tat win Axelrod's iterated prisoner's dilemma tournaments despite its simplicity?
Read more about the topic
The explanation above is written with AI assistance. These are the originals — go to them to check it.
- The Evolution of Cooperation — Tit for Tat (Axelrod's tournaments)Robert Axelrod / Wikipedia
The Prisoner's Dilemma
"Two rational actors who cannot communicate or trust each other will often choose mutual betrayal even when mutual cooperation would leave both better off."