Cooperation in the prisoner's dilemma

What makes this fascinating

• Betrayal is the “rational” move — Game theory says two self-interested players should defect — yet both then do worse than if they'd cooperated.

• Why cooperation thrives anyway — Repetition, reputation, and kinship let cooperation evolve despite the constant temptation to cheat.

• Tit-for-tat — A famously simple strategy — cooperate first, then mirror your partner — won Axelrod's tournaments.

Frequently asked questions

What is the prisoner's dilemma?

A scenario where two rational, self-interested players both do better by cooperating, yet each is individually tempted to betray — so pure self-interest predicts mutual defection and a worse outcome for both.

Why does cooperation evolve despite the prisoner's dilemma?

When the game is repeated, strategies like tit-for-tat reward cooperation and punish betrayal; reciprocity, reputation, and kinship all help cooperation emerge — but fully explaining real-world cooperation remains an active question.

Why does it matter?

The dilemma models everything from arms races to climate agreements to everyday trust, so understanding when cooperation wins has wide implications across biology, economics, and politics.

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