Iterated Prisoner's Dilemma
The same dilemma played repeatedly by the same participants, where today's choice shapes tomorrow's treatment.
Why it matters now
Repetition is the most reliable engine of cooperation known. When participants expect to meet again, generous and forgiving strategies outperform ruthless ones. Nearly every workable environmental institution is a machine for making sure the players meet again: annual conferences, renewable licences, ratchet mechanisms, public scorecards.
Where this is happening on Earth
- North AmericaRobert Axelrod's tournaments, University of MichiganA simple strategy that cooperates first and then mirrors its partner beat every elaborate rival, and the lesson has shaped diplomacy since.
- EuropeParis Agreement ratchet cycleFive-year rounds of pledge, review, and revision deliberately convert a one-shot bargain into a repeated one.
- AsiaJapanese satoyama landscapesVillage commons of woodland, paddy, and stream sustained for centuries by households who knew they would face each other every season.
- AfricaMaasai grazing agreements, Kenya and TanzaniaHerders who share dry-season pasture year after year enforce rotation through reputation rather than fences.
- OceaniaRāhui closures, Aotearoa New ZealandTemporary Māori-led bans on harvesting a reef or river are respected because the community expects to return to the same waters.
The idea itself
The encyclopedia entry first, then live searches at journals and magazines that keep returning current work on this specific idea.
Current reporting from around the world
Standing feeds at reputable periodicals. These stay fresh on their own, which is why they are here instead of a list of articles that would be out of date within a season.