Theory 029/Life & Evolution /Social evolution
Cooperation Needs Cheap Partner Choice
Cooperation is explained by kinship and by reciprocity. The ability to leave may matter more than either.
Cooperation collapses when partner choice is costly rather than when relatedness is low, so interventions that reduce the cost of switching partners should stabilise cooperation more than interventions that increase kinship.
01The evidence
Cooperation persists in some unrelated groups and fails in some related ones, and the difference often tracks whether individuals can choose partners.
02The tension
Kin-selection and reciprocity models explain cooperation in their respective regimes and predict collapse outside them, yet cooperation persists in cases where both are weak.
03The mechanism
If partners can be chosen cheaply, cheaters are abandoned and cooperators assort. When choice is costly, cheaters cannot be avoided and cooperation erodes even among relatives.
That makes the cost of partner choice the controlling variable, and predicts that reducing switching costs should restore cooperation at any relatedness.
04What this is not
Those models condition cooperation on relatedness or on repeated interaction. This conditions it on the cost of leaving, which explains persistence outside both regimes.
05Predictions
- P1Cooperation should track switching cost better than relatedness.
- P2Lowering choice costs should stabilise cooperation.
- P3Cooperation should persist among unrelated partners when choice is cheap.
06Refutation
Cooperation tracking relatedness at controlled choice cost would leave kin selection in control.
07What it changes
It would suggest institutional design through reduced exit costs.