Strong reciprocity is real, but there is no evidence that uncoordinated costly punishment sustains cooperation in the...

I argue in my target article that field evidence does not support the costly punishment hypothesis. Some commentators object to my reading of the evidence, while others agree that evidence in favour of costly punishment is scant. Most importantly, no rigorous measurement of cost-benefit ratios in the field has been attempted so far. This lack of evidence does not rule out costly punishment as a cause of human cooperation, but it does pre-empt some overconfident claims made in the past. Other commentators have interpreted my article as an anti-experimental pamphlet or as a flat denial of the existence of pro-social motives--which it was not intended to be. While we have enough data to establish the existence (and theoretical relevance) of strong reciprocity motives, I argue in this response that their efficacy (and policy relevance) has not been demonstrated.