Direct Reciprocity Under Uncertainty Does Not Explain One-Shot Cooperation, But It Can Explain Norm Psychology

Humans in many societies cooperate in economic experiments at much higher levels than would be expected if their goal was maximizing economic returns even when interactions are anonymous and one-shot. This is a puzzle because paying a cost to benefit another player in one-shot interactions has no direct benefit to the cooperator. This paper explores the logic of two competing evolutionary hypotheses to explain this behavior. The \"norm psychology\" hypothesis holds that a players choice of strategy is heavily influenced by socially-learned cultural norms. Its premise is that over the course of human evolutionary history, cultural norms varied considerably across human societies and through a