Repeated interactions provide a prominent but paradoxical hypothesis for human cooperation in one-shot interactions. Intergroup competitions provide a different hypothesis that is intuitively appealing but heterodox. We show that neither mechanism reliably supports the evolution of cooperation...

Repeated interactions provide a prominent but paradoxical hypothesis for human cooperation in one-shot interactions. Intergroup competitions provide a different hypothesis that is intuitively appealing but heterodox. We show that neither mechanism reliably supports the evolution of cooperation...

Repeated interactions provide a prominent but paradoxical hypothesis for human cooperation in one-shot interactions 1–3. Intergroup competitions 4–7 provide a different hypothesis that is intuitively appealing but heterodox. We show that neither mechanism reliably supports the evolution of...