title: Human cooperation.
abstract: Why should you help a competitor? Why should you contribute to the public good if free riders reap the benefits of your generosity? Cooperation in a competitive world is a conundrum. Natural selection opposes the evolution of cooperation unless specific mechanisms are at work. Five such mechanisms have been proposed: direct reciprocity, indirect reciprocity, spatial selection, multilevel selection, and kin selection. Here we discuss empirical evidence from laboratory experiments and field studies of human interactions for each mechanism. We also consider cooperation in one-shot, anonymous interactions for which no mechanisms are apparent. We argue that this behavior reflects the overgeneralization of cooperative strategies learned in the context of direct and indirect reciprocity: we show that automatic, intuitive responses favor cooperative strategies that reciprocate.
authors.affiliation: Department of Psychology, Department of Economics, Program in Cognitive Science, School of Management, Yale University, New Haven, CT, USA.
authors.forename: David G
authors.initials: DG
authors.lastname: Rand
authors.forename: Martin A
authors.initials: MA
authors.lastname: Nowak
mesh_terms: D002755:Choice Behavior; D003299:Cooperative Behavior; D006801:Humans; D007398:Interpersonal Relations; D008960:Models, Psychological