The existence of cooperation and social order among genetically unrelated individuals is a fundamental problem in the behavioural sciences. The prevailing approaches in biology and economics view cooperation exclusively as self-interested behaviour— unrelated individuals cooperate only if they...

Human cooperation is an evolutionary puzzle. Unlike other creatures, people frequently cooperate with genetically unrelated strangers, often in large groups, with people they will never meet again, and when reputation gains are small or absent. These patterns of cooperation cannot be explained...

This paper provides strong evidence challenging the self-interest assumption that dominates the behavioral sciences and much evolutionary thinking. The evidence indicates that many people have a tendency to voluntarily cooperate, if treated fairly, and to punish non-cooperators. We call this...