The Emergence of Altruistic Punishment: Via Freedom to Enforcement

In human societies, cooperative behaviour in public goods interactions is usually enforced through institutions that impose sanctions on free-riders. Many experiments on public goods games have shown that in the absence of such institutions, individuals are often willing to punish defectors, even at a cost to themselves, effectively taking the law into their own hands. Theoretical models confirm that social norms prescribing the punishment of deviant behaviour are stable: once established, they prevent invasion by dissident minorities. But how can such costly punishing behaviour gain a foothold in the population? A surprisingly simple model shows that if individuals have the option to stand aside and abstain from the public goods interaction, this paves the way for the emergence and establishment of cooperative behaviour based on the punishment of defectors. Thus the freedom to withdraw from the public enterprise leads to a self-enforcing prosocial norm. Paradoxically, the option of individual autarky may be an important step for the emergence of institutions punishing the non-cooperation of their members. Conversely, public goods interactions which are obligatory rather than voluntary are unlikely to gain a foothold in the population