Freedom, enforcement, and the social dilemma of strong altruism

Cooperation in joint enterprises poses a social dilemma. How can altruistic behavior be sustained if selfish alternatives provide a higher payoff? This social dilemma can be overcome by the threat of sanctions. But a sanctioning system is itself a public good and poses a second-order social dilemma. In this paper, we show by means of deterministic and stochastic evolutionary game theory that imitation-driven evolution can lead to the emergence of cooperation based on punishment, provided the participation in the joint enterprise is not compulsory. This surprising result—cooperation can be enforced if participation is voluntary—holds even in the case of ‘strong altruism’, when the benefits of a player’s contribution are reaped by the other participants only.