Altruistic punishment and the origin of cooperation

Abstract

How did human cooperation evolve? Recent evidence shows that many people are willing to engage in altruistic punishment, voluntarily paying a cost to punish noncooperators. Although this behavior helps to explain how cooperation can persist, it creates an important puzzle. If altruistic punishment provides benefits to nonpunishers and is costly to punishers, then how could it evolve? Drawing on recent insights from voluntary public goods games, I present a simple evolutionary model in which altruistic punishers can enter and will always come to dominate a population of contributors, defectors, and nonparticipants. The model suggests that the cycle of strategies in voluntary public goods games does not persist in the presence of punishment strategies. It also suggests that punishment can only enforce payoff-improving strategies, contrary to a widely cited "folk theorem" result that suggests that punishment can allow the evolution of any strategy.

Fig. 1.

Population dynamics in the public goods game without (a) and with (b and c) altruistic punishers. The vertices denote homogenous populations of defectors, nonparticipants, and contributors (a) or contributors and punishers (b and c). The hue of the orbit denotes the ratio of punishers to contributors (lighter, more contributors; darker, more punishers). A stationary point Q appears for some parameter combinations as in c, but it is never stable (see Appendix). Parameters are as follows: b = 3 and c = 1; p = 2, k = 1, and α = 0.1 (b); and p = 3, k = 1, and α = 0.2 (c).