Selfish punishment: Altruism can be maintained by competition among cheaters

Altruistic punishment refers to a class of behaviors that deters cheating at a cost to the punisher, making it a form of second-order altruism. Usually, it is assumed that the punishers are themselves “solid citizens” who refrain from cheating. We show in a simulation model that altruism and punishment paradoxically become negatively correlated, leading to a form of selfish punishment. Examples of selfish punishment can be found in organisms as diverse as wasps, birds, and humans.