Polarize, catalyze, and stabilize: how a minority of norm internalizers amplify group selection and punishment

Many mechanisms behind the evolution of cooperation, such as reciprocity, indirect reciprocity, and altruistic punishment, require group knowledge of individual actions. But what keeps people cooperating when no one is looking? Conformist norm internalization, the tendency to abide by the behavior of the majority of the group, even when it is individually harmful, could be the answer. In this paper, we analyze a world where (1) there is group selection and punishment by indirect reciprocity, but (2) many actions (half) go unobserved and therefore unpunished. Can norm internalization fill this “observation gap” and lead to high levels of cooperation, even when agents may in principle cooperate only when likely to be caught and punished? Specifically, we seek to understand whether adding norm internalization to the strategy space in a public goods game can lead to higher levels of cooperation when both norm internalization and cooperation start out rare. We found the answer to be positive, but, interestingly, not because norm internalizers end up making up a substantial fraction of the population, nor because they cooperate much more than other agent types. Instead, norm internalizers, by polarizing, catalyzing, and stabilizing cooperation, can increase levels of cooperation of other agent types, while only making up a minority of the population themselves. Significance statement What keeps people cooperating when no one is looking? Group selection favoring cooperative groups does not require observers, but often works best when there is some other norm enforcement mechanism to supplement it. But most norm enforcement mechanisms require observers in order to function. Here, we examine whether norm internalization could fill this enforcement gap, by acting as an “internal enforcer” of norms. Perhaps surprisingly, we discovered in our simulations that the population of norm internalizers always remained quite small, and norm internalizers did not necessarily cooperate more than other agent types. Nevertheless, under certain conditions, they were able to spark significantly higher mean levels of cooperation, by causing other agents to cooperate more—partly by setting off bouts of high cooperation after periods of very low cooperation, and partly by helping maintain those bouts of high cooperation for longer.