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.

翻译：许多合作演化的机制，如互惠、间接互惠和利他惩罚，都需要群体了解个体行为。但当无人监督时，是什么促使人们持续合作？从众规范内化——即即使对个体有害也倾向于遵从群体多数行为的倾向——可能是答案。本文分析了一个兼具以下特征的世界：(1) 存在群体选择与基于间接互惠的惩罚机制，但(2) 许多行为（一半）未被观测，因而未受惩罚。规范内化能否填补这一"观测缺口"，并在代理者原则上仅当可能被捕获并受罚时才合作的情况下，仍能维持高水平的合作？具体而言，我们试图探究在公共物品博弈的策略空间中引入规范内化后，当规范内化与合作均以罕见状态起步时，能否提升合作水平。结果证明答案是肯定的，但有趣的是，这并非因为规范内化最终构成人口中的显著比例，也非因为他们比其他代理者类型的合作程度高出许多。相反，规范内化者通过极化、催化与稳定合作过程，仅作为人口中的少数群体，即可提升其他代理者类型的合作水平。