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 (about 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：合作演化的许多机制，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，是什么促使人们保持合作？从众性规范内化——即使对个体有害也倾向于遵循群体大多数行为的倾向——可能是答案。本文分析了一个世界，其中（1）存在通过间接互惠实现的群体选择和惩罚，但（2）许多行为（约一半）未被观察，因此不受惩罚。规范内化能否填补这一“观察缺口”，并即使代理人在原则上仅在可能被抓获和惩罚时才合作，也能导致高水平的合作？具体而言，我们试图理解在公共物品博弈的策略空间中引入规范内化，是否能在规范内化和合作都初始罕见时带来更高水平的合作。答案发现是肯定的，但有趣的是，这并非因为规范内化者最终构成人口的大部分，也非因为他们比其他代理人类型合作更多。相反，规范内化者通过极化、催化并稳定合作，能够提升其他代理人类型的合作水平，而他们自身仅占人口的少数。