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：合作演化背后的许多机制，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？从众规范内化——即遵守群体多数行为倾向，即使这对个体有害——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（半数）未被观测，因此未受惩罚。规范内化能否填补这一“观测缺口”，并在原则上只有当个体可能被捕获与惩罚时才选择合作的情况下，仍能促成高水平合作？具体而言，我们探究在公共物品博弈的策略空间中引入规范内化，当规范内化与合作行为均始于罕见状态时，是否能提升合作水平。答案虽为肯定，但有趣的是，这并非因为规范内化者最终构成人口显著比例，也非因其合作程度远高于其他类型个体。相反，规范内化者通过极化、催化与稳定合作行为，能在自身仅占人口少数的情况下，提升其他类型个体的合作水平。