Hübner Valentin, Schmid Laura, Hilbe Christian, Chatterjee Krishnendu
Institute of Science and Technology Austria, Klosterneuburg 3400, Austria.
Kim Jaechul Graduate School of AI, Korea Advanced Institute of Science and Technology, Seoul 02455, Republic of Korea.
PNAS Nexus. 2025 May 10;4(5):pgaf154. doi: 10.1093/pnasnexus/pgaf154. eCollection 2025 May.
Social dilemmas are collective-action problems where individual interests are at odds with group interests. Such dilemmas occur frequently at all scales of human interactions. When dealing with collective-action problems, people often act reciprocally. They adjust their behavior to match the previous behavior of the recipient. The literature distinguishes two kinds of reciprocity. According to direct reciprocity, individuals react to their immediate experiences with the recipient. They are more likely to cooperate if the recipient previously cooperated with them. According to indirect reciprocity, individuals react to the recipient's general behavior, irrespectively of whether or not they benefited directly. In practice, the two kinds of reciprocity are often intertwined; people typically base their decisions on both direct experiences and indirect observations. Yet only recently have researchers begun to explore how the two kinds of reciprocity interact. So far, this research only addresses a single type of social dilemma, the donation game, where the effects of individual behaviors are independent. Instead, here we allow for all pairwise social dilemmas. By applying novel techniques to generalize the theory of zero-determinant strategies, we establish an important proof of principle: In all social dilemmas, socially optimal outcomes can be sustained as an equilibrium, using either direct or indirect reciprocity, or arbitrary mixtures thereof. These results neither require games to be repeated infinitely often, nor that individual opinions are synchronized. In this way, we considerably generalize the scope of models of reciprocity, and we build further bridges between the literatures on direct and indirect reciprocity.
社会困境是个体利益与群体利益相悖的集体行动问题。此类困境在人类互动的各个层面频繁出现。在应对集体行动问题时，人们常常采取互惠行为。他们会调整自身行为以匹配接受者先前的行为。文献中区分了两种互惠形式。根据直接互惠，个体对与接受者的直接体验做出反应。如果接受者先前与他们合作，他们就更有可能合作。根据间接互惠，个体对接受者的一般行为做出反应，而不论他们是否直接受益。在实践中，这两种互惠形式常常相互交织；人们通常基于直接体验和间接观察来做出决策。然而，直到最近研究人员才开始探索这两种互惠形式是如何相互作用的。到目前为止，这项研究仅涉及一种单一类型的社会困境，即捐赠博弈，其中个体行为的影响是独立的。相反，在这里我们考虑所有成对的社会困境。通过应用新颖的技术来推广零行列式策略理论，我们建立了一个重要的原理证明：在所有社会困境中，社会最优结果可以作为一种均衡得以维持，使用直接互惠、间接互惠或它们的任意混合形式。这些结果既不要求博弈无限次重复，也不要求个体意见同步。通过这种方式，我们极大地拓展了互惠模型的范围，并在直接互惠和间接互惠的文献之间搭建了进一步的桥梁。
