Direct reciprocity is a mechanism for the evolution of cooperation in repeated social interactions. According to this literature, individuals naturally learn to adopt conditionally cooperative strategies if they have multiple encounters with their partner. Corresponding models have greatly facilitated our understanding of cooperation, yet they often make strong assumptions on how individuals remember and process payoff information. For example, when strategies are updated through social learning, it is commonly assumed that individuals compare their average payoffs. This would require them to compute (or remember) their payoffs against everyone else in the population. To understand how more realistic constraints influence direct reciprocity, we consider the evolution of conditional behaviors when individuals learn based on more recent experiences. Even in the most extreme case that they only take into account their very last interaction, we find that cooperation can still evolve. However, such individuals adopt less generous strategies, and they tend to cooperate less often than in the classical setup with average payoffs. Interestingly, once individuals remember the payoffs of two or three recent interactions, cooperation rates quickly approach the classical limit. These findings contribute to a literature that explores which kind of cognitive capabilities are required for reciprocal cooperation. While our results suggest that some rudimentary form of payoff memory is necessary, it already suffices to remember a few interactions.

翻译：直接互惠是重复社会互动中合作演化的一种机制。根据相关文献，若个体与合作伙伴有多次接触，他们自然会学会采取条件性合作策略。相应的模型极大地促进了我们对合作的理解，但这些模型通常对个体如何记忆和处理收益信息提出了较强的假设。例如，当策略通过社会学习更新时，通常假设个体会比较其平均收益。这要求他们计算（或记忆）与群体中其他所有人的收益。为了探究更现实的约束如何影响直接互惠，我们考虑当个体基于较近期的经验进行学习时条件性行为的演化。即使是在最极端的情况下，即个体仅考虑最近一次互动，我们仍发现合作可以演化。然而，这些个体倾向于采取较不慷慨的策略，且其合作频率通常低于经典平均收益设置下的情况。有趣的是，一旦个体记住最近两到三次互动的收益，合作率迅速接近经典极限。这些发现为探究互惠合作需要何种认知能力的文献做出了贡献。我们的结果表明，虽然某种基本的收益记忆形式是必要的，但仅需记住少数几次互动就已足够。