The other side of the coin: Recipient norms and their impact on indirect reciprocity and cooperation

Human cooperation thrives under indirect reciprocity. Typically using a donation game in an infinitely large population, previous studies explore the concept of indirect reciprocity driven by donor-centered reputation update. As the other side of the coin, however, recipients can also affect reputation updates, as in the virtuous victim effect. To address this issue, here we examine how updating the reputations of recipients influences cooperation. Our work adds a time-scale parameter for updating donor and recipient reputations, giving rise to dueling updates between the two sides. We find a trade-off between the level of cooperation and evolutionary stability influenced by social norms. ‘Forgiving’ recipient norms enhance cooperation but increase susceptibility to defectors, whereas ‘unforgiving’ norms reduce cooperation but defend against invasion by defectors. Expanding to include gossip groups allows us to analyze the evolutionary dynamics of the time-scale parameter, identifying ‘generous’ norms that support cooperation, and ‘strict’ norms that discourage such generosity, ultimately showing vulnerability to defector invasions and potential cooperation collapse.