Simple Records Support Robust Indirect Reciprocity

Abstract

Existing models of indirect reciprocity fail to robustly support social cooperation: image scoring models [74] fail to provide robust incentives, while social standing models [96,63,85,93] are not informationally robust. Here we provide a new model of indirect reciprocity based on simple, decentralized records: each individual's record depends on their own past behavior alone, and not on their partners' past behavior or their partners' partners' past behavior. When social dilemmas exhibit a coordination motive (or strategic complementarity ), tolerant trigger strategies based on simple records can robustly support positive social cooperation and exhibit strong stability properties. In the opposite case of strategic substitutability, positive social cooperation cannot be robustly supported. Thus, the strength of short-run coordination motives in social dilemmas determines the prospects for robust long-run cooperation.People (and perhaps also other animals) often trust each other to cooperate even when they know they will never meet again. Such indirect reciprocity relies on individuals having some information about how their partners have behaved in the past.Existing models of indirect reciprocity fall into two paradigms. In the image scoring paradigm, each individual carries an image that improves when they help others, and 1