Response of social norms to individual differences in error-proneness

Indirect reciprocity explains the evolution of cooperation by considering how our cooperative behavior toward someone is reciprocated by someone else who has observed us. A cohesive society has a shared norm that prescribes how to assess observed behavior as well as how to behave toward others based on the assessments, and the eight social norms that are evolutionarily stable against the invasion of mutants with different behavioral rules are referred to as the leading eight, whose member norms are called L1 to L8, respectively. Among the leading eight, L8 (also known as `Judging') has been deemed mostly irrelevant due to its poor performance in maintaining cooperation when each person may have a different opinion about someone instead of forming a public consensus. In this work, we propose that L8 can nevertheless be best protected from assessment errors among the leading eight if we take into account the intrinsic heterogeneity of error proneness among individuals because this norm heavily punishes those who are prone to errors in following its assessment rule. This finding suggests that individual differences should be explicitly taken into account as quenched randomness to obtain a thorough understanding of a social norm working in a heterogeneous environment.