強い互恵性と集団規範の維持

—義憤・第三者罰の存在をめぐる議論—

抄録

Human societies are characterized by large-scale cooperation among genetically unrelated individuals. One evolutionary explanation for such human ultra-sociality is the notion of “strong reciprocity,” which posits that strong reciprocators not only unconditionally cooperate but also punish non-cooperators in order to enforce cooperative norms within their groups. Supportive evidence for strong reciprocity is that people tend to punish non-cooperators in various experimental settings. However, employing more precise definitions and refined methodologies, recent studies cast serious doubt on the presence of punitive sentiments/behaviors toward non-cooperators. Nonetheless, people do report anger toward violators of shared norms of their community. In addition, violation of the honesty norm (presumably, an instance of widely shared norms) seems to reliably trigger third-party punishment. It seems important to clearly distinguish “shared-norm violators” from “non-cooperators” in order to understand human ultra-sociality.