豚レンサ球菌の食肉汚染に関する研究

学位の種別: 課程博士審査委員会委員 : （主査）東京大学教授 関崎 勉, 東京大学教授 山田 章雄, 東京大学准教授 平山 和宏, 神戸大学教授 大澤 朗, 大阪府立大学教授 山崎 伸二University of Tokyo(東京大学

Motivational systems in dyadic cooperation are designed for reputation-based partner choice

Dyadic cooperation is the building block of human social exchange. But forming cooperative partnerships poses two problems: choosing partners and being chosen by partners. A growing body of research suggests that reputation-based partner choice creates competition to be chosen by desirable cooperative partners and therefore motivates people to behave generously and acquire a reputation as a valuable cooperator. However, a reputation as a cooperator may also attract cheaters, undesirable partners who do not reciprocate cooperation. Evidence indicates that inflicting punishment can deter cheating, but appearing punitive may drive away cooperators as well. Despite the apparent dilemma, little is known about motivations to punish in the presence of competition to be chosen. I hypothesize that motivational systems are designed to attract desirable partners and manage reputations by up-regulating cooperation and down-regulating punishment behaviors; systems will do so in response to cues of reputation-based partner choice—cues indicating that one is in competition to be chosen as a partner. Three studies tested this hypothesis. Studies 1 and 2 assessed motivations to cooperate and punish using economic games with a punishment option. Cues of reputation-based partner choice were either measured (as estimates of how many outside options potential partners would have; study 1) or experimentally manipulated (in study 2; cues of group membership and anonymity indicated whether one is being evaluated as a potential partner). Study 3 examined whether there is a trade-off between acquiring cooperative versus punitive reputations. Results support the hypothesis. The cues of reputation-based partner choice up-regulated motivations to cooperate while down-regulating motivations to punish. It is also shown that punishing harms one’s cooperative reputation and lowers the probability of attracting partners, confirming that the function of these motivational calibrations is to improve one’s reputation as a cooperation partner. The present research provides evidence that motivational systems are designed for managing reputations to be chosen by desirable cooperation partners

Group as a biological market: Eliminating reputation concern decreases ingroup-favouring cooperation and punishment

Accumulating evidence suggests that group is a cue of reputation-based partner choice: it evokes an assumption that one is being recognized and evaluated as a cooperation partner and thereby triggers reputation concern. For instance, studies have demonstrated that people cooperate more with ingroup than outgroup members, but this bias disappears when the beneficiary does not know the donor is a fellow ingroup member and, thus, is unlikely to evaluate the donor as a partner. Here, we further examined this hypothesis by (i) testing whether people avoid reputation-harming behaviour, such as second-party punishment, and (ii) manipulating anonymity instead of membership knowledge. Across three experiments (N = 723), participants were less likely to punish ingroup than outgroup partners, while cooperating more with ingroup partners. However, when participants were anonymous, the degree to which people favoured ingroup decreased regardless of study setting (online vs. in-person) or sample (convenience vs. college). That is, without reputation concern, people donated less to ingroup members and were less hesitant to punish them. The results illustrate that our mind perceives one’s group as a “market” for cooperation partners and employs a default reputation-management strategy—up-regulating motivations to cooperate while down-regulating punitive motivations—unless other cues challenge its necessity