Tanaka, Ohtsuki, & Ohtsubo (2016)

Tanaka, H.（田中大貴）, Ohtsuki, H., & Ohtsubo, Y.（大坪庸介） (2016).
The price of being seen to be just: An intention signalling strategy for indirect reciprocity.
正当と見なされるためのコスト：間接互恵性状況での意図シグナル戦略
Proceedings of the Royal Society B: Biological Sciences, 20160694. 
doi: 10.1098/rspb.2016.0694

Cooperation among strangers is a marked characteristic of human sociality. One prominent evolutionary explanation for this form of human cooperation is indirect reciprocity, whereby each individual selectively helps people with a ‘good’, but not ‘bad’ reputation. Some evolutionary analyses have underscored the importance of second-order reputation information (the reputation of a current partner’s previous partner) for indirect reciprocity as it allows players to discriminate justified ‘good’ defectors, who selectively deny giving help to ‘bad’ partners, from unjustified ‘bad’ defectors. Nevertheless, it is not clearwhether people in fact make use of second-order information in indirect reciprocity settings. As an alternative, we propose the intention signalling strategy, whereby defectors are given the option to abandon a resource as a means of expunging their ‘bad’ reputation. Our model deviates from traditional modelling approaches in the indirect reciprocity literature in a crucial way—we show that first-order information is sufficient to maintain cooperation if players are given an option to signal their intention. Importantly, our model is robust against invasion by both unconditionally cooperative and uncooperative strategies, a first step towards demonstrating its viability as an evolutionarily stable strategy. Furthermore, in two behavioural experiments, when participants were given the option to abandon a resource so as to mend a tarnished reputation, participants not only spontaneously began to use this option, they also interpreted others’ use of this option as a signal of cooperative intent. （間接互恵状況での評判について再検討した研究です。これまでの間接互恵性研究では、非協力者への協力を拒むという正当な理由に基づく非協力を、正当なものかどうか判断するのは観察者の役割とされてきました。しかし、それでは観察者は多くの情報を利用してひとりの非協力者の行為が正当かどうかを判断せねばならず、実験をすると必ずしもそのような複雑な判断がなされていないということがわかっていました。そこで、本研究では、非協力した人自身に自分の意図をシグナルする機会を与えることで間接互恵性の評判がうまく機能することをモデルの分析で示し、その後、実験で人々が意図シグナル戦略を用いることを示しました。）