Data from: The price of being seen to be just: an intention signalling strategy for indirect reciprocity

Cooperation amongst 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 clear whether 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 utilise this option, they also interpreted others’ use of this option as a signal of cooperative intent.

陌生人之间的合作是人类社会性的显著特征。针对人类此类合作形式的一种核心演化解释为间接互惠（indirect reciprocity），即每个个体会有选择性地向拥有“良好”而非“不良”声誉的对象提供帮助。部分演化分析强调了二阶声誉信息（second-order reputation information）——即当前合作对象的前任搭档的声誉——对于间接互惠的重要性，因为该信息可使博弈者区分正当的“良好”背叛者与不正当的“不良”背叛者：前者仅会拒绝向“不良”对象施以帮助。尽管如此，目前仍不明确人们在间接互惠场景中是否真的会利用二阶声誉信息。作为替代方案，我们提出了意图信号策略（intention signalling strategy），即允许背叛者通过放弃一项资源来消除自身的“不良”声誉。我们的模型在关键层面背离了间接互惠领域的传统建模思路：研究证明，若博弈者拥有传递自身意图的选项，仅需一阶信息（first-order information）即可维持合作。尤为关键的是，我们的模型能够抵御无条件合作策略与无条件不合作策略的入侵，这是验证其作为演化稳定策略（evolutionarily stable strategy）可行性的首要步骤。此外，在两项行为实验中，当参与者被允许通过放弃资源以修复受损声誉时，参与者不仅会自发启用这一选项，还会将他人使用该选项的行为解读为合作意图的信号。