Kawamura, Y. (河村悠太), & Inaba, M. (稲葉美里) (2023). Trivial giving as a signal of trustworthiness. 信頼性のシグナルとしての些細な贈与 Evolution and Human Behavior. https://doi.org/10.1016/j.evolhumbehav.2023.04.001
Trivial giving—the small-stakes giving that does not produce any further benefit, such as sharing food with neighbors and exchanging gifts with friends—has been widely observed in societies ranging from hunter-gatherers to modern communities. However, previous studies have not examined the adaptive value of trivial giving. The present study proposes that trivial giving functions as a signal of an actor’s cooperative traits or intentions (i.e., trustworthiness). To test this hypothesis, we designed a modified version of the prisoner’s dilemma game experiment with two types of payoff matrics: trivial giving trials featured by a benefit/cost (b/c) ratio of 1 and cooperation trials featured by a b/c ratio of 3. The experiment (N = 82; University students) demonstrated that participants engage in trivial giving when there are future opportunities to cooperate with their partners, that is, when there is a need to signal their trustworthiness. Moreover, the alternative possibility that trivial giving in the experimental condition is a product of the spillover effect from nontrivial cooperation was rejected. Therefore, the present study suggests that seemingly useless trivial giving, widespread in human society, functions as a signal of trustworthiness.