Horita, Y.（堀田結孝）, Takezawa, M.（竹澤正哲）, Kinjo, T.（金城卓司）, Nakawake, Y.（中分遥）, & Masuda, N. (2016). Transient nature of cooperation by pay-it-forward reciprocity. 「恩送り」互酬性による協力のはかなさ Scientific Reports, 6, Article Number: 19471. doi: 10.1038/srep19471
Humans often forward kindness received from others to strangers, a phenomenon called the upstream or pay-it-forward indirect reciprocity. Some field observations and laboratory experiments found evidence of pay-it-forward reciprocity in which chains of cooperative acts persist in social dilemma situations. Theoretically, however, cooperation based on pay-it-forward reciprocity is not sustainable. We carried out laboratory experiments of a pay-it-forward indirect reciprocity game (i.e., chained gift-giving game) on a large scale in terms of group size and time. We found that cooperation consistent with pay-it-forward reciprocity occurred only in a first few decisions per participant and that cooperation originated from inherent pro-sociality of individuals. In contrast, the same groups of participants showed persisting chains of cooperation in a different indirect reciprocity game in which participants earned reputation by cooperating. Our experimental results suggest that pay-it-forward reciprocity is transient and disappears when a person makes decisions repeatedly, whereas the reputation-based reciprocity is stable in the same situation.