A research team led by Hitoshi Yamamoto from Rissho University has analyzed how the social norm of indirect reciprocity is adopted in human society and revealed results that contradict previous theoretical predictions. The study was carried out in collaboration with colleagues Takahisa Suzuki (Tsuda University) and Ryohei Umetani (Rissho University), and its results were published in the open-access journal PLOS ONE on June 30, 2020.