Seminar: "Indirect reciprocity under private observation" by Prof. Hisashi Ohtsuki (SOKENDAI)


2023年9月26日 (火) 14:30 15:00


Seminar Room L4F01 (Lab4 F floor)



Indirect reciprocity under private observation


Indirect reciprocity is a mechanism of evolution of cooperation, where reputations bridge individuals. Those who help others acquire a good reputation, and those who have a good reputation receive help from a third party. Many previous models of indirect reciprocity assumed the case of public reputation, where people can reach agreements on who is good and who is bad. It has been believed that without such an agreement, cooperation never evolves. Here I talk about my recent finding that cooperation can evolve even without such an agreement. I study the case where individuals independently evaluate others, and hence no agreement is established. I have found that the key to success in cooperation is that everyone uses a simple rule to evaluate others. With a complex rule, cooperation collapses. This is the first study that has shown that cooperation by indirect reciprocity is evolutionarily stable under private observation.


Fujimoto Y & Ohtsuki H (2023). Evolutionary stability of cooperation in indirect reciprocity under noisy and private assessment. PNAS 120(20): e2300544120.


Hisashi Ohtsuki received his Ph.D. in Science from Kyushu University in 2006. After working as a Post-Doctoral Fellow at Harvard University and as a PRESTO Researcher at the Japan Science and Technology Agency, he was hired by SOKENDAI as Assistant Professor in 2011, as Lecturer in 2015, as Associate Professor in 2019 at the Department of Evolutionary Studies of Biosystems, and as Associate Professor in 2022 at the Research Center for Integrative Evolutionary Science. His main research topics are Evolutionary Game Theory, Social Evolution, Cultural Evolution, and Evolutionary Anthropology.

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