People can collaborate with strangers who cannot expect direct rewards.In order to maintain such cooperative behavior, it is necessary to have a mechanism for returning profits to the individuals who cooperated, as the saying goes, "Pity is not good for people."The function (norms) that humans judge right from wrong is considered to work as one of such mechanisms, and what kind of norms evolve and become established in a wide range of fields such as mathematics, physics, economics, and psychology. Research has been done.

　Theoretical research predictions so far require an evaluation rule that "it is good not to help bad people (justified non-cooperation)" in order to maintain stable cooperative behavior. , Has been said.Without this evaluation rule, a person who did not cooperate with a non-cooperative person (bad person) would be regarded as a non-cooperative person by the action, and a chain of non-cooperation would occur. ..

　This time, the research team conducted multiple online experiments centered on the question, "Is justified non-cooperation really justified?"We analyzed the norms that people actually adopt.As a result, it was found that, unlike the theoretical predictions so far, people take a neutral attitude toward justified non-cooperation, avoiding good and bad judgments.On the other hand, he judged that "helping bad people (unjustified cooperation)" was good.

　From the results of the experiment, Professor Yamamoto pointed out that "an approach that incorporates the possibility that people withhold evaluation in indirect reciprocal situations will be important in research on the evolution of cooperation."

Paper information:[PLOS ONE] Justified defection is neither justified nor unjustified in indirect reciprocity