Title: A norm knockout method on indirect reciprocity to reveal indispensable norms,
Abstract: Although various norms for reciprocity-based cooperation have been suggested
that are evolutionarily stable against invasion from free riders, the process
of alternation of norms and the role of diversified norms remain unclear in the
evolution of cooperation. We clarify the co-evolutionary dynamics of norms and
cooperation in indirect reciprocity and also identify the indispensable norms
for the evolution of cooperation. Inspired by the gene knockout method, a
genetic engineering technique, we developed the norm knockout method and
clarified the norms necessary for the establishment of cooperation. The results
of numerical investigations revealed that the majority of norms gradually
transitioned to tolerant norms after defectors are eliminated by strict norms.
Furthermore, no cooperation emerges when specific norms that are intolerant to
defectors are knocked out.