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 …