Mayuko Nakamaru
(Tokyo Institute of Technology)

06/01/24, 15:30 at Room 1203 (2nd floor of building 1 of the Faculty of Sciences)

Punishment is an important mechanism promoting the evolution of altruism among nonrelatives. We investigate the coevolution of altruism and punitive behavior, considering four possible strategies: the altruist-punisher (AP, a cooperator who punishes defectors), the altruist-nonpunisher (AN, a pure cooperator), the selfish punisher (SP, a defector who punishes defectors), and the selfish nonpunisher (SN, a pure defector). The selfish punisher uses a paradoxical strategy as it punishes other defectors. We analyze the effects of SP and AN on the coevolution of altruism and punishment. We study both the score-dependent viability model (whereby the game's score affects survivorship only) and the score-dependent fertility model (whereby the score affects fertility only). In the viability model of a completely mixed population, SP first drives out SN, and hence it helps cooperators (AP and AN) to evolve. In contrast, in the fertility model of a completely mixed population, neither SP nor AN helps the evolution of cooperation. In both the viability and fertility models of a lattice-structured population, SP promotes the spread of AP. In contrast, AN discourages the evolution of AP. These results can be understood that punishment is a form of spite behavior, paying a cost to reduce the fitness of the opponents, and that different models give different magnitude of advantage to spite behavior.

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