title: Group Cooperation without Group Selection: Modest Punishment Can Recruit Much Cooperation.
abstract: Humans everywhere cooperate in groups to achieve benefits not attainable by individuals. Individual effort is often not automatically tied to a proportionate share of group benefits. This decoupling allows for free-riding, a strategy that (absent countermeasures) outcompetes cooperation. Empirically and formally, punishment potentially solves the evolutionary puzzle of group cooperation. Nevertheless, standard analyses appear to show that punishment alone is insufficient, because second-order free riders (those who cooperate but do not punish) can be shown to outcompete punishers. Consequently, many have concluded that other processes, such as cultural or genetic group selection, are required. Here, we present a series of agent-based simulations that show that group cooperation sustained by punishment easily evolves by individual selection when you introduce into standard models more biologically plausible assumptions about the social ecology and psychology of ancestral humans. We relax three unrealistic assumptions of past models. First, past models assume all punishers must punish every act of free riding in their group. We instead allow punishment to be probabilistic, meaning punishers can evolve to only punish some free riders some of the time. This drastically lowers the cost of punishment as group size increases. Second, most models unrealistically do not allow punishment to recruit labor; punishment merely reduces the punished agent's fitness. We instead realistically allow punished free riders to cooperate in the future to avoid punishment. Third, past models usually restrict agents to interact in a single group their entire lives. We instead introduce realistic social ecologies in which agents participate in multiple, partially overlapping groups. Because of this, punitive tendencies are more expressed and therefore more exposed to natural selection. These three moves toward greater model realism reveal that punishment and cooperation easily evolve by direct selection--even in sizeable groups.
authors.affiliation: Department of Psychology, Harvard University, Cambridge, Massachusetts, United States of America.
authors.forename: Max M
authors.initials: MM
authors.lastname: Krasnow
authors.affiliation: Department of Political Science, College of Business, Center for Behavioral Political Economy, Stony Brook University, Stony Brook, New York, United States of America.
authors.forename: Andrew W
authors.initials: AW
authors.lastname: Delton
authors.affiliation: Center for Evolutionary Psychology, University of California Santa Barbara, Santa Barbara, California, United States of America; Department of Psychological and Brain Sciences, University of California Santa Barbara, Santa Barbara, California, United States of America.
authors.forename: Leda
authors.initials: L
authors.lastname: Cosmides
authors.affiliation: Center for Evolutionary Psychology, University of California Santa Barbara, Santa Barbara, California, United States of America; Department of Anthropology, University of California Santa Barbara, Santa Barbara, California, United States of America.
authors.forename: John
authors.initials: J
authors.lastname: Tooby
mesh_terms: D005075:Biological Evolution; D003198:Computer Simulation; D003299:Cooperative Behavior; D005716:Game Theory; D006126:Group Processes; D006801:Humans; D007398:Interpersonal Relations; D011336:Probability; D011678:Punishment / Q000523:psychology*; D012931:Social Environment