STUDY 2: Honour, Morality, Reputation (3)

Chudek, M., & Henrich, J. (2011). Culture–gene coevolution, norm-psychology and the emergence of human prosociality. Trends in cognitive sciences, 15(5), 218-226.

Box 2. Mechanisms for sustaining cooperation and other norms 

Generally, formal evolutionary models act as mental prostheses that help build intuitions about how complex evolutionary dynamics operate. For cooperation, theoretical models strive to explain the persistence of individually costly cooperation by describing strategies which, when sufficiently common, allow cooperators to outcompete non- cooperators while ‘paying’ for themselves [17,31,34,35]. These mechanisms share two important features. First, cooperative strategies cannot spread when rare, but are stable once common. The initial emergence of costly norms requires other mechanisms, such as stochastic fluctuations, non-random group fragmentations or other shocks. Cultural learning psychology and norm-psychology help fill this role: prestige- and success-biases allow influential leaders to seed new behavioral norms in small founder groups, which can then grow large; conformist-learning and norm-psychology ensure that new migrants to those groups conform to these norms (generating phenotypic assortment); cultural group selection spreads the more cooperative norms. Second, these models specify strategies that, once common, stabilize either cooperation or any other arbitrary norm. Because, in a public goods game (e.g. community defense or well-digging), the costs of cooperation create fitness differences among strategies but the benefits do not (i.e. they are shared equally), any mechanism that sustains this form of cooperation can sustain any equivalently costly behavior. Although these mechanisms are all conceptually rather different, they all yield higher fitness for individuals who behave according to arbitrary, individually costly local norms. Here we summarize four types of mechanisms.

Reputation: ‘indirect reciprocity’ proposes that choices in one type of interaction have consequences in future interactions with other individuals in different contexts. In such models, defection in largescale cooperative interactions (or any norm violation) can be sanctioned by others in dyadic interactions with violators [31], for example by not helping them. Norm violators accrue bad reputations, which allow others to exploit them without reputational damage. 

Costly punishment: punishment-enforced, large-scale cooperation can be undermined by the proliferation of second order free riders, who cooperate but do not punish non-cooperators. One way to address this is to realize that learners use conformist transmission when payoff differences among alternative strategies become small [35,36]. Although conformist transmission might be too weak to maintain cooperation or punishing non-cooperators, it can (for example) maintain the punishment of non-punishers, which then stabilizes punishment and then cooperation. Alternatively, another way to resolve this is by establishing a ‘punishment pool’ [33], such as a police force, which can become self-sustaining by punishing those who do not contribute resources to it and can then sustain other costly behaviors.

Signaling intentions: the second order free rider problem can also be resolved if cooperators send an honest, costly signal of their intention to punish [37]. Fitness benefits accrue to those who adopt two different community-enforced norms: performing the costly signal and the costly behavior it stabilizes. Individuals effectively make a costly, norm-specified commitment to punish norm violators.

Signaling quality: if the quality of potential social partners is difficult to observe, and high quality individuals can signal their quality by punishing norm violators, then costly norms can be sustained by punishment. Here, having honestly communicated their higher quality to others, signaler-punishers obtain the benefits of preferred matings/alliances [34].