Abstract
In many species, mutual cooperation is stabilized by forms of policing and peer punishment: if cheaters are punished, there is a strong selective pressure to cooperate. Most human societies have complemented, and sometimes even replaced, such peer punishment mechanisms with pool punishment, where punishment is outsourced to central institutions such as the police. Even before free-riding occurs, such institutions require investments, which could serve as costly signals. Here, we show with a game theoretical model that this signaling effect in turn can be crucial for the evolution of punishment institutions: In the absence of such signals, pool punishment is only stable with second-order punishment and can only evolve when individuals have the freedom not to take part in any interaction. With such signals, individuals can opportunistically adjust their behavior, which promotes the evolution of stable pool punishment even in situations where no one can stand aside. Thus, the human propensity to react opportunistically to credible punishment threats is often sufficient to establish stable punishment institutions and to maintain high levels of cooperation.
Highlights
When individuals share common resources, or when they engage in mutualistic relationships, they may be tempted to reap the benefits without paying the associated costs (Hardin, 1968; Trivers, 1971)
A similar cycle characterizes the dynamics among loners, cooperators, opportunists, as the latter always act as defectors in the absence of the threat of punishment
If only defectors and opportunists are present in the population, the dynamics is governed by neutral drift
Summary
When individuals share common resources, or when they engage in mutualistic relationships, they may be tempted to reap the benefits without paying the associated costs (Hardin, 1968; Trivers, 1971). In view of these shortcomings, many human societies have delegated the prosecution of wrong-doers to central sanctioning institutions (Sigmund et al, 2010, 2011; Baldassari and Grossman, 2011; Sasaki et al, 2012; Cressman et al, 2012; Perc, 2012; Traulsen et al, 2012; Zhang et al, 2013; Hilbe et al, 2014) Maintaining such pool punishment institutions is costly and requires financial contributions in the form of taxes and fees, ideally paid by all beneficiaries. This implies that in contrast to previous work (Sigmund et al, 2010; Traulsen et al, 2012), second-order punishment is not required for the stability of the punishment institution if the institution's existence is known before the public goods game takes place.
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