While empirical evidence highlights the importance of punishment for cooperation in collective action, it remains disputed how responsible sanctions targeted predominantly at uncooperative subjects can evolve. Punishment is costly; in order to spread it typically requires local interactions, voluntary participation, or rewards. Moreover, theory and experiments indicate that some subjects abuse sanctioning opportunities by engaging in antisocial punishment (which harms cooperators), spiteful acts (harming everyone) or revenge (as a response to being punished). These arguments have led to the conclusion that punishment is maladaptive. Here, we use evolutionary game theory to show that this conclusion is premature: If interactions are non-anonymous, cooperation and punishment evolve even if initially rare, and sanctions are directed towards non-cooperators only. Thus, our willingness to punish free riders is ultimately a selfish decision rather than an altruistic act; punishment serves as a warning, showing that one is not willing to accept unfair treatments. N umerous experiments demonstrate that human subjects are eager to punish others for unjust behaviour [1] [2] [3] [4] [5] [6] , thereby suggesting that we are equipped with an inclination for retaliation 7 . The evolutionary origin of this inclination, however, is puzzling because punishment is costly and therefore unlikely to evolve unless it results in direct or indirect benefits [8] [9] [10] [11] [12] [13] . One avenue of research has argued that sanctions are more costly for the punished and that punishment thus gives a relative payoff advantage to the punisher 9, 11, 12, 14 . In these models, punishment can evolve, sometimes even if punishers are initially rare, if there are accompanying mechanisms such as voluntary participation in the collective endeavor 11, 12 , local interactions on a lattice or on a network 9, [15] [16] [17] [18] [19] , or the option to reward cooperators 13 . Surprisingly, it was also demonstrated that defectors who punish other defectors help to pave the way for a cooperative society [14] [15] [16] . However, while a relative payoff advantage for the punisher may explain the emergence of punishment, it cannot account for the emergence of responsible punishment, targeted at defectors only. If the mere act of punishing others gives an edge to the punisher, then spite and antisocial punishment should eventually take over. Most previous studies presumed that only defectors are punished, which is clearly contradicting experimental evidence from numerous countries 20 . Two recent models that also allow cooperators to be punished have shown that anti-social punishment can fully prevent the evolution of cooperation and responsible sanctions in both, well-mixed 21 and lattice-structured 22 populations. Therefore, the question arises whether punishment can promote cooperation at all 6 . However, in most real interactions, the decision to punish others does not only affect the relative payoffs of the players, but also their reputation. If the punishment act can be observed by others, it can pay to sanction only defectors. A recent experiment suggests that emotions such as anger or moral disgust may have evolved as a commitment device; they lead people to disregard the immediate consequences of their behaviour in order to preserve integrity and to maintain their reputation . Here, we underpin this argument with an evolutionary model. We derive an exact condition for the evolution of responsible punishment in the presence of antisocial punishment. Our model shows that reputation allows the co-evolution of cooperation and responsible sanctions even if both are initially rare.
In this manner, social punishers can benefit indirectly through maintaining a reputation of punishing unjust behaviour REF .
Emergence of responsible sanctions without second order free riders, antisocial punishment or spite
Scientific Reports
Scientific Reports
Psychology Medicine