Evolution of cooperation and altruistic punishment when retaliation is possible

Altruistic punishment is suggested to explain observed high levels of cooperation among non-kin related humans. However, laboratory experiments as well as ethnographic evidence suggest that people might retaliate if being punished, and that this reduces the level of cooperation. Building on existing models on the evolution of cooperation and altruistic punishment, we explore the consequences of the option of retaliation. We find that cooperation and altruistic punishment does not evolve with larger population levels if the option of retaliation is included.     

The economics of altruistic punishment and the maintenance of cooperation

Explaining the evolution and maintenance of cooperation among unrelated individuals is one of the fundamental problems in biology and the social sciences. Recent findings suggest that altruistic punishment is an important mechanism maintaining cooperation among humans. We experimentally explore the boundaries of altruistic punishment to maintain cooperation by varying both the cost and the impact of punishment, using an exceptionally extensive subject pool. Our results show that cooperation is only maintained if conditions for altruistic punishment are relatively favourable: low cost for the punisher and high impact on the punished. Our results indicate that punishment is strongly governed by its cost-to-impact ratio and that its effect on cooperation can be pinned down to one single variable: the threshold level of free-riding that goes unpunished. Additionally, actual pay-offs are the lowest when altruistic punishment maintains cooperation, because the pay-off destroyed through punishment exceeds the gains from increased cooperation. Our results are consistent with the interpretation that punishment decisions come from an amalgam of emotional response and cognitive cost-impact analysis and suggest that altruistic punishment alone can hardly maintain cooperation under multi-level natural selection. Uncovering the workings of altruistic punishment as has been done here is important because it helps predicting under which conditions altruistic punishment is expected to maintain cooperation.     

Hadza Cooperation

Strong reciprocity is an effective way to promote cooperation. This is especially true when one not only cooperates with cooperators and defects on defectors (second-party punishment) but even punishes those who defect on others (third-party, “altruistic” punishment). Some suggest we humans have a taste for such altruistic punishment and that this was important in the evolution of human cooperation. To assess this we need to look across a wide range of cultures. As part of a cross-cultural project, I played three experimental economics games with the Hadza, who are hunter-gatherers in Tanzania. The Hadza frequently engaged in second-party punishment but they rarely engaged in third-party punishment. Other small-scale societies engaged in less third-party punishment as well. I suggest third-party punishment only became more important in large, complex societies to solve more pressing collective-action problems.     

Persistent cooperators in nature

The evolution and maintenance of cooperation fascinated researchers for several decades. Recently, theoretical models and experimental evidence show that costly punishment may facilitate cooperation in human societies. The puzzle how the costly punishment behaviour evolves can be solved under voluntary participation. Could the punishers emerge if participation is compulsory? Is the punishment inevitably a selfish behaviour or an altruistic behaviour? The motivations behind punishment are still an enigma. Based on public goods interactions, we present a model in which just a certain portion of the public good is divided equally among all members. The other portion is distributed to contributors when paying a second cost. The contributors who are willing to pay a second cost are called the persistent cooperators (PC), indicating their desire to retrieve the proportion of the payoff derived from their own contributions with persistent efforts. We show that the persistent cooperators can be costly punishers, which may account for the origin of human costly punishment behaviour under compulsory participation. In this sense our models may show theoretically that the original motivation behind punishment is to retrieve deserved payoff from their own contributions, a selfish incentive. But the persistent cooperators can also flourish or dominate the population in other situations. We list many real examples in which contributors are the persistent cooperators, and they benefit. This indicates a simple norm promoting cooperation: contributing more and gaining more.     

The evolution of strong reciprocity: cooperation in heterogeneous populations

How do human groups maintain a high level of cooperation despite a low level of genetic relatedness among group members? We suggest that many humans have a predisposition to punish those who violate group-beneficial norms, even when this imposes a fitness cost on the punisher. Such altruistic punishment is widely observed to sustain high levels of cooperation in behavioral experiments and in natural settings. We offer a model of cooperation and punishment that we call STRONG RECIPROCITY: where members of a group benefit from mutual adherence to a social norm, strong reciprocators obey the norm and punish its violators, even though as a result they receive lower payoffs than other group members, such as selfish agents who violate the norm and do not punish, and pure cooperators who adhere to the norm but free-ride by never punishing. Our agent-based simulations show that, under assumptions approximating likely human environments over the 100000 years prior to the domestication of animals and plants, the proliferation of strong reciprocators when initially rare is highly likely, and that substantial frequencies of all three behavioral types can be sustained in a population. As a result, high levels of cooperation are sustained. Our results do not require that group members be related or that group extinctions occur.     

人类的利他性惩罚：认知神经科学的视角

利他性惩罚广泛存在于人类社会中,在群体合作与规范维护方面起着重要的积极作用．个体作为潜在的惩罚者,从知觉到不公平事件到做出惩罚行为,需要经过一系列的认知和情绪过程,包括公平判断、奖赏加工、自我控制以及心理化等过程,并且调用相应的神经生理机制．认知神经科学为理解人类的利他性惩罚行为提供了新的视角和方法．本文基于最新的研究发现,综述了利他性惩罚相关的神经生理基础．     

A structured ancestral population for the evolution of modern humans

The view that modern humans evolved through a bottleneck from a single founding group of archaic Homo is being challenged by new analyses of contemporary genetic variation. A wide range of middle to late Pleistocene ages for gene genealogies and evidence for early population structures point to a diverse and scattered ancestry associated with a metapopulation history of local extinctions, re-colonization and admixture. A different balance of the same processes has shaped chimpanzee diversity.     

Reward from Punishment Does Not Emerge at All Costs

The conundrum of cooperation has received increasing attention during the last decade. In this quest, the role of altruistic punishment has been identified as a mechanism promoting cooperation. Here we investigate the role of altruistic punishment on the emergence and maintenance of cooperation in structured populations exhibiting connectivity patterns recently identified as key elements of social networks. We do so in the framework of Evolutionary Game Theory, employing the Prisoner''s Dilemma and the Stag-Hunt metaphors to model the conflict between individual and collective interests regarding cooperation. We find that the impact of altruistic punishment strongly depends on the ratio q/p between the cost of punishing a defecting partner (q) and the actual punishment incurred by the partner (p). We show that whenever q/p<1, altruistic punishment turns out to be detrimental for cooperation for a wide range of payoff parameters, when compared to the scenario without punishment. The results imply that while locally, the introduction of peer punishment may seem to reduce the chances of free-riding, realistic population structure may drive the population towards the opposite scenario. Hence, structured populations effectively reduce the expected beneficial contribution of punishment to the emergence of cooperation which, if not carefully dosed, may in fact hinder the chances of widespread cooperation.     

The evolution of punishment through reputation

Punishment of non-cooperators has been observed to promote cooperation. Such punishment is an evolutionary puzzle because it is costly to the punisher while beneficial to others, for example, through increased social cohesion. Recent studies have concluded that punishing strategies usually pay less than some non-punishing strategies. These findings suggest that punishment could not have directly evolved to promote cooperation. However, while it is well established that reputation plays a key role in human cooperation, the simple threat from a reputation of being a punisher may not have been sufficiently explored yet in order to explain the evolution of costly punishment. Here, we first show analytically that punishment can lead to long-term benefits if it influences one''s reputation and thereby makes the punisher more likely to receive help in future interactions. Then, in computer simulations, we incorporate up to 40 more complex strategies that use different kinds of reputations (e.g. from generous actions), or strategies that not only include punitive behaviours directed towards defectors but also towards cooperators for example. Our findings demonstrate that punishment can directly evolve through a simple reputation system. We conclude that reputation is crucial for the evolution of punishment by making a punisher more likely to receive help in future interactions, and that experiments investigating the beneficial effects of punishment in humans should include reputation as an explicit feature.     

Rare but severe concerted punishment that favors cooperation

As one of the mechanisms that are supposed to explain the evolution of cooperation among unrelated individuals, costly punishment, in which altruistic individuals privately bear the cost to punish defection, suffers from such drawbacks as decreasing individuals’ welfare, inducing second-order free riding, the difficulty of catching defection, and the possibility of triggering retaliation. To improve this promising mechanism, here we propose an extended Public Goods game with rare but severe concerted punishment, in which once a defector is caught punishment is triggered and the cost of punishment is equally shared among the remainder of the group. Analytical results show that, when the probability for concerted punishment is above a threshold, cooperating is, while defecting is not, an evolutionarily stable strategy in finite populations, and that this way of punishment can considerably decrease the total cost of inhibiting defection, especially in large populations.     

Rewiring cell signaling: the logic and plasticity of eukaryotic protein circuitry

Living cells rival computers in their ability to process external information and make complex behavioral decisions. Many of these decisions are made by networks of interacting signaling proteins. Ongoing structural, biochemical and cell-based studies have begun to reveal several common principles by which protein components are used to specifically transmit and process information. Recent engineering studies demonstrate that these relatively simple principles can be used to rewire signaling behavior in a process that mimics the evolution of new phenotypic responses.     

Functional microcircuitry in the accumbens underlying drug addiction: insights from real-time signaling during behavior

An understanding of the neurobiological basis of drug addiction requires examination of real-time (subsecond) cellular and chemical responses in the brain reward system during drug-seeking and drug-taking behavior. Electrophysiological and electrochemical studies in the rodent nucleus accumbens have examined changes in cell firing and rapid dopamine signaling during crucial periods of behavioral responding for drugs, and show the associative nature of those signals. These findings are considered with respect to the functional microcircuitry in the nucleus accumbens that underlies goal-directed behavior and the role of this circuit in drug addiction.     

HUMAN COOPERATION BASED ON PUNISHMENT REPUTATION

The threat of punishment usually promotes cooperation. However, punishing itself is costly, rare in nonhuman animals, and humans who punish often finish with low payoffs in economic experiments. The evolution of punishment has therefore been unclear. Recent theoretical developments suggest that punishment has evolved in the context of reputation games. We tested this idea in a simple helping game with observers and with punishment and punishment reputation (experimentally controlling for other possible reputational effects). We show that punishers fully compensate their costs as they receive help more often. The more likely defection is punished within a group, the higher the level of within‐group cooperation. These beneficial effects perish if the punishment reputation is removed. We conclude that reputation is key to the evolution of punishment.     

Genetic differentiation and the evolution of cooperation in chimpanzees and humans

It has been proposed that human cooperation is unique among animals for its scale and complexity, its altruistic nature and its occurrence among large groups of individuals that are not closely related or are even strangers. One potential solution to this puzzle is that the unique aspects of human cooperation evolved as a result of high levels of lethal competition (i.e. warfare) between genetically differentiated groups. Although between-group migration would seem to make this scenario unlikely, the plausibility of the between-group competition model has recently been supported by analyses using estimates of genetic differentiation derived from contemporary human groups hypothesized to be representative of those that existed during the time period when human cooperation evolved. Here, we examine levels of between-group genetic differentiation in a large sample of contemporary human groups selected to overcome some of the problems with earlier estimates, and compare them with those of chimpanzees. We find that our estimates of between-group genetic differentiation in contemporary humans are lower than those used in previous tests, and not higher than those of chimpanzees. Because levels of between-group competition in contemporary humans and chimpanzees are also similar, these findings suggest that the identification of other factors that differ between chimpanzees and humans may be needed to provide a compelling explanation of why humans, but not chimpanzees, display the unique features of human cooperation.     

Outsourcing punishment to God: beliefs in divine control reduce earthly punishment

The sanctioning of norm-transgressors is a necessary--though often costly--task for maintaining a well-functioning society. Prior to effective and reliable secular institutions for punishment, large-scale societies depended on individuals engaging in 'altruistic punishment'--bearing the costs of punishment individually, for the benefit of society. Evolutionary approaches to religion suggest that beliefs in powerful, moralizing Gods, who can distribute rewards and punishments, emerged as a way to augment earthly punishment in large societies that could not effectively monitor norm violations. In five studies, we investigate whether such beliefs in God can replace people's motivation to engage in altruistic punishment, and their support for state-sponsored punishment. Results show that, although religiosity generally predicts higher levels of punishment, the specific belief in powerful, intervening Gods reduces altruistic punishment and support for state-sponsored punishment. Moreover, these effects are specifically owing to differences in people's perceptions that humans are responsible for punishing wrongdoers.     

Anti-social punishment can prevent the co-evolution of punishment and cooperation

The evolution of cooperation is one of the great puzzles in evolutionary biology. Punishment has been suggested as one solution to this problem. Here punishment is generally defined as incurring a cost to inflict harm on a wrong-doer. In the presence of punishers, cooperators can gain higher payoffs than non-cooperators. Therefore cooperation may evolve as long as punishment is prevalent in the population. Theoretical models have revealed that spatial structure can favor the co-evolution of punishment and cooperation, by allowing individuals to only play and compete with those in their immediate neighborhood. However, those models have usually assumed that punishment is always targeted at non-cooperators. In light of recent empirical evidence of punishment targeted at cooperators, we relax this assumption and study the effect of so-called ‘anti-social punishment’. We find that evolution can favor anti-social punishment, and that when anti-social punishment is possible costly punishment no longer promotes cooperation. As there is no reason to assume that cooperators cannot be the target of punishment during evolution, our results demonstrate serious restrictions on the ability of costly punishment to allow the evolution of cooperation in spatially structured populations. Our results also help to make sense of the empirical observation that defectors will sometimes pay to punish cooperators.     

Does dishonesty really invite third-party punishment? Results of a more stringent test

Many experiments have demonstrated that people are willing to incur cost to punish norm violators even when they are not directly harmed by the violation. Such altruistic third-party punishment is often considered an evolutionary underpinning of large-scale human cooperation. However, some scholars argue that previously demonstrated altruistic third-party punishment against fairness-norm violations may be an experimental artefact. For example, envy-driven retaliatory behaviour (i.e. spite) towards better-off unfair game players may be misidentified as altruistic punishment. Indeed, a recent experiment demonstrated that participants ceased to inflict third-party punishment against an unfair player once a series of key methodological problems were systematically controlled for. Noticing that a previous finding regarding apparently altruistic third-party punishment against honesty-norm violations may have been subject to methodological issues, we used a different and what we consider to be a more sound design to evaluate these findings. Third-party punishment against dishonest players withstood this more stringent test.     

The evolution of punishment in n-player public goods games: a volunteer's dilemma

The evolution of punishment to stabilize cooperation in n-player games has been treated as a second-order social dilemma, where contributions to punishment of free-riders are altruistic. Hence it may only evolve under highly restricted conditions. Here, we build on recent insights using the volunteer's dilemma as an alternative payoff matrix for the evolution of cooperation. The key feature of a volunteer's dilemma is that the benefits of cooperation are a nonlinear function of the number of contributors, meaning that cooperation is negatively frequency dependent. We propose that nonlinear returns are also an inherent feature of punishment and that this insight allows for a simple and novel explanation of how punishment evolves in groups.     

Love or fear: Can punishment promote cooperation?

Cooperation is a paradox: Why should one perform a costly behavior only to increase the fitness of another? Human societies, in which individuals cooperate with genetically unrelated individuals on a considerably larger scale than most mammals do, are especially puzzling in this regard. Recently, the threat of punishment has been given substantial attention as one of the mechanisms that could help sustain human cooperation in such situations. Nevertheless, using punishment to explain cooperation only leads to further questions: Why spend precious resources to penalize free‐riders, especially if others can avoid this investment and cheaters can punish you back? Here, it is argued that current evidence supports punishment as an efficient means for the maintenance of cooperation, and that the gravity of proposed limitations of punishment for maintaining cooperation may have been overestimated in previous studies due to the features of experimental design. Most notably, the importance of factors as characteristic of human societies as reputation and language has been greatly neglected. Ironically, it was largely the combination of the two that enabled humans to shape costly punishment into numerous low‐cost and less detrimental strategies that clearly can promote human cooperation.