Evolution Of Human Cooperation Research Articles

No unique effect of intergroup competition on cooperation: non-competitive thresholds are as effective as competitions between groups for increasing human cooperative behavior

Explaining cooperation remains a central topic for evolutionary theorists. Many have argued that group selection provides such an explanation: theoretical models show that intergroup competition could have given rise to cooperation that is costly for the individual. Whether group selection actually did play an important role in the evolution of human cooperation, however, is much debated. Recent experiments have shown that intergroup competitions do increase human cooperation, which has been taken as evidence for group selection as a mechanism for the evolution of cooperation. Here we challenge this standard interpretation. Competitions change the payoff structure by creating a threshold effect whereby the group that contributes more earns an additional prize, which creates some incentive for individuals to cooperate. We present four studies that disentangle competition and thresholds, and strongly suggest that it is thresholds – rather than competitions per se – that increase cooperation. Thus, prior intergroup competition experiments provide no evidence of a unique or special role for intergroup competition in promoting human cooperation, and shed no light on whether group selection shaped human evolution.

The evolution of human cooperation

We argue that cooperation is instinctual. Human cooperation conferred advantages to individuals in the ancestral environment in which evolution occurred. Explanations of the evolution of cooperation for any species (human, pre-human, and non-human) have to be consistent with the biological, physiological, and environmental constraints that existed in the ancestral environment during which evolutionary selection occurred. Our explanation is consistent with: (1) the anatomical evolution of humanity; (2) the paleontological and chronological evidence; and (3) modern biology.

Political Competition, Partisanship and Interpersonal Trust in Electoral Democracies

How does democratic politics inform the interdisciplinary debate on the evolution of human co-operation and the social preferences (for example, trust, altruism and reciprocity) that support it? This article advances a theory of partisan trust discrimination in electoral democracies based on social identity, cognitive heuristics and interparty competition. Evidence from behavioral experiments in eight democracies show ‘trust gaps’ between co- and rival partisans are ubiquitous, and larger than trust gaps based on the social identities that undergird the party system. A natural experiment found that partisan trust gaps in the United States disappeared immediately following the killing of Osama bin Laden. But observational data indicate that partisan trust gaps track with perceptions of party polarization in all eight cases. Finally, the effects of partisanship on trust outstrip minimal group treatments, yet minimal-group effects are on par with the effects of most treatments for ascriptive characteristics in the literature. In sum, these findings suggest political competition dramatically shapes the salience of partisanship in interpersonal trust, the foundation of co-operation.

The early evolution of cooperation in humans. On cheating, group identity and group size

The evolution of cooperation is difficult to understand, because cheaters — individuals who profit without cooperating themselves — have a benefit in interaction with cooperators. Cooperation among humans is even more difficult to understand, because cooperation occurs in large groups, making cheating a bigger threat. Restricting cooperation to members of one’s own group based on some tag-based recognition of non-group members (allorecognition) has been shown to stabilise cooperation. We address how spatial structure and group size affect the opportunities for cheating such tag-based cooperation in a spatially explicit simulation. We show that increased group diversity, under conditions of limited dispersal, reduces the selective opportunities for cheaters. A small number can already be sufficient to keep cheating at a low frequency. We discuss how marginal additional benefits of increased group size, above the benefits of local cooperation, can provide the selective pressure to reduce the number of group identities and discuss possible examples.

The empirical evidence that does not support cultural group selection models for the evolution of human cooperation

I outline key empirical evidence from my research and that of other scholars, testing the role of cultural group selection (CGS) in the evolution of human cooperation, which Richerson et al. failed to mention and which fails to support the CGS hypothesis.

Partner choice creates fairness in humans.

Many studies demonstrate that partner choice has played an important role in the evolution of human cooperation, but little work has tested its impact on the evolution of human fairness. In experiments involving divisions of money, people become either over-generous or over-selfish when they are in competition to be chosen as cooperative partners. Hence, it is difficult to see how partner choice could result in the evolution of fair, equal divisions. Here, we show that this puzzle can be solved if we consider the outside options on which partner choice operates. We conduct a behavioural experiment, run agent-based simulations and analyse a game-theoretic model to understand how outside options affect partner choice and fairness. All support the conclusion that partner choice leads to fairness only when individuals have equal outside options. We discuss how this condition has been met in our evolutionary history, and the implications of these findings for our understanding of other aspects of fairness less specific than preferences for equal divisions of resources.

Should Law Keep Pace with Society? Relative Update Rates Determine the Co-Evolution of Institutional Punishment and Citizen Contributions to Public Goods

Until recently, theorists considering the evolution of human cooperation have paid little attention to institutional punishment, a defining feature of large-scale human societies. Compared to individually-administered punishment, institutional punishment offers a unique potential advantage: the ability to control how quickly legal rules of punishment evolve relative to social behavior that legal punishment regulates. However, at what rate should legal rules evolve relative to society to maximize compliance? We investigate this question by modeling the co-evolution of law and cooperation in a public goods game with centralized punishment. We vary the rate at which States update their legal punishment strategy relative to Citizens’ updating of their contribution strategy and observe the effect on Citizen cooperation. We find that when States have unlimited resources, slower State updating lead to more Citizen cooperation: by updating more slowly, States force Citizens to adapt to the legal punishment rules. When States depend on Citizens to finance their punishment activities, however, we find evidence of a ‘Goldilocks’ effect: optimal compliance is achieved when legal rules evolve at a critical evolutionary rate that is slow enough to force citizens to adapt, but fast enough to enable states to quickly respond to outbreaks of citizen lawlessness.

Did sexual equality fuel the evolution of human cooperation?

Did sexual equality fuel the evolution of human cooperation?

Moderate tolerance promotes tag-mediated cooperation in spatial Prisoner’s dilemma game

Humans often behave discriminatorily towards others depending on their group membership. In this work, we establish a spatial Prisoner’s dilemma model to investigate the relation between tag-mediated discrimination and cooperation. By introducing tag-mediated selective interaction, we find that if tag length is sufficiently large and individuals have moderate tolerance, cooperation can be promoted. Interestingly, both too high or too low tolerance may inhibit the emergence and maintenance of cooperation, which means that individuals may benefit from moderate tolerance in society. It is also shown that the high levels of cooperation stem from the high heterogeneity and clear boundaries between clusters. Our work should be helpful to understand both the evolution of human cooperation and the science of social identity.

Cooperation and conflict: field experiments in Northern Ireland.

The idea that cohesive groups, in which individuals help each other, have a competitive advantage over groups composed of selfish individuals has been widely suggested as an explanation for the evolution of cooperation in humans. Recent theoretical models propose the coevolution of parochial altruism and intergroup conflict, when in-group altruism and out-group hostility contribute to the group's success in these conflicts. However, the few empirical attempts to test this hypothesis do not use natural groups and conflate measures of in-group and unbiased cooperative behaviour. We conducted field experiments based on naturalistic measures of cooperation (school/charity donations and lost letters' returns) with two religious groups with an on-going history of conflict—Catholics and Protestants in Northern Ireland. Conflict was associated with reduced donations to out-group schools and the return of out-group letters, but we found no evidence that it influences in-group cooperation. Rather, socio-economic status was the major determinant of cooperative behaviour. Our study presents a challenge to dominant perspectives on the origins of human cooperation, and has implications for initiatives aiming to promote conflict resolution and social cohesion.

Should Law Keep Pace with Society?

Until recently, theorists considering the evolution of human cooperation have paid little attention to institutional punishment, a defining feature of large-scale human societies. Compared to individually administered punishment, institutional punishment offers a unique potential advantage: the ability to control how quickly legal rules of punishment evolve relative to social behavior that legal punishment regulates. But at what rate should legal rules evolve relative to society to maximize compliance? We investigate this question by modeling the co-evolution of law and cooperation in a public goods game with centralized punishment. We vary the rate at which the State updates the legal punishment strategy relative to Citizens' updating of their contribution strategy, and observe the effect on Citizen cooperation. When States have unlimited resources, slower State leads to more Citizen cooperation: by updating more slowly, States forces Citizens to adapt to the legal punishment rules. When States depend on Citizens to finance their punishment activities, however, we find evidence of a Goldilocks'' effect: the optimal outcome is achieved when legal rules evolve at a critical evolutionary rate that is slow enough to allow citizens to adapt, but fast enough to enable states to quickly respond to outbreaks of citizen lawlessness.

Similarity increases altruistic punishment in humans

Humans are attracted to similar others. As a consequence, social networks are homogeneous in sociodemographic, intrapersonal, and other characteristics--a principle called homophily. Despite abundant evidence showing the importance of interpersonal similarity and homophily for human relationships, their behavioral correlates and cognitive foundations are poorly understood. Here, we show that perceived similarity substantially increases altruistic punishment, a key mechanism underlying human cooperation. We induced (dis)similarity perception by manipulating basic cognitive mechanisms in an economic cooperation game that included a punishment phase. We found that similarity-focused participants were more willing to punish others' uncooperative behavior. This influence of similarity is not explained by group identity, which has the opposite effect on altruistic punishment. Our findings demonstrate that pure similarity promotes reciprocity in ways known to encourage cooperation. At the same time, the increased willingness to punish norm violations among similarity-focused participants provides a rationale for why similar people are more likely to build stable social relationships. Finally, our findings show that altruistic punishment is differentially involved in encouraging cooperation under pure similarity vs. in-group conditions.

Cultural evolution of cooperation: The interplay between forms of social learning and group selection

The role of cultural group selection in the evolution of human cooperation is hotly debated. It has been argued that group selection is more effective in cultural evolution than in genetic evolution, because some forms of cultural transmission (conformism and/or the tendency to follow a leader) reduce intra-group variation while creating stable cultural variation between groups. This view is supported by some models, while other models lead to contrasting and sometimes opposite conclusions. A consensus view has not yet been achieved, partly because the modelling studies differ in their assumptions on the dynamics of cultural transmission and the mode of group selection. To clarify matters, we created an individual-based model allowing for a systematic comparison of how different social learning rules governing cultural transmission affect the evolution of cooperation in a group-structured population. We consider two modes of group selection (selection by group replacement or by group contagion) and systematically vary the frequency and impact of group-level processes. From our simulations we conclude that the outcome of cultural evolution strongly reflects the interplay of social learning rules and the mode of group selection. For example, conformism hampers or even prevents the evolution of cooperation if group selection acts via contagion; it may facilitate the evolution of cooperation if group selection acts via replacement. In contrast, leader-imitation promotes the evolution of cooperation under a broader range of conditions.

Intergroup Conflict May Inhibit Coalescing of Large Human Groups and Decrease Returns from Cooperation

Recent theoretical advances and quasi-experimental evidence from modern conflict areas suggest that intergroup conflict and ostracism play a pivotal role in the evolution of cooperation. However, relatively little is known about the role of intergroup conflict and ostracism on group formation and human migration. Here, we show that intergroup conflict may inhibit coalescing of large human groups and decrease net returns from cooperative behaviors. Moreover, we find that competitive pressure between groups decreases the likelihood of being punished through ostracism. Our results suggest the importance of stable group boundaries on the evolution of human cooperation through intergroup conflict and point to the dangers of implementing group contests to foster human cooperation.

Behavioral Responses to Inequity in Reward Distribution and Working Effort in Crows and Ravens

Sensitivity to inequity is considered to be a crucial cognitive tool in the evolution of human cooperation. The ability has recently been shown also in primates and dogs, raising the question of an evolutionary basis of inequity aversion. We present first evidence that two bird species are sensitive to other individuals' efforts and payoffs. In a token exchange task we tested both behavioral responses to inequity in the quality of reward (preferred versus non-preferred food) and to the absence of reward in the presence of a rewarded partner, in 5 pairs of corvids (6 crows, 4 ravens). Birds decreased their exchange performance when the experimental partner received the reward as a gift, which indicates that they are sensitive to other individuals' working effort. They also decreased their exchange performance in the inequity compared with the equity condition. Notably, corvids refused to take the reward after a successful exchange more often in the inequity compared with the other conditions. Our findings indicate that awareness to other individuals' efforts and payoffs may evolve independently of phylogeny in systems with a given degree of social complexity.

Variants at serotonin transporter and 2A receptor genes predict cooperative behavior differentially according to presence of punishment

Punishment of free-riding has been implicated in the evolution of cooperation in humans, and yet mechanisms for punishment avoidance remain largely uninvestigated. Individual variation in these mechanisms may stem from variation in the serotonergic system, which modulates processing of aversive stimuli. Functional serotonin gene variants have been associated with variation in the processing of aversive stimuli and widely studied as risk factors for psychiatric disorders. We show that variants at the serotonin transporter gene (SLC6A4) and serotonin 2A receptor gene (HTR2A) predict contributions to the public good in economic games, dependent upon whether contribution behavior can be punished. Participants with a variant at the serotonin transporter gene contribute more, leading to group-level differences in cooperation, but this effect dissipates in the presence of punishment. When contribution behavior can be punished, those with a variant at the serotonin 2A receptor gene contribute more than those without it. This variant also predicts a more stressful experience of the games. The diversity of institutions (including norms) that govern cooperation and punishment may create selective pressures for punishment avoidance that change rapidly across time and space. Variant-specific epigenetic regulation of these genes, as well as population-level variation in the frequencies of these variants, may facilitate adaptation to local norms of cooperation and punishment.

Young Children Enforce Social Norms

Social norms have played a key role in the evolution of human cooperation, serving to stabilize prosocial and egalitarian behavior despite the self-serving motives of individuals. Young children’s behavior mostly conforms to social norms, as they follow adult behavioral directives and instructions. But it turns out that even preschool children also actively enforce social norms on others, often using generic normative language to do so. This behavior is not easily explained by individualistic motives; it is more likely a result of children’s growing identification with their cultural group, which leads to prosocial motives for preserving its ways of doing things.

Tolerance-based punishment in continuous public goods game

Altruistic punishment for defectors is considered as a key motive for the explanation of cooperation. However, there is no clear border between the cooperative and defective behaviors in a continuous strategy game. We propose a model to study the effect of punishment on the evolution of cooperation in continuous public goods game, wherein individuals have the traits to punish the co-players based on social tolerance. We show that a reasonable punishment with a uniform tolerance can spur individuals to make more investments. Additionally, for a fixed punishment cost and a fixed fine, a moderate value of tolerance can result in the best promotion of cooperation. Furthermore, we investigate the coevolutionary dynamics of investment and tolerance. We find that the population splits into two branches: high-tolerance individuals who make high investments and low-tolerance individuals who make low investments. A dynamic equilibrium is achieved between these two types of individuals. Our work extends punishment to continuous cooperative behaviors and the results may enhance the understanding of altruistic punishment in the evolution of human cooperation.

Children, but Not Chimpanzees, Prefer to Collaborate

Human societies are built on collaborative activities. Already from early childhood, human children are skillful and proficient collaborators. They recognize when they need help in solving a problem and actively recruit collaborators [1, 2]. The societies of other primates are also to some degree cooperative. Chimpanzees, for example, engage in a variety of cooperative activities such as border patrols, group hunting, and intra- and intergroup coalitionary behavior [3-5]. Recent studies have shown that chimpanzees possess many of the cognitive prerequisites necessary for human-like collaboration. Chimpanzees have been shown to recognize when they need help in solving a problem and to actively recruit good over bad collaborators [6, 7]. However, cognitive abilities might not be all that differs between chimpanzees and humans when it comes to cooperation. Another factor might be the motivation to engage in a cooperative activity. Here, we hypothesized that a key difference between human and chimpanzee collaboration-and so potentially a key mechanism in the evolution of human cooperation-is a simple preference for collaborating (versus acting alone) to obtain food. Our results supported this hypothesis, finding that whereas children strongly prefer to work together with another to obtain food, chimpanzees show no such preference.

Conflict, sticks and carrots: war increases prosocial punishments and rewards

Unlike most species, humans cooperate extensively with group members who are not closely related to them, a pattern sustained in part by punishing non-cooperators and rewarding cooperators. Because internally cooperative groups prevail over less cooperative rival groups, it is thought that violent intergroup conflict played a key role in the evolution of human cooperation. Consequently, it is plausible that propensities to punish and reward will be elevated during intergroup conflict. Using experiments conducted before, during and after the 2006 Israel-Hezbollah war, we show that, during wartime, people are more willing to pay costs to punish non-cooperative group members and reward cooperative group members. Rather than simply increasing within-group solidarity, violent intergroup conflict thus elicits behaviours that, writ large, enhance cooperation within the group, thereby making victory more likely.