Human cooperation

Multivariate pattern analysis of cooperation and competition in constructive action

The neural underpinning of cooperative and competitive constructive activity has been investigated using mass-univariate approaches. In this study, we sought to compare the results of these approaches with the results of multivariate pattern analysis (MVPA). In particular, we wanted to test whether MVPA supports the claim made in previous studies that cooperation is associated with the activity of reward-related brain circuits. Participants were required to construct a pattern on the screen either individually or in cooperation or competition with another person during an fMRI scan. Both the MVPA classification methods and the representational similarity analysis indicated the involvement of orbitofrontal and ventromedial prefrontal areas in processes that distinguish between cooperation and competition, and activation analysis showed that these areas are more active during cooperation than during competition. However, a single trial analysis showed that the effect was reversed when only winning trials were considered. In these trials, activation of reward-related areas was higher during competition than during cooperation. Moreover, the contrast between won and lost trials in terms of reward circuits involvement was sharper under competition than under cooperation. Thus, although cooperation can be generally more rewarding than competition, it is associated with smaller difference between trials lost and trials won in terms of reward circuits activation. One may speculate that in cooperation, victory and defeat are shared with the partner and, contrary to competition, are not experienced as personal achievement or failure.

The nasty neighbor effect in humans

Like other group-living species, humans often cooperate more with an in-group member than with out-group members and strangers. Greater in-group favoritism should imply that people also compete less with in-group members than with out-group members and strangers. However, in situations where people could invest to take other's resources and invest to protect against exploitation, we observed the opposite. Akin to what in other species is known as the "nasty neighbor effect," people invested more when facing an in-group rather than out-group member or stranger across 51 nations, in different communities in Kenya, and in representative samples from the United Kingdom. This "nasty neighbor" behavior is independent of in-group favoritism in trust and emerges when people perceive within-group resource scarcity. We discuss how to reconcile that humans exhibit nastiness and favoritism toward in-group members with existing theory on in-group favoritism.

High consistency of cheating and honesty in early childhood

Three preregistered studies examined whether 5-year-old children cheat consistently or remain honest across multiple math tests. We observed high consistency in both honesty and cheating. All children who cheated on the first test continued cheating on subsequent tests, with shorter cheating latencies over time. In contrast, 77% of initially honest children maintained honesty despite repeated failure to complete the tests successfully. A brief integrity intervention helped initially honest children remain honest but failed to dissuade initially cheating children from cheating. These findings demonstrate that cheating emerges early and persists strongly in young children, underscoring the importance of early prevention efforts. They also suggest that bolstering honesty from the start may be more effective than attempting to remedy cheating after it has occurred. RESEARCH HIGHLIGHTS: Our research examines whether 5-year-old children, once they have started cheating, will continue to do so consistently. We also investigate whether 5-year-old children who are initially honest will continue to be honest subsequently. We discovered high consistency in both honesty and cheating among 5-year-old children. Almost all the children who initially cheated continued this behavior, while those who were honest stayed honest. A brief integrity-boosting intervention successfully helped 5-year-old children maintain their honesty. However, the same intervention failed to deter cheaters from cheating again. These findings underscore the importance of implementing integrity intervention as early as possible, potentially before children have had their first experience of cheating.

Social decision-making in major depressive disorder: A three-level meta-analysis

Major Depressive Disorder (MDD) is frequently associated with social dysfunction and impaired decision-making, but its impact on social decisions remains unclear. Thus, we conducted a series of meta-analyses to examine the effects of MDD on key social decision phenomena, including trust, altruistic punishment, and cooperation. We searched Web of Science, PubMed, PsycINFO, and Embase up to December 2023, using Hedges' g to compare social decision-making between MDD patients and healthy controls (HCs). Meta-analytic results showed that MDD patients exhibited a significant reduction in trust (Hedges' g = -0.347, p < 0.001), no significant difference in altruistic punishment (Hedges' g = 0.232, p = 0.149), and an increase in cooperative behaviors (Hedges' g = 0.361, p = 0.002) compared to HCs. The moderation analysis revealed that age (p = 0.039) and region (p = 0.007) significantly moderated altruistic punishment, with older MDD patients and those from Asian and European regions having larger MDD-HC contrast than others. Regarding cooperation, moderation analysis indicated that age (p = 0.028), years of education (p = 0.054), and treatment coverage (p = 0.042) were significant moderators, indicating larger MDD-HC contrast in older, less-educated and better-treated people. These findings suggest MDD has different impacts on different social decisions, highlighting the need for fine-tuned therapeutic interventions that address these differences. The data also underscores the importance of considering demographic and treatment-related variables in managing MDD, which could inform personalized treatment strategies and improve social functionality and patient outcomes.

Repeated rock, paper, scissors play reveals limits in adaptive sequential behavior

How do people adapt to others in adversarial settings? Prior work has shown that people often violate rational models of adversarial decision-making in repeated interactions. In particular, in mixed strategy equilibrium (MSE) games, where optimal action selection entails choosing moves randomly, people often do not play randomly, but instead try to outwit their opponents. However, little is known about the adaptive reasoning that underlies these deviations from random behavior. Here, we examine strategic decision-making across repeated rounds of rock, paper, scissors, a well-known MSE game. In experiment 1, participants were paired with bot opponents that exhibited distinct stable move patterns, allowing us to identify the bounds of the complexity of opponent behavior that people can detect and adapt to. In experiment 2, bot opponents instead exploited stable patterns in the human participants' moves, providing a symmetrical bound on the complexity of patterns people can revise in their own behavior. Across both experiments, people exhibited a robust and flexible attention to transition patterns from one move to the next, exploiting these patterns in opponents and modifying them strategically in their own moves. However, their adaptive reasoning showed strong limitations with respect to more sophisticated patterns. Together, results provide a precise and consistent account of the surprisingly limited scope of people's adaptive decision-making in this setting.

Perceived overqualification and knowledge sharing: The role of organizational identity and psychological entitlement

BACKGROUND

Employees' perception of being overqualified is a critical factor in influencing their knowledge sharing behavior. However previous studies have not examined the internal mechanism by which perceived overqualification affects knowledge sharing.

OBJECTIVE

Drawing on social exchange theory, the present study aimed to explore the relationship between perceived overqualification and knowledge sharing and to examine the mediating effect of organizational identity and the moderating role of psychological entitlement.

METHODS

Participants were 284 full-time employees from different companies in China. They answered self-report questionnaires that assessed perceived overqualification, knowledge sharing, organizational identity, and psychological entitlement. Path analyses were conducted, and the latent moderated structural equations were used to judge the significance of the mediation and moderation.

RESULTS

The results revealed that overqualified employees were less willing to share knowledge, and the mediating role of organizational identity was significant. Further, the presence of high psychological entitlement would diminish the beneficial effect of organizational identity on employee knowledge sharing.

CONCLUSIONS

The findings of the study enrich and expand our knowledge on the relationship between overqualification and knowledge sharing and have theoretical and practical implications for promoting constructive behavior among overqualified employees.

Children cooperate more with in-group members than with out-group members in an iterated face-to-face Prisoner's Dilemma Game

Adults are more likely to cooperate with in-group members than with out-group members in the context of social dilemmas, situations in which self-interest is in conflict with collective interest. This bias has the potential to profoundly shape human cooperation, and therefore it is important to understand when it emerges in development. Here we asked whether 6- to 9-year-old children (N = 146) preferentially cooperate with in-group members in the context of a well-studied social dilemma, the iterated Prisoner's Dilemma Game. We assigned children to minimal groups and paired them with unfamiliar same-age and same-gender peers. Consistent with our predictions, children were more likely to cooperate with in-group members than with out-group members in this minimal group context. This finding adds to the current literature on group bias in children's prosocial behavior by showing that it affects decision making in a context that calls on strategic cooperation. In addition, our analyses revealed an effect of gender, with girls more likely to cooperate than boys regardless of the group membership of their partner. Exploring this gender effect further, we found an interaction between gender and age across condition, with older girls showing less sensitivity to the group membership of their partner than younger girls and with older boys showing more sensitivity to the group membership of the partner than younger boys. Our findings suggest that risky cooperation in the face of social dilemmas is shaped by group bias during childhood, highlighting the potentially deeply rooted ties between cooperation and parochialism in humans.

Migration costs and rewarding schemes in spatial public goods games

This study explores the influence of migration costs and rewarding schemes on cooperation through the implementation of computational behavioral models in spatial public goods games. The former involves a cost for agents to migrate to a neighboring group, while the latter rewards them for remaining in the same group for multiple rounds. By analyzing these mechanisms separately and in combination, we unveil their effects on cooperative behavior. The grid-based game dynamics begins with equal size groups, and agents can adjust their contributions each round, with the option to migrate if unsatisfied. Our findings reveal that when considered separately, the rewarding scheme is not as effective in achieving full cooperation as the migration cost scheme. Combining migration costs and rewards instead yields high cooperation levels with low public goods game enhancement factors and migration probability. Our results offer valuable insights for contexts where promoting cooperative behavior is crucial, such as community engagement development and public policies.

Replicator-mutator dynamics with evolutionary public goods game-environmental feedbacks

Feedback loops between strategies and the environment are commonly observed in socio-ecological, evolution-ecological, and psychology-economic systems. However, the impact of mutations in these feedback processes is often overlooked. This study proposes a novel model that integrates the public goods game with environmental feedback, considering the presence of mutations. In our model, the enhancement factor of the public goods game combines positive and negative incentives from the environment. By employing replicator-mutator (RM) equations, we provide an objective understanding of the system's evolutionary state, focusing on identifying conditions that foster cooperation and prevent the tragedy of the commons. Specifically, mutations play a crucial role in the RM dynamics, leading to the emergence of an oscillatory tragedy of the commons. By verifying the Hopf bifurcation condition, we establish the existence of a stable limit cycle, providing valuable insights into sustained oscillation strategies. Moreover, the feedback mechanism inherent in the public goods game model offers a fresh perspective on effectively addressing the classic dilemma of the tragedy of the commons.

Success-driven opinion formation determines social tensions

Polarization is common in politics and public opinion. It is believed to be shaped by media as well as ideologies, and often incited by misinformation. However, little is known about the microscopic dynamics behind polarization and the resulting social tensions. By coupling opinion formation with the strategy selection in different social dilemmas, we reveal how success at an individual level transforms to global consensus or lack thereof. When defection carries with it the fear of punishment in the absence of greed, as in the stag-hunt game, opinion fragmentation is the smallest. Conversely, if defection promises a higher payoff and also evokes greed, like in the prisoner's dilemma and snowdrift game, consensus is more difficult to attain. Our research thus challenges the top-down narrative of social tensions, showing they might originate from fundamental principles at individual level, like the desire to prevail in pairwise evolutionary comparisons.

When do stereotypes undermine indirect reciprocity?

Social reputations provide a powerful mechanism to stimulate human cooperation, but observing individual reputations can be cognitively costly. To ease this burden, people may rely on proxies such as stereotypes, or generalized reputations assigned to groups. Such stereotypes are less accurate than individual reputations, and so they could disrupt the positive feedback between altruistic behavior and social standing, undermining cooperation. How do stereotypes impact cooperation by indirect reciprocity? We develop a theoretical model of group-structured populations in which individuals are assigned either individual reputations based on their own actions or stereotyped reputations based on their groups' behavior. We find that using stereotypes can produce either more or less cooperation than using individual reputations, depending on how widely reputations are shared. Deleterious outcomes can arise when individuals adapt their propensity to stereotype. Stereotyping behavior can spread and can be difficult to displace, even when it compromises collective cooperation and even though it makes a population vulnerable to invasion by defectors. We discuss the implications of our results for the prevalence of stereotyping and for reputation-based cooperation in structured populations.

Group Formation and the Evolution of Human Social Organization

Humans operate in groups that are oftentimes nested in multilayered collectives such as work units within departments and companies, neighborhoods within cities, and regions within nation states. With psychological science mostly focusing on proximate reasons for individuals to join existing groups and how existing groups function, we still poorly understand why groups form ex nihilo, how groups evolve into complex multilayered social structures, and what explains fission-fusion dynamics. Here we address group formation and the evolution of social organization at both the proximate and ultimate level of analysis. Building on models of fitness interdependence and cooperation, we propose that socioecologies can create positive interdependencies among strangers and pave the way for the formation of stable coalitions and groups through reciprocity and reputation-based partner selection. Such groups are marked by in-group bounded, parochial cooperation together with an array of social institutions for managing the commons, allowing groups to scale in size and complexity while avoiding the breakdown of cooperation. Our analysis reveals how distinct group cultures can endogenously emerge from reciprocal cooperation, shows that social identification and group commitment are likely consequences rather than causes of group cooperation, and explains when intergroup relations gravitate toward peaceful coexistence, integration, or conflict.

Evolution of cooperation in deme-structured populations on graphs

Understanding how cooperation can evolve in populations despite its cost to individual cooperators is an important challenge. Models of spatially structured populations with one individual per node of a graph have shown that cooperation, modeled via the prisoner's dilemma, can be favored by natural selection. These results depend on microscopic update rules, which determine how birth, death, and migration on the graph are coupled. Recently, we developed coarse-grained models of spatially structured populations on graphs, where each node comprises a well-mixed deme, and where migration is independent from division and death, thus bypassing the need for update rules. Here, we study the evolution of cooperation in these models in the rare-migration regime, within the prisoner's dilemma. We find that cooperation is not favored by natural selection in these coarse-grained models on graphs where overall deme fitness does not directly impact migration from a deme. This is due to a separation of scales, whereby cooperation occurs at a local level within demes, while spatial structure matters between demes.

Residential mobility and psychological transformation in China: From relational to institutional trust

As one of the important drivers of social change in China, residential mobility has caused a dramatic change in the interpersonal environment, but it remained little known how residential mobility would influence the basis of interpersonal interaction-trust. The present research aimed to explore the effect of residential mobility on two kinds of trust, relational trust and institutional trust, by two studies. Study 1 explored the correlational relationship between regional residential mobility and two kinds of trust using data from the China General Social Survey 2010 and the Sixth National Population Census of China, and analyzed the data using hierarchical linear modeling. Study 2 switched to the individual level and investigated the causal relationship between individual residential mobility and two kinds of trust in the laboratory using the writing task for priming residential mobility and the situational selection task for trust. Study 1 found that individuals exhibited lower relational trust when they lived in a region of higher residential mobility. For institutional trust, the indicator about the permission to register household in inflow cities could significantly positively predict this. Study 2 found that the primed mindset of high (vs. low) residential mobility reduces relational trust and enhances institutional trust. In conclusion, the present research revealed that residential mobility promotes the transformation of individuals' trust mode from relational to institutional trust in social life, thus expanding the research field of residential mobility as a socioecological factor and extended the understanding of psychological transformation under the background of social change in China.

Bonus-based mercenary punishment promotes cooperation in public goods games

Various regions often adopt punish strategies to solve traffic congestion problems. Punishing defectors is an effective strategy to solve the first-order free-rider problem in a public goods game. But this behavior is costly because the punisher is often also involved in the original joint venture and therefore vulnerable, which jeopardizes the effectiveness of this incentive. As an option, we could hire special players whose sole duty would be to monitor the population and punish defectors. The fines collected by various regions will also be used to subsidize the construction of public transportation. Thereby, we derive inspiration, and propose an improved public goods game model based on bonus and mercenary punishment. Research has shown that after cooperator gives the punisher an appropriate bonus, cooperators can strengthen the punisher, thereby weakening the defector's advantage and indirectly promoting cooperation by stabilizing the punisher's position in the system. In addition, the mechanism of reusing the fines collected from defectors and then subsidize to other players in the system can directly promote the emergence of cooperation.

Disrupting the Dorsolateral Prefrontal Cortex Attenuates the Difference in Decision-Making for Altruistic Punishment Between the Gain and Loss Contexts

Altruistic punishment is a primary response to social norms violations; its neural mechanism has also attracted extensive research attention. In the present studies, we applied a low-frequency repetitive transcranial magnetic stimulation (rTMS) to the bilateral dorsolateral prefrontal cortex (DLPFC) while participants engaged in a modified Ultimatum Game (Study 1) and third-party punishment game (Study 2) to explore how the bilateral DLPFC disruption affects people's perception of violation of fairness norms and altruistic punishment decision in the gain and loss contexts. Typically, punishers intervene more often against and show more social outrage towards Dictators/Proposers who unfairly distribute losses than those who unfairly share gains. We found that disrupting the function of the left DLPFC in the second-party punishment and the bilateral DLPFC in the third-party punishment with rTMS effectively obliterated this difference, making participants punish unfairly shared gains as often as they usually would punish unfairly shared losses. In the altruistic punishment of maintaining the social fairness norms, the inhibition of the right DLPFC function will affect the deviation of individual information integration ability; the inhibition of the left DLPFC function will affect the assessment of the degree of violation of fairness norms and weaken impulse control, leading to attenuate the moderating effect of gain and loss contexts on altruistic punishment. Our findings emphasize that DLPFC is closely related to altruistic punishment and provide causal neuroscientific evidence.

Dispositional compassion shifts social preferences in systematic ways

INTRODUCTION

How people attach value to the outcomes of self and other-social preferences-is central to social behavior. Recently, how dispositional and state emotion shape such social preferences has received researchers' attention.

METHOD

The present investigation asked whether and to what extent dispositional and state compassion predict shifts in social preferences across 4 samples: two correlational samples (final ns 153 & 368, study 1a and 1b) and two experimental samples (final ns: 430 & 530, studies 2 and 3).

RESULTS

In keeping with recent accounts of compassion, dispositional compassion predicted general preference for equality, expressed as dispreference for both monetary advantage over another (interaction βs = -0.36, -0.33, -0.25, -0.22; all p < 0.001) and monetary disadvantage relative to others (βs: 0.26, 0.27, 0.28, 0.17; all p < 0.01; positive coefficients imply dispreference). This dispositional effect persisted when controlling for prosociality, positivity, agreeableness, and respectfulness. Furthermore, these dispositional compassion effects were relatively unchanged by experimental emotion inductions in studies 3 and 4. The experimental inductions of state compassion and state pride showed little evidence of systematic effects on social preferences relative to each other or a neutral condition.

DISCUSSION

Discussion focused on individual differences in emotion and social preferences.

Behavioral evidence for global consciousness transcending national parochialism

While national parochialism is commonplace, individual differences explain more variance in it than cross-national differences. Global consciousness (GC), a multi-dimensional concept that includes identification with all humanity, cosmopolitan orientation, and global orientation, transcends national parochialism. Across six societies (N = 11,163), most notably the USA and China, individuals high in GC were more generous allocating funds to the other in a dictator game, cooperated more in a one-shot prisoner's dilemma, and differentiated less between the ingroup and outgroup on these actions. They gave more to the world and kept less for the self in a multi-level public goods dilemma. GC profiles showed 80% test-retest stability over 8 months. Implications of GC for cultural evolution in the face of trans-border problems are discussed.

Selection and adaptation in human migration

This article reviews the ways migration shapes human biology. This includes the physiological and genetic, but also socio-cultural aspects such as organization, behavior, and culture. Across disciplines I highlight the multiple levels of cultural and genetic selection whereby individuals and groups adapt to pressures along a migration timeline: the origin, transit, and destination. Generally, the evidence suggests that selective pressures and adaptations occur at the individual, family, and community levels. Consequently, across levels there are negotiations, interactions, and feedbacks that shape migration outcomes and the trajectory of evolutionary change. The rise and persistence of migration-relevant adaptations emerges as a central question, including the maintenance of cumulative culture adaptations, the persistence of "cultures of migration," as well as the individual-level physiological and cognitive adaptations applied to successful transit and settlement in novel environments.

Cognitive-attentional mechanisms of cooperation-with implications for attention-deficit hyperactivity disorder and cognitive neuroscience

People's cooperativeness depends on many factors, such as their motives, cognition, experiences, and the situation they are in. To date, it is unclear how these factors interact and shape the decision to cooperate. We present a computational account of cooperation that not only provides insights for the design of effective incentive structures but also redefines neglected social-cognitive characteristics associated with attention-deficit hyperactivity disorder (ADHD). Leveraging game theory, we demonstrate that the source and magnitude of conflict between different motives affected the speed and frequency of cooperation. Integrating eye-tracking to measure motivation-based information processing during decision-making shows that participants' visual fixations on the gains of cooperation rather than its costs and risks predicted their cooperativeness on a trial-by-trial basis. Using Bayesian hierarchical modeling, we find that a situation's prosociality and participants' past experience each bias the decision-making process distinctively. ADHD characteristics explain individual differences in responsiveness across contexts, highlighting the clinical importance of experimentally studying reactivity in social interactions. We demonstrate how the use of eye-tracking and computational modeling can be used to experimentally investigate social-cognitive characteristics in clinical populations. We also discuss possible underlying neural mechanisms to be investigated in future studies.

Tax thresholds yield multiple optimal cooperation levels in the spatial public goods game

Income redistribution, which involves transferring income from certain individuals to others, plays a crucial role in human societies. Previous research has indicated that tax-based redistribution can promote cooperation by enhancing incentives for cooperators. In such a tax system, all individuals, irrespective of their income levels, contribute to the tax system, and the tax revenue is subsequently redistributed to everyone. In this study, we relax this assumption by introducing a tax threshold, signifying that only individuals with incomes exceeding the threshold will be subject to taxation. In particular, we employ the spatial public goods game to investigate the influence of tax rates-the percentage of income allocated to tax-and tax thresholds, which determine the income level at which individuals become taxable, on the evolution of cooperation. Our extensive numerical simulations disclose that tax thresholds produce complex outcomes for the evolution of cooperation, depending on tax rates. Notably, at low tax rates (i.e., below 0.41), as the tax threshold increases, discontinuous phase transitions in cooperation performance suggest the presence of multiple intervals of effective tax thresholds that promote peak cooperation levels. Nevertheless, irrespective of the chosen tax rate, once the tax threshold surpasses a critical threshold, the redistribution mechanism fails, causing the collapse of cooperation. Evolutionary snapshots show that self-organized redistribution forms an intermediary layer on the peripheries of cooperative clusters, effectively shielding cooperators from potential defectors. Quantitative analyses shed light on how self-organized redistribution narrows the income gap between cooperators and defectors through precise identification of tax-exempt entities, thereby amplifying the cooperative advantage. Collectively, these findings enhance our comprehension of how income redistribution influences cooperation, highlighting the pivotal role of tax thresholds.

Emotion expression and cooperation under collective risks

The difficulties associated with solving Humanity's major global challenges have increasingly led world leaders and everyday citizens to publicly adopt strong emotional responses, with either mixed or unknown impacts on others' actions. Here, we present two experiments showing that non-verbal emotional expressions in group interactions play a critical role in determining how individuals behave when contributing to public goods entailing future and uncertain returns. Participants' investments were not only shaped by emotional expressions but also enhanced by anger when compared with joy. Our results suggest that global coordination may benefit from interaction in which emotion expressions can be paramount.

Individual differences in cooperative and competitive play strategies

INTRODUCTION

Cooperation and competition are common in social interactions. It is not clear how individual differences in personality may predict performance strategies under these two contexts. We evaluated whether instructions to play cooperatively and competitively would differentially affect dyads playing a Pong video game. We hypothesized that instructions to play cooperatively would result in lower overall points scored and differences in paddle control kinematics relative to when participants were instructed to play competitively. We also predicted that higher scores in prosociality and Sportspersonship would be related to better performance during cooperative than competitive conditions.

METHODS

Pairs of participants played a Pong video game under cooperative and competitive instructions. During competitive trials, participants were instructed to score more points against one another to win the game. During the cooperative trials, participants were instructed to work together to score as few points against one another as possible. After game play, each participant completed surveys so we could measure their trait prosociality and Sportspersonship.

RESULTS

Condition was a significant predictor of where along the paddle participants hit the ball, which controlled ball exit angles. Specifically, during cooperation participants concentrated ball contacts on the paddle towards the center to produce more consistent rebound angles. We found a significant correlation of Sex and the average points scored by participants during cooperative games, competitive games, and across all trials. Sex was also significantly correlated with paddle kinematics during cooperative games. The overall scores on the prosociality and Sportspersonship surveys were not significantly correlated with the performance outcomes in cooperative and competitive games. The dimension of prosociality assessing empathic concern was significantly correlated with performance outcomes during cooperative video game play.

DISCUSSION

No Sportspersonship survey score was able to predict cooperative or competitive game performance, suggesting that Sportspersonship personality assessments are not reliable predictors of cooperative or competitive behaviors translated to a virtual game setting. Survey items and dimensions probing broader empathic concern may be more effective predictors of cooperative and competitive performance during interactive video game play. Further testing is encouraged to assess the efficacy of prosocial personality traits as predictors of cooperative and competitive video game behavior.

Vacancies in growing habitats promote the evolution of cooperation

We study evolutionary game dynamics in a growing habitat with vacancies. Fitness is determined by the global effect of the environment and a local prisoner's dilemma among neighbors. We study population growth on a one-dimensional lattice and analyze how the environment affects evolutionary competition. As the environment becomes harsh, an absorbing phase transition from growing populations to extinction occurs. The transition point depends on which strategies are present in the population. In particular, we find a 'cooperative window' in parameter space, where only cooperators can survive. A mutant defector in a cooperative community might briefly proliferate, but over time naturally occurring vacancies separate cooperators from defectors, thereby driving defectors to extinction. Our model reveals that vacancies provide a strong boost for cooperation by spatial selection.

Warming up cool cooperators

Explaining why someone repeats high-cost cooperation towards non-reciprocating strangers is difficult. Warm glow offers an explanation. We argue that warm glow, as a mechanism to sustain long-term cooperation, cools off over time but can be warmed up with a simple intervention message. We tested our predictions in the context of repeat voluntary blood donation (high-cost helping of a non-reciprocating stranger) across 6 studies: a field-based experiment (n = 5,821) comparing warm-glow and impure-altruism messages; an implementation study comparing a 3-yr pre-implementation period among all first-time donors in Australia (N = 270,353) with a 2-yr post-implementation period (N = 170, 317); and 4 studies (n = 716, 1,124, 932, 1,592) exploring mechanisms. We show that there are relatively warm and cool cooperators, not cooling cooperators. Cooperation among cool cooperators is enhanced by a warm-glow-plus-identity message. Furthermore, the behavioural facilitation of future cooperation, by booking an appointment, is associated with being a warm cooperator. Societal implications are discussed.

The evolution of cooperation in the unidirectional division of labour on a tree network

Division of labour on complex networks is rarely investigated using evolutionary game theory. We investigate a division of labour where divided roles are assigned to groups on the nodes of a general unidirectional finite tree graph network. From the network's original node, a task flows and is divided along the branches. A player is randomly selected in each group of cooperators and defectors, who receives a benefit from a cooperator in the upstream group and a part of the task. A cooperator completes their part by paying a cost and then passing it downstream until the entire task is completed. Defectors do not do anything and the division of labour stops, causing all groups to suffer losses due to the incomplete task. We develop a novel method to analyse the local stability in this general tree. We discover that not the benefits but the costs of the cooperation influence the evolution of cooperation, and defections in groups that are directly related to that group's task cause damage to players in that group. We introduce two sanction systems, one of which induces the evolution of cooperation more than the system without sanctions, and promote the coexistence of cooperator and defector groups.

Guinea baboons are strategic cooperators

Humans are strategic cooperators; we make decisions on the basis of costs and benefits to maintain high levels of cooperation, and this is thought to have played a key role in human evolution. In comparison, monkeys and apes might lack the cognitive capacities necessary to develop flexible forms of cooperation. We show that Guinea baboons (Papio papio) can use direct reciprocity and partner choice to develop and maintain high levels of cooperation in a prosocial choice task. Our findings demonstrate that monkeys have the cognitive capacities to adjust their level of cooperation strategically using a combination of partner choice and partner control strategies. Such capacities were likely present in our common ancestor and would have provided the foundations for the evolution of typically human forms of cooperation.

Cost optimisation of hybrid institutional incentives for promoting cooperation in finite populations

In this paper, we rigorously study the problem of cost optimisation of hybrid (mixed) institutional incentives, which are a plan of actions involving the use of reward and punishment by an external decision-maker, for maximising the level (or guaranteeing at least a certain level) of cooperative behaviour in a well-mixed, finite population of self-regarding individuals who interact via cooperation dilemmas (Donation Game or Public Goods Game). We show that a mixed incentive scheme can offer a more cost-efficient approach for providing incentives while ensuring the same level or standard of cooperation in the long-run. We establish the asymptotic behaviour (namely neutral drift, strong selection, and infinite-population limits). We prove the existence of a phase transition, obtaining the critical threshold of the strength of selection at which the monotonicity of the cost function changes and providing an algorithm for finding the optimal value of the individual incentive cost. Our analytical results are illustrated with numerical investigations. Overall, our analysis provides novel theoretical insights into the design of cost-efficient institutional incentive mechanisms for promoting the evolution of cooperation in stochastic systems.

Partner choice and cooperation in social dilemmas can increase resource inequality

Cooperation is more likely when individuals can choose their interaction partner. However, partner choice may be detrimental in unequal societies, in which individuals differ in available resources and productivity, and thus in their attractiveness as interaction partners. Here we experimentally examine this conjecture in a repeated public goods game. Individuals (n = 336), participating in groups of eight participants, are assigned a high or low endowment and a high or low productivity factor (the value that their cooperation generates), creating four unique participant types. On each round, individuals are either assigned a partner (assigned partner condition) or paired based on their self-indicated preference for a partner type (partner choice condition). Results show that under partner choice, individuals who were assigned a high endowment and high productivity almost exclusively interact with each other, forcing other individuals into less valuable pairs. Consequently, pre-existing resource differences between individuals increase. These findings show how partner choice in social dilemmas can amplify resource inequality.

Evolution as a result of resource flow in ecosystems: Ecological dynamics can drive evolution

To see how the flow of energy across ecosystems can derive evolution, I introduce a framework in which individuals interact with their peers and environment to accumulate resources, and use the resources to pay for their metabolic costs, grow and reproduce. I show that two conservation principles determine the system's equilibrium state: conservation of resources- a physical principle stating that in the equilibrium, resource production and consumption should balance, and payoff equality- an economic principle, stating that the payoffs of different types in equilibrium should equal. Besides the equilibrium state, the system shows non-equilibrium fluctuations derived by the exponential growth of the individuals in which the payoff equality principle does not hold. A simple gradient-ascend dynamical mean-field equation predicts the onset of non-equilibrium fluctuations. As an example, I study the evolution of cooperation in public goods games. In both mixed and structured populations, cooperation evolves naturally in resource-poor environments but not in resource-rich environments. Population viscosity facilitates cooperation in poor environments but can be detrimental to cooperation in rich environments. In addition, cooperators and defectors show different life-history strategies: Cooperators live shorter lives and reproduce more than defectors. Both population structure and, more significantly, population viscosity reduce lifespan and life history differences between cooperators and defectors.

Reputation and reciprocity

Reputation and reciprocity are key mechanisms for cooperation in human societies, often going hand in hand to favor prosocial behavior over selfish actions. Here we review recent researches at the interface of physics and evolutionary game theory that explored these two mechanisms. We focus on image scoring as the bearer of reputation, as well as on various types of reciprocity, including direct, indirect, and network reciprocity. We review different definitions of reputation and reciprocity dynamics, and we show how these affect the evolution of cooperation in social dilemmas. We consider first-order, second-order, as well as higher-order models in well-mixed and structured populations, and we review experimental works that support and inform the results of mathematical modeling and simulations. We also provide a synthesis of the reviewed researches along with an outlook in terms of six directions that seem particularly promising to explore in the future.

Effects of co-players' identity and reputation in the public goods game

Players' identity and their reputation are known to influence cooperation in economic games, but little is known about how they interact. Our study aimed to understand how presenting pre-programmed co-players' identities (face photos; names) along with their previous cooperation history (reputation) could influence participants' cooperative decisions in a public goods game. Participants (N = 759) were allocated to one of six experimental groups: (i) control (no information); (ii) only reputation (neutral, free-rider, or cooperative); (iii) only face; (iv) face with reputation; (v) only name; (vi) name with reputation. In the reputation group, cooperation significantly decreased when free-riders were playing and significantly increased when they were cooperators. Person's identity affected cooperativeness only when combined with reputation: face photo mitigated the negative effect of the free-rider reputation, while name identity mitigated any significant effect expected for reputation. Our study suggests a hierarchy: reputation changes cooperation, but a person's identity can modulate reputation.

Mixture of personality improved spiking actor network for efficient multi-agent cooperation

Adaptive multi-agent cooperation with especially unseen partners is becoming more challenging in multi-agent reinforcement learning (MARL) research, whereby conventional deep-learning-based algorithms suffer from the poor new-player-generalization problem, possibly caused by not considering theory-of-mind theory (ToM). Inspired by the ToM personality in cognitive psychology, where a human can easily resolve this problem by predicting others' intuitive personality first before complex actions, we propose a biologically-plausible algorithm named the mixture of personality (MoP) improved spiking actor network (SAN). The MoP module contains a determinantal point process to simulate the formation and integration of different personality types, and the SAN module contains spiking neurons for efficient reinforcement learning. The experimental results on the benchmark cooperative overcooked task showed that the proposed MoP-SAN algorithm could achieve higher performance for the paradigms with (learning) and without (generalization) unseen partners. Furthermore, ablation experiments highlighted the contribution of MoP in SAN learning, and some visualization analysis explained why the proposed algorithm is superior to some counterpart deep actor networks.

Strategic Task Decomposition in Joint Action

The core of human cooperation is people's ability to perform joint actions. Frequently, this requires effectively decomposing a joint task into individual subtasks, for example, when jointly shopping at the market to buy food. Surprisingly, little is known about how collaborators balance the costs of establishing a joint strategy for such decompositions and its expected benefits for a joint goal. We created a new online task that required pairs of randomly matched participants to jointly collect colored items. We then systematically varied the cognitive costs and benefits of applying a color-splitting strategy. The results showed that pairs adopted a color-splitting strategy more often when necessary to lower cognitive costs. However, once the strategy was jointly adopted, it continued to be used even when the cost-benefits changed. Our results provide first insights on how people decompose joint tasks into individual components and how decomposition strategies may evolve into conventions.

Strengths of social ties modulate brain computations for third-party punishment

Costly punishment of social norm transgressors by third-parties has been considered as a decisive stage in the evolution of human cooperation. An important facet of social relationship knowledge concerns the strength of the social ties between individuals, as measured by social distance. Yet, it is unclear how the enforcement of social norms is influenced by the social distance between a third-party and a norm violator at the behavioral and the brain system levels. Here, we investigated how social distance between punishers and norm-violators influences third-party punishment. Participants as third-party punished norm violators more severely as social distance between them increased. Using model-based fMRI, we disentangled key computations contributing to third-party punishment: inequity aversion, social distance between participant and norm violator and integration of the cost to punish with these signals. Inequity aversion increased activity in the anterior cingulate cortex and bilateral insula, and processing social distance engaged a bilateral fronto-parietal cortex brain network. These two brain signals and the cost to punish were integrated in a subjective value signal of sanctions that modulated activity in the ventromedial prefrontal cortex. Together, our results reveal the neurocomputational underpinnings of third-party punishment and how social distance modulates enforcement of social norms in humans.

Extending and refining the fearful ape hypothesis

The fearful ape hypothesis (FAH) presents an evolutionary-developmental framework stipulating that in the context of cooperative caregiving, unique to human great ape group life, heightened fearfulness was adaptive. This is because from early in human ontogeny fearfulness expressed and perceived enhanced care-based responding and cooperation with mothers and others. This response extends and refines the FAH by incorporating the commentaries' suggestions and additional lines of empirical work, providing a more comprehensive and nuanced version of the FAH. Specifically, it encourages and hopes to inspire cross-species and cross-cultural, longitudinal work elucidating evolutionary and developmental functions of fear in context. Beyond fear, it can be seen as a call for an evolutionary-developmental approach to affective science.

Remission of social behavior impairment by oral administration of a precursor of NAD in CD157, but not in CD38, knockout mice

Nicotinamide adenine dinucleotide (NAD) is a substrate of adenosine diphosphate (ADP)-ribosyl cyclase and is catalyzed to cyclic ADP-ribose (cADPR) by CD38 and/or CD157. cADPR, a Ca²⁺ mobilizing second messenger, is critical in releasing oxytocin from the hypothalamus into the brain. Although NAD precursors effectively play a role in neurodegenerative disorders, muscular dystrophy, and senescence, the beneficial effects of elevating NAD by NAD precursor supplementation on brain function, especially social interaction, and whether CD38 is required in this response, has not been intensely studied. Here, we report that oral gavage administration of nicotinamide riboside, a perspective NAD precursor with high bioavailability, for 12 days did not show any suppressive or increasing effects on sociability (mouse's interest in social targets compared to non-social targets) in both CD157KO and CD38KO male mice models in a three-chamber test. CD157KO and CD38KO mice displayed no social preference (that is, more interest towards a novel mouse than a familiar one) behavior. This defect was rescued after oral gavage administration of nicotinamide riboside for 12 days in CD157KO mice, but not in CD38KO mice. Social memory was not observed in CD157KO and CD38KO mice; subsequently, nicotinamide riboside administration had no effect on social memory. Together with the results that nicotinamide riboside had essentially no or little effect on body weight during treatment in CD157KO mice, nicotinamide riboside is less harmful and has beneficial effect on defects in recovery from social behavioral, for which CD38 is required in mice.

How Lévy Flights Triggered by the Presence of Defectors Affect Evolution of Cooperation in Spatial Games

Cooperation among individuals has been key to sustaining societies. However, natural selection favors defection over cooperation. Cooperation can be favored when the mobility of individuals allows cooperators to form a cluster (or group). Mobility patterns of animals sometimes follow a Lévy flight. A Lévy flight is a kind of random walk but it is composed of many small movements with a few big movements. The role of Lévy flights for cooperation has been studied by Antonioni and Tomassini, who showed that Lévy flights promoted cooperation combined with conditional movements triggered by neighboring defectors. However, the optimal condition for neighboring defectors and how the condition changes with the intensity of Lévy flights are still unclear. Here, we developed an agent-based model in a square lattice where agents perform Lévy flights depending on the fraction of neighboring defectors. We systematically studied the relationships among three factors for cooperation: sensitivity to defectors, the intensity of Lévy flights, and population density. Results of evolutionary simulations showed that moderate sensitivity most promoted cooperation. Then, we found that the shortest movements were best for cooperation when the sensitivity to defectors was high. In contrast, when the sensitivity was low, longer movements were best for cooperation. Thus, Lévy flights, the balance between short and long jumps, promoted cooperation in any sensitivity, which was confirmed by evolutionary simulations. Finally, as the population density became larger, higher sensitivity was more beneficial for cooperation to evolve. Our study highlights that Lévy flights are an optimal searching strategy not only for foraging but also for constructing cooperative relationships with others.

How video calls affect mimicry and trust during interactions

Many social species, humans included, mimic emotional expressions, with important consequences for social bonding. Although humans increasingly interact via video calls, little is known about the effect of these online interactions on the mimicry of scratching and yawning, and their linkage with trust. The current study investigated whether mimicry and trust are affected by these new communication media. Using participant-confederate dyads (n = 27), we tested the mimicry of four behaviours across three different conditions: watching a pre-recorded video, online video call, and face-to-face. We measured mimicry of target behaviours frequently observed in emotional situations, yawn and scratch and control behaviours, lip-bite and face-touch. In addition, trust in the confederate was assessed via a trust game. Our study revealed that (i) mimicry and trust did not differ between face-to-face and video calls, but were significantly lower in the pre-recorded condition; and (ii) target behaviours were significantly more mimicked than the control behaviours. This negative relationship can possibly be explained by the negative connotation usually associated with the behaviours included in this study. Overall, this study showed that video calls might provide enough interaction cues for mimicry to occur in our student population and during interactions between strangers. This article is part of a discussion meeting issue 'Face2face: advancing the science of social interaction'.

Does Spending More Always Ensure Higher Cooperation? An Analysis of Institutional Incentives on Heterogeneous Networks

Humans have developed considerable machinery used at scale to create policies and to distribute incentives, yet we are forever seeking ways in which to improve upon these, our institutions. Especially when funding is limited, it is imperative to optimise spending without sacrificing positive outcomes, a challenge which has often been approached within several areas of social, life and engineering sciences. These studies often neglect the availability of information, cost restraints or the underlying complex network structures, which define real-world populations. Here, we have extended these models, including the aforementioned concerns, but also tested the robustness of their findings to stochastic social learning paradigms. Akin to real-world decisions on how best to distribute endowments, we study several incentive schemes, which consider information about the overall population, local neighbourhoods or the level of influence which a cooperative node has in the network, selectively rewarding cooperative behaviour if certain criteria are met. Following a transition towards a more realistic network setting and stochastic behavioural update rule, we found that carelessly promoting cooperators can often lead to their downfall in socially diverse settings. These emergent cyclic patterns not only damage cooperation, but also decimate the budgets of external investors. Our findings highlight the complexity of designing effective and cogent investment policies in socially diverse populations.

Spillover effects of competition outcome on future risky cooperation

There is growing evidence that risky cooperation is regulated by the experience of previous interactions with others. However, it is unclear how the evaluation of outcomes from competitive interactions can affect individuals' subsequent cooperative behavior. To address this issue, we examined how participants cooperated with a partner having just competed with them. While competing, participants (N = 164) were randomly assigned to receive one of four types of outcome feedback regarding their performance (victory vs. defeat vs. uncertain vs. no competition (control)). We found that both the experience of defeats and of uncertainty as competitive outcomes exerted a negative impact on the extent to which participants then engaged in cooperative behavior with their recent opponents. This only occurred when such subsequent cooperative behavior involved a high potential for incurring personal costs but not when there was no risk of incurring personal costs and a positive return. Finally, mediation analysis revealed that the effect of defeat was mediated by participants' level of interpersonal trust and the extent to which participants were willing to cooperate, while the effect of the uncertain competitive outcome was mediated only by the extent to which participants were willing to cooperate. These findings offer novel insights into how risky cooperation is modulated by previous competition.

Rational learners and parochial norms

Parochial norms are narrow in social scope, meaning they apply to certain groups but not to others. Accounts of norm acquisition typically invoke tribal biases: from an early age, people assume a group's behavioral regularities are prescribed and bounded by mere group membership. However, another possibility is rational learning: given the available evidence, people infer the social scope of norms in statistically appropriate ways. With this paper, we introduce a rational learning account of parochial norm acquisition and test a unique prediction that it makes. In one study with adults (N = 480) and one study with children ages 5- to 8-years-old (N = 120), participants viewed violations of a novel rule sampled from one of two unfamiliar social groups. We found that adults judgments of social scope - whether the rule applied only to the sampled group (parochial scope), or other groups (inclusive scope) - were appropriately sensitive to the relevant features of their statistical evidence (Study 1). In children (Study 2) we found an age difference: 7- to 8-year-olds used statistical evidence to infer that norms were parochial or inclusive, whereas 5- to 6-year olds were overall inclusive regardless of statistical evidence. A Bayesian analysis shows a possible inclusivity bias: adults and children inferred inclusive rules more frequently than predicted by a naïve Bayesian model with unbiased priors. This work highlights that tribalist biases in social cognition are not necessary to explain the acquisition of parochial norms.

Evolutionary and neuroendocrine foundations of human aggression

Humans present a behavioural paradox: they are peaceful in many circumstances, but they are also violent and kill conspecifics at high rates. We describe a social evolutionary theory to resolve this paradox. The theory interprets human aggression as a combination of low propensities for reactive aggression and coercive behaviour and high propensities for some forms of proactive aggression (especially coalitionary proactive aggression). These tendencies are associated with the evolution of groupishness, self-domestication, and social norms. This human aggression profile is expected to demand substantial plasticity in the evolved biological mechanisms responsible for aggression. We discuss the contributions of various social signalling molecules (testosterone, cortisol, oxytocin, vasopressin, serotonin, and dopamine) as the neuroendocrine foundation conferring such plasticity.

Age-dependent changes in intuitive and deliberative cooperation

Cooperation is one of the most advantageous strategies to have evolved in small- and large-scale human societies, often considered essential to their success or survival. We investigated how cooperation and the mechanisms influencing it change across the lifespan, by assessing cooperative choices from adolescence to old age (12-79 years, N = 382) forcing participants to decide either intuitively or deliberatively through the use of randomised time constraints. As determinants of these choices, we considered participants' level of altruism, their reciprocity expectations, their optimism, their desire to be socially accepted, and their attitude toward risk. We found that intuitive decision-making favours cooperation, but only from age 20 when a shift occurs: whereas in young adults, intuition favours cooperation, in adolescents it is reflection that favours cooperation. Participants' decisions were shown to be rooted in their expectations about other people's cooperative behaviour and influenced by individuals' level of optimism about their own future, revealing that the journey to the cooperative humans we become is shaped by reciprocity expectations and individual predispositions.

The evolution of cooperation in the unidirectional linear division of labour of finite roles

Evolution of cooperation is a puzzle in evolutionary biology and social sciences. Previous studies assumed that players are equal and have symmetric relationships. In our society, players are in different roles, have an asymmetric relationship and cooperate together. We focused on the linear division of labour in a unidirectional chain that has finite roles, each of which is assigned to one group with cooperators and defectors. A cooperator in an upstream group produces and modifies a product, paying a cost of cooperation, and hands it to a player in a downstream group who obtains the benefit from the product. If players in all roles cooperate, a final product can be completed. However, if a player in a group chooses defection, the division of labour stops, the final product cannot be completed and all players in all roles suffer damage. By using the replicator equations of the asymmetric game, we investigate which sanction system promotes the evolution of cooperation in the division of labour. We find that not the benefit of the product but the cost of cooperation matters to the evolutionary dynamics and that the probability of finding a defector determines which sanction system promotes the evolution of cooperation.