Biological markets and the effects of partner choice on cooperation and friendship

Willingness valued more than ability in partner choice: Insights into behavioral and ERP data

In human cooperation, people prefer to choose partners with high willingness and ability-while both are valued by partners, individuals often prioritize willingness. Two event-related potential (ERP) experiments were conducted to discern the neural processes underpinning this preference. In the first experiment, participants made a choice between two potential partners and received feedback on the selected partner's willingness to cooperate. This was followed by feedback on the partner's task performance (ability) or a gambling outcome. In contrast, the second experiment first provided feedback on ability, then presented feedback on willingness or a gambling outcome. This study revealed that a potential partner's willingness trait significantly influences individuals' emotional evaluations and monetary allocations than the ability trait. Electrophysiological data indicated that low-willingness feedback elicited a diminished feedback-related negative (FRN) and an amplified P3 compared to high-willingness feedback. In contrast, no such difference was discernible between high- and low-ability feedback. Moreover, the P3 difference from high versus low willingness was considerably more pronounced than that from gambling outcomes, whereas the difference wave between high and low ability paralleled gambling outcomes. These findings bolster the novel finding that partner willingness may provide more substantial social rewards than ability. Furthermore, this study provides the first ERP evidence of willingness and ability trait perceptions in partner choice decisions.

Young children's adaptive partner choice in cooperation and competition contexts

Choosing adequate partners is essential for cooperation, but how children calibrate their partner choice to specific social challenges is unknown. In two experiments, 4- to 7-year-olds (N = 189, 49% girls, mostly White, data collection: 03.2021-09.2022) were presented with partners in possession of different positive qualities. Children then recruited partners for hypothetical tasks that differed with respect to the quality necessary for success. Children and the selected partner either worked together toward a common goal or competed against each other. From age 5, children selectively chose individuals in possession of task-relevant qualities as cooperative partners while avoiding them as competitors. Younger children chose partners indiscriminately. Children thus learn to strategically adjust their partner choice depending on context-specific task demands and different social goals.

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.

Infants are sensitive to the social signaling value of shared inefficient behaviors

Actions that are blatantly inefficient to achieve non-social goals are often used to convey information about agents' social affiliation, as in the case of rituals. We argue that when reproduced, actions that are individually inefficient acquire a social signaling value owing to the mechanisms that support humans' intuitive analysis of actions. We tested our hypothesis on 15-month-old infants who were familiarized with an agent that reproduced or merely observed the actions of efficient and inefficient individuals. Subsequently, we measured the infants' expectations of the agent's preferences for efficient and inefficient individuals. Our results confirmed that when agents act alone, infants expect a third-party to prefer efficient over inefficient agents. However, this pattern is entirely flipped if the third-party reproduces the agents' actions. In that case, infants expect inefficient agents to be preferred over efficient ones. Thus, reproducing actions whose rational basis is elusive can serve a critical social signaling function, accounting for why such behaviors are pervasive in human groups.

Emotions and courtship help bonded pairs cooperate, but emotional agents are vulnerable to deceit

Coordinated pair bonds are common in birds and also occur in many other taxa. How do animals solve the social dilemmas they face in coordinating with a partner? We developed an evolutionary model to explore this question, based on observations that a) neuroendocrine feedback provides emotional bookkeeping which is thought to play a key role in vertebrate social bonds and b) these bonds are developed and maintained via courtship interactions that include low-stakes social dilemmas. Using agent-based simulation, we found that emotional bookkeeping and courtship sustained cooperation in the iterated prisoner's dilemma in noisy environments, especially when combined. However, when deceitful defection was possible at low cost, courtship often increased cooperation, whereas emotional bookkeeping decreased it.

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.

Ownership psychology, its antecedents and consequences

Commentators discussed the coherence and validity of a minimalist approach to ownership intuitions, in ways that make it possible to clarify the model, re-evaluate its cognitive underpinnings, and sketch some of its implications. This response summarizes the model; addresses issues concerning the need for a special technical lexicon when describing cognitive semantics; the psychology involved in contexts of competitive acquisition and their consequences for possession and use of rival resources; the role of cooperative expectations in creating mutually beneficial allocation of resources; the consequences of ownership psychology for social interaction and the production of social norms of property; and the relations between psychological processes and legal institutions in the domain, before proposing some final thoughts.

Shibboleth: An agent-based model of signalling mimicry

Mimicry is an essential strategy for exploiting competitors in competitive co-evolutionary relationships. Protection against mimicry may, furthermore, be a driving force in human linguistic diversity: the potential harm caused by failing to detect mimicked group-identity signals may select for high sensitivity to mimicry of honest group members. Here we describe the results of five agent-based models that simulate multi-generational interactions between two groups of individuals: original members of a group with an honest identity signal, and members of an outsider group who mimic that signal, aiming to pass as members of the in-group. The models correspond to the Biblical story of Shibboleth, where a tribe in conflict with another determines tribe affiliation by asking individuals to pronounce the word, 'Shibboleth.' In the story, failure to reproduce the word phonetically resulted in death. Here, we run five different versions of a 'Shibboleth' model: a first, simple version, which evaluates whether a composite variable of mimicry quality and detection quality is a superior predictor to the model's outcome than is cost of detection. The models thereafter evaluate variations on the simple model, incorporating group-level behaviours such as altruistic punishment. Our results suggest that group members' sensitivity to mimicry of the Shibboleth-signal is a better predictor of whether any signal of group identity goes into fixation in the overall population than is the cost of mimicry detection. Thus, the likelihood of being detected as a mimic may be more important than the costs imposed on mimics who are detected. This suggests that theoretical models in biology should place greater emphasis on the likelihood of detection, which does not explicitly entail costs, rather than on the costs to individuals who are detected. From a language learning perspective, the results suggest that admission to group membership through linguistic signals is powered by the ability to imitate and evade detection as an outsider by existing group members.

Virtue Discounting: Observability Reduces Moral Actors' Perceived Virtue

Performing prosociality in public presents a paradox: only by doing so can people demonstrate their virtue and also influence others through their example, yet observers may derogate actors' behavior as mere "virtue signaling." Here we investigate the role of observability of actors' behavior as one reason that people engage in such "virtue discounting." Further, we investigate observers' motivational inferences as a mechanism of this effect, using the comparison of generosity and fairness as a case study among virtues. Across 14 studies (7 preregistered, total N = 9,360), we show that public actors are perceived as less virtuous than private actors, and that this effect is stronger for generosity compared to fairness (i.e., differential virtue discounting). Exploratory factor analysis suggests that three types of motives-principled, reputation-signaling, and norm-signaling-affect virtue discounting. Using structural equation modeling, we show that observability's effect on actors' trait virtue ratings is largely explained by inferences that actors have less principled motivations. Further, we leverage experimental evidence to provide stronger causal evidence of these effects. We discuss theoretical and practical implications of our findings, as well as future directions for research on the social perception of virtue.

Inferences about interdependence shape cooperation

During social interactions in daily life, people possess imperfect knowledge of their interdependence (i.e., how behaviors affect each person's outcomes), and what people infer about their interdependence can shape their behaviors. We review theory and research that suggests people can infer their interdependence with others along several dimensions, including mutual dependence, power, and corresponding-versus-conflicting interests. We discuss how perceptions of interdependence affect how people cooperate and punish others' defection in everyday life. We propose that people understand their interdependence with others through knowledge of the action space, cues during social interactions (e.g., partner behaviors), and priors based on experience. Finally, we describe how learning interdependence could occur through domain-specific and domain-general mechanisms.

Partner choice does not predict prosociality across countries

Why does human prosociality vary around the world? Evolutionary models and laboratory experiments suggest that possibilities for partner choice (i.e. the ability to leave unprofitable relationships and strike up new ones) should promote cooperation across human societies. Leveraging the Global Preferences Survey (n = 27,125; 27 countries) and the World Values Survey (n = 54,728; 32 countries), we test this theory by estimating the associations between relational mobility, a socioecological measure of partner choice, and a wide variety of prosocial attitudes and behaviours, including impersonal altruism, reciprocity, trust, collective action and moral judgements of antisocial behaviour. Contrary to our pre-registered predictions, we found little evidence that partner choice is related to prosociality across countries. After controlling for shared causes of relational mobility and prosociality - environmental harshness, subsistence style and geographic and linguistic proximity - we found that only altruism and trust in people from another religion are positively related to relational mobility. We did not find positive relationships between relational mobility and reciprocity, generalised trust, collective action or moral judgements. These findings challenge evolutionary theories of human cooperation which emphasise partner choice as a key explanatory mechanism, and highlight the need to generalise models and experiments to global samples.

COVID-19 alters the relationship between relational mobility and helping behavior

To determine if helping behaviors are affected by socioecological variables such as relational mobility and the COVID-19 pandemic, we investigated the impact of relational mobility on helping behaviors before (Study 1) and during (Study 2) COVID-19 in China via two experiments. In Study 1, we manipulated participants’ relational mobility and found that a greater proportion of participants in the high relational mobility condition signed up for another psychological experiment, relative to the low relational mobility condition. In Study 2, the manipulation of relational mobility was embedded in a phone interview, and we found that a high relational mobility condition caused fewer signups for a COVID-19 support program relative to a low relational mobility condition. These results extend our understanding of the meaning of relational mobility under different ecological contexts.

Hadza hunter-gatherers with greater exposure to other cultures share more with generous campmates

Humans are motivated to compete for access to valuable social partners, which is a function of their willingness to share and ability to generate resources. However, relative preferences for each trait should be responsive to socioecological conditions. Here, we test the flexibility of partner choice psychology among Hadza hunter-gatherers of Tanzania. Ninety-two Hadza ranked their campmates on generosity and foraging ability and then shared resources with those campmates. We found Hadza with greater exposure to other cultures shared more with campmates ranked higher on generosity, whereas Hadza with lower exposure showed a smaller preference for sharing with generous campmates. This moderating effect was specific to generosity-regardless of exposure, Hadza showed only a small preference for sharing with better foragers. We argue this difference in preferences is due to high exposure Hadza having more experience cooperating with others in the absence of strong norms of sharing, and thus are exposed to greater variance in willingness to cooperate among potential partners increasing the benefits of choosing partners based on generosity. As such, participants place a greater emphasis on choosing more generous partners, highlighting the flexibility of partner preferences.

Why Warmth Matters More Than Competence: A New Evolutionary Approach

Multiple lines of evidence suggest that there are two major dimensions of social perception, often called warmth and competence, and that warmth is prioritized over competence in multiple types of social decision-making. Existing explanations for this prioritization argue that warmth is more consequential for an observer's welfare than is competence. We present a new explanation for the prioritization of warmth based on humans' evolutionary history of cooperative partner choice. We argue that the prioritization of warmth evolved because ancestral humans faced greater variance in the warmth of potential cooperative partners than in their competence but greater variance in competence over time within cooperative relationships. These each made warmth more predictive than competence of the future benefits of a relationship, but because of differences in the distributions of these traits, not because of differences in their intrinsic consequentiality. A broad, synthetic review of the anthropological literature suggests that these conditions were characteristic of the ecologies in which human social cognition evolved, and agent-based models demonstrate the plausibility of these selection pressures. We conclude with future directions for the study of preferences and the further integration of social and evolutionary psychology.

Runaway Social Selection in Human Evolution

Darwin posited that social competition among conspecifics could be a powerful selective pressure. Alexander proposed a model of human evolution involving a runaway process of social competition based on Darwin’s insight. Here we briefly review Alexander’s logic, and then expand upon his model by elucidating six core arenas of social selection that involve runaway, positive-feedback processes, and that were likely involved in the evolution of the remarkable combination of adaptations in humans. We discuss how these ideas fit with the hypothesis that a key life history innovation that opened the door to runaway social selection, and cumulative culture, during hominin evolution was increased cooperation among individuals in small fission-fusion groups.

Four Puzzles of Reputation-Based Cooperation : Content, Process, Honesty, and Structure

Research in various disciplines has highlighted that humans are uniquely able to solve the problem of cooperation through the informal mechanisms of reputation and gossip. Reputation coordinates the evaluative judgments of individuals about one another. Direct observation of actions and communication are the essential routes that are used to establish and update reputations. In large groups, where opportunities for direct observation are limited, gossip becomes an important channel to share individual perceptions and evaluations of others that can be used to condition cooperative action. Although reputation and gossip might consequently support large-scale human cooperation, four puzzles need to be resolved to understand the operation of reputation-based mechanisms. First, we need empirical evidence of the processes and content that form reputations and how this may vary cross-culturally. Second, we lack an understanding of how reputation is determined from the muddle of imperfect, biased inputs people receive. Third, coordination between individuals is only possible if reputation sharing and signaling is to a large extent reliable and valid. Communication, however, is not necessarily honest and reliable, so theoretical and empirical work is needed to understand how gossip and reputation can effectively promote cooperation despite the circulation of dishonest gossip. Fourth, reputation is not constructed in a social vacuum; hence we need a better understanding of the way in which the structure of interactions affects the efficiency of gossip for establishing reputations and fostering cooperation.

Third-party punishers do not compete to be chosen as partners in an experimental game

Third-party punishment is thought to act as an honest signal of cooperative intent and such signals might escalate when competing to be chosen as a partner. Here, we investigate whether partner choice competition prompts escalating investment in third-party punishment. We also consider the case of signalling via helpful acts to provide a direct test of the relative strength of the two types of signals. Individuals invested more in third-party helping than third-party punishment and invested more in both signals when observed compared to when investments would be unseen. We found no clear effect of partner choice (over and above mere observation) on investments in either punishment or helping. Third-parties who invested more than a partner were preferentially chosen for a subsequent Trust Game although the preference to interact with the higher investor was more pronounced in the help than in the punishment condition. Third-parties who invested more were entrusted with more money and investments in third-party punishment or helping reliably signalled trustworthiness. Individuals who did not invest in third-party helping were more likely to be untrustworthy than those who did not invest in third-party punishment. This supports the conception of punishment as a more ambiguous signal of cooperative intent compared to help.

Expression unleashed: The evolutionary and cognitive foundations of human communication

Human expression is open-ended, versatile, and diverse, ranging from ordinary language use to painting, from exaggerated displays of affection to micro-movements that aid coordination. Here we present and defend the claim that this expressive diversity is united by an interrelated suite of cognitive capacities, the evolved functions of which are the expression and recognition of informative intentions. We describe how evolutionary dynamics normally leash communication to narrow domains of statistical mutual benefit, and how expression is unleashed in humans. The relevant cognitive capacities are cognitive adaptations to living in a partner choice social ecology; and they are, correspondingly, part of the ordinarily developing human cognitive phenotype, emerging early and reliably in ontogeny. In other words, we identify distinctive features of our species' social ecology to explain how and why humans, and only humans, evolved the cognitive capacities that, in turn, lead to massive diversity and open-endedness in means and modes of expression. Language use is but one of these modes of expression, albeit one of manifestly high importance. We make cross-species comparisons, describe how the relevant cognitive capacities can evolve in a gradual manner, and survey how unleashed expression facilitates not only language use, but also novel behaviour in many other domains too, focusing on the examples of joint action, teaching, punishment, and art, all of which are ubiquitous in human societies but relatively rare in other species. Much of this diversity derives from graded aspects of human expression, which can be used to satisfy informative intentions in creative and new ways. We aim to help reorient cognitive pragmatics, as a phenomenon that is not a supplement to linguistic communication and on the periphery of language science, but rather the foundation of the many of the most distinctive features of human behaviour, society, and culture.

The impact of positive and negative testimony on children's attitudes toward others

Children can identify who is benevolent or malevolent not only through first-hand experiences and observations but also from the testimony of others. In this study, we investigated whether 5- and 7-year-olds (N = 128) would form their attitudes toward others after hearing testimony about that person’s past moral behavior and whether the valence of testimony would differently influence the children. In the positive condition, half of the participants gained information about three puppets: puppet A’s prosocial behavior by their own first-hand observation, testimony about puppet B’s past prosocial behavior, and testimony about puppet C’s past neutral behavior. In the negative condition, the other half also learned information about the three puppets: puppet A’s antisocial behavior by their own first-hand observation, testimony about puppet B’s past antisocial behavior, and testimony about puppet C’s past neutral behavior. Then they engaged in tasks that measured their behavioral attitudes toward the puppets and evaluated the goodness of each puppet to assess their attitudes at a cognitive level. Our results concluded that the children form their behavioral attitudes toward others based on testimony starting at the age of 7, and attitude formation at the cognitive level based on testimony is seen at age 5. Negative testimony, rather than positive testimony, influences the children’s attitudes toward others. In addition, the 7-year-olds’ use of testimony differs depending whether they are the allocators or the receivers of rewards. Our findings deepen understanding of how children rely on the verbal information around themselves when they navigate interactions with others.

The benefits of being seen to help others: indirect reciprocity and reputation-based partner choice

When one individual helps another, it benefits the recipient and may also gain a reputation for being cooperative. This may induce others to favour the helper in subsequent interactions, so investing in being seen to help others may be adaptive. The best-known mechanism for this is indirect reciprocity (IR), in which the profit comes from an observer who pays a cost to benefit the original helper. IR has attracted considerable theoretical and empirical interest, but it is not the only way in which cooperative reputations can bring benefits. Signalling theory proposes that paying a cost to benefit others is a strategic investment which benefits the signaller through changing receiver behaviour, in particular by being more likely to choose the signaller as a partner. This reputation-based partner choice can result in competitive helping whereby those who help are favoured as partners. These theories have been confused in the literature. We therefore set out the assumptions, the mechanisms and the predictions of each theory for how developing a cooperative reputation can be adaptive. The benefits of being seen to be cooperative may have been a major driver of sociality, especially in humans. This article is part of the theme issue 'The language of cooperation: reputation and honest signalling'.

The psychological foundations of reputation-based cooperation

Humans care about having a positive reputation, which may prompt them to help in scenarios where the return benefits are not obvious. Various game-theoretical models support the hypothesis that concern for reputation may stabilize cooperation beyond kin, pairs or small groups. However, such models are not explicit about the underlying psychological mechanisms that support reputation-based cooperation. These models therefore cannot account for the apparent rarity of reputation-based cooperation in other species. Here, we identify the cognitive mechanisms that may support reputation-based cooperation in the absence of language. We argue that a large working memory enhances the ability to delay gratification, to understand others' mental states (which allows for perspective-taking and attribution of intentions) and to create and follow norms, which are key building blocks for increasingly complex reputation-based cooperation. We review the existing evidence for the appearance of these processes during human ontogeny as well as their presence in non-human apes and other vertebrates. Based on this review, we predict that most non-human species are cognitively constrained to show only simple forms of reputation-based cooperation. This article is part of the theme issue 'The language of cooperation: reputation and honest signalling'.

Networks of reliable reputations and cooperation: a review

Reputation has been shown to provide an informal solution to the problem of cooperation in human societies. After reviewing models that connect reputations and cooperation, we address how reputation results from information exchange embedded in a social network that changes endogenously itself. Theoretical studies highlight that network topologies have different effects on the extent of cooperation, since they can foster or hinder the flow of reputational information. Subsequently, we review models and empirical studies that intend to grasp the coevolution of reputations, cooperation and social networks. We identify open questions in the literature concerning how networks affect the accuracy of reputations, the honesty of shared information and the spread of reputational information. Certain network topologies may facilitate biased beliefs and intergroup competition or in-group identity formation that could lead to high cooperation within but conflicts between different subgroups of a network. Our review covers theoretical, experimental and field studies across various disciplines that target these questions and could explain how the dynamics of interactions and reputations help or prevent the establishment and sustainability of cooperation in small- and large-scale societies.

This article is part of the theme issue ‘The language of cooperation: reputation and honest signalling’.

The language of cooperation: reputation and honest signalling

Large-scale non-kin cooperation is a unique ingredient of human success. This type of cooperation is challenging to explain in a world of self-interested individuals. There is overwhelming empirical evidence from different disciplines that reputation and gossip promote cooperation in humans in different contexts. Despite decades of research, important details of reputation systems are still unclear. Our goal with this theme issue is to promote an interdisciplinary approach that allows us to explore and understand the evolution and maintenance of reputation systems with a special emphasis on gossip and honest signalling. The theme issue is organized around four main questions: What are the necessary conditions for reputation-based systems? What is the content and context of reputation systems? How can reputations promote cooperation? And, what is the role of gossip in maintaining reputation systems and thus cooperation? This article is part of the theme issue 'The language of cooperation: reputation and honest signalling'.

No good deed goes unpunished: the social costs of prosocial behaviour

Performing costly helpful behaviours can allow individuals to improve their reputation. Those who gain a good reputation are often preferred as interaction partners and are consequently better able to access support through cooperative relationships with others. However, investing in prosocial displays can sometimes yield social costs: excessively generous individuals risk losing their good reputation, and even being vilified, ostracised or antisocially punished. As a consequence, people frequently try to downplay their prosocial actions or hide them from others. In this review, we explore when and why investments in prosocial behaviour are likely to yield social costs. We propose two key features of interactions that make it more likely that generous individuals will incur social costs when: (a) observers infer that helpful behaviour is motivated by strategic or selfish motives; and (b) observers infer that helpful behaviour is detrimental to them. We describe how the cognition required to consider ulterior motives emerges over development and how these tendencies vary across cultures - and discuss how the potential for helpful actions to result in social costs might place boundaries on prosocial behaviour as well as limiting the contexts in which it might occur. We end by outlining the key avenues and priorities for future research.

Experimental evidence that apologies promote forgiveness by communicating relationship value

Robust evidence supports the importance of apologies for promoting forgiveness. Yet less is known about how apologies exert their effects. Here, we focus on their potential to promote forgiveness by way of increasing perceptions of relationship value. We used a method for directly testing these causal claims by manipulating both the independent variable and the proposed mediator. Namely, we use a 2 (Apology: yes vs. no) × 2 (Value: high vs. low) concurrent double-randomization design to test whether apologies cause forgiveness by affecting the same causal pathway as relationship value. In addition to supporting this causal claim, we also find that apologies had weaker effects on forgiveness when received from high-value transgressors, suggesting that the forgiveness-relevant information provided by apologies is redundant with relationship value. Taken together, these findings from a rigorous methodological paradigm help us parse out how apologies promote relationship repair.

Nothing better to do? Environment quality and the evolution of cooperation by partner choice

The effects of partner choice have been documented in a large number of biological systems such as sexual markets, interspecific mutualisms, or human cooperation. There are, however, a number of situations in which one would expect this mechanism to play a role, but where no such effect has ever been demonstrated. This is the case in particular in many intraspecific interactions, such as collective hunts, in non-human animals. Here we use individual-based simulations to solve this apparent paradox. We show that the conditions for partner choice to operate are in fact restrictive. They entail that individuals can compare social opportunities and choose the best. The challenge is that social opportunities are often rare because they necessitate the co-occurrence of (i) at least one available partner, and (ii) a resource to exploit together with this partner. This has three consequences. First, partner choice cannot lead to the evolution of cooperation when resources are scarce, which explains that this mechanism could never be observed in many cases of intraspecific cooperation in animals. Second, partner choice can operate when partners constitute in themselves a resource, which is the case in sexual interactions and interspecific mutualisms. Third, partner choice can lead to the evolution of cooperation when individuals live in a rich environment, and/or when they are highly efficient at extracting resources from their environment.

Market Cognition: How Exchange Norms Alter Social Experience

Market exchange and the ideologies that accompany it pervade human social interaction. How does this affect people’s beliefs about themselves, each other, and human nature? Here we describe market cognition as social inferences and behaviors that are intensified by market contexts. We focus on prosociality and two countervailing ways in which market cognition can affect it. On the one hand, marketplaces incentivize individuals to behave prosocially in order to be chosen as exchange partners—thereby generalizing cooperation and trust beyond group boundaries. On the other hand, markets encourage a view of people as self-interested and can thus taint people’s interpretation of prosocial actions and erode more communal forms of cooperation. We close by considering how market cognition can become self-fulfilling, altering relationships, communities, and cultural norms.

Cooperative partner choice in multi-level male dolphin alliances

Investigations into cooperative partner choice should consider both potential and realised partners, allowing for the comparison of traits across all those available. Male bottlenose dolphins form persisting multi-level alliances. Second-order alliances of 4–14 males are the core social unit, within which 2–3 males form first-order alliances to sequester females during consortships. We compared social bond strength, relatedness and age similarity of potential and realised partners of individual males in two age periods: (i) adolescence, when second-order alliances are formed from all available associates, and (ii) adulthood, when first-order allies are selected from within second-order alliances. Social bond strength during adolescence predicted second-order alliance membership in adulthood. Moreover, males preferred same-aged or older males as second-order allies. Within second-order alliances, non-mating season social bond strength predicted first-order partner preferences during mating season consortships. Relatedness did not influence partner choice on either alliance level. There is thus a striking resemblance between male dolphins, chimpanzees and humans, where closely bonded non-relatives engage in higher-level, polyadic cooperative acts. To that end, our study extends the scope of taxa in which social bonds rather than kinship explain cooperation, providing the first evidence that such traits might have evolved independently in marine and terrestrial realms.

Nationality dominates gender in decision-making in the Dictator and Prisoner's Dilemma Games

Across a variety of contexts, adults tend to cooperate more with ingroup members than outgroup members. However, humans belong to multiple social groups simultaneously and we know little about how this cross-categorization affects cooperative decision-making. Nationality and gender are two social categories that are ripe for exploration in this regard: They regularly intersect in the real world and we know that each affects cooperation in isolation. Here we explore two hypotheses concerning the effects of cross-categorization on cooperative decision-making. First, the additivity hypothesis (H1), which proposes that the effects of social categories are additive, suggesting that people will be most likely to cooperate with partners who are nationality and gender ingroup members. Second, the category dominance hypothesis (H2), which proposes that one category will outcompete the other in driving decision-making, suggesting that either nationality or gender information will be privileged in cooperative contexts. Secondarily, we test whether identification with-and implicit bias toward-nationality and gender categories predict decision-making. Indian and US Americans (N = 479), made decisions in two cooperative contexts-the Dictator and Prisoner's Dilemma Games-when paired with partners of all four social categories: Indian women and men, and US American women and men. Nationality exerted a stronger influence than gender: people shared and cooperated more with own-nationality partners and believed that own-nationality partners would be more cooperative. Both identification with-and implicit preferences for-own-nationality, led to more sharing in the Dictator Game. Our findings are most consistent with H2, suggesting that when presented simultaneously, nationality, but not gender, exerts an important influence on cooperative decision-making. Our study highlights the importance of testing cooperation in more realistic intergroup contexts, ones in which multiple social categories are in play.

A branded bandage is worth a thousand words: blood branded bandages signal men's generosity and morality

BACKGROUND AND OBJECTIVE

Recruiting and retaining male donors remain an ongoing challenge for blood collection agencies. Research suggests that interventions based on costly signalling theory that allows donors to unobtrusively but publicly signal their donor status may be effective. However, what functions as such a signal and how it is interpreted has not been determined.

MATERIALS AND METHODS

A total of 242 Australian residents (127 female; 115 male) recruited through an online research platform rated their perceptions of a male target wearing (a) no bandage, (b) a regular unmarked bandage or (c) a blood donor branded bandage.

RESULTS

The target wearing a blood donor branded bandage was rated as significantly more generous by female participants and moral compared to both the target who wore no bandage and the target wearing a regular unmarked bandage. The target wearing the unmarked bandage was perceived as significantly less healthy and competent compared to the target not wearing a bandage.

CONCLUSION

A public signal of public donor status conveys the generosity and morality of the wearer. The bandage applied to donors after they have donated can act as such an effective signal, but only when these bandages are clearly branded as resulting from donating blood.

The effects of social vs. asocial threats on group cooperation and manipulation of perceived threats

Individuals benefit from maintaining the well-being of their social groups and helping their groups to survive threats such as intergroup competition, harsh environments and epidemics. Correspondingly, much research shows that groups cooperate more when competing against other groups. However, 'social' threats (i.e. outgroups) should elicit stronger cooperation than 'asocial' threats (e.g. environments, diseases) because (a) social losses involve a competitor's gain and (b) a strong cooperative reaction to defend the group may deter future outgroup threats. We tested this prediction in a multiround public goods game where groups faced periodic risks of failure (i.e. loss of earnings) which could be overcome by sufficient cooperation. This threat of failure was framed as either a social threat (intergroup competition) or an asocial threat (harsh environment). We find that cooperation was higher in response to social threats than asocial threats. We also examined participants' willingness to manipulate apparent threats to the group: participants raised the perceived threat level similarly for social and asocial threats, but high-ranking participants increased the appearance of social threats more than low-ranking participants did. These results show that people treat social threats differently than asocial threats, and support previous work on leaders' willingness to manipulate perceived threats.

Experimental Games and Social Decision Making

Experimental games model situations in which the future outcomes of individuals and groups depend on their own choices and on those of other (groups of) individuals. Games are a powerful tool to identify the neural and psychological mechanisms underlying interpersonal and group cooperation and coordination. Here we discuss recent developments in how experimental games are used and adapted, with an increased focus on repeated interactions, partner control through sanctioning, and partner (de)selection for future interactions. Important advances have been made in uncovering the neurobiological underpinnings of key factors involved in cooperation and coordination, including social preferences, cooperative beliefs, (emotion) signaling, and, in particular, reputations and (in)direct reciprocity. Emerging trends at the cross-sections of psychology, economics, and the neurosciences include an increased focus on group heterogeneities, intergroup polarization and conflict, cross-cultural differences in cooperation and norm enforcement, and neurocomputational modeling of the formation and updating of social preferences and beliefs.

Disgust, Anger, and Aggression: Further Tests of the Equivalence of Moral Emotions

People often report disgust toward moral violations. Some perspectives posit that this disgust is indistinct from anger. Here, we replicate and extend recent work suggesting that disgust and anger toward moral violations are in fact distinct in terms of the situations in which they are activated and their correspondence with aggressive sentiments. We tested three hypotheses concerning emotional responses to moral violations: (1) disgust is associated with lower-cost, indirectly aggressive motives (e.g., gossip and social exclusion), whereas anger is associated with higher-cost, directly aggressive motives (e.g., physical violence); (2) disgust is higher toward violations affecting others than it is toward violations affecting the self, and anger is higher toward violations affecting the self than it is toward violations affecting others; and (3) abilities to inflict costs on or withhold benefits from others (measured via physical strength and physical attractiveness, respectively) relate to anger, but not to disgust. These hypotheses were tested in a within-subjects study in which 233 participants came to the lab twice and reported their emotional responses and aggressive sentiments toward self-targeting and other-targeting moral violations. Participants’ upper body strength and physical attractiveness were also measured with a dynamometer and photograph ratings, respectively. The first two hypotheses were supported – disgust (but not anger) was related to indirect aggression whereas anger (but not disgust) was related to direct aggression, and disgust was higher toward other-targeting violations whereas anger was higher toward self-targeting violations. However, physical strength and physical attractiveness were unrelated to anger or disgust or to endorsements of direct or indirect aggression.

Reciprocity creates a stake in one's partner, or why you should cooperate even when anonymous

Why do we care so much for friends, even making sacrifices for them they cannot repay or never know about? When organisms engage in reciprocity, they have a stake in their partner's survival and wellbeing so the reciprocal relationship can persist. This stake (aka fitness interdependence) makes organisms willing to help beyond the existing reciprocal arrangement (e.g. anonymously). I demonstrate this with two mathematical models in which organisms play a prisoner's dilemma, and where helping keeps their partner alive and well. Both models shows that reciprocity creates a stake in partners' welfare: those who help a cooperative partner--even when anonymous--do better than those who do not, because they keep that cooperative partner in good enough condition to continue the reciprocal relationship. 'Machiavellian' cooperators, who defect when anonymous, do worse because their partners become incapacitated. This work highlights the fact that reciprocity and stake are not separate evolutionary processes, but are inherently linked.

Feelings of obligation are valuations of signaling-mediated social payoffs

We extend Tomasello's framework by addressing the functional challenge of obligation. If the long-run social consequences of a decision are sufficiently costly, obligation motivates the actor to forgo potential immediate benefits in favor of long-term social interests. Thus, obligation psychology balances the downstream socially-mediated payoffs from a decision. This perspective can predict when and why obligation will be experienced.