Neural representations of others' traits predict social decisions.

To guide social interaction, people often rely on expectations about the traits of other people, based on markers of social group membership (i.e., stereotypes). Although the influence of stereotypes on social behavior is widespread, key questions remain about how traits inferred from social-group membership are instantiated in the brain and incorporated into neural computations that guide social behavior. Here, we show that the human lateral orbitofrontal cortex (OFC) represents the content of stereotypes about members of different social groups in the service of social decision-making. During functional MRI scanning, participants decided how to distribute resources across themselves and members of a variety of social groups in a modified Dictator Game. Behaviorally, we replicated our recent finding that inferences about others' traits, captured by a two-dimensional framework of stereotype content (warmth and competence), had dissociable effects on participants' monetary-allocation choices: recipients' warmth increased participants' aversion to advantageous inequity (i.e., earning more than recipients), and recipients' competence increased participants' aversion to disadvantageous inequity (i.e., earning less than recipients). Neurally, representational similarity analysis revealed that others' traits in the two-dimensional space were represented in the temporoparietal junction and superior temporal sulcus, two regions associated with mentalizing, and in the lateral OFC, known to represent inferred features of a decision context outside the social domain. Critically, only the latter predicted individual choices, suggesting that the effect of stereotypes on behavior is mediated by inference-based decision-making processes in the OFC.

Distinct Inhibitory-Control Processes Underlie Children's Judgments of Fairness.

We examined how 5- to 8-year-olds (N = 51; Mage = 83 months; 27 female, 24 male; 69% White, 12% Black/African American, 8% Asian/Asian American, 6% Hispanic, 6% not reported) and adults (N = 18; Mage = 20.13 years; 11 female, 7 male) accepted or rejected different distributions of resources between themselves and others. We used a reach-tracking method to track finger movement in 3D space over time. This allowed us to dissociate two inhibitory processes. One involved pausing motor responses to detect conflict between observed information and how participants thought resources should be divided; the other involved resolving the conflict between the response and the alternative. Reasoning about disadvantageous inequities involved more of the first system, and this was stable across development. Reasoning about advantageous inequities involved more of the second system and showed more of a developmental progression. Generally, reach tracking offers an on-line measure of inhibitory control for the study of cognition.

Developmental patterns and computational mechanisms of school-aged children's fairness-related decision making under social comparison.

The developmental patterns and computational mechanisms underlying the impact of unfair offers and social comparisons on school-aged children's fairness-related decision making remain unclear. To address this, we recruited 190 children aged 8 to 12 years (52.1% female) in a multi-responder ultimatum game. Results revealed an age-related decline in children's tendency to reject unfair offers, partially mediated by emotions, alongside a slight increase in rejecting inferior social comparisons. Computational modeling identified two distinct motivations guiding children's rejection behavior: inequity aversion and inferior social comparison avoidance. Furthermore, there was significant variability in responses to superior social comparisons, with some children displaying aversion and others seeking. Our refined model enhances the explanatory power of inequity aversion theory in complex multi-player social scenarios, validating and refining existing theories. In addition, the exploration of superior social comparison tendencies reveals individual heterogeneity, enriching our understanding of children's social comparisons. These findings contribute to elucidating the developmental patterns and internal mechanisms of children's socialization processes, offering implications for promoting their social adaptation and mental health.

Association between arginine vasopressin receptor 1A (AVPR1A) polymorphism and inequity aversion.

Although numerous studies have focused on brain functions related to inequity aversion, few have examined its genetic basis. Here, we show the association between estimated inequity aversion and polymorphisms in three genes associated with human sociality. Non-student adult participants took part in five economic game experiments on different days. Disadvantageous inequity aversion (DIA) and advantageous inequity aversion (AIA) were calculated from behavioural responses using Bayesian estimation. We investigated the association between genetic polymorphisms in the oxytocin receptor (OXTR rs53576), arginine vasopressin receptor 1A (AVPR1A RS3) and opioid receptor mu 1 (OPRM1 rs1799971) and inequity aversion. Regarding AVPR1A RS3, participants with the SS genotype had higher AIA than those with the SL or LL genotypes, but no association was found for DIA. Moreover, we observed no aversion associations for OXTR rs53576 or OPRM1 rs1799971. The results suggest that AVPR1A plays an important role in aversion when one's own gain is greater than that of others. Our findings may provide a solid theoretical basis for future studies on the relationship between genetic polymorphisms and inequity aversion.

Are you better than me? Social comparisons in carrion crows (Corvus corone).

Comparing oneself to others is a key process in humans that allows individuals to gauge their performances and abilities and thus develop and calibrate their self-image. Little is known about its evolutionary foundations. A key feature of social comparison is the sensitivity to other individuals' performance. Recent studies on primates produced equivocal results, leading us to distinguish between a 'strong' variant of the social comparison hypothesis formulated for humans and a 'weak' variant found in non-human primates that would comprise some elements of human social comparison. Here, we focus on corvids that are distantly related to primates and renowned for their socio-cognitive skills. We were interested in whether crows' task performances were influenced (i) by the presence of a conspecific co-actor performing the same discrimination task and (ii) by the simulated acoustic cues of a putative co-actor performing better or worse than themselves. Crows reached a learning criterion quicker when tested simultaneously as compared to when tested alone, indicating a facilitating effect of social context. The performance of a putative co-actor influenced their performance: crows were better at discriminating familiar images when their co-actor was better than they were. Standard extremity (how pronounced the difference was between the performance of the subject and that of the co-actor), and category membership (affiliation status and sex), of the putative co-actors had no effect on their performance. Our findings are in line with the 'weak' variant of social comparison and indicate that elements of human social comparison can be found outside of primates.

Willingness to produce disadvantageous outcomes in cooperative tasks is modulated by recent experience.

Cooperative behavior represents a situation in which individuals sometimes act in a way that produces a gain to another at a cost to themselves. This may be explained by a history of repeated interactions with others in which such behavior has resulted in reciprocal cooperation from others. Sometimes, even with reciprocal cooperation, gains and costs are unbalanced between partners. In this case, there is evidence that people may present an aversion to both disadvantageous and advantageous distributions of gains. In other words, they may act in such a way as to ensure an equal outcome among all group members. Aversion to inequity that benefits oneself (advantageous inequity (AI) aversion) may be more dependent on social and cultural cues than aversion to inequity that benefits others (disadvantageous inequity (DI) aversion). Using both between-subjects (Experiment 1) and within-subjects (Experiment 2) manipulations, the influence of recent experience with AI on participants' willingness to produce DI was explored within the context of a two-player card game. In initial game phases, the percentage of trials in which the participant experienced AI was manipulated. In subsequent game phases, participants had the opportunity to produce DI to themselves. The results from both experiments suggest that aversion to DI is reduced by recent experience with AI. This procedure allows social influences on DI to be tested, which may be important for providing a psychological explanation of cultural differences in aversion to DI.

Distinct roles of the medial prefrontal cortex in advantageous and disadvantageous inequity aversion.

Human beings have a strong preference for the fair distribution of resources in situations of both advantageous and disadvantageous inequity. Neuroimaging studies have shown that the process of advantageous and disadvantageous inequity aversion involves distinct brain regions. However, little is known about the causal roles of the dorsal medial prefrontal cortex (dmPFC) in these two types of inequity aversion. To clarify the roles of the dmPFC in both types of inequity aversion, 70 subjects were recruited and randomly assigned to two anodal transcranial direct current stimulation (tDCS) groups: tDCS over the dmPFC and tDCS over the primary visual cortex. Participants then completed a dictator game, which was used to measure the aversion to inequity. This study found that tDCS over the dmPFC decreased the aversion to disadvantageous inequity, but not that to advantageous inequity, and the treatment effect was modulated by equity cost. These results show that the dmPFC plays different roles in these two types of inequity aversion.

Empirical assumptions behind the violation of expectation experiments in human and non-human animals.

One of the most widely used procedures applied to non-human animals or pre-linguistic humans is the "violation of expectation paradigm". Curiously there is almost no discussion in the philosophical literature about it. Our objective will be to provide a first approach to the meta-theoretical nature of the assumptions behind the procedure that appeals to the violation of expectation and to extract some consequences. We show that behind them exists an empirical principle that affirms that the violation of the expectation of certain mental rules generates surprise. We then proceeded to discuss the nature of these "mental rules". We show that, as is often the case with theoretical concepts proposed by theories, they do not have a fixed interpretation. This will allow us to show that the usual relationship found in the developmental psychology literature between this experimental paradigm and cognitive approaches (which interpret experimental results in terms of higher-level mental activities) is not necessary. Finally, we relate this experimental design with the mark test and the inequity aversion test and discuss the possible ampliation of the application of the empirical principle of violation of expectation.

Generosity, selfishness and exploitation as optimal greedy strategies for resource sharing.

Resource sharing outside the kinship bonds is rare. Besides humans, it occurs in chimpanzee, wild dogs and hyenas, as well as in vampire bats. Resource sharing is an instance of animal cooperation, where an animal gives away part of the resources that it owns for the benefit of a recipient. Taking inspiration from blood-sharing in vampire bats, here we show the emergence of generosity in a Markov game, which couples the resource sharing between two players with the gathering task of that resource. At variance with the classical evolutionary models for cooperation, the optimal strategies of this game can be potentially learned by animals during their life-time. The players act greedily, that is, they try to individually maximize only their personal income. Nonetheless, the analytical solution of the model shows that three non trivial optimal behaviours emerge depending on conditions. Besides the obvious case when players are selfish in their choice of resource division, there are conditions under which both players are generous. Moreover, we also found a range of situations in which one selfish player exploits another generous individual, for the satisfaction of both players. Our results show that resource sharing is favoured by three factors: a long time horizon over which the players try to optimize their own game, the similarity among players in their ability of performing the resource-gathering task, as well as by the availability of resources in the environment. These concurrent requirements lead to identify necessary conditions for the emergence of generosity.

Children's fairness in two Chinese schools: A combined ethnographic and experimental study.

Recent research has shown that children's sense of fairness is shaped in part by cultural practices, values, and norms. However, the specific social factors that motivate children's fairness decisions remain poorly understood. The current study combined an ethnographic approach with experimental tests of fairness (the Inequity Game) in two Chinese schools with qualitatively different practices and norms. In the "University school," children received explicit moral instruction on fairness reinforced by adults when supervising children's activities. By contrast, in the "Community school," children received less formal moral education and little adult supervision during play time, but norms of cooperation and fairness emerged through informal interactions with peers and other members of the community. Contrary to our predictions, children in both schools (N = 66) rejected both disadvantageous and advantageous allocations of resources in the test trials. However, in the very first practice trials, children from the Community school tended to reject all inequalities, whereas children from the University school tended to accept inequalities. We draw on the ethnographies of the schools to interpret these results, concluding that, despite the similarities in the experimental results, different motivations and social factors likely underlie the rejection of inequality in the two schools.

Conditional cooperation and confusion in public-goods experiments.

Economic experiments are often used to study if humans altruistically value the welfare of others. A canonical result from public-good games is that humans vary in how they value the welfare of others, dividing into fair-minded conditional cooperators, who match the cooperation of others, and selfish noncooperators. However, an alternative explanation for the data are that individuals vary in their understanding of how to maximize income, with misunderstanding leading to the appearance of cooperation. We show that (i) individuals divide into the same behavioral types when playing with computers, whom they cannot be concerned with the welfare of; (ii) behavior across games with computers and humans is correlated and can be explained by variation in understanding of how to maximize income; (iii) misunderstanding correlates with higher levels of cooperation; and (iv) standard control questions do not guarantee understanding. These results cast doubt on certain experimental methods and demonstrate that a common assumption in behavioral economics experiments, that choices reveal motivations, will not necessarily hold.

Inequity aversion in dogs: a review.

The study of inequity aversion in animals debuted with a report of the behaviour in capuchin monkeys (Cebus apella). This report generated many debates following a number of criticisms. Ultimately, however, the finding stimulated widespread interest, and multiple studies have since attempted to demonstrate inequity aversion in various other non-human animal species, with many positive results in addition to many studies in which no response to inequity was found. Domestic dogs represent an interesting case as, unlike many primates, they do not respond negatively to inequity in reward quality but do, however, respond negatively to being unrewarded in the presence of a rewarded partner. Numerous studies have been published on inequity aversion in dogs in recent years. Combining three tasks and seven peer-reviewed publications, over 140 individual dogs have been tested in inequity experiments. Consequently, dogs are one of the best studied species in this field and could offer insights into inequity aversion in other non-human animal species. In this review, we summarise and critically evaluate the current evidence for inequity aversion in dogs. Additionally, we provide a comprehensive discussion of two understudied aspects of inequity aversion, the underlying mechanisms and the ultimate function, drawing on the latest findings on these topics in dogs while also placing these developments in the context of what is known, or thought to be the case, in other non-human animal species. Finally, we highlight gaps in our understanding of inequity aversion in dogs and thereby identify potential avenues for future research in this area.

Social disappointment explains chimpanzees' behaviour in the inequity aversion task.

Chimpanzees' refusal of less-preferred food when an experimenter has previously provided preferred food to a conspecific has been taken as evidence for a sense of fairness. Here, we present a novel hypothesis-the social disappointment hypothesis-according to which food refusals express chimpanzees' disappointment in the human experimenter for not rewarding them as well as they could have. We tested this hypothesis using a two-by-two design in which food was either distributed by an experimenter or a machine and with a partner present or absent. We found that chimpanzees were more likely to reject food when it was distributed by an experimenter rather than by a machine and that they were not more likely to do so when a partner was present. These results suggest that chimpanzees' refusal of less-preferred food stems from social disappointment in the experimenter and not from a sense of fairness.

Young children, but not chimpanzees, are averse to disadvantageous and advantageous inequities.

The age at which young children show an aversion to inequitable resource distributions, especially those favoring themselves, is unclear. It is also unclear whether great apes, as humans' nearest evolutionary relatives, have an aversion to inequitable resource distributions at all. Using a common methodology across species and child ages, the current two studies found that 3- and 4-year-old children (N=64) not only objected when they received less than a collaborative partner but also sacrificed to equalize when they received more. They did neither of these things in a nonsocial situation, demonstrating the fundamental role of social comparison. In contrast, chimpanzees (N=9) showed no aversion to inequitable distributions, only a concern for maximizing their own resources, with no differences between social and nonsocial conditions. These results underscore the unique importance for humans, even early in ontogeny, for treating others fairly, presumably as a way of becoming a cooperative member of one's cultural group.

Direct reciprocity in animals: The roles of bonding and affective processes.

The presence of direct reciprocity in animals is a debated topic, because, despite its evolutionary plausibility, it is believed to be uncommon. Some authors claim that stable reciprocal exchanges require sophisticated cognition which has acted as a constraint on its evolution across species. In contrast, a more recent trend of research has focused on the possibility that direct reciprocity occurs within long-term bonds and relies on simple as well as more complex affective mechanisms such as emotional book-keeping, rudimentary and higher forms of empathy, and inequity aversion, among others. First, we present evidence supporting the occurrence of long-term reciprocity in the context of existing bonds in social birds and mammals. Second, we discuss the evidence for affective responses which, modulated by bonding, may underlie altruistic behaviours in different species. We conclude that the mechanisms that may underlie reciprocal exchanges are diverse, and that some act in interaction with bonding processes. From simple associative learning in social contexts, through emotional contagion and behavioural mimicry, to empathy and a sense of fairness, widespread and diverse social affective mechanisms may explain why direct reciprocity may not be a rare phenomenon among social vertebrates.

The Development of Inequity Aversion.

Children and adults respond negatively to inequity. Traditional accounts of inequity aversion suggest that as children mature into adults, they become less likely to endorse all forms of inequity. We challenge the idea that children have a unified concern with inequity that simply becomes stronger with age. Instead, we argue that the developmental trajectory of inequity aversion depends on whether the inequity is seen as fair or unfair. In three studies ( N = 501), 7- to 8-year-olds were more likely than 4- to 6-year-olds to create inequity that disadvantaged themselves-a fair type of inequity. In findings consistent with our theory, 7- to 8-year-olds were not more likely than 4- to 6-year-olds to endorse advantageous inequity (Study 1) or inequity created by third parties (Studies 2 and 3)-unfair types of inequity. We discuss how these results expand on recent accounts of children's developing concerns with generosity and partiality.

Do monkeys compare themselves to others?

Social comparisons are a fundamental characteristic of human behaviour, yet relatively little is known about their evolutionary foundations. Adapting the co-acting paradigm from human research (Seta in J Pers Soc Psychol 42:281-291, 1982. doi: 10.1037//0022-3514.42.2.281), we examined how the performance of a partner influenced subjects' performance in long-tailed macaques (Macaca fascicularis). Using parallel testing in touch screen setups in which subjects had to discriminate familiar and novel photographs of men and women, we investigated whether accuracy and reaction time were influenced by partner performance and relationship quality (affiliate vs. non-affiliate). Auditory feedback about the alleged performance of the co-actor was provided via playback; partner performance was either moderately or extremely better or worse than subject performance. We predicted that subjects would assimilate to moderately different comparison standards as well as to affiliates and contrast away from extreme standards and non-affiliates. Subjects instantly generalized to novel pictures. While accuracy was not affected by any of the factors, long reaction times occurred more frequently when subjects were tested with a non-affiliate who was performing worse, compared to one who was doing better than them (80% quantile worse: 5.1, better: 4.3 s). For affiliate co-actors, there was no marked effect (worse: 4.4, better: 4.6 s). In a control condition with no auditory feedback, subjects performed somewhat better in the presence of affiliates (M = 77.8% correct) compared to non-affiliates (M = 71.1%), while reaction time was not affected. Apparently, subjects were sensitive to partner identity and performance, yet variation in motivation rather than assimilation and contrast effects may account for the observed effects.

Do sex and age affect strategic behavior and inequity aversion in children?

The ultimatum game is commonly used to explore fairness in adults in bargaining situations. Although the changes in responses that occur during development have been investigated in children, the results have been mixed. Whereas some studies show that proposers offer more when they grow older, others indicate the opposite. Moreover, these studies are outcome-based and leave intentions out of the scene, although intentions play a relevant role in daily life. The mini-ultimatum game offers the opportunity to test both outcomes and intentions, but one major obstacle for accurately pinpointing developmental transitions in strategic behavior and inequity aversion so far has been the multiple confounds that have plagued previous studies, including different methods, small sample sizes, and reduced age differences. We administered an anonymous direct-method one-shot mini-ultimatum game to 478 6- and 10-year-old children. Strategic behavior was present at 10 years of age; older participants matched more accurately what responders would accept than younger participants. However, this was true only for older girls. No sex differences were detected in younger children. No age group seemed to consider the proposer's intentions given that the rejections of the default option were not significant across conditions. Both disadvantageous and advantageous inequity aversions were present in 6-year-olds. However, older children exhibited significantly more disadvantageous inequity aversion than younger children. This contrast made the pattern of rejection of 6-year-olds look more similar to the pattern of rejection found in adults. No sex differences were found in responders' behavior.

Payoff-based learning explains the decline in cooperation in public goods games.

Economic games such as the public goods game are increasingly being used to measure social behaviours in humans and non-human primates. The results of such games have been used to argue that people are pro-social, and that humans are uniquely altruistic, willingly sacrificing their own welfare in order to benefit others. However, an alternative explanation for the empirical observations is that individuals are mistaken, but learn, during the game, how to improve their personal payoff. We test between these competing hypotheses, by comparing the explanatory power of different behavioural rules, in public goods games, where individuals are given different amounts of information. We find: (i) that individual behaviour is best explained by a learning rule that is trying to maximize personal income; (ii) that conditional cooperation disappears when the consequences of cooperation are made clearer; and (iii) that social preferences, if they exist, are more anti-social than pro-social.

Governing for the Common Good.

The proper object of global health governance (GHG) should be the common good, ensuring that all people have the opportunity to flourish. A well-organized global society that promotes the common good is to everyone's advantage. Enabling people to flourish includes enabling their ability to be healthy. Thus, we must assess health governance by its effectiveness in enhancing health capabilities. Current GHG fails to support human flourishing, diminishes health capabilities and thus does not serve the common good. The provincial globalism theory of health governance proposes a Global Health Constitution and an accompanying Global Institute of Health and Medicine that together propose to transform health governance. Multiple lines of empirical research suggest that these institutions would be effective, offering the most promising path to a healthier, more just world.