The evolution of altruistic social preferences in human groups

Act generously when others do so: Majority influence on young children's sharing behavior

Children's sharing behavior is profoundly shaped by social norms within their society, and they can learn these norms by directly observing how most others share in their immediate environment. Here we systematically investigated the impact of majority influence on the sharing behavior of young Chinese children through three studies (N = 336, 168 girls). Four- and 6-year-olds were allowed to choose 10 favorite stickers and had an opportunity to engage in anonymous sharing. Before making the sharing decision, children were assigned to one of two conditions: watching a video in which three peers all shared 8 out of 10 stickers (i.e., the majority sharing condition) or making their decisions without watching the video (i.e., the control condition). Results showed that both the 4- and 6-year-old children shared more stickers in the majority sharing condition than in the control condition (Studies 1 & 2). Moreover, the influence of the majority had a stronger effect compared to the influence of a single role model. Children shared more stickers after observing three peers sharing, compared to watching one peer sharing three times (Study 2). Furthermore, children were less likely to copy the majority's non-sharing behavior when it came to giving away stickers without prosocial outcomes, which was particularly evident among 4-year-olds (Study 3). The results reveal that majority influence uniquely shapes children's sharing behavior and that children selectively follow the majority based on whether the behavior exhibits prosocial attributes. A video abstract of this article can be viewed at https://youtu.be/8qNNhf9754I?si=7YfpaFpcD_IjlXjJ RESEARCH HIGHLIGHTS: Observing a majority of three peers' unanimous generous sharing promoted sharing behavior in both 4- and 6-year-olds. The influence of three peers on children's sharing was stronger than that of one peer sharing three times. Four-year-olds, but not 6-year-olds, did not copy the non-sharing behavior of the majority as it did not lead to prosocial outcomes.

Domestic pigs (Sus scrofa) engage in non-random post-conflict affiliation with third parties: cognitive and functional implications

In social mammals, conflict resolution involves the reunion of former opponents (aggressor and victim) after an aggressive event (reconciliation) or post-conflict triadic contacts with a third party, started by either opponent (solicited-TSC) or spontaneously offered by the third party (unsolicited-TUC). These post-conflict strategies can serve different functions, including consolation (specifically when TUCs reduce the victim's anxiety). We investigated the possible presence and modulating factors of such strategies on semi-free ranging pigs (Sus scrofa; N = 104), housed at the ethical farm Parva Domus (Cavagnolo, Italy). Kinship was known. Reconciliation was present and mainly occurred between weakly related pigs to possibly improve tolerant cohabitation. Triadic contacts (all present except aggressor TSCs) mostly occurred between close kin. TSCs enacted by victims reduced neither their post-conflict anxiety behaviors nor further attacks by the previous aggressor, possibly because TSCs remained largely unreciprocated. TUCs towards aggressors did not reduce aggressor post-conflict anxiety but limited aggression redirection towards third parties. TUCs towards the victim reduced the victim but not the third-party's anxiety. However, TUCs may also provide inclusive fitness benefits to third parties by benefiting close kin. In sum, pigs engaged in non-random solicited/unsolicited triadic contacts, which suggests that pigs might possess socio-emotional regulation abilities to change their own or others' experience and elements of social appraisal, necessary to detect the emotional arousal of relevant others and (in case of TUCs) take the agency to restore homeostasis.

Is Distributional Justice Equivalent to Prosocial Sharing in Children’s Cognition?

Distribution and sharing are social preference behaviors supported and shaped by selection pressures, which express individuals’ concern for the welfare of others. Distributive behavior results in distributive justice, which is at the core of moral justice. Sharing is a feature of the prosocial realm. The connotations of distribution and sharing are different, so the principles, research paradigms, and social functions of the two are also different. Three potential causes of confusion between the two in the current research on distribution and sharing are discussed. First, they share common factors in terms of individual cognition, situation, and social factors. Second, although they are conceptually different, prosocial sharing and distribution fairness sensitivity are mutually predictive in individual infants. Similarly, neural differences in preschoolers’ perception of distribution fairness predict their subsequent sharing generosity. Finally, similar activation regions are relevant to distribution and sharing situations that need behavioral control on a neural basis.

Comparative connectomics of the primate social brain

Social interaction is thought to provide a selection pressure for human intelligence, yet little is known about its neurobiological basis and evolution throughout the primate lineage. Recent advances in neuroimaging have enabled whole brain investigation of brain structure, function, and connectivity in humans and non-human primates (NHPs), leading to a nascent field of comparative connectomics. However, linking social behavior to brain organization across the primates remains challenging. Here, we review the current understanding of the macroscale neural mechanisms of social behaviors from the viewpoint of system neuroscience. We first demonstrate an association between the number of cortical neurons and the size of social groups across primates, suggesting a link between neural information-processing capacity and social capabilities. Moreover, by capitalizing on recent advances in species-harmonized functional MRI, we demonstrate that portions of the mirror neuron system and default-mode networks, which are thought to be important for representation of the other's actions and sense of self, respectively, exhibit similarities in functional organization in macaque monkeys and humans, suggesting possible homologies. With respect to these two networks, we describe recent developments in the neurobiology of social perception, joint attention, personality and social complexity. Together, the Human Connectome Project (HCP)-style comparative neuroimaging, hyperscanning, behavioral, and other multi-modal investigations are expected to yield important insights into the evolutionary foundations of human social behavior.

Games and enculturation: A cross-cultural analysis of cooperative goal structures in Austronesian games

While most animals play, only humans play games. As animal play serves to teach offspring important life-skills in a safe scenario, human games might, in similar ways, teach important culturally relevant skills. Humans in all cultures play games; however, it is not clear whether variation in the characteristics of games across cultural groups is related to group-level attributes. Here we investigate specifically whether the cooperativeness of games covaries with socio-ecological differences across cultural groups. We hypothesize that cultural groups that engage in frequent inter-group conflict, cooperative sustenance acquisition, or that have less stratified social structures, might more frequently play cooperative games as compared to groups that do not share these characteristics. To test these hypotheses, we gathered data from the ethnographic record on 25 ethnolinguistic groups in the Austronesian language family. We show that cultural groups with higher levels of inter-group conflict and cooperative land-based hunting play cooperative games more frequently than other groups. Additionally, cultural groups with higher levels of intra-group conflict play competitive games more frequently than other groups. These findings indicate that games are not randomly distributed among cultures, but rather relate to the socio-ecological settings of the cultural groups that practice them. We argue that games serve as training grounds for group-specific norms and values and thereby have an important function in enculturation during childhood. Moreover, games might server an important role in the maintenance of cultural diversity.

What isn't social tolerance? The past, present, and possible future of an overused term in the field of primatology

In the past four decades, the term social tolerance has been utilized to describe, explain, and predict many different aspects of primates' sociality and has been measured with a large range of traits and behaviors. To date, however, there has been little discussion on whether these different phenomena all reflect one and the same construct. This paper opens the discussion by presenting the historical development of the term social tolerance and a structured overview of its current, overextended use. We argue that social tolerance has developed to describe two distinct concepts: social tolerance as the social structure of a group and social tolerance as the dyadic or group-level manifestation of tolerant behaviors. We highlight how these two concepts are based on conflicting theoretical understandings and practical assessments. In conclusion, we present suggestions for future research on primate social tolerance, which will allow for a more systematic and comparable investigation of primate sociality.

Looking Like a Million Dollars: Does Attractiveness Priming Increase Altruistic Behavior in Experimental Games?

The emergence of altruistic behavior constitutes one of the most widely studied problems in evolutionary biology and behavioral science. Multiple explanations have been proposed, most importantly including kin selection, reciprocity, and costly signaling in sexual selection. In order to test the latter, this study investigated whether people behave more altruistically when primed by photographs of attractive faces and whether more or less altruistic people differ in the number of sexual and romantic partners. Participants in the general population (N = 158, 84 F, 74 M) first rated the attractiveness of photographs of 20 faces of the opposite (sexually preferred) sex and then played the Dictator and Ultimatum Games (DG and UG). The photograph rating acted as priming; half the participants received photographs of people rated as more attractive than average in an earlier study, and the other half received photographs previously rated as less attractive. The attractiveness-primed participants, especially men, were expected to behave more altruistically-signaling that they are desirable, resource-possessing partners. We also expected altruists to self-report more sexual and romantic partners. The observed difference between altruistic behaviors in the attractiveness- and unattractiveness-primed groups occurred in UG offers, however, in the opposite than expected direction in women. The number of sexual partners was positively correlated to minimum acceptable offers (MAOs) in the UG, in line with expectations based on the theory of costly signaling.

Human infants can override possessive tendencies to share valued items with others

Possessiveness toward objects and sharing are competing tendencies that influence dyadic and group interactions within the primate lineage. A distinctive form of sharing in adult Homo sapiens involves active giving of high-valued possessions to others, without an immediate reciprocal benefit. In two Experiments with 19-month-old human infants (N = 96), we found that despite measurable possessive behavior toward their own personal objects (favorite toy, bottle), infants spontaneously gave these items to a begging stranger. Moreover, human infants exhibited this behavior across different types of objects that are relevant to theory (personal objects, sweet food, and common objects)-showing flexible generalizability not evidenced in non-human primates. We combined these data with a previous dataset, yielding a large sample of infants (N = 192), and identified sociocultural factors that may calibrate young infants' sharing of objects with others. The current findings show a proclivity that is rare or absent in our closest living relatives-the capacity to override possessive behavior toward personally valued objects by sharing those same desired objects with others.

Political games of attack and defence

Political conflicts often revolve around changing versus defending a status quo. We propose to capture the dynamics between proponents and opponents of political change in terms of an asymmetric game of attack and defence with its equilibrium in mixed strategies. Formal analyses generate predictions about effort expended on revising and protecting the status quo, the form and function of false signalling and cheap talk, how power differences impact conflict intensity and the likelihood of status quo revision. Laboratory experiments on the neurocognitive and hormonal foundations of attack and defence reveal that out-of-equilibrium investments in attack emerge because of non-selfish preferences, limited capacity to compute costs and benefits and optimistic beliefs about the chances of winning from one's rival. We conclude with implications for the likelihood of political change and inertia, and discuss the role of ideology in political games of attack and defence.

This article is part of the theme issue ‘The political brain: neurocognitive and computational mechanisms’.

The neurodevelopment of social preferences in early childhood

Human social preferences are the product of gene-culture coevolution, and rely on predispositions that emerge early in development. These social preferences encompasse distinct motivations, mechanisms, and behaviors, that facilitate social cohesion and cooperation. Developmental social neuroscience critically contributes in elucidating the proximate mechanisms involved in social decision-making and prosociality, and their gradual maturation in interaction with the social and cultural environment.

Can morphological and behavioral traits predict the foraging and feeding dynamics of social arachnids?

Complex social insect species exhibit task specialization mediated by morphological and behavioral traits. However, evidence of such traits is scarce for other social arthropods. We investigated whether the social pseudoscorpion Paratemnoides nidificator exhibits morphologically and behaviorally specialized individuals in prey capture. We measured body and chela sizes of adult pseudoscorpions and analyzed predation processes. Larger individuals spent more time moving through the colony and foraging than smaller pseudoscorpions. Individuals that captured prey had increased body and absolute chelae sizes. Although larger individuals had relatively small chelae size, they showed a higher probability of prey capture. Larger individuals manipulated prey often, although they fed less than smaller pseudoscorpions. Individuals that initiated captures fed more frequently and for more time than the others. Natural selection might be favoring individuals specialized in foraging and colony protection, allowing smaller and less efficient adults to avoid contact with dangerous prey. To our knowledge, there is incipient information regarding specialized individuals in arachnids, and our results might indicate the emergence of a morphologically specialized group in this species.

The Origins and Psychology of Human Cooperation

Humans are an ultrasocial species. This sociality, however, cannot be fully explained by the canonical approaches found in evolutionary biology, psychology, or economics. Understanding our unique social psychology requires accounting not only for the breadth and intensity of human cooperation but also for the variation found across societies, over history, and among behavioral domains. Here, we introduce an expanded evolutionary approach that considers how genetic and cultural evolution, and their interaction, may have shaped both the reliably developing features of our minds and the well-documented differences in cultural psychologies around the globe. We review the major evolutionary mechanisms that have been proposed to explain human cooperation, including kinship, reciprocity, reputation, signaling, and punishment; we discuss key culture-gene coevolutionary hypotheses, such as those surrounding self-domestication and norm psychology; and we consider the role of religions and marriage systems. Empirically, we synthesize experimental and observational evidence from studies of children and adults from diverse societies with research among nonhuman primates.

Intergenerational resource sharing and mortality in a global perspective

Resource sharing has always been a central component of human sociality. Children require heavy investments in human capital; during working years, help is needed due to illness, disability, or bad luck. While hunter-gatherer elders assisted their descendants, more recently, elderly withdraw from work and require assistance as well. Willingness to share has been critically important for our past evolutionary success and our present daily lives. Here, we document a strong linear relationship between the public and private sharing generosity of a society and the average length of life of its members. Our findings from 34 countries on six continents suggest that survival is higher in societies that provide more support and care for one another. We suggest that this support reduces mortality by meeting urgent material needs, but also that sharing generosity may reflect the strength of social connectedness, which itself benefits human health and wellbeing and indirectly raises survival.

Caring babies: Concern for others in distress during infancy

Concern for distressed others is a highly valued human capacity, but little is known about its early ontogeny. Theoretical accounts of empathy development have emphasized stages, but this has been called into question. This study sheds new light on four key issues: onset, consistency, development, and predictive power of early manifestations of concern for others. Three-month-old Israei infants (N = 165) were followed longitudinally at ages 6, 12, and 18 months, and their observed responses to others' distress were assessed. Concern for distressed others was seen early in the first year of life, long before previous theories assumed. Empathic concern was moderately consistent across both situation and age, from as early as 3 months. Concern for others grew only modestly with age, plateauing during the second year, whereas prosocial behavior increased rapidly during the second year. Early individual differences in concern for others predicted later prosocial behavior on behalf of distressed others. Findings underscore the early roots of caring, and appear to refute assumptions of prior stage theories of empathy development, by showing that concern for others develops much earlier and more gradually than previously assumed.

The relations of White parents' implicit racial attitudes to their children's differential empathic concern toward White and Black victims

The goal of this study was to investigate the relations between White parents' implicit racial attitudes and their children's racially based bias in empathic concern toward White and Black victims of injustice as well as the moderating role of children's age in this relation. Children aged 5-9 years (N = 190) reported how sorry (i.e., sympathy) and nervous (i.e., personal distress) they felt after watching sympathy-inducing videos in which either a White (non-Hispanic) child or a Black child was teased by peers. Participants' primary caregivers (mostly mothers) completed a computerized Implicit Association Test to assess their implicit racial attitudes. Parents' implicit race bias was associated with their children's reported sympathy toward Black victims and their sympathetic bias (i.e., relative sympathy toward White vs. Black victims); however, results were moderated by children's age. Specifically, parents with higher implicit race bias tended to have children with lower levels of sympathy toward Black victims for younger children and higher levels of sympathetic bias for younger and average-aged children but not for older children. Older children tended to report relatively high levels of sympathy toward Black victims and low levels of sympathetic bias regardless of their parents' implicit attitudes. The importance of parents' implicit attitudes in understanding young children's race-based moral emotional responses and the implications for intervention work are discussed.

The emergence of emotionally modern humans: implications for language and learning

According to the Cooperative Breeding Hypothesis, apes with the life-history attributes of those in the line leading to the genus Homo could not have evolved unless male and female allomothers had begun to help mothers care for and provision offspring. As proposed elsewhere, the unusual way hominins reared their young generated novel phenotypes subsequently subjected to Darwinian social selection favouring those young apes best at monitoring the intentions, mental states and preferences of others and most motivated to attract and appeal to caretakers. Not only were youngsters acquiring information in social contexts different from those of other apes, but they would also have been emotionally and neurophysiologically different from them in ways that are relevant to how humans learn. Contingently delivered rewards to dependents who attracted and ingratiated themselves with allomothers shaped their behaviours and vocalizations and transformed the way developing youngsters learned from others and internalized their preferences. This article is part of the theme issue 'Life history and learning: how childhood, caregiving and old age shape cognition and culture in humans and other animals'.

Approach to Resource Management and Physical Strength Predict Differences in Helping: Evidence From Two Small-Scale Societies

Helping behavior is likely to have evolved to increase chances of survival of an individual and their group. Nevertheless, populations differ significantly in their eagerness to help, and little is known about populational and inter-individual determinants of these differences. Previous studies indicated that economic and physiological factors might influence helping behavior. The aim of the present study was to investigate the effects of approach to resource management of a society (immediate-return economy vs. delayed-return economy), prenatal androgenization (based on second-to-fourth digit ratio), and physical strength (based on hand grip strength) on helping behavior toward others. Helping was assessed in terms of both general eagerness to help and differential helping toward: (1) kin, (2) other group members indiscriminately, (3) friends, and (4) those from whom help was obtained in the past. Based on data collected in two small-scale societies (n = 306), we found that people in the egalitarian immediate-return society (the Hadza hunter-gatherers of Tanzania) displayed helping behavior significantly more often than people in a more stratified delayed-return economy (Yali horticulturalists of Papua). Additionally, our results revealed that physical strength was a significant predictor of helping behavior in women but not in men. We discuss our findings in the light of the adaptive value of helping behavior.

He had it Comin': ERPs Reveal a Facilitation for the Processing of Misfortunes to Antisocial Characters

Human sociality and prosociality rely on social and moral feelings of empathy, compassion, envy, schadenfreude, as well as on the preference for prosocial over antisocial others. We examined the neural underpinnings of the processing of lexical input designed to tap into these type of social feelings. Brainwave responses from 20 participants were measured as they read sentences comprising a randomly delivered ending outcome (fortunate or unfortunate) to social agents previously profiled as prosocial or antisocial individuals. Fortunate outcomes delivered to prosocial and antisocial agents aimed to tap into empathy and envy/annoying feelings, respectively, whereas unfortunate ones into compassion for prosocial agents and schadenfreude for antisocial ones. ERP modulations in early attention-capture (100-200 ms), semantic fit (400 ms), and late reanalysis processes (600 ms) were analyzed. According to the functional interpretation of each of these event-related electrophysiological effects, we conclude that: 1) a higher capture of attention is initially obtained in response to any type of outcome delivered to a prosocial versus an antisocial agent (frontal P2); 2) a facilitated semantic processing occurs for unfortunate outcomes delivered to antisocial agents (N400); and 3) regardless of the protagonist's social profile, an increased later reevaluation for overall unfortunate versus fortunate outcomes takes place (Late Positive Potential). Thus, neural online measures capture a stepwise unfolding impact of social factors during language comprehension, which include a facilitated processing of misfortunes when they happen to occur to antisocial peers (i.e., schadenfreude).

Challenges in the comparative study of empathy and related phenomena in animals

The aim of this review is to discuss recent arguments and findings in the comparative study of empathy. Based on a multidisciplinary approach including psychology and ethology, we review the non-human animal literature concerning theoretical frameworks, methodology, and research outcomes. One specific objective is to highlight discrepancies between theory and empirical findings, and to discuss ambiguities present in current data and their interpretation. In particular, we focus on emotional contagion and its experimental investigation, and on consolation and targeted helping as measures for sympathy. Additionally, we address the feasibility of comparing across species with behavioural data alone. One main conclusion of our review is that animal research on empathy still faces the challenge of closing the gap between theoretical concepts and empirical evidence. To advance our knowledge, we propose to focus more on the emotional basis of empathy, rather than on possibly ambiguous behavioural indicators, and we provide suggestions to overcome the limitations of previous research .

Chimpanzees monopolize and children take turns in a limited resource problem

Competition over scarce resources is common across the animal kingdom. Here we investigate the strategies of chimpanzees and children in a limited resource problem. Both species were presented with a tug-of-war apparatus in which each individual in a dyad received a tool to access a reward, but tools could not be used simultaneously. We assessed the equality of tool use as well as the frequency of turn taking. Both species managed to overcome this conflict of interest but used different strategies to do so. While there was substantial variation in chimpanzee behaviour, monopolization was the common course of action: tool use was asymmetric with individual chimpanzees monopolizing the resource. In children, turn-taking emerged as the dominant strategy: tool use was symmetric and children alternated access to the tool at a high rate. These results suggest that while both species possess strategies for solving limited resource problems, humans might have evolved species unique motivations and socio-cognitive skills for dealing with such conflicts of interest.

Inspired to Lend a Hand? Attempts to Elicit Prosocial Behavior Through Goal Contagion

Helping often occurs in a broader social context. Every day, people observe others who require help, but also others who provide help. Research on goal contagion suggests that observing other people's goal-directed behavior (like helping) activates the same goal in the observer. Thus, merely observing a prosocial act could inspire people to act on the same goal. This effect should be even stronger, the more the observer's disposition makes him or her value the goal. In the case of prosocial goals, we looked at the observer's social value orientation (SVO) as a moderator of the process. In three studies (N = 126, N = 162, and N = 371), we tested the hypothesis that prosocial observations (vs. control) will trigger more subsequent casual prosocial behavior the more the observer is prosocially oriented. In line with the original research, we used texts as stimulus material in Study 1 and short video clips in Study 2 and 3. In Study 1 and 2, SVO was measured directly before the manipulation was induced and in Study 3 even a week prior to the actual experiment. Additionally, we included a second control condition video clip in Study 3, which did not depict human beings. Despite thoroughly developed stimulus material and methods, we found no support for an effect of the interaction, nor of the prosocial observation, but some support for an effect of SVO on casual helping behavior in Study 1 and 2. A mini meta-analysis revealed an effect equivalent to zero for goal contagion and a small, but robust SVO effect across studies. The main implication for the theory of goal contagion is that prosocial goals might not be as contagious as other goals addressed in the literature. We suggest a meta-analytic review of the literature to identify suitable goals and moderators for the goal contagion process.

Routine allomaternal nursing in a free-ranging Old World monkey

While regular allomaternal nursing (suckling) has been documented in a number of rodent and carnivore species, as well as in some prosimians, New World monkeys, and humans, it is not common in Old World monkeys and apes. Here, we present a detailed field study of allomaternal nursing in golden snub-nosed monkeys (Rhinopithecus roxellana, Colobinae). We found that more than 87% of infants were nursed by females other than their mothers. Allomaternal nursing was largely confined to the first 3 months of an infant's life and occurred predominantly between related females who nursed each other's offspring in a reciprocal manner. Allomaternal nursing enhanced infant survivorship and did not have a negative impact on the future reproductive success of allonursers. Our findings expand the taxonomic distribution of allomaternal nursing and provide fresh insight into the possible factors driving evolution of allomaternal nursing behavior in primates, including humans.

Greenness and Pricing Decisions of Cooperative Supply Chains Considering Altruistic Preferences

With the development of the economy and science technology, global resource shortages and environmental pressures have become the focus of attention. More and more consumers tend to buy non-polluting and environmentally friendly green products, and many manufacturers and retailers are beginning to produce or sell green products to enhance their competitive advantage in the market. Considering the green preference attributes of consumers, the altruistic preference is introduced into the supply chain, and we establish four models: two cooperative manufacturers and one retailer are completely self-interested, one retailer has altruistic preference, two cooperative manufacturers have altruistic preferences, and two cooperative manufacturers and one retailer have altruistic preferences. We address the optimal greenness and pricing decisions of supply chain members, and analyze the impact of altruistic preferences on supply chain decision-making and profits. The results show that the altruistic preference coefficient can significantly affect the decision-making and the profits of supply chain members, and when two manufacturers and one retailer consider altruistic preferences, the altruistic preference coefficients adopted by the three parties are in the certain ranges, the supply chain members' altruistic preference coefficients can increase the whole supply chain profit. Through analysis, in the three cases where the retailer has altruistic preferences, two manufacturers have altruistic preferences, and two manufacturers and one retailer have altruistic preferences, two manufacturers should adopt higher altruistic preference coefficients, and the retailer should adopt a lower altruistic preference coefficient, and the product greenness under the three altruistic preferences is higher than the product greenness when there is no altruistic preference.

Equality over intentionality: The normative social preferences of neutral third-parties

This paper studies whether intentionality is more prevalent than fairness in social preferences. We do this by introducing a new three-player game in which the choices of neutral third-party arbiters are isolated from any monetary or strategic concerns. This allows us to study the normative preferences of subjects, and to compare the relative weight they give to intentions and inequality. The results show that arbiters are mainly concerned with inequality, while other’s (selfish) intentions seem to play a minor role in their preferences. This result is robust to a series of experimental designs, suggesting that the role of intentions in social preferences might be smaller than implied by the previous literature.

Experimental evidence of selective inattention in reputation-based cooperation

Reputation-based cooperation is often observed in modern society. People gain several types of information by assessing others. Among these, the most important information is the actions of people and those of their recipients. However, almost all studies assume that people consider all of the information they receive. This assumption is extreme, and people engaging in reputation-based cooperation may not pay attention to some information, i.e., they may display selective inattention. We demonstrate that subjects’ decision-making in relation to cooperative action depends on the content of the information they receive about their recipients. Our results show that subjects either consider or ignore information depending on the content of that information. When their recipients had cooperated previously, subjects cooperated without considering the information they received. When the recipients had played before with those who had bad reputations, subjects did not use that information, regardless of whether it was disclosed proactively. In other cases, subjects considered information on both the previous actions of recipients and those of the recipients’ own recipients. We found that subjects did not always use the information to make decisions, although they willingly received information about their recipients. This supports the proposition that selective inattention occurs in reputation-based cooperation.

Bonobos voluntarily hand food to others but not toys or tools

A key feature of human prosociality is direct transfers, the most active form of sharing in which donors voluntarily hand over resources in their possession Direct transfers buffer hunter-gatherers against foraging shortfalls. The emergence and elaboration of this behaviour thus likely played a key role in human evolution by promoting cooperative interdependence and ensuring that humans' growing energetic needs (e.g. for increasing brain size) were more reliably met. According to the strong prosociality hypothesis, among great apes only humans exhibit sufficiently strong prosocial motivations to directly transfer food. The versatile prosociality hypothesis suggests instead that while other apes may make transfers in constrained settings, only humans share flexibly across food and non-food contexts. In controlled experiments, chimpanzees typically transfer objects but not food, supporting both hypotheses. In this paper, we show in two experiments that bonobos directly transfer food but not non-food items. These findings show that, in some contexts, bonobos exhibit a human-like motivation for direct food transfer. However, humans share across a far wider range of contexts, lending support to the versatile prosociality hypothesis. Our species' unusual prosocial flexibility is likely built on a prosocial foundation we share through common descent with the other apes.

Neurobiological Evidence for the Primacy of Mania Hypothesis

BACKGROUND

Athanasios Koukopoulos proposed the primacy of mania hypothesis (PoM) in a 2006 book chapter and later, in two peer-reviewed papers with Nassir Ghaemi and other collaborators. This hypothesis supports that in bipolar disorder, mania leads to depression, while depression does not lead to mania.

OBJECTIVE

To identify evidence in literature that supports or falsifies this hypothesis.

METHOD

We searched the medical literature (PubMed, Embase, PsycINFO, and the Cochrane Library) for peer-reviewed papers on the primacy of mania, the default mode function of the brain in normal people and in bipolar disorder patients, and on illusion superiority until 6 June, 2016. Papers resulting from searches were considered for appropriateness to our objective. We adopted the PRISMA method for our review. The search for consistency with PoM was filtered through the neurobiological results of superiority illusion studies.

RESULTS

Out of a grand total of 139 records, 59 were included in our analysis. Of these, 36 were of uncertain value as to the primacy of mania hypothesis, 22 favoured it, and 1 was contrary, but the latter pooled patients in their manic and depressive phases, so to invalidate possible conclusions about its consistency with regard to PoM. All considered studies were not focused on PoM or superiority illusion, hence most of their results were, as expected, unrelated to the circuitry involved in superiority illusion. A considerable amount of evidence is consistent with the hypothesis, although indirectly so.

LIMITATIONS

Only few studies compared manic with depressive phases, with the majority including patients in euthymia.

CONCLUSION

It is possible that humans have a natural tendency for elation/optimism and positive self-consideration, that are more akin to mania; the depressive state could be a consequence of frustrated or unsustainable mania. This would be consistent with PoM.

Looking for unity in diversity: human cooperative childcare in comparative perspective

Humans engage in cooperative childcare, which includes some elements not found in other animals, such as the presence of post-reproductive helpers, extensive food sharing among adults and a pervasive sexual division of labour. In animals, cooperative offspring care has typically been studied in two different contexts. The first mainly involves helpers contributing care in cooperatively breeding family groups; the second context is allomaternal care in species usually not categorized as cooperative breeders (e.g. plural and communal breeders, often without male care). Comparative analyses suggest that cooperative breeding and allomaternal care in plural and communal breeders have distinct evolutionary origins, with humans fitting neither pathway entirely. Nevertheless, some critical proximate mechanisms of helping, including hormonal regulators, are likely to be shared across species. Other mechanisms may vary among species, such as social tolerance, proactive prosociality or conditional mother-infant bonding. These are presumably associated with specific details of the care system, such as whether all group members contribute, or whether mothers can potentially raise offspring alone. Thus, cooperative offspring care is seen in different contexts across animal lineages, but may nonetheless share several important psychological characteristics. We end by discussing how work on humans may play a unifying role in studying cooperative offspring care.

Social status and prenatal testosterone exposure assessed via second-to-fourth digit ratio affect 6-9-year-old children's prosocial choices

Prosocial behaviour (i.e., voluntary behaviour intended to benefit another) seems to be fully developed in children by the age of 6 years. However, questions about which factors modify prosocial behaviour at that age remain understudied. Here we used a resource allocation paradigm to test prosocial behaviour in 6-9-year-old school children. They could decide between a "selfish" (i.e., one sticker for themselves) and a "prosocial" option (i.e., one sticker for themselves and one for the receiver) and we tested whether friendship, social status and prenatal androgen exposure (approximated by the 2nd to 4th digit ratio; 2D:4D) influenced children's prosocial choices. We found that children behaved prosocially, and that their prosocial tendencies were negatively correlated with prenatal androgen exposure; i.e., children with high 2D:4D ratios (reflecting low prenatal androgen exposure) acted more prosocially than children with low 2D:4D ratios. Further, their social status in the classroom influenced their choices: children with fewer interaction partners chose the "prosocial" option more often than more 'popular' children. However, they did so irrespectively of whether they were paired with a recipient or not. Our results highlight the importance of considering social, as well as physiological factors when investigating prosocial behaviour in children.

Meerkats (Suricata suricatta) fail to prosocially donate food in an experimental set-up

Although humans are usually believed to be prosocial, the evolutionary origins of prosociality are largely debated. One hypothesis is that cooperative breeding has been one major precursor to the emergence of prosociality. In vertebrates, however, experimental evidence of prosociality has been mainly gathered in non-human primates. In this study, we tested the cooperative breeding hypothesis in cooperative breeding meerkats (Suricata suricatta). In particular, we tested whether meerkats take into account partners' benefits when distributing food rewards. Nine individuals were presented with two platforms baited with different food distributions (providing food to themselves, to a partner or both). In all conditions, the decision to operate the apparatus was based on the presence of food on the subject's side, and not on the possible benefits to partners. Despite being cooperative breeders, meerkats in this study failed to be prosocial, suggesting that prosociality in this species may be limited to specific contexts.

Fundamental problems with the cooperative breeding hypothesis. A reply to Burkart & van Schaik

The cooperative breeding hypothesis (CBH) states that cooperative breeding, a social system in which group members help to rear offspring that are not their own, has important socio‐cognitive consequences. Thornton & McAuliffe (2015; henceforth T&M) critiqued this idea on both conceptual and empirical grounds, arguing that there is no reason to predict that cooperative breeding should favour the evolution of enhanced social cognition or larger brains, nor any clear evidence that it does. In response to this critique, Burkart & van Schaik (2016 henceforth B&vS) attempt to clarify the causal logic of the CBH, revisit the data and raise the possibility that the hypothesis may only apply to primates. They concede that cooperative breeding is unlikely to generate selection pressures for enhanced socio‐cognitive abilities, but argue instead that the CBH operates purely through cooperative breeding reducing social or energetic constraints. Here, we argue that this revised hypothesis is also untenable because: (1) it cannot explain why resources so released would be allocated to cognitive traits per se rather than any other fitness‐related traits, (2) key assumptions are inconsistent with available evidence and (3) ambiguity regarding the predictions leaves it unclear what evidence would be required to falsify it. Ultimately, the absence of any compelling evidence that cooperative breeding is associated with elevated cognitive ability or large brains (indeed data suggest the opposite is true in non‐human primates) also casts doubt on the capacity of the CBH to explain variation in cognitive traits.

Correlated pay-offs are key to cooperation

The general belief that cooperation and altruism in social groups result primarily from kin selection has recently been challenged, not least because results from cooperatively breeding insects and vertebrates have shown that groups may be composed mainly of non-relatives. This allows testing predictions of reciprocity theory without the confounding effect of relatedness. Here, we review complementary and alternative evolutionary mechanisms to kin selection theory and provide empirical examples of cooperative behaviour among unrelated individuals in a wide range of taxa. In particular, we focus on the different forms of reciprocity and on their underlying decision rules, asking about evolutionary stability, the conditions selecting for reciprocity and the factors constraining reciprocal cooperation. We find that neither the cognitive requirements of reciprocal cooperation nor the often sequential nature of interactions are insuperable stumbling blocks for the evolution of reciprocity. We argue that simple decision rules such as 'help anyone if helped by someone' should get more attention in future research, because empirical studies show that animals apply such rules, and theoretical models find that they can create stable levels of cooperation under a wide range of conditions. Owing to its simplicity, behaviour based on such a heuristic may in fact be ubiquitous. Finally, we argue that the evolution of exchange and trading of service and commodities among social partners needs greater scientific focus.