The study involved 336 children aged four to nine from six distinct cultural groups. The participants included children from Germany, as well as the Wichí of Argentina, the ≠Akhoe Hai||om of Namibia, and the Samburu and Kikuyu of Kenya, and the Quechua of Bolivia. This diverse sample allowed the researchers to examine helping behavior across a wide spectrum of social and economic environments, ranging from large-scale industrialized societies to small-scale foraging, farming, and pastoralist communities. By selecting populations with such varied lifestyles, the team aimed to determine whether the foundations of cooperative behavior are consistent across different human societies or if they vary significantly based on environmental and cultural factors.

To capture spontaneous helping behavior in a manner that felt natural to children in all settings, the researchers designed a playful experimental setup centered on a marble game. Pairs of children of the same age took turns playing, with one child observing the other encounter specific difficulties. These difficulties included a box that would not open or a container that spilled its marbles onto the floor. The observing child had previously learned how to solve both problems and was given the choice to help by explaining the solution, solving the problem hands-on, or doing both simultaneously. This task provided a direct and comparable measure of how children choose to assist their peers when given the opportunity, allowing for a standardized assessment across all six cultural groups.

The results indicated that helping behavior was consistent across all six cultures. Children reliably helped their partners, and they did so more frequently when the assistance was genuinely necessary. For instance, children were more likely to help a peer who was struggling to open a box than a peer who was picking up scattered marbles, a task that could easily be completed alone. This sensitivity to the partner’s actual needs became more pronounced with age. Younger children tended to help in both situations at similar rates, whereas older children increasingly reserved their assistance for moments when it clearly made a difference, demonstrating a growing ability to assess the necessity of intervention.

The manner in which children provided help also evolved with age. Younger children primarily relied on practical assistance, choosing to perform the task for their peer rather than instructing them. In contrast, older children increasingly offered informational support, explaining how a problem could be solved rather than solving it themselves. This shift suggests a developmental trajectory in which children move from direct physical aid to more cognitive and instructional forms of cooperation as they mature, reflecting a broader understanding of their peers’ capabilities and the nature of the tasks at hand.

Despite the overall consistency in the frequency and necessity of helping, the study revealed subtle yet reliable cultural differences in helping styles. German children were significantly more likely than those in any other group to provide both types of help simultaneously, solving the problem while also explaining the solution. Conversely, Kikuyu children were somewhat less inclined to provide practical assistance compared to children in other cultures. These variations highlight that while the underlying motivation to help is universal, the expression of that motivation is filtered through cultural lenses that emphasize different modes of interaction and support.

The researchers suggest that these patterns mirror the everyday interactions that children are familiar with in their respective communities. In many rural, subsistence-based communities, children often learn largely by observing and helping out, with little verbal explanation involved. In contrast, in Germany and similar industrialized settings, parents tend to combine hands-on demonstrations with detailed verbal instructions. The study indicates that children seem to apply these familiar approaches when helping their peers, effectively replicating the communication styles they have absorbed from their primary caregivers and social environments.

Importantly, the researchers found no meaningful differences in helping behavior between boys and girls, challenging any assumptions that prosocial behavior might be gendered in early childhood. Furthermore, the cultural differences that did emerge were modest in scale. None of the six populations stood out as clearly different from the overall cross-cultural pattern, suggesting that the shared foundations of helping behavior are robust enough to withstand significant cultural variation. This finding underscores the idea that while local customs shape the details of social interaction, the core capacity for cooperation remains a stable feature of human development across diverse societies.

Daniel Haun, a senior author of the study and director at the Max Planck Institute for Evolutionary Anthropology, noted that helping is one of the clearest expressions of the species’ capacity for cooperation. The data show that this capacity reliably emerges in children everywhere but is fine-tuned by the specific social world in which each child grows up. The study concludes that children do not just learn whether to help; they also learn how to help in ways that make sense within their own community. This nuanced understanding provides rare insight into how deeply rooted yet flexible children’s helping behavior really is, offering a new perspective on the interplay between universal human tendencies and local cultural practices.

Subject of Research: Developmental Psychology

Article Title: Children from six cultures reliably help their peers – but in different ways

Article References: Children from six cultures reliably help their peers – but in different ways. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: child development, cross-cultural study, prosocial behavior, cooperation, anthropology, Children, cultures, reliably, help, peers, different, ways

The research, led by Oded Ritov, a psychology Ph.D. student in Berkeley’s Social Origins Lab, used an ingeniously simple setup involving pineapple, ropes, and two connected rooms. Over the course of more than 800 hours of observation, the team studied 26 chimpanzees at the Ngamba Island Chimpanzee Sanctuary in Uganda, documenting grooming patterns, daily interactions, and how regularly individuals stayed within arm’s reach of one another. From these observations, the researchers identified which chimps appeared to be closely bonded, effectively mapping the friendship networks of the sanctuary’s residents.

Once those relationships were established, the experiment began. One chimpanzee, designated the victim, was placed in a room containing three trays baited with pineapple. A rope attached to the trays ran into an adjacent room, where a second chimpanzee, the potential thief, could either leave the rope untouched or yank it to pull the fruit toward itself and steal the pineapple. The design allowed researchers to compare how the same individual behaved when paired with a close friend versus a non-friend, a within-subject approach that strengthens confidence that observed differences reflect the relationship itself rather than individual personality.

The results were striking. Chimpanzees stole in 70 percent of trials involving non-friends, but only 61 percent of trials involving friends. While a nine percentage point difference might appear modest at first glance, the methodological design gives it considerable weight. Because each chimp experienced both the friend and non-friend conditions, the researchers could be more confident that the reduction in stealing was a meaningful response to relationship status rather than random variation. According to Ritov, this is the first study to demonstrate that chimpanzees are able to hold back antisocial behavior specifically toward their friends.

Just as revealing were the emotional dynamics that unfolded after a theft. The researchers evaluated victims’ responses by measuring stomping, fist-pounding, and screeching, behaviors that serve as visible indicators of agitation in chimpanzees. Victims were initially angrier when a friend stole from them, an outcome that may reflect the violation of expectations that come with closeness. Yet they calmed down noticeably faster when the thief was a friend compared with when the thief was a non-friend, suggesting that the underlying bond helped de-escalate the emotional fallout of the transgression.

The thieves’ behavior changed as well. When the thief and victim were not friends, the thief expressed negative emotions for a much longer period, indicating that the interaction was perceived as more hostile. When stealing from a bonded partner, thieves showed less hostility, hinting that the act itself carried a different emotional texture depending on who was on the receiving end. Taken together, these patterns suggest that both parties in a chimpanzee friendship carry expectations about how they should be treated, and that violations of those expectations register emotionally on both sides.

“This suggests that there may be mutual expectations in chimps from both sides of the friendship, which makes it seem more like the complex friendships we see in humans,” Ritov said. The idea of mutual expectation is critical. Previous research has documented relationship-specific intentions in nonhuman primates, such as preferential grooming and selective food sharing, but intentions are only one component of what makes human friendships distinctive. Jan Engelmann, an associate professor of psychology and senior author of the paper, argues that the stronger ingredient is expectation.

“We expect more of our friends,” Engelmann said. “These findings really deepen our understanding of the evolutionary roots of friendships. This is, to my knowledge, the first evidence showing that also chimpanzees expect and maybe demand special treatment from their friends. These kinds of social expectations might form the basis of human moral principles.” In other words, the study hints that the normative glue binding human societies, the sense that certain people owe us certain treatment and that we owe it in return, may not have emerged from nothing but may instead trace back to social dynamics already present in the common ancestor we share with chimpanzees.

Scientists have long been cautious about labeling close chimpanzee relationships as friendships in the human sense, arguing that we cannot fully grasp the cognitive and emotional complexity behind their behavior. The new study addresses that skepticism by combining long-term observational data with a controlled experimental task, allowing researchers to move beyond correlation. The observation that closely bonded chimps groom together and share food more often had already suggested prosocial preferences; the theft experiment adds an antisocial dimension, showing that the same bonds restrain harmful behavior and shape emotional responses when harm occurs anyway.

The work fits into a broader research program by Ritov examining the evolution of human behavior and the possibility that morals and norms are part of our core being, traceable to other animals. He has recently investigated whether nonhuman animals possess a sense of fairness, and he is broadly interested in how emotions unfold across cultures and species. “We think that these expectations might be the basic building blocks of the larger-scale cooperation we see in humans,” Ritov said. “The expectations that chimpanzees have from their friends or close collaborative partners might have scaled up to more generalized expectations for how we should treat each other.”

That scaling hypothesis carries significant implications. If the expectations embedded in chimpanzee friendships represent the raw material from which human moral systems evolved, then the emotional underpinnings of our social lives, our sense of obligation, our outrage at betrayal, our capacity to forgive those we love, may be far older than our species. Collaborative relationships are important for our well-being, health, and survival, Ritov notes, and increasingly researchers are recognizing that this is not unique to humans. Other animals have friends as well, and with those friendships come expectations that, when broken, are felt on both sides of the relationship. The pineapple heists at Ngamba Island may be a small drama, but they illuminate something profound about where human morality may have begun.

Subject of Research: Experimental study of how chimpanzee friendships influence stealing behavior and emotional responses

Article Title: Chimps plunder less pineapple from friends — and expect them to do the same

Article References: Chimps plunder less pineapple from friends — and expect them to do the same. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: chimpanzees, friendship, social expectations, evolutionary psychology, antisocial behavior, emotions, cooperation, Ngamba Island, UC Berkeley, Evolution and Human Behavior, primates, moral evolution

The research addresses a long-standing puzzle in the science of cooperation. Human societies sustain remarkably high levels of collaboration among genetically unrelated individuals, and one of the most influential theoretical explanations is indirect reciprocity. Under indirect reciprocity, people decide whether to help someone based on that person’s reputation: those known to help others earn a good standing, which makes third parties more willing to assist them in the future, while defectors acquire bad standing and are shunned. Because reputational information circulates socially, an individual can benefit from a good reputation even with people they have never met. Decades of theoretical modeling and behavioral experiments have explored how such reputation-based systems can stabilize cooperation, but most of this work has focused on socially shared information—what everyone in a group supposedly knows about everyone else.

Everyday life, however, rarely presents reputation and experience in neat agreement. A coworker may be widely praised yet have treated you badly, or a neighbor may carry a poor reputation despite having personally helped you when you needed it. Yamamoto and his colleagues set out to examine precisely this conflict: how do people evaluate another person’s decision to cooperate or refuse when the public standing of the individual involved contradicts what the evaluator has directly experienced? The question matters because evaluations are the currency of indirect reciprocity. If people’s judgments are swayed by private history rather than shared reputation, the mechanics of reputation-based cooperation may be more complicated than standard models assume.

To investigate, the team conducted two scenario-based experiments with participants in Japan. The scenarios were deliberately grounded in familiar social settings: one involved coworkers at a restaurant, and the other involved neighbors in a residential community. In each scenario, participants read about a situation in which one person either cooperated with or refused a request made by another person. The researchers systematically varied two factors. The first was the reputation of the person making the request—whether that individual was publicly regarded as good or bad. The second was the participant’s own prior experience with the person responding to the request—whether that responder had previously cooperated with or refused to cooperate with the participant personally. Participants then evaluated the person who had responded, allowing the researchers to measure how reputation and personal experience each shaped moral judgment.

The results revealed a striking asymmetry between cooperation and non-cooperation. When the responder refused the request, evaluations of that refusal depended heavily on the participant’s own prior experience with the responder. Even when the responder carried a bad public reputation, the refusal was judged more negatively if that responder had previously helped the participant. Conversely, even when the responder enjoyed a good reputation, the refusal was judged more positively if that responder had previously refused to help the participant. In other words, when public reputation and personal experience pointed in opposite directions, it was the private, firsthand history that strongly colored how participants rated the act of non-cooperation. The shared social record, which much of the indirect reciprocity literature treats as the decisive input, was effectively pushed aside.

Cooperative behavior told a different story. Acts of cooperation were generally evaluated positively regardless of the other person’s reputation and regardless of how that person had previously treated the participant. This suggests that the human evaluative system does not process cooperation and defection symmetrically. Cooperation appears to be rewarded almost automatically, insulated from the evaluator’s private grievances and from the target’s public standing. Defection, by contrast, invites a more contextualized judgment—one in which the evaluator asks not simply whether the refusal was socially acceptable, but how the person on the receiving end had previously treated them personally.

Perhaps the most sobering finding concerned a scenario in which refusing seemed entirely justified. When the person being refused had both a bad public reputation and a personal history of refusing to cooperate with the participant—conditions under which there appeared to be good reason to withhold help—the refusal itself was still evaluated neutrally rather than positively. Refusing, in other words, was not converted into a virtuous act even when the circumstances seemed to warrant it. This indicates that while people may tolerate or excuse non-cooperation under certain conditions, they do not necessarily celebrate it as positively good. The moral ledger of everyday cooperation appears to reserve its positive marks for helping, with refusal occupying at best a neutral zone even when justified.

From a technical perspective, the findings challenge a simplifying assumption embedded in many formal models of indirect reciprocity. Standard models typically treat reputational information as a single, socially shared signal that determines who deserves help. The new results suggest that human evaluators integrate at least two distinct channels—socially transmitted reputation and privately accumulated experience—and that the weighting between these channels depends on the type of behavior being judged. For defection, the private channel dominates; for cooperation, the evaluation is largely insensitive to either channel. This kind of asymmetric integration could have important consequences for how reputation-based cooperation actually operates in groups, because it implies that shared reputational records may be less powerful in governing sanctions and forgiveness than theorists have often assumed. It also hints at why personal grudges and personal loyalties can persist within communities even when everyone has access to the same public information about one another.

The study also clarifies the scope of previous research. Earlier work on indirect reciprocity concentrated mainly on how socially shared reputational information guides decisions about whom to cooperate with, leaving open the question of what happens when that shared information conflicts with lived experience. By manipulating reputation and personal experience independently within controlled scenarios, Yamamoto and his colleagues were able to isolate the contribution of each source and demonstrate that direct experience is not merely one input among many but can override reputation altogether in judgments of defection. The use of two distinct social contexts—workplace and neighborhood—suggests the pattern is not confined to a single type of relationship, although the scenarios were hypothetical and conducted with participants in Japan, so further work will be needed to test how general the effect is across cultures and real-world interactions.

Professor Yamamoto framed the work as a step toward understanding how people combine heterogeneous information when judging others. “In everyday life, we judge others by combining many different kinds of information, including what we hear about them from others and what we have experienced ourselves,” he said. “Our study provides one clue to understanding how people make judgments when these sources of information do not agree.” He also outlined where the research program is headed next: “In future research, we would like to examine how people use reputational information in environments where direct personal experience is limited, such as online rating systems and AI-mediated judgments.” That direction is increasingly urgent. On digital platforms, ratings and reviews function as public reputations, yet users often have little or no direct experience with the sellers, drivers, or service providers they evaluate. If human judgment naturally privileges firsthand experience where it exists, the design of reputation systems for environments that lack such experience becomes a genuinely open scientific and engineering question—one that this study helps to define.

Subject of Research: How direct personal experience and public reputation interact in human evaluations of cooperation and defection in indirect reciprocity

Article Title: “Public reputation” or “Personal experience”?

Article References: “Public reputation” or “Personal experience”?. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: indirect reciprocity, cooperation, reputation, defection, social evaluation, human behavior, evolutionary psychology, moral judgment, personal experience, scenario experiments, Evolution and Human Behavior, prosocial behavior

The experimental design was elegantly simple in concept but rich in the behavioral data it generated. Two groups of captive brown capuchin monkeys, one containing 22 individuals and the other 18, were given access to an apparatus featuring five distinct options. At the center stood the Stag box, a cooperative device that required two monkeys to press levers simultaneously to release high-value rewards. Surrounding it were four Hare boxes, individually operable devices that dispensed lower-value rewards to any single monkey willing to work alone. Because the animals could move freely among all five options and select any partner they wished across six testing sessions, the setup captured the genuine social dynamics of partner choice rather than forcing arbitrary pairings on unwilling participants.

The results were striking in their breadth. Most individuals in both groups engaged in successful cooperative bouts at the Stag box, demonstrating that the majority of capuchins in the study were both willing and able to coordinate their actions with a partner when the payoff justified the effort. At the same time, the monkeys did not neglect the safer alternative, regularly obtaining rewards on their own from the Hare boxes. This pattern mirrors the fundamental tension built into the Stag Hunt paradigm: cooperating with a partner promises a bigger prize but carries the risk of failure if the partner does not pull their weight, while working alone guarantees a modest but reliable return.

To disentangle the factors driving cooperative decisions, the researchers turned to generalized linear mixed models, a statistical framework well suited to behavioral data in which many observations are nested within individuals and dyads. The analysis revealed that dyadic tolerance, a measure of how comfortably two particular monkeys could share space and resources without conflict, significantly predicted the likelihood of cooperation in both groups. In other words, capuchins were not choosing partners at random. They were systematically more likely to attempt the demanding joint task with partners they tolerated well, suggesting that the quality of a social relationship acts as a gatekeeper for cooperative ventures in this species.

Individual characteristics mattered as well. The models showed that more exploratory monkeys, those that readily investigated novel objects and environments, participated in more cooperative interactions than their less adventurous groupmates. Dyads involving juveniles also engaged in more cooperative bouts, hinting that younger animals may be especially motivated to experiment with the apparatus or that their playful dispositions make them attractive or available partners. These findings underscore that cooperation is not solely a property of relationships; the personalities and life stages of the individuals involved shape how often cooperative opportunities are taken up in the first place.

Perhaps the most technically intriguing results came from a finer-grained analysis of pressing behavior, which examined how the mere presence of a partner influenced how hard monkeys worked at each type of box. Here the two groups diverged in unexpected ways. In the East Group, the presence of a partner increased pressing at the Stag box while simultaneously lowering pressing at the Hare boxes, a pattern consistent with genuine social facilitation of cooperation and a devaluation of the solo option when a collaborator was available. In the West Group, by contrast, Stag-box pressing increased steadily across sessions regardless of whether a partner was present or absent, suggesting that learning and familiarity with the apparatus, rather than partner presence, drove much of the cooperative effort in that group.

This group-level divergence carries important methodological implications for the field of comparative cognition. It demonstrates that ostensibly identical experimental conditions can produce different behavioral signatures in different social groups, and that conclusions about partner sensitivity drawn from a single group may not generalize. The authors argue that this variability is precisely why paradigms allowing free partner choice are so valuable: they reveal the social dynamics underlying cooperation rather than smoothing them away under the constraints of forced pairing. When animals can vote with their feet, researchers gain access to the decision processes that matter in the real world where cooperation evolved.

The study also speaks to a long-standing debate about the evolutionary foundations of mutualism. Mutualistic cooperation with free partner choice is widely considered a key pillar in the evolution of cooperative behavior, including in humans, because it allows individuals to shop for reliable partners and abandon unreliable ones, creating selection pressure for trustworthiness and coordination. Yet many experimental studies of animal cooperation have restricted partner choice or offered few alternatives, limiting insight into the factors that actually shape cooperative decisions. By combining a cooperative option with multiple solo alternatives in an open social setting, the Stag Hunt apparatus used here brings experimental designs closer to the ecological realities in which cooperative psychology took shape.

The ethical design of the research deserves note as well. The study was entirely non-invasive and relied exclusively on voluntary participation: no animal was food-deprived, socially separated, restrained, or physically handled for the purposes of the experiment. Multiple apparatuses were installed simultaneously to reduce monopolization by dominant individuals, and zoo staff implemented scattered feeding during testing to maintain naturalistic foraging dispersion and minimize competition. All rewards formed part of the animals’ regular diet, and no violent or injurious interactions were observed in connection with the procedures. The work was approved by the School of Psychology and Neuroscience Ethics Committee at the University of St Andrews and conducted in close collaboration with zoo authorities at Living Links, Edinburgh Zoo.

Taken together, the findings highlight the importance of integrating social relationships and individual traits into any account of cooperative decision-making in primates. Tolerance between partners determines whether cooperation is attempted at all; exploratory tendencies and youth shape how often individuals engage; and the influence of a partner’s presence on effort can vary from group to group. For capuchins, at least, the road to the big prize runs through social tolerance, and the willingness to take that road depends on who is standing beside you. As researchers continue to probe the roots of cooperation across species, studies like this one demonstrate that the richest answers emerge not from forcing animals into prescribed partnerships, but from letting them choose for themselves.

Subject of Research: Cooperative behavior and partner choice in brown capuchin monkeys tested with a Stag Hunt cooperation task

Article Title: Cooperation in brown capuchin monkeys: social tolerance, individual traits, and partner sensitivity in a Stag Hunt task

Article References: Baruah, K. M., Call, J., & Seed, A. M. (2026). Cooperation in brown capuchin monkeys: social tolerance, individual traits, and partner sensitivity in a Stag Hunt task. Animal Cognition. https://doi.org/10.1007/s10071-026-02107-8

Image Credits: AI Generated

DOI: 10.1007/s10071-026-02107-8

Keywords: capuchin monkeys, cooperation, Stag Hunt, partner choice, social tolerance, animal cognition, primates, mutualism, exploration, behavioral ecology, comparative psychology, social behavior