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Risk preference impacts how people make key life decisions related to health, wealth, and well-being. Systematic variations in risk-taking behavior can be the result of differences in fitness expectations, as predicted by life-history theory. Yet the evolutionary roots of human risk-taking behavior remain poorly understood. Here, we studied risk preferences of chimpanzees (86 Pan troglodytes; 47 females; age = 2–40 years) using a multimethod approach that combined observer ratings with behavioral choice experiments. We found that chimpanzees’ willingness to take risks shared structural similarities with that of humans. First, chimpanzees’ risk preference manifested as a traitlike preference that was consistent across domains and measurements. Second, chimpanzees were ambiguity averse. Third, males were more risk prone than females. Fourth, the appetite for risk showed an inverted-U-shaped relation to age and peaked in young adulthood. Our findings suggest that key dimensions of risk preference appear to emerge independently of the influence of human cultural evolution.

Two preregistered experiments (N = 218) investigated children's developing ability to respond reasonably to disagreement. U.S. children aged 4-9, and adults (50% female, mostly white) formed an initial belief, and were confronted with the belief of a disagreeing other, whose evidence was weaker, stronger than, or equal to participants' evidence. With age, participants were increasingly likely to maintain their initial belief when their own evidence was stronger, adopt the other's belief when their evidence was weaker, and suspend judgment when both had equally strong evidence. Interestingly, 4- to 6-year-olds only suspended judgment reliably when this was assessed via the search for additional information (Experiment 2). Together, our experiments suggest that the ability to respond reasonably to disagreement develops over the preschool years.

People rely on reputational information communicated via gossip when deciding about with whom to cooperate, whom to believe, and whom to trust. In two studies, we investigated whether 5- and 7-year-old children trust in gossip when determining a course of action. In Study 1, 5- and 7-year-old German-speaking peer dyads (

We investigated children's positive emotions as an indicator of their underlying prosocial motivation. In Study 1, 2-, and 5-year-old children (N=64) could either help an individual or watch as another person provided help. Following the helping event and using depth sensor imaging, we measured children's positive emotions through changes in postural elevation. For 2-year-olds, helping the individual and watching another person help was equally rewarding; 5-year-olds showed greater postural elevation after actively helping. In Study 2, 5-year-olds' (N=59) positive emotions following helping were greater when an audience was watching. Together, these results suggest that 2-year-old children have an intrinsic concern that individuals be helped whereas 5-year-old children have an additional, strategic motivation to improve their reputation by helping.

Judgements of wrongdoing in humans often hinge upon an assessment of whether a perpetrator acted out of free choice: whether they had more than one option. The classic inhibitors of free choice are constraint (e.g. having your hands tied together) and ignorance (e.g. being unaware that an alternative exists). Here, across two studies, we investigate whether chimpanzees consider these factors in their evaluation of social action. Chimpanzees interacted with a human experimenter who handed them a non-preferred item of food, either because they were physically constrained from accessing the preferred item (Experiment 1) or because they were ignorant of the availability of the preferred item (Experiment 2). We found that chimpanzees were more likely to accept the non-preferred food and showed fewer negative emotional responses when the experimenter was physically constrained compared with when they had free choice. We did not, however, find an effect of ignorance on chimpanzee's evaluation. Freedom of choice factors into chimpanzees' evaluation of how they are treated, but it is unclear whether mental state reasoning is involved in this assessment.

Summary Humans reason not only about actual events (what is), but also about possible events (what could be). Many key operations of human cognition involve the representation of possibilities, including moral judgment, future planning, and causal understanding 1 . But little is known about the evolutionary roots of this kind of thought. Humans’ closest relatives, chimpanzees, possess several cognitive abilities that are closely related to reasoning about alternatives: they plan for the future 2 , evaluate other’s actions 3 , and reason causally 4 . However, in the first direct test of the ability to consider alternatives, Redshaw and Suddendorf 5 claim that chimpanzees are not able to represent alternative possibilities. Here, using a novel method, we challenge this conclusion: our results suggest that, like human cognition, chimpanzee thought is not limited to what is, but also involves reasoning about what could be the case.

One influential view holds that children's sense of fairness emerges at age 8 and is rooted in the development of an aversion to unequal resource distributions. Here, we suggest two amendments to this view. First, we argue and present evidence that children's sense of fairness emerges already at age 3 in (and only in) the context of collaborative activities. This is because, in our theoretical view, collaboration creates a sense of equal respect among partners. Second, we argue and present evidence that children's judgments about what is fair are essentially judgments about the social meaning of the distributive act; for example, children accept unequal distributions if the procedure gave everyone an equal chance (so-called distributive justice). Children thus respond to unequal (and other) distributions not based on material concerns, but rather based on interpersonal concerns: they want equal respect.

Uncertainty can arise in interactions with both social partners and nonliving objects. Previous research has shown that humans display higher aversion to uncertainty arising from social interactions than to uncertainty caused by interactions with objects such as gambling machines, and that this difference may be mediated by betrayal aversion. We investigated whether chimpanzees, Pan troglodytes, differentiate between social and nonsocial forms of uncertainty. Subjects participated in two experiments, each involving a social and a nonsocial condition. In both experiments, choosing the safe option resulted in immediate access to low-value food. Choosing the uncertain option could result in access to high-value food, but only if the partner (social condition) or a machine (nonsocial condition) proved trustworthy. In experiment 1, where chimpanzees had no prior information on reciprocation rates (i.e. decided under uncertainty), chimpanzees were less likely to choose the uncertain option when they interacted with a partner than with a machine. When they did choose the uncertain option, chimpanzees also hesitated longer in the social condition. In experiment 2, where chimpanzees had learned the statistical probabilities on reciprocation rates (i.e. decided under risk), they did not distinguish between social and nonsocial situations and were generally risk averse. These results suggest that chimpanzees are more averse to engaging in uncertain choices when the source of uncertainty is a conspecific than when it is a machine; when confronted with risky choices, chimpanzees show no such tendency.

Recent work has suggested that principles of fairness that seem like natural laws to the Western mind, such as sharing more of the spoils with those who contributed more, can in fact vary significantly across populations. To build a better understanding of the developmental roots of population differences with respect to fairness, we investigated whether 7-year-old children (N = 432) from three cultural backgrounds—Kenya, China, and Germany—consider friendship and merit in their distribution of resources and how they resolve conflicts between the two. We found that friendship had considerable and consistent influence as a cross-culturally recurrent motivation: children in all three cultures preferentially shared with a friend rather than with a neutral familiar peer. On the other hand, the role of merit in distribution seemed to differ cross-culturally: children in China and Germany, but not in Kenya, selectively distributed resources to individuals who worked more. When we pitted friendship against merit, there was an approximately even split in all three cultures between children who favored the undeserving friend and children who shared with the hard-working neutral individual. These results demonstrate commonalities and variability in fairness perceptions across distinct cultures and speak to the importance of cross-cultural research in understanding the development of the human mind.

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.

From early on in ontogeny, young children hear things being said about particular individuals. Here we investigate the ways in which testimony with social content, that is, gossip, influences children's decision-making. We explored whether five-year-old (N = 72) and seven-year-old (N = 72) children trust gossip or firsthand observation in a partner choice setting. Seven-year-old children preferentially trusted what they had seen firsthand over gossip; five-year-old children, in contrast, did not differentiate between these two sources of information. However, five-year-old children (but not seven-year-olds) generally gave negative information more weight, that is, they showed a “negativity bias.” These results suggest that at around school age, young children become more “epistemically vigilant” about gossip.

Children must sometimes decide between conforming to peer behavior and doing what is right. While research shows that children have a strong inclination to act prosocially and to help conspecifics in need, many studies also demonstrate that children tend to adopt peer behavior. In two studies ( N = 96), we investigated whether children would conform to an antisocial majority or, whether they would do the right thing even under peer pressure. Results show that if a recipient is in need, 5-year-old children act prosocially in two different contexts even when there is a strong selfish incentive not to. However, once the severity of the recipient’s need is reduced, children conform to the antisocial group. The current studies suggest that children’s prosocial motivation sometimes wins out against more selfish drives.

Providing evaluative information to others about absent third parties helps them to identify cooperators and avoid cheaters. Here, we show that 5-year-olds, but not 3-year-olds, reliably engage in such prosocial gossip. In an experimental setting, 5-year-old children spontaneously offered relevant reputational information to guide a peer towards a cooperative partner. Three-year-old children offered such evaluative information only rarely, although they still showed a willingness to inform in a non-evaluative manner. A follow-up study revealed that one component involved in this age difference is children's developing ability to provide justifications. The current results extend previous work on young children's tendency to manage their own reputation by showing that preschoolers also influence others' reputations via gossip.

Human evolutionary success is often argued to be rooted in specialized social skills and motivations that result in more prosocial, rational and cooperative decisions. One manifestation of human ultra-sociality is the tendency to engage in social comparison. While social comparison studies typically focus on cooperative behaviour and emphasize concern for fairness and equality, here we investigate the competitive dimension of social comparison: a preference for getting more than others, expressed in a willingness to maximize relative payoff at the cost of absolute payoff. Chimpanzees and human children (5–6- and 9–10-year-olds) could decide between an option that maximized their absolute payoff (but put their partner at an advantage) and an option that maximized their relative payoff (but decreased their own and their partner's payoff). Results show that, in contrast to chimpanzees and young children, who consistently selected the rational and payoff-maximizing option, older children paid a cost to reduce their partner's payoff to a level below their own. This finding demonstrates that uniquely human social skills and motivations do not necessarily lead to more prosocial, rational and cooperative decision-making.

Friendship naturally leads to treating some people differently from the way we treat everyone else. One manifestation of such preferential treatment is in the domain of prosociality: we are more likely to extend favors towards our friends. Little is known about the developmental and evolutionary roots of such preferential prosociality. Here, we investigate whether young children and chimpanzees show partiality towards friends in helping contexts. Results show that young children at the age of three – when they first form preferential peer relationships – already bias their helping decisions in favor of their friends, both when they have to make a choice whether to help a friend or a neutral peer (Study 1) and when measuring their overall motivation to help (Study 2). In Study 3, by combining observational and experimental methods, we demonstrate similar though less robust motivations to provide help preferentially to friends in our closest living relatives, chimpanzees. Taken together, these studies suggest that partiality towards friends is grounded early in ontogeny and human evolution.

Reputational concerns are known to promote cooperation. Individuals regularly act more prosocially when their behavior is observable by others. Here, we investigate 4- and 5-year-old (N = 144) children's reputational strategies in a competitive group setting. The aim of the current study was to explore whether children's sharing behavior is affected by the future possibility of being singled out publicly as the most generous or, alternatively, the least generous member of the group. Children were told that they could share stickers with other children and that the picture of either the (1) most generous or (2) least generous donor would be displayed publicly. In both conditions, children shared significantly more than in a control condition. Moreover, 5-year-old, but not 4-year-old children's sharing was affected more by the possibility of being presented as the most generous than being presented as the least generous member of the group. This study is the first to show that children as young as 4 invest in their future reputation and that by age 5 children flexibly apply different reputational strategies depending on context. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Humans cultivate their reputations as good cooperators, sometimes even competing with group mates, to appear most cooperative to individuals during the process of selecting partners. To investigate the ontogenetic origins of such “competitive altruism,” we presented 5- and 8-year-old children with a dyadic sharing game in which both children simultaneously decided how many rewards to share with each other. The children were either observed by a third-person peer or not. In addition, the children either knew that one of them would be picked for a subsequent collaborative game or had no such knowledge. We found that by 8 years of age, children were more generous in the sharing game not only when their behavior was observed by a third party but also when it could affect their chances of being chosen for a subsequent game. This is the first demonstration of competitive altruism in young children, and as such it underscores the important role of partner choice (and individual awareness of the process) in encouraging human cooperation from an early age.

The identification and recruitment of trustworthy partners represents an important adaptive challenge for any species that relies heavily on cooperation [1, 2]. From an evolutionary perspective, trust is difficult to account for as it involves, by definition, a risk of non-reciprocation and defection by cheaters [3, 4]. One solution for this problem is to form close emotional bonds, i.e., friendships, which enable trust even in contexts where cheating would be profitable [5]. Little is known about the evolutionary origins of the human tendency to form close social bonds to overcome the trust problem. Studying chimpanzees (Pan troglodytes), one of our closest living relatives, is one way of identifying these origins. While a growing body of research indicates that at least some of the properties of close human relationships find parallels in the social bonds of chimpanzees [6-10] and that chimpanzees extend favors preferentially toward selected individuals [11-14], it is unclear whether such interactions are based on trust. To fill this gap in knowledge, we observed the social interactions of a group of chimpanzees and established dyadic friendship relations. We then presented chimpanzees with a modified, non-verbal version of the human trust game and found that chimpanzees trust their friends significantly more frequently than their non-friends. These results suggest that trust within closely bonded dyads is not unique to humans but rather has its evolutionary roots in the social relationships of our closest primate relatives.

The motivation to build and maintain a positive personal reputation promotes prosocial behavior. But individuals also identify with their groups, and so it is possible that the desire to maintain or enhance group reputation may have similar effects. Here, we show that 5-year-old children actively invest in the reputation of their group by acting more generously when their group’s reputation is at stake. Children shared significantly more resources with fictitious other children not only when their individual donations were public rather than private but also when their group’s donations (effacing individual donations) were public rather than private. These results provide the first experimental evidence that concern for group reputation can lead to higher levels of prosociality.

While it is well known that reputational concerns promote prosociality in adults, their ontogenetic origins remain poorly understood. Here we review evidence suggesting that the first prosocial acts of young children are not aimed at gaining reputational credit. However, at approximately five years of age, children come to be concerned about their reputations, and their prosocial behaviors show the signature of self-promotional strategies: increased prosociality in public compared to private settings. In middle childhood, at around eight years of age, children acquire further abilities to control the image they project and start to reason explicitly about their reputation. We discuss potential social and cognitive factors-Partner Choice and Theory of Mind-that contribute to the developmental emergence of self-presentational behavior.

An important debate centres around the nature of prosociality in nonhuman primates. Chimpanzees help other individuals in some experimental settings, yet they do not readily share food. One solution to this paradox is that they are motivated to help others provided there are no competing interests. However, benefits to recipients could arise as by-products of testing. Here we report two studies that separate by-product from intended helping in chimpanzees using a GO/NO-GO paradigm. Actors in one group could help a recipient by releasing a food box, but the same action for another group prevented a recipient from being able to get food. We find no evidence for helping-chimpanzees engaged in the test regardless of the effects on their partners. Illusory prosocial behaviour could arise as a by-product of task design.

The current study explored how freedom of choice affects preschoolers' prosocial motivation. Children (3- and 5-year-olds) participated in either a choice condition (where they could decide for themselves whether to help or not) or a no-choice condition (where they were instructed to help). Prosocial motivation was subsequently assessed by measuring the amount children helped an absent peer in the face of an attractive alternative game. The 5-year-olds provided with choice helped more than the children not provided with choice, and this effect was stronger for girls than for boys. There was no difference between conditions for the 3-year-olds. These results highlight the importance of choice in young children's prosocial development.

Animals react in many different ways to being watched by others. In the context of cooperation, many theories emphasize reputational effects: Individuals should cooperate more if other potential cooperators are watching. In the context of competition, individuals might want to show off their strength and prowess if other potential competitors are watching. In the current study, we observed chimpanzees and human children in three experimental conditions involving resource acquisition: Participants were either in the presence of a passive observer (observed condition), an active observer who engaged in the same task as the participant (competition condition), or in the presence of but not directly observed by a conspecific (mere presence condition). While both species worked to acquire more resources in the competition condition, children but not chimpanzees also worked to acquire more resources in the observer condition (compared to the mere presence condition). These results suggest evolutionary continuity with regard to competition-based observer effects, but an additional observer effect in young children, potentially arising from an evolutionary-based concern for cooperative reputation.

Many of humans' most important social interactions rely on trust, including most notably among strangers. But little is known about the evolutionary roots of human trust. We presented chimpanzees ( Pan troglodytes ) with a modified version of the human trust game—trust in reciprocity—in which subjects could opt either to obtain a small but safe reward on their own or else to send a larger reward to a partner and trust her to reciprocate a part of the reward that she could not access herself. In a series of three studies, we found strong evidence that in interacting with a conspecific, chimpanzees show spontaneous trust in a novel context; flexibly adjust their level of trust to the trustworthiness of their partner and develop patterns of trusting reciprocity over time. At least in some contexts then, trust in reciprocity is not unique to humans, but rather has its evolutionary roots in the social interactions of humans' closest primate relatives.

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.

Human cooperation depends on individuals caring about their reputation, and so they sometimes attempt to manage them strategically. Here we show that even 5-year-old children strategically manage their reputation. In an experimental setting, children shared significantly more resources with an anonymous recipient when (1) the child watching them could reciprocate later, and (2) the child watching them was an ingroup rather than an outgroup member (as established by minimal group markers). This study is not only the first to show that young children selectively invest in their reputation with specific individuals, but also the first to show that we care more about our reputation with ingroup than with outgroup members.