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A foundational mechanism underlying human cooperation is reciprocity. In the context of repeated interactions with others, it is not always clear the degree to which in-kind responses reflect responsiveness to partners' prior behaviors ("reactive" responses), an interest unrelated to the partner ("nonreactive" responses), or any combination of the two. To disentangle these two types of responses, we presented children with sequential, one-shot, and costly interactions between themselves and either egalitarian or selfish peers. Study 1 tested direct, generalized, and normative reciprocal scenarios ( N = 144 seven-year-old German children; 50% girls and 50% boys), finding that "nonreactive" responses were dominant for boys and manifested in the form of "selfish" resource distribution. Among girls, "reactive" responses were dominant and manifested in the form of in-kind resource distribution. Study 2 addressed even younger German children ( N = 144; 4- to 8-year-old German children; 50% girls and 50% boys), exposing the same phenomenon among 4-year-olds, but not among 5.5-year-olds. Study 3 addressed 7-year-old Israeli children ( N = 95; 49% girls and 51% boys), and replicated the basic phenomenon, with an additional cultural variation. The early emergence of gender differences in reciprocity and implications are discussed in cultural, socio-developmental, and evolutionary accounts. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Young children share equally when they acquire resources through collaboration with a partner, yet it is unclear whether they do so because in such contexts resources are encountered as common and distributed in front of the recipient or because collaboration promotes a sense of work-based fairness. In the current studies, 5- and 8-year-old children from Germany (N = 193) acquired resources either by working individually alongside or by collaborating with a peer. After finding out that the partner's container was empty, they decided in private whether they wanted to donate some resources to the peer. When both partners had worked with equal efforts (Study 1), children shared more after collaboration than after individual work. When one partner had worked with much more effort than the other (Study 2), children shared more with a harder-working partner than with a less-working partner independently of whether they had collaborated or worked individually. Younger children were more generous than older children, in particular after collaboration. These findings support the view that collaboration promotes a genuine sense of fairness in young children, but they also indicate that merit-based notions of fairness in the context of work may develop independently of collaboration, at least by the beginning of middle childhood and in Western societies., (Copyright © 2022 Elsevier Inc. All rights reserved.)

By around 3 years of age, collaboration induces in young children a normative sense of "we" that creates a sense of obligation (e.g., commitment, fairness) toward their collaborative partner. The current study investigated whether this normative sense of we could be induced purely verbally in 3- and 4-year-old children. Children joined a puppet at a table to draw. In one condition the puppet repeatedly framed things as "we" are going to sit at the table, "we" are going to draw, and so forth, whereas in the other condition the pronoun used was always "you." Dependent measures gauged children's commitment, resource distribution, and helping behavior toward their partner. Results showed that both 3- and 4-year-olds felt a greater sense of commitment to their partner after "we"-framing than after "you"-framing. The 4-year-olds evidenced this commitment by showing a greater reluctance to abandon their partner for a more fun game compared with the 3-year-olds. The 3-year-olds did not share this reluctance, but when they did abandon their partner they more often took leave following we-framing by "announcing" their leaving. There were no effects of we-framing on children's sharing with their partner or helping behavior. These results suggest that verbal we-framing, as compared with you-framing, is an effective means of inducing in children a sense of shared agency and commitment with a partner., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Humans possess some unique social-cognitive skills and motivations, involving such things as joint attention, cooperative communication, dual-level collaboration and cultural learning. These are almost certainly adaptations for humans' especially complex sociocultural lives. The common assumption has been that these unique skills and motivations emerge in human infancy and early childhood as preparations for the challenges of adult life, for example, in collaborative foraging. In the current paper, I propose that the curiously early emergence of these skills in infancy--well before they are needed in adulthood--along with other pieces of evidence (such as almost exclusive use with adults not peers) suggests that aspects of the evolution of these skills represent ontogenetic adaptations to the unique socio-ecological challenges human infants face in the context of a regime of cooperative breeding and childcare. 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'.

People frequently need to cooperate despite having strong self-serving motives. In the current study, pairs of 5- and 7-year-olds ( N = 160) faced a one-shot coordination problem: To benefit, children had to choose the same of 3 reward divisions. They could not communicate or see each other and thus had to accurately predict each other's choices to succeed. One division split the rewards evenly, while the others each favored one child. Five-year-olds mostly chose the division favorable to themselves, resulting in coordination failure. By contrast, 7-year-olds mostly coordinated successfully by choosing the division that split the rewards equally (even though they behaved selfishly in a control condition in which they could choose independently). This suggests that by age 7, children jointly expect benefits to be shared among interdependent social partners "fairly" and that fair compromises can emanate from a cooperative rationality adapted for social coordination. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Collaborative reasoning requires partners to evaluate options and the evidence for or against each option. We investigated whether preschoolers can explain why one option is best (direct reasons) and why the other option is not (indirect reasons), looking at both problems that have a correct answer and those that require choosing the better option. In Study 1, both age groups produced direct reasons equally frequently in both problems. However, 5-year-olds produced indirect reasons more often than 3-year-olds, especially when there was a correct answer. In Study 2 with a nonverbal task with a correct answer, 3-year-olds produced indirect reasons more often than in Study 1, although 5-year-olds' indirect reasons were more efficiently stated. These results demonstrate that even 3-year-olds, and even nonverbally, can point out to a partner a fact that constitutes a reason for them to arrive at a correct joint decision., (Copyright © 2020 Elsevier Inc. All rights reserved.)

In both the wild and captivity, chimpanzees engage in reciprocal patterns of prosocial behavior. However, the proximate mechanisms underlying these patterns are unclear. In the current study, we investigated whether chimpanzees prefer to act prosocially toward conspecifics who have directly benefited them (perhaps based on an affective bond) or whether they simply observe the prosocial behavior of others in general (including indirectly to third parties) and preferentially interact with and behave prosocially toward the most prosocial individuals. We found good evidence for direct reciprocity but little evidence for a general (indirect) preference for prosocial individuals. These results suggest that cooperative reciprocity in chimpanzees may be based mostly on social-affective processes and direct interactions. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Access to and control of resources is a major source of costly conflicts. Animals, under some conditions, respect what others control and use (i.e. possession). Humans not only respect possession of resources, they also respect ownership. Ownership can be viewed as a cooperative arrangement, where individuals inhibit their tendency to take others' property on the condition that those others will do the same. We investigated to what degree great apes follow this principle, as compared to human children. We conducted two experiments, in which dyads of individuals could access the same food resources. The main test of respect for ownership was whether individuals would refrain from taking their partner's resources even when the partner could not immediately access and control them. Captive apes (N = 14 dyads) failed to respect their partner's claim on food resources and frequently monopolized the resources when given the opportunity. Human children (N = 14 dyads), tested with a similar apparatus and procedure, respected their partner's claim and made spontaneous verbal references to ownership. Such respect for the property of others highlights the uniquely cooperative nature of human ownership arrangements., (© 2019 John Wiley & Sons Ltd.)

This study investigated the influence of underlying intentions and outcomes of a partner's sharing behavior on young children's reciprocity. We provided 3- and 5-year-old children with the opportunity to share with a partner following different treatments of a partner's intention (to share or not to share) that led to different outcomes (children got or did not get stickers from their partner). For the 3-year-olds, we found that the outcome of the previous interaction influenced how much they shared, whereas the intention of their partner affected how readily they initiated sharing in response to social cues. For the 5-year-olds, we found that both outcome and intention affected how much they shared as well as how readily they initiated sharing. This suggests that already 3-year-olds are able to take into account outcome and intention information separately in reciprocal sharing. However, only 5-year-olds can combine both to flexibly maintain social interactions without running the risk of being exploited by others., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Children's moral behavior is guided, in part, by adults teaching children how to treat others. However, when circumstances change, such instructions may become either unhelpful or limiting. In the current study, 48 dyads of 5-year-olds played a collaborative game and either (a) received an instruction by an adult to share the spoils of the game equally, (b) did not receive any instruction (but still chose to share equally), or (c) agreed between themselves on a rule to share equally. Afterward, each child played with a new partner who was needier or worked harder in his or her collaboration and so plausibly deserved more than just half of the spoils. Results showed that children who were instructed by an adult shared less with their more deserving partner than children who did not receive any instruction. Thus, moral instruction by adults may, in some circumstances, make children more rigid in their moral decisions., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Chimpanzees hunt cooperatively in the wild, but the factors influencing food sharing after the hunt are not well understood. In an experimental study, groups of three captive chimpanzees obtained a monopolizable food resource, either via two individuals cooperating (with the third as bystander) or via one individual acting alone alongside two bystanders. The individual that obtained the resource first retained most of the food but the other two individuals attempted to obtain food from the "captor" by begging. We found the main predictor of the overall amount of food obtained by bystanders was proximity to the food at the moment it was obtained by the captor. Whether or not an individual had cooperated to obtain the food had no effect. Interestingly, however, cooperators begged more from captors than did bystanders, suggesting that they were more motivated or had a greater expectation to obtain food. These results suggest that while chimpanzee captors in cooperative hunting may not reward cooperative participation directly, cooperators may influence sharing behavior through increased begging., Competing Interests: The authors have declared that no competing interests exist.

When young children form a joint commitment with a partner, they understand that this agreement generates obligations. In this study, we investigated whether young children understand that joint commitments, and their associated obligations, may likewise be dissolved by agreement. The participants (3- and 5-year-olds; N = 144) formed a joint commitment with a puppet to play a collaborative game. In one condition, the puppet asked permission to break off and the children agreed; in a second condition, the puppet notified the children of his or her leaving; and in a third condition, the puppet just left abruptly. Children at both ages protested more and waited longer for the puppet's return (and said that the puppet deserved scolding and no prize at the end) when the puppet left abruptly than in the other two conditions (with "asking permission" leading to the least protest of all). Overall, 3-year-olds protested more, and waited longer for the partner's return, than 5-year-olds. Preschool children understand that the obligations of a joint commitment may be dissolved by agreement or, to a lesser degree, by notification., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Humans create social closeness with one another through a variety of shared social activities in which they align their emotions or mental states towards an external stimulus such as dancing to music together, playing board games together or even engaging in minimal shared experiences such as watching a movie together. Although these specific behaviours would seem to be uniquely human, it is unclear whether the underlying psychology is unique to the species, or if other species might possess some form of this psychological mechanism as well. Here we show that great apes who have visually attended to a video together with a human (study 1) and a conspecific (study 2) subsequently approach that individual faster (study 1) or spend more time in their proximity (study 2) than when they had attended to something different. Our results suggest that one of the most basic mechanisms of human social bonding-feeling closer to those with whom we act or attend together-is present in both humans and great apes, and thus has deeper evolutionary roots than previously suspected.

Humans are frequently required to coordinate their actions in social dilemmas (e.g. when one of two drivers has to yield for the other at an intersection). This is commonly achieved by individuals following communally known rules that prescribe how people should behave. From relatively early in development, children swiftly pick up the rules of their culture and even start creating game rules among peers. Thus far, however, little is known about children's abilities create rules to regulate their own interactions in social dilemma situations in which individuals' interests are partially in conflict. Here, we repeatedly selected dyads of children (5- and 8-year-olds, N = 144) at random from a group and presented them with a chicken game - a social dilemma in which individuals have conflicting motives but coordination is required to avoid mutual failure. In game breaks, groups reconvened and had the opportunity to think of additional game rules. Eight- but not five-year-olds readily came up with and agreed upon impartial rules to guide their subsequent game behavior (but only after adult prompting). Moreover, when playing by the self-made rules, children achieved higher payoffs, had fewer conflicts, and coordinated with greater efficiency than when playing without a rule - which mimics the functional consequences of rules on a societal level. These findings suggest that by at least age 8, children are capable of using rules to independently self-regulate potential conflicts of interest with peers., (Copyright © 2018 Elsevier Inc. 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., (Copyright © 2018 Elsevier Inc. All rights reserved.)

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).

The problem with collaboration is that there are temptations to defect. Explicit joint commitments are designed to mitigate some of the risks, but people also feel committed to others implicitly when they both know together that they each hold the other's fate in their hands. In the current study, pairs of 3-year-old and 5-year-old children ( N = 192) played a collaborative game. One child was offered individual rewards (bribed) to opt out of the collaboration. In 3 different conditions, the level of the commitment was manipulated. Three-year-old children were more likely to resist the bribes when there was an explicit joint commitment to the partner than when they were only playing in parallel, with their reactions to an implicit commitment falling in between. Five-year-olds were more likely to resist bribes in both the implicit and explicit commitment conditions than in the no-commitment condition. Thus, children at both ages showed some level of commitment to a collaborative partner in the face of bribes to defect, but only 5-year-olds clearly appreciated that a common-ground understanding of interdependence between partners generates an implicit commitment or obligation. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

Making commitments to cooperate facilitates cooperation. There is a long-standing theoretical debate about how promissory obligations come into existence, and whether linguistic acts (such as saying "I promise") are a necessary part of the process. To inform this debate we experimentally investigated whether even minimal, nonverbal behavior can be taken as a commitment to cooperate, as long as it is communicative. Five- to 7-year-old children played a Stag Hunt coordination game in which they needed to decide whether to cooperate or play individually. During the decision-making phase, children's partner made either ostensive, communicative eye contact or looked non-communicatively at them. In Study 1 we found that communicative looks produced an expectation of collaboration in children. In Study 2 we found that children in the communicative look condition normatively protested when their partner did not cooperate, thus showing an understanding of the communicative looks as a commitment to cooperate. This is the first experimental evidence, in adults or children, that in the right context, communicative, but not non-communicative, looks can signal a commitment., (Copyright © 2018 Elsevier B.V. All rights reserved.)

When children make a joint commitment to collaborate, obligations are created. Pairs of 3-year-old children (N = 144) made a joint commitment to play a game. In three different conditions the game was interrupted in the middle either because: (a) the partner child intentionally defected, (b) the partner child was ignorant about how to play, or (c) the apparatus broke. The subject child reacted differently in the three cases, protesting normatively against defection (with emotional arousal and later tattling), teaching when the partner seemed to be ignorant, or simply blaming the apparatus when it broke. These results suggest that 3-year-old children are competent in making appropriate normative evaluations of intentions and obligations of collaborative partners., (© 2017 The Authors. Child Development © 2017 Society for Research in Child Development, Inc.)

Young children engage in direct reciprocity, but the mechanisms underlying such reciprocity remain unclear. In particular, prior work leaves unclear whether children's reciprocity is simply a response to receiving benefits (regardless of whether the benefits were intended) or driven by a mechanism of rewarding or preferring all benefactors (regardless of whom they benefited). Alternatively, perhaps children engage in genuine reciprocity such that they are particularly prosocial toward benefactors who intentionally provided them with benefits. Our findings support this third, richer possibility; the 3-year-olds who received benefits through the good intentions of a benefactor were subsequently more generous toward the benefactor than children who either (a) received the same benefits from the benefactor unintentionally or (b) observed the benefactor bestow the same benefits on another individual. Thus, young children are especially motivated to benefit those who have demonstrated goodwill toward them, suggesting, as one possible mechanism, an early sense of gratitude., (Copyright © 2017 Elsevier Inc. All rights reserved.)

We report two studies that demonstrate how five- and seven-year-olds adapt their production of arguments to either a cooperative or a competitive context. Two games elicited agreements from peer dyads about placing animals on either of two halves of a playing field owned by either child. Children had to produce arguments to justify these decisions. Played in a competitive context that encouraged placing animals on one's own half, children's arguments showed a bias that was the result of withholding known arguments. In a cooperative context, children produced not only more arguments, but also more 'two-sided' arguments. Also, seven-year-olds demonstrated a more frequent and strategic use of arguments that specifically refuted decisions that would favour their peers. The results suggest that cooperative contexts provide a more motivating context for children to produce arguments. Statement of contribution What is already known on this subject? Reasoning is a social skill that allows people to reach joint decisions. Preschoolers give reasons for their proposals in their peer conversations. By adolescence, children use sophisticated arguments (e.g., refutations and rebuttals). What the present study adds? Cooperation offers a more motivating context for children's argument production. Seven-year-olds are more strategic than five-year-olds in their reasoning with peers. Children's reasoning with others becomes more sophisticated after preschool years., (© 2017 The British Psychological Society.)

In collaborative decision making, children must evaluate the evidence behind their respective claims and the rationality of their respective proposals with their partners. In the main study, 5- and 7-year-old peer dyads (N = 196) were presented with a novel animal. In the key condition, children in a dyad individually received conflicting information about what the animal needs (e.g., rocks vs. sand for food) from sources that differ in reliability (with first-hand vs. indirect evidence). Dyads in both age groups were able to reliably settle on the option with the best supporting evidence. Moreover, in making their decision, children, especially 7-year-olds, engaged in various kinds of meta-talk about the evidence and its validity. In a modified version of the key condition in Study 2, 3- and 5-year-olds (N = 120) interacted with a puppet who tried to convince children to change their minds by producing meta-talk. When the puppet insisted and produced meta-talk, 5-year-olds, but not 3-year-olds, were more likely to change their minds if their information was unreliable. These results suggest that even preschoolers can engage in collaborative reasoning successfully, but the ability to reflect on the process by stepping back to jointly examine the evidence emerges only during the early school years., (Copyright © 2017 Elsevier Inc. All rights reserved.)

To explain the evolutionary emergence of uniquely human skills and motivations for cooperation, Tomasello et al. (2012, in Current Anthropology 53(6):673-92) proposed the interdependence hypothesis. The key adaptive context in this account was the obligate collaborative foraging of early human adults. Hawkes (2014, in Human Nature 25(1):28-48), following Hrdy (Mothers and Others, Harvard University Press, 2009), provided an alternative account for the emergence of uniquely human cooperative skills in which the key was early human infants' attempts to solicit care and attention from adults in a cooperative breeding context. Here we attempt to reconcile these two accounts. Our composite account accepts Hrdy's and Hawkes's contention that the extremely early emergence of human infants' cooperative skills suggests an important role for cooperative breeding as adaptive context, perhaps in early Homo. But our account also insists that human cooperation goes well beyond these nascent skills to include such things as the communicative and cultural conventions, norms, and institutions created by later Homo and early modern humans to deal with adult problems of social coordination. As part of this account we hypothesize how each of the main stages of human ontogeny (infancy, childhood, adolescence) was transformed during evolution both by infants' cooperative skills "migrating up" in age and by adults' cooperative skills "migrating down" in age.

Humans regularly provide others with resources at a personal cost to themselves. Chimpanzees engage in some cooperative behaviors in the wild as well, but their motivational underpinnings are unclear. In three experiments, chimpanzees ( Pan troglodytes ) always chose between an option delivering food both to themselves and a partner and one delivering food only to themselves. In one condition, a conspecific partner had just previously taken a personal risk to make this choice available. In another condition, no assistance from the partner preceded the subject's decision. Chimpanzees made significantly more prosocial choices after receiving their partner's assistance than when no assistance was given (experiment 1) and, crucially, this was the case even when choosing the prosocial option was materially costly for the subject (experiment 2). Moreover, subjects appeared sensitive to the risk of their partner's assistance and chose prosocially more often when their partner risked losing food by helping (experiment 3). These findings demonstrate experimentally that chimpanzees are willing to incur a material cost to deliver rewards to a conspecific, but only if that conspecific previously assisted them, and particularly when this assistance was risky. Some key motivations involved in human cooperation thus may have deeper phylogenetic roots than previously suspected., Competing Interests: The authors declare no conflict of interest.

Social animals need to coordinate with others to reap the benefits of group-living even when individuals' interests are misaligned. We compare how chimpanzees, bonobos and children coordinate their actions with a conspecific in a Snowdrift game, which provides a model for understanding how organisms coordinate and make decisions under conflict. In study 1, we presented pairs of chimpanzees, bonobos and children with an unequal reward distribution. In the critical condition, the preferred reward could only be obtained by waiting for the partner to act, with the risk that if no one acted, both would lose the rewards. Apes and children successfully coordinated to obtain the rewards. Children used a 'both-partner-pull' strategy and communicated during the task, while some apes relied on an 'only-one-partner-pulls' strategy to solve the task, although there were also signs of strategic behaviour as they waited for their partner to pull when that strategy led to the preferred reward. In study 2, we presented pairs of chimpanzees and bonobos with the same set-up as in study 1 with the addition of a non-social option that provided them with a secure reward. In this situation, apes had to actively decide between the unequal distribution and the alternative. In this set-up, apes maximized their rewards by taking their partners' potential actions into account. In conclusion, children and apes showed clear instances of strategic decision-making to maximize their own rewards while maintaining successful coordination., (© 2017 The Author(s).)

The age at which young children show an aversion to inequitable resource distributions, especially those favoring themselves, is unclear. It is also unclear whether great apes, as humans' nearest evolutionary relatives, have an aversion to inequitable resource distributions at all. Using a common methodology across species and child ages, the current two studies found that 3- and 4-year-old children (N=64) not only objected when they received less than a collaborative partner but also sacrificed to equalize when they received more. They did neither of these things in a nonsocial situation, demonstrating the fundamental role of social comparison. In contrast, chimpanzees (N=9) showed no aversion to inequitable distributions, only a concern for maximizing their own resources, with no differences between social and nonsocial conditions. These results underscore the unique importance for humans, even early in ontogeny, for treating others fairly, presumably as a way of becoming a cooperative member of one's cultural group., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Humans constantly have to coordinate their decisions with others even when their interests are conflicting (e.g., when 2 drivers have to decide who yields at an intersection). So far, however, little is known about the development of these abilities. Here, we present dyads of 5-year-olds (N = 40) with a repeated chicken game using a novel methodology: Two children each steered an automated toy train carrying a reward. The trains simultaneously moved toward each other so that in order to avoid a crash-which left both children empty-handed-1 train had to swerve. By swerving, however, the trains lost a portion of the rewards so that it was in each child's interest to go straight. Children coordinated their decisions successfully over multiple rounds, and they mostly did so by taking turns at swerving. In dyads in which turn-taking was rare, dominant children obtained significantly higher payoffs than their partners. Moreover, the coordination process was more efficient in turn-taking dyads as indicated by a significant reduction in conflicts and verbal protest. These findings indicate that already by the late preschool years children can independently coordinate decisions with peers in recurrent conflicts of interest. (PsycINFO Database Record, ((c) 2017 APA, all rights reserved).)

Large-scale human cooperation among unrelated individuals requires the enforcement of social norms. However, such enforcement poses a problem because non-enforcers can free ride on others' costly and risky enforcement. One solution is that enforcers receive benefits relative to non-enforcers. Here we show that this solution becomes functional during the preschool years: 5-year-old (but not 4-year-old) children judged enforcers of norms more positively, preferred enforcers, and distributed more resources to enforcers than to non-enforcers. The ability to sustain not only first-order but also second-order cooperation thus emerges quite early in human ontogeny, providing a viable solution to the problem of higher-order cooperation., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Two studies investigated the influence of external rewards and social praise in young children's fairness-related behavior. The motivation of ninety-six 3-year-olds' to equalize unfair resource allocations was measured in three scenarios (collaboration, windfall, and dictator game) following three different treatments (material reward, verbal praise, and neutral response). In all scenarios, children's willingness to engage in costly sharing was negatively influenced when they had received a reward for equal sharing during treatment than when they had received praise or no reward. The negative effect of material rewards was not due to subjects responding in kind to their partner's termination of rewards. These results provide new evidence for the intrinsic motivation of prosociality-in this case, costly sharing behavior-in preschool children., (© 2016 The Authors. Child Development © 2016 Society for Research in Child Development, Inc.)

Long-term collaborative relationships require that any jointly produced resources be shared in mutually satisfactory ways. Prototypically, this sharing involves partners dividing up simultaneously available resources, but sometimes the collaboration makes a resource available to only one individual, and any sharing of resources must take place across repeated instances over time. Here, we show that beginning at 5 years of age, human children stabilize cooperation in such cases by taking turns across instances of obtaining a resource. In contrast, chimpanzees do not take turns in this way, and so their collaboration tends to disintegrate over time. Alternating turns in obtaining a collaboratively produced resource does not necessarily require a prosocial concern for the other, but rather requires only a strategic judgment that partners need incentives to continue collaborating. These results suggest that human beings are adapted for thinking strategically in ways that sustain long-term cooperative relationships and that are absent in their nearest primate relatives., (© The Author(s) 2016.)

Some problems of resource distribution can be solved on equal terms only by taking turns. We presented such a problem to 168 pairs of 5- to 10-year-old children from one Western and two non-Western societies (German, Samburu, Kikuyu). Almost all German pairs solved the problem by taking turns immediately, resulting in an equal distribution of resources throughout the game. In the other groups, one child usually monopolized the resource in Trial 1 and sometimes let the partner monopolize it in Trial 2, resulting in an equal distribution in only half the dyads. These results suggest that turn-taking is not a natural strategy uniformly across human cultures, but rather that different cultures use it to different degrees and in different contexts., (© 2016 The Authors. Child Development © 2016 Society for Research in Child Development, Inc.)

To date, developmental research on groups has focused mainly on in-group biases and intergroup relations. However, little is known about children's general understanding of social groups and their perceptions of different forms of group. In this study, 5- to 6-year-old children were asked to evaluate prototypes of four key types of groups: an intimacy group (friends), a task group (people who are collaborating), a social category (people who look alike), and a loose association (people who coincidently meet at a tram stop). In line with previous work with adults, the vast majority of children perceived the intimacy group, task group, and social category, but not the loose association, to possess entitativity, that is, to be a 'real group.' In addition, children evaluated group member properties, social relations, and social obligations differently in each type of group, demonstrating that young children are able to distinguish between different types of in-group relations. The origins of the general group typology used by adults thus appear early in development. These findings contribute to our knowledge about children's intuitive understanding of groups and group members' behavior.

Human institutional practices often involve competition within a cooperative structure of mutually accepted rules. In a competitive game, for instance, we not only expect adherence to the rules of the game but also expect an opponent who tries to win and, thus, follows a rational game-playing strategy. We had 3- and 5-year-olds (N=48) play for a prize against an opponent (a puppet) who played either rationally (trying to win) or irrationally (helping the children to win) while either following or breaking the rules of the game. Both age groups performed costly protest against an opponent who followed the rules but played irrationally by helping the children to win. When facing a rule-breaking opponent, 3-year-olds protested only the rule breaches of an irrational opponent but not irrational play. Five-year-olds also protested the rule breaches of a rational opponent, but in contrast to the 3-year-olds, they protested irrational behavior even in the context of rule breaches. Moreover, many children, in particular 3-year-olds, refrained from protesting. These findings suggest that 5-year-olds, but not 3-year-olds, fully understand the dual-level normative structure of cooperatively regulated competition., (Copyright © 2015 Elsevier Inc. All rights reserved.)

In the context of joint decision-making, we investigated whether preschoolers alter the informativeness of their justifications depending on the common ground that they share with their partner. Pairs of 3- and 5-year-olds (N = 146) were introduced to a novel animal with unique characteristics (e.g., eating rocks). In the common ground condition, the children learned about the animal together. In the one-expert condition, one learned about it, the other was naïve. In the two-experts condition, children learned about it separately. Later, the pairs had to decide together on 3 items that the novel animal might need. Both age groups referred to the unique characteristics of the animal in their justifications more in the 2 conditions without common ground than in the common ground condition. Thus, preschoolers begin to use common ground flexibly in their justifications and reason-giving in peer interactions., ((c) 2016 APA, all rights reserved).)

Recent theoretical work has highlighted potential links between interpersonal collaboration and group membership in the evolution of human sociality. Here we compared the effects of collaboration and minimal-group membership on young children's prosocial behavior (i.e., helping and resource allocation), liking, affiliation, and trust. In a design that matched as closely as possible these two ways of connecting with others, we showed that 5-year-olds' behavior was affected similarly by collaboration and minimal-group membership; both increased children's preference for their partners on multiple dimensions and produced overall effects of a similar magnitude. In contrast, 3.5-year-olds did not have a strong preference for either collaborators or minimal in-group members. Thus, both collaboration and minimal-group membership are similarly effective in their influence on children's prosocial behavior and social preferences., (Copyright © 2015 Elsevier Inc. All rights reserved.)

Humans are routinely required to coordinate with others. When communication is not possible, adults often achieve this by using salient cues in the environment (e.g. going to the Eiffel Tower, as an obvious meeting point). To explore the development of this capacity, we presented dyads of 3-, 5-, and 8-year-olds (N = 144) with a coordination problem: Two balls had to be inserted into the same of four boxes to obtain a reward. Identical pictures were attached to three boxes whereas a unique--and thus salient--picture was attached to the fourth. Children either received one ball each, and so had to choose the same box (experimental condition), or they received both balls and could get the reward independently (control condition). In all cases, children could neither communicate nor see each other's choices. Children were significantly more likely to choose the salient option in the experimental condition than in the control condition. However, only the two older age groups chose the salient box above chance levels. This study is the first to show that children from at least age 5 can solve coordination problems by converging on a salient solution., (© 2014 John Wiley & Sons Ltd.)

In face-to-face bargaining tasks human adults almost always agree on an equal split of resources. This is due to mutually recognized fairness and equality norms. Early developmental studies on sharing and equality norms found that egalitarian allocations of resources are not common before children are 5 or 6 years old. However, recent studies have shown that in some face-to face collaborative situations, or when recipients express their desires, children at much younger ages choose equal allocations. We investigated the ability of 3.5 and 5-year-olds to negotiate face-to-face, whether to collaborate to obtain an equal or an unequal distribution of rewards. We hypothesized that the face-to-face interaction and interdependency between partners would facilitate egalitarian outcomes at both ages. In the first experiment we found that 5-year-olds were more egalitarian than 3.5-year-olds, but neither of the age classes shared equally. In the second experiment, in which we increased the magnitude of the inequality, we found that children at both ages mostly agreed on the unequal distribution. These results show that communication and face-to-face interactions are not sufficient to guarantee equal allocations at 3-5 years of age. These results add to previous findings suggesting that in the context of non-collaboratively produced resources it is only after 5 years of age that children use equality norms to allocate resources.

Humans are constantly required to coordinate their behaviour with others. As this often relies on everyone's convergence on the same strategy (e.g., driving on the left side of the road), a common solution is to conform to majority behaviour. In this study, we presented 5-year-old children with a coordination problem: To retrieve some rewards, they had to choose the same of four options as a peer partner--in reality a stooge--whose decision they were unable to see. Before making a choice, they watched a video showing how other children from their partner's peer group had behaved; a majority chose the same option and a minority chose a different one. In a control condition, children watched the same video but could then retrieve the reward irrespective of their partner's choice (i.e., no coordination was necessary). Children followed the majority more often when coordination was required. Moreover, conformers mostly justified their choices by referring to the majority from the video demonstration. This study is the first to show that young children are able to strategically coordinate decisions with peers by conforming to the majority., (© 2014 The British Psychological Society.)

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., (© 2015 The Author(s) Published by the Royal Society. All rights reserved.)

Property as a social "agreement" comprises both a communicative component, in which someone makes a claim that she is entitled to some piece of property, and a cooperative component, in which others in the community respect that claim as legitimate. In the current study, preschool children were (a) given the opportunity to mark some objects as "theirs" (to claim them in the face of other fictitious children who would supposedly enter the room later); and (b) confronted with stickers in various spatial arrangements (e.g., piled up neatly vs. scattered), told that a fictitious child had previously chosen some for herself but had to suddenly leave the room, and then invited first to choose some stickers for themselves and second to identify which stickers had already been claimed by the fictitious child. Five-year-olds but not 3-year-olds were skillful in both of these tasks, demonstrating an understanding of the crucial role of communication in asserting property claims and the crucial role of cooperation in respecting them., (PsycINFO Database Record (c) 2015 APA, all rights reserved.)

Much of human cooperation takes place in mutualistic contexts in which the main challenge for individuals is how to coordinate decisions. In the current studies, we compared the abilities of chimpanzees and young children to coordinate with a partner in two versions of a Stag Hunt game. When risks were low (the hare was of low value) and information was cheap (the partner's behaviour was readily observable), partners of both species were able to successfully coordinate on the higher value stag more than 90% of the time. By contrast, when the risks were raised and observing the partner was more difficult, the chimpanzees became less successful, whereas the children compensated, and so remained highly successful, by communicating more often and more specifically. This pattern of results is consistent with the hypothesis that humans evolved unique skills of coordination and communication in the context of especially risky coordination problems., (© 2014 The Author(s) Published by the Royal Society. All rights reserved.)

Chimpanzees cooperate in a variety of contexts, but communicating to influence and regulate cooperative activities is rare. It is unclear whether this reflects chimpanzees' general inability or whether they have found other means to coordinate cooperative activities. In the present study chimpanzees could help a partner play her role in a mutually beneficial food-retrieval task either by transferring a needed tool (transfer condition) or by visually or acoustically communicating the hiding-location of the needed tool (communication condition). Overall, chimpanzees readily helped their partner by delivering the needed tool, but none of them communicated the hiding location of the tool to their partner reliably across trials. These results demonstrate that although chimpanzees can coordinate their cooperative activities by instrumentally helping their partner in her role, they do not readily use communication with their partner for this same end.

This study investigates how children negotiate social norms with peers. In Study 1, 48 pairs of 3- and 5-year-olds (N = 96) and in Study 2, 48 pairs of 5- and 7-year-olds (N = 96) were presented with sorting tasks with conflicting instructions (one child by color, the other by shape) or identical instructions. Three-year-olds differed from older children: They were less selective for the contexts in which they enforced norms, and they (as well as the older children to a lesser extent) used grammatical constructions objectifying the norms ("It works like this" rather than "You must do it like this"). These results suggested that children's understanding of social norms becomes more flexible during the preschool years., (© 2013 The Authors. Child Development © 2013 Society for Research in Child Development, Inc.)

The present study investigated young preschoolers' proportional allocation of rewards in 2 different work contexts. We presented 32 pairs of 3.5-year-old peers with a collaborative task to obtain rewards by pulling ropes. In order to establish differences in work input, 1 child's rope was not immediately accessible but had to be retrieved from the apparatus by means of a specific tool, while the other child had no such additional work to do. The result of the game was that 1 individual received 1 toy and the other received 3 toys. In the Deserving condition, the working child received the 3 toys (thus work and reward matched), whereas in the Undeserving condition, the other child received the 3 toys (he or she was overpaid, and the working child was underpaid). Another 32 dyads participated in a noncollaborative, parallel work task, again in a Deserving condition and an Undeserving condition. On average, children with 3 toys shared with their partner more in the Undeserving condition than in the Deserving condition after collaboration but not in a parallel work setup. These results suggest that young children take merit into account in distributing resources at a much younger age than previously believed and that peer collaboration is an especially facilitative context for children's attention to norms of fairness., (PsycINFO Database Record (c) 2014 APA, all rights reserved.)

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., (© 2013 John Wiley & Sons Ltd.)

Contingent reciprocity is important in theories of the evolution of human cooperation, but it has been very little studied in ontogeny. We gave 2- and 3-year-old children the opportunity to either help or share with a partner after that partner either had or had not previously helped or shared with the children. Previous helping did not influence children's helping. In contrast, previous sharing by the partner led to greater sharing in 3-year-olds but not in 2-year-olds. These results do not support theories claiming either that reciprocity is fundamental to the origins of children's prosocial behavior or that it is irrelevant. Instead, they support an account in which children's prosocial behavior emerges spontaneously but is later mediated by reciprocity., (Copyright © 2013 Elsevier Inc. All rights reserved.)

Here we investigate the extent of children's understanding of the joint commitments inherent in joint activities. Three-year-old children either made a joint commitment to assemble a puzzle with a puppet partner, or else the child and puppet each assembled their own puzzle. Afterwards, children who had made the joint commitment were more likely to stop and wait for their partner on their way to fetch something, more likely to spontaneously help their partner when needed, and more likely to take over their partner's role when necessary. There was no clear difference in children's tendency to tattle on their partner's cheating behavior or their tendency to distribute rewards equally at the end. It thus appears that by 3 years of age making a joint commitment to act together with others is beginning to engender in children a "we"-intentionality which holds across at least most of the process of the joint activity until the shared goal is achieved, and which withstands at least some of the perturbations to the joint activity children experience.

Cooperative hunting is a cognitively challenging activity since individuals have to coordinate movements with a partner and at the same time react to the prey. Domestic dogs evolved from wolves, who engage in cooperative hunting regularly, but it is not clear whether dogs have kept their cooperative hunting skills. We presented pairs of dogs with a reward behind a fence with two openings in it. A sliding door operated by the experimenter could block one opening but not both simultaneously. The dogs needed to coordinate their actions, so that each was in front of a different opening, if one of them was to cross through and get food. All 24 dog pairs solved the problem. In study 1, we demonstrated that dogs understood how the apparatus worked. In study 2, we found that, although the performance of the pairs did not depend on the divisibility of the reward, pairs were quicker at coordinating their actions when both anticipated rewards. However, the dogs did not monitor one another, suggesting that their solutions were achieved by each individual attempting to maximize for itself.

Many animal species cooperate, but the underlying proximate mechanisms are often unclear. We presented chimpanzees with a mutualistic collaborative food-retrieval task requiring complementary roles, and tested subjects' ability to help their partner perform her role. For each role, subjects required a different tool, and the tools were not interchangeable. We gave one individual in each dyad both tools, and measured subjects' willingness to transfer a tool to their partner as well as which tool (correct versus incorrect) they transferred. Most subjects helped their partner and transferred the tool the partner needed. Thus, chimpanzees not only coordinate different roles, but they also know which particular action the partner needs to perform. These results add to previous findings suggesting that many of chimpanzees' limitations in collaboration are, perhaps, more motivational than cognitive.

Recent studies have shown that in situations where resources have been acquired collaboratively, children at around 3 years of age share mostly equally. We investigated 3-year-olds' sharing behavior with a collaborating partner and a free-riding partner who explicitly expressed her preference not to collaborate. Children shared more equally with the collaborating partner than with the free rider. These results suggest that young children are sensitive to the contributions made by others to a collaborative effort (and possibly their reasons for not collaborating) and distribute resources accordingly., (Copyright © 2012 Elsevier Inc. All rights reserved.)