Children across societies enforce conventional norms but in culturally variable ways.

Individuals in all societies conform to their cultural group's conventional norms, from how to dress on certain occasions to how to play certain games. It is an open question, however, whether individuals in all societies actively enforce the group's conventional norms when others break them. We investigated third-party enforcement of conventional norms in 5- to 8-y-old children (n = 376) from eight diverse small-scale and large-scale societies. Children learned the rules for playing a new sorting game and then, observed a peer who was apparently breaking them. Across societies, observer children intervened frequently to correct their misguided peer (i.e., more frequently than when the peer was following the rules). However, both the magnitude and the style of interventions varied across societies. Detailed analyses of children's interactions revealed societal differences in children's verbal protest styles as well as in their use of actions, gestures, and nonverbal expressions to intervene. Observers' interventions predicted whether their peer adopted the observer's sorting rule. Enforcement of conventional norms appears to be an early emerging human universal that comes to be expressed in culturally variable ways.

Thought and language: Effects of group-mindedness on young children's interpretation of exclusive we.

The current study investigated whether age-related changes in the conceptualization of social groups influences interpretation of the pronoun we. Sixty-four 2- and 4-year-olds (N = 29 female, 50 White-identifying) viewed scenarios in which it was ambiguous how many puppets performed an activity together. When asked who performed the activity, a speaker puppet responded, "We did!" In one condition, the speaker was near one and distant from another puppet, implying a dyadic interpretation of we. In another condition, the speaker was distant from both, thus pulling for a group interpretation. In the former condition, 2- and 4-year-olds favored the dyadic interpretation. In the latter condition, only 4-year-olds favored the group interpretation. Age-related conceptual development "expands" the set of conceivable plural person referents.

From what I want to do to what we decided to do: 5-year-olds, but not 3-year-olds, honor their agreements with peers.

Sometimes we have a personal preference but we agree with others to follow a different course of action. In this study, 3- and 5-year-old children (N = 160) expressed a preference for playing a game one way and were then confronted with peers who expressed a different preference. The experimenter then either got the participants to agree with the peers explicitly or just shrugged her shoulders and moved on. The children were then left alone to play the game unobserved. Only the older children stuck to their agreement to play the game as the peers wished. These results suggest that by 5 years of age children's sense of commitment to agreements is strong enough to override their personal preferences.

Three- and 5-year-old children know their current belief might be wrong.

By 4 or 5 years of age, children understand when their own past beliefs were incorrect, or when others' current beliefs are incorrect. In the current study, we asked whether young children understand when their own current belief might be incorrect. 3- and 5-year old children (N = 77) made a judgment and then experienced a puppet making a judgment about the same situation. Children of both ages rechecked their evidence more often when the puppet disagreed with them than when it agreed with them (and the nature of their rechecking was different in the two conditions as well). These results suggest that already by 3 years of age children understand that they might currently be wrong, and they know that rechecking the evidence can resolve their uncertainty.

Apes reciprocate food positively and negatively.

Reciprocal food exchange is widespread in human societies but not among great apes, who may view food mainly as a target for competition. Understanding the similarities and differences between great apes' and humans' willingness to exchange food is important for our models regarding the origins of uniquely human forms of cooperation. Here, we demonstrate in-kind food exchanges in experimental settings with great apes for the first time. The initial sample consisted of 13 chimpanzees and 5 bonobos in the control phases, and the test phases included 10 chimpanzees and 2 bonobos, compared with a sample of 48 human children aged 4 years. First, we replicated prior findings showing no spontaneous food exchanges in great apes. Second, we discovered that when apes believe that conspecifics have 'intentionally' transferred food to them, positive reciprocal food exchanges (food-for-food) are not only possible but reach the same levels as in young children (approx. 75-80%). Third, we found that great apes engage in negative reciprocal food exchanges (no-food for no-food) but to a lower extent than children. This provides evidence for reciprocal food exchange in great apes in experimental settings and suggests that while a potential mechanism of fostering cooperation (via positive reciprocal exchanges) may be shared across species, a stabilizing mechanism (via negative reciprocity) is not.

Social cognition and metacognition in great apes: a theory.

Twenty-five years ago, at the founding of this journal, there existed only a few conflicting findings about great apes' social-cognitive skills (theory of mind). In the 2 ½ decades since, we have discovered that great apes understand the goals, intentions, perceptions, and knowledge of others, and they use this knowledge to their advantage in competitive interactions. Twenty-five years ago there existed basically no studies on great apes' metacognitive skills. In the 2 ½ decades since, we have discovered that great apes monitor their uncertainty and base their decisions on that, or else decide to gather more information to make better decisions. The current paper reviews the past 25 years of research on great ape social cognition and metacognition and proposes a theory about how the two are evolutionarily related.

Evidence for a developmental shift in the motivation underlying helping in early childhood.

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.

Five-year-old children show cooperative preferences for faces with white sclera.

The cooperative eye hypothesis posits that human eye morphology evolved to facilitate cooperation. Although it is known that young children prefer stimuli with eyes that contain white sclera, it is unknown whether white sclera influences children's perception of a partner's cooperativeness specifically. In the current studies, we used an online methodology to present 5-year-old children with moving three-dimensional face models in which facial morphology was manipulated. Children found "alien" faces with human eyes more cooperative than faces with dark sclera (Study 2) but not faces with enlarged irises (Study 1). For more human-like faces (Study 3), children found human eyes more cooperative than either enlarged irises or dark sclera and found faces with enlarged irises cuter (but not more cooperative) than eyes with dark sclera. Together, these results provide strong support for the cooperative eye hypothesis.

Children's consideration of collaboration and merit when making sharing decisions in private.

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.

Great apes and human children rationally monitor their decisions.

Several species can detect when they are uncertain about what decision to make-revealed by opting out of the choice, or by seeking more information before deciding. However, we do not know whether any nonhuman animals recognize when they need more information to make a decision because new evidence contradicts an already-formed belief. Here, we explore this ability in great apes and human children. First, we show that after great apes saw new evidence contradicting their belief about which of two rewards was greater, they stopped to recheck the evidence for their belief before deciding. This indicates the ability to keep track of the reasons for their decisions, or 'rational monitoring' of the decision-making process. Children did the same at 5 years of age, but not at 3 years. In a second study, participants formed a belief about a reward's location, but then a social partner contradicted them, by picking the opposite location. This time even 3-year-old children rechecked the evidence, while apes ignored the disagreement. While apes were sensitive only to the conflict in physical evidence, the youngest children were more sensitive to peer disagreement than conflicting physical evidence.

How fairness and dominance guide young children's bargaining decisions.

Reaching agreements in conflicts is an important developmental challenge. Here, German 5-year-olds (N = 284, 49% female, mostly White, mixed socioeconomic backgrounds; data collection: June 2016-November 2017) faced repeated face-to-face bargaining problems in which they chose between fair and unfair reward divisions. Across three studies, children mostly settled on fair divisions. However, dominant children tended to benefit more from bargaining outcomes (in Study 1 and 2 but not Study 3) and children mostly failed to use leverage to enforce fairness. Communication analyses revealed that children giving orders to their partner had a bargaining advantage and that children provided and responded to fairness reasons. These findings indicate that fairness concerns and dominance are both key factors that shape young children's bargaining decisions.

Disagreement, justification, and equitable moral judgments: A brief training study.

Although theorists agree that social interactions play a major role in moral development, previous research has not experimentally assessed how specific features of social interactions affect children's moral judgments and reasoning. The current study assessed two features: disagreement and justification. In a brief training phase, children aged 4-5.5 years (N = 129) discussed simple moral scenarios about issues of fairness (how to allocate things between individuals) with a puppet who, in a between-participants factorial design, either agreed or disagreed with the children's ideas and either asked or did not ask the children to justify their ideas. Children then responded to another set of moral scenarios in a test phase that was the same for all children. Children in the "agree and do not justify" baseline condition showed an inflexible equality bias (preferring only equal allocations regardless of context), but children who had experiences of disagreement or experiences of being asked to justify themselves shifted toward making equitable decisions based on common ground norms and values. Furthermore, false belief competence was related to children's decisions and justifications. These findings support the classic Piagetian hypothesis that social interactions are a catalyst of cognitive disequilibrium and moral development.

Effects of "we"-framing on young children's commitment, sharing, and helping.

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.

Young children spontaneously recreate core properties of language in a new modality.

How the world's 6,000+ natural languages have arisen is mostly unknown. Yet, new sign languages have emerged recently among deaf people brought together in a community, offering insights into the dynamics of language evolution. However, documenting the emergence of these languages has mostly consisted of studying the end product; the process by which ad hoc signs are transformed into a structured communication system has not been directly observed. Here we show how young children create new communication systems that exhibit core features of natural languages in less than 30 min. In a controlled setting, we blocked the possibility of using spoken language. In order to communicate novel messages, including abstract concepts, dyads of children spontaneously created novel gestural signs. Over usage, these signs became increasingly arbitrary and conventionalized. When confronted with the need to communicate more complex meanings, children began to grammatically structure their gestures. Together with previous work, these results suggest that children have the basic skills necessary, not only to acquire a natural language, but also to spontaneously create a new one. The speed with which children create these structured systems has profound implications for theorizing about language evolution, a process which is generally thought to span across many generations, if not millennia.

The Development of the Liking Gap: Children Older Than 5 Years Think That Partners Evaluate Them Less Positively Than They Evaluate Their Partners.

After two strangers have briefly interacted with one another, both believe that they like their partner more than their partner likes them. A plausible explanation for this liking gap is that people are constantly worrying about how others are evaluating them. If so, one would expect the liking gap to emerge in young children as they become more concerned with their reputations and the impression they make on other people. The current study (N = 241 U.S. children; age range = 4-11 years) supported this hypothesis, showing a liking gap beginning when children were 5 years old, the age at which they first become concerned with other people's evaluations of them. Moreover, the liking gap became more pronounced as children got older. These findings provide the first developmental description of the liking gap and support the hypothesis that this phenomenon is related to individuals' concerns for how others evaluate them.

Toddlers Prefer Adults as Informants: 2- and 3-Year-Olds' Use of and Attention to Pointing Gestures From Peer and Adult Partners.

Two- and 3-year-old children (N = 96) were tested in an object-choice task with video presentations of peer and adult partners. An immersive, semi-interactive procedure enabled both the close matching of adult and peer conditions and the combination of participants' choice behavior with looking time measures. Children were more likely to use information provided by adults. As the effect was more pronounced in the younger age-group, the observed bias may fade during toddlerhood. As there were no differences in children's propensity to follow peer and adult gestures with their gaze, these findings provide some of the earliest evidence to date that young children take an interlocutor's age into account when judging ostensively communicated testimony.

Common knowledge that help is needed increases helping behavior in children.

Although there is considerable evidence that at least some helping behavior is motivated by genuine concern for others' well-being, sometimes we also help solely out of a sense of obligation to the persons in need. Our sense of obligation to help may be particularly strong when there is common knowledge between the helper and the helpee that the helpee needs help. To test whether children's helping behavior is affected by having common knowledge with the recipient about the recipient's need, 6-year-olds faced a dilemma: They could either collect stickers or help an experimenter. Children were more likely to help when they and the experimenter had common knowledge about the experimenter's plight (because they heard it together) than when they each had private knowledge about it (because they heard it individually). These results suggest that already in young children common knowledge can heighten the sense of obligation to help others in need.

How children come to understand false beliefs: A shared intentionality account.

To predict and explain the behavior of others, one must understand that their actions are determined not by reality but by their beliefs about reality. Classically, children come to understand beliefs, including false beliefs, at about 4-5 y of age, but recent studies using different response measures suggest that even infants (and apes!) have some skills as well. Resolving this discrepancy is not possible with current theories based on individual cognition. Instead, what is needed is an account recognizing that the key processes in constructing an understanding of belief are social and mental coordination with other persons and their (sometimes conflicting) perspectives. Engaging in such social and mental coordination involves species-unique skills and motivations of shared intentionality, especially as they are manifest in joint attention and linguistic communication, as well as sophisticated skills of executive function to coordinate the different perspectives involved. This shared intentionality account accords well with documented differences in the cognitive capacities of great apes and human children, and it explains why infants and apes pass some versions of false-belief tasks whereas only older children pass others.

Knowledge-by-acquaintance before propositional knowledge/belief.

More basic than the authors' distinction between knowing and believing is a distinction between knowledge-by-acquaintance (I know John Smith) and propositional knowledge/belief (I know/believe that John Smith lives in Durham). This distinction provides a better account of both the comparative and developmental data.

Learning Novel Skills From Iconic Gestures: A Developmental and Evolutionary Perspective.

Cumulative cultural learning has been argued to rely on high-fidelity copying of other individuals' actions. Iconic gestures of actions have no physical effect on objects in the world but merely represent actions that would have an effect. Learning from iconic gestures thus requires paying close attention to the teacher's precise bodily movements-a prerequisite for high-fidelity copying. In three studies, we investigated whether 2- and 3-year-old children (N = 122) and great apes (N = 36) learn novel skills from iconic gestures. When faced with a novel apparatus, participants watched an experimenter perform either an iconic gesture depicting the action necessary to open the apparatus or a gesture depicting a different action. Children, but not great apes, profited from iconic gestures, with older children doing so to a larger extent. These results suggest that high-fidelity copying abilities are firmly in place in humans by at least 3 years of age.