Human cooperation is a key driving force behind the evolutionary success of our hominin lineage. At the proximate level, biologists and social scientists have identified other-regarding preferences – such as fairness based on egalitarian motives, and altruism – as likely candidates for fostering large-scale cooperation. A critical question concerns the ontogenetic origins of these constituents of cooperative behavior, as well as whether they emerge independently or in an interrelated fashion. The answer to this question will shed light on the interdisciplinary debate regarding the significance of such preferences for explaining how humans become such cooperative beings. We investigated 15-month-old infants' sensitivity to fairness, and their altruistic behavior, assessed via infants' reactions to a third-party resource distribution task, and via a sharing task. Our results challenge current models of the development of fairness and altruism in two ways. First, in contrast to past work suggesting that fairness and altruism may not emerge until early to mid-childhood, 15-month-old infants are sensitive to fairness and can engage in altruistic sharing. Second, infants' degree of sensitivity to fairness as a third-party observer was related to whether they shared toys altruistically or selfishly, indicating that moral evaluations and prosocial behavior are heavily interconnected from early in development. Our results present the first evidence that the roots of a basic sense of fairness and altruism can be found in infancy, and that these other-regarding preferences develop in a parallel and interwoven fashion. These findings support arguments for an evolutionary basis – most likely in dialectical manner including both biological and cultural mechanisms – of human egalitarianism given the rapidly developing nature of other-regarding preferences and their role in the evolution of human-specific forms of cooperation. Future work of this kind will help determine to what extent uniquely human sociality and morality depend on other-regarding preferences emerging early in life.

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Recent research has produced new insights into the early development of social cognition and social learning. Even very young children learn and understand social activities as governed by conventional norms that (a) are arbitrary and shared by the community, (b) have normative force and apply to all participants, and (c) are valid in context‐relative ways. Importantly, such understanding is revealed both in the fact that children themselves follow the norms, and in the fact that they actively enforce them toward third parties. Human social cognition thus has a fundamental normative dimension that begins early. This norm psychology plausibly evolved due to its role in stabilizing group coordination and cooperation, and is one of the foundations of what is uniquely human social learning and culture.

Recent work provides evidence that expectations regarding a fair (i.e., equal) distribution of goods and resources arise sometime in the second year of life. To investigate the developmental trajectory of fairness expectations, and their potential relation to prosocial behavior, infants participated in a violation‐of‐expectancy (VOE) paradigm designed to assess expectations regarding how resources are typically distributed, and in a sharing task, an informational helping task, and an instrumental helping task. Infants’ expectations regarding resource distribution showed age‐related changes between 12 and 15 months, with only 15‐month‐old infants showing greater attention to unfair (unequal) over fair (equal) outcomes in the VOE. Individual differences in infants’ sensitivity to unfair outcomes were related to infants’ willingness to share a preferred toy. In contrast, helping behavior was unrelated to infants’ sensitivity to unfair outcomes and did not vary according to whether infants shared a preferred or non‐preferred toy during the sharing task. Our findings suggest a developmental transition in expectations regarding how resources are distributed from 12 to 15 months of age, linked to infants’ sharing behavior, suggesting that such expectations are learned through experience. Our results also contribute to the ongoing discussion regarding how best to assess the construct of prosociality in infancy.

Young children interpret some acts performed by adults as normatively governed, that is, as capable of being performed either rightly or wrongly. In previous experiments, children have made this interpretation when adults introduced them to novel acts with normative language (e.g. 'this is the way it goes'), along with pedagogical cues signaling culturally important information, and with social-pragmatic marking that this action is a token of a familiar type. In the current experiment, we exposed children to novel actions with no normative language, and we systematically varied pedagogical and social-pragmatic cues in an attempt to identify which of them, if either, would lead children to normative interpretations. We found that young 3-year-old children inferred normativity without any normative language and without any pedagogical cues. The only cue they used was adult social-pragmatic marking of the action as familiar, as if it were a token of a well-known type (as opposed to performing it, as if inventing it on the spot). These results suggest that - in the absence of explicit normative language - young children interpret adult actions as normatively governed based mainly on the intentionality (perhaps signaling conventionality) with which they are performed.

a b s t r a c tRecent research on distributive justice suggests that young children prefer equal distributions. But sometimes unequal distributions are justified, such as when some individuals deserve more than others based on merit, need, or agreed-upon rules. When and how do children start incorporating such factors in their distributive decisions? Three-, 5-, and 8-year-old children (N = 72) had the opportunity to allocate several items to two individuals. One individual was neutral and the other provided a reason why she should be favored. Three of these reasons were legitimate (based on merit, need, or agreed-upon rules) whereas a fourth was idiosyncratic ("I just want more."). We found that with age, children's equality preference diminished and their acceptance of various reasons for privileged treatment increased. It was not until 8 years, however, that they differentiated between legitimate and idiosyncratic reasons for inequality. These findings suggest that children's sense of distributive justice develops from an early equality preference to a more flexible understanding of the basic normative reasons that inequality may, in some cases, be just.

Social norms have played a key role in the evolution of human cooperation, serving to stabilize prosocial and egalitarian behavior despite the self-serving motives of individuals. Young children's behavior mostly conforms to social norms, as they follow adult behavioral directives and instructions. But it turns out that even preschool children also actively enforce social norms on others, often using generic normative language to do so. This behavior is not easily explained by individualistic motives; it is more likely a result of children's growing identification with their cultural group, which leads to prosocial motives for preserving its ways of doing things.

Human social life depends heavily on social norms that prescribe and proscribe specific actions. Typically, young children learn social norms from adult instruction. In the work reported here, we showed that this is not the whole story: Three-year-old children are promiscuous normativists. In other words, they spontaneously inferred the presence of social norms even when an adult had done nothing to indicate such a norm in either language or behavior. And children of this age even went so far as to enforce these self-inferred norms when third parties “broke” them. These results suggest that children do not just passively acquire social norms from adult behavior and instruction; rather, they have a natural and proactive tendency to go from “is” to “ought.” That is, children go from observed actions to prescribed actions and do not perceive them simply as guidelines for their own behavior but rather as objective normative rules applying to everyone equally.