Moral views about what is right, wrong, good, and bad change across the lifespan and across history. Infants who hit, bite, or kick their caregivers typically grow into children who condemn most forms of violence. Societies that once accepted slavery and torture now prohibit both, and their values keep changing as youth develop moral views that challenge those of older generations. Explaining how morality develops across the lifespan—along universal or unique trajectories—is the task of research on moral development.

History

Since antiquity, many thinkers have considered whether morality stems from nature or nurture: Is morality hardwired into our genes by natural selection, or is it learned from our experiences [see Cognitive Development]? Some theories focus on nature, some focus on nurture, and, increasingly, many focus on both. Even contemporary nativist accounts—which propose that an innate moral sense evolved in humans to facilitate large-scale cooperation—also reserve an elaborative role for cultural learning (Haidt, 2012; Hamlin, 2013). And whereas the behaviorists of the 20th century believed that experiential conditioning could explain all moral tendencies, today’s socialization theories are not concerned with rebutting nativism but with showing how parents and other socialization agents lead children to adopt their cultural values (Grusec et al., 2014).

When comparing moral views across cultures, the innate components are sometimes put forward to explain universal similarities in moral development, with the learned components accounting for cultural variability. Nativist and socialization theories, however, have not typically tried to explain why new generations sometimes reject the moral views of older generations or why moral views have changed across history.

In contrast, constructivist theories have been less interested in determining which parts of morality are innate and which are learned. These approaches treat morality as the product of minds working actively to make sense of their reciprocal interactions with their social worlds. Early constructivist theories proposed that young children go through a stage in which they confuse morality and convention (Kohlberg, 1971; Piaget, 1932), a claim challenged by later constructivist theories (Turiel, 2002). Despite such differences, constructivists share the idea that children develop moral views that are neither preprogrammed from birth nor copied from their parents.

Core concepts

Defining morality

Most definitions of morality include concerns with how we ought to treat each other—concerns with others’ welfare, rights, justice, and fairness—and the reasoning, judgments, emotions, and actions that reflect those concerns (Haidt, 2012; Killen & Smetana, 2015) [see Morality; Ownership]. Most theories also hold that children and adults make judgments based on other normative concerns, for instance, with authorities, loyalty, or purity, whether they call these additional concerns “moral,” “conventional,” or something else [see Normativity]. Regardless of how one defines the word “morality,” people everywhere care about the question that also animates much research on moral development: How do people form their views about how they ought to treat others?

Research on moral development can be split into three ontogenetic phases, relative to when children show clear signs of morality.

Precursors to morality

One of the earliest developing morally relevant precursors is infants’ responsiveness to others’ distress. In the hours after birth, newborns cry more when they hear another newborn cry, and concerns with others’ distress grow over the first two years of life (Hoffman, 2000; Roth-Hanania et al., 2011). By their second birthday, most children sometimes try to comfort others in distress.

Another relevant precursor is infants’ social preferences (Hamlin, 2013). After observing puppets helping and hindering others, infants have shown significant preferences for looking or reaching toward the prosocial puppets. Although scholars debate how these preferences relate to the moral judgments of older children and adults—and even whether the findings on infants’ social preferences are replicable (Lucca et al., 2025)—infants are undeniably attuned to morally laden interactions.

By their first birthday, infants show many everyday actions that impinge on others in morally relevant ways. They help others, but also hit others, at increasing rates, and family members respond to these actions with strong signals of encouragement and disapproval (Dahl et al., 2022; Warneken & Tomasello, 2009). In these early interactions, infants and toddlers cooperate, clash, and negotiate with peers, siblings, and parents.

Emergence of morality

By their third birthday, children’s judgments, reasoning, emotions, and actions reveal a moral perspective on their own and others’ actions. Children often protest when one puppet destroys another’s property, try to distribute resources fairly among others, show guilt over their own misbehavior, judge that hitting others is wrong, and justify their judgment by explaining that hitting causes harm (McAuliffe et al., 2017; Paulus et al., 2018; Smetana et al., 2018; Tomasello, 2018; Vaish, 2018). Because they base their judgments on moral concerns with welfare and rights, and not merely on commands from authorities, 3- to 4-year-old children typically say that hitting would be wrong in a context that had no rules against it, even if adults had given permission to hit. Thus, by the preschool years, children demonstrate a moral sense that lets them distinguish morality from convention and disagree with authorities and prevailing norms.

Developments in morality

Moral views keep changing. As children become adolescents and adolescents become adults, they develop nuanced views on social inequality, climate change, and other issues beyond the grasp of preschoolers (Killen & Smetana, 2015). These developments show both similarities and differences across cultures; for instance, although most children everywhere think unprovoked violence is wrong (Yazdi et al., 2026), they differ in their views about whether it is okay to use force to defend one’s honor or when ordered by an authority (Fiske & Rai, 2014).

One source of developmental change is the acquisition of new moral and nonmoral concerns, for instance, with political rights or divine commands (Helwig & To, 2017; Srinivasan et al., 2019). A second source of change is in the ability to coordinate competing considerations; from preschool age and into later childhood, children appear to become more open to making exceptions to general principles such as by judging that it is sometimes okay to distribute resources unequally or to refrain from helping a person in need (Killen et al., 2018; Nucci et al., 2017). A third source of change is the acquisition of new knowledge (Wainryb, 1991) that allows children to apply their moral concerns in new ways. For example, with age, youth can become more aware of structural sources of inequalities, leading them to be more supportive of economic redistribution (Elenbaas et al., 2020; Hussak & Cimpian, 2018). Each of these sources of moral change occurs across the lifespan and drives moral changes that can either align with or challenge dominant views.

Questions, controversies, and new developments

Research on morality and moral development continues to grapple with several big, open questions. One is about the relation between reason and emotion: Are our developing moral judgments rooted in reasons, or are they dominated by emotions? Much research on the moral development of children and youth has granted a central role to moral reasoning (Turiel, 2002). By contrast, leading scholars in research on morality in infancy and adulthood have treated reasoning as peripheral to moral judgments, proposing instead that moral judgments arise from automatic and affective intuitions (Haidt, 2012; Hamlin, 2013). Resolving this tension will require researchers to integrate across modalities and phases of moral development, for instance, by jointly studying emotional reactions and reasoning from childhood to adulthood.

A second big question is whether moral development proceeds in broadly similar or different ways across cultures. All communities share basic moral concerns with protecting and promoting others’ welfare. Within and between those communities, people also disagree—among other things—about which creatures have which moral standings, which authorities to obey, and which groups to be loyal to. Some researchers have proposed that different communities have fundamentally distinct moralities, whereas others have characterized all moralities as grounded in the same basic concerns (Haidt, 2012; Shweder et al., 1997; Turiel, 2002). To test these competing visions, and explain how children across the world develop a moral sense, it will be necessary to sample from a broader range of communities and—as importantly—to move beyond the description of cultural variabilities and similarities to research that advances and tests explanations of how children acquire their distinct moral views (Blake et al., 2015; see WEIRD).

The science of moral development has exciting opportunities for growth. One area is the integration of separated traditions. As noted above, this can happen within psychology by integrating research on children’s moral development with research on adult moral psychology to better capture moral development across the lifespan. It can also happen across scientific fields by integrating psychological research on moral change in individuals with historical research on moral change in societies (Muthukrishna et al., 2021). The individuals who change must be the ones to make their society change, yet these two levels of analysis have mostly been pursued independently.

Ultimately, a more integrated understanding of moral development can help us make sense of one of the great puzzles of human nature: Why do we all share a moral sense, when moral views vary across individuals, societies, and generations?

Broader connections

Because morality requires a capacity to care about, understand, and connect with others, moral development depends on social, emotional, and cognitive development; it involves empathy as well as theory of mind and shared intentionality [see Cognitive Development; Shared Intentionality; Theory of Mind]. In a conceptual hierarchy, morality sits below normativity, which usually includes conventional, religious, prudential, and other nonmoral concerns, and above specific moral phenomena such as ownership [see Normativity; Ownership]. Crossing levels of analysis, the moral development of individuals intersects with larger changes and continuities, at sociological, historical, and evolutionary levels, that link the moralities of the present to the moralities of the past and future.

Acknowledgments

The authors would like to thank Kiley Hamlin, Judi Smetana, Amrisha Vaish, and two anonymous reviewers for comments on an earlier version of this entry.

Further reading

• Smetana, J. G., & Yoo, H. N. (2022). Development and variations in moral and social-conventional judgments: A social domain theory approach. In M. Killen & J. G. Smetana (Eds.), Handbook of moral development (3rd ed.). Routledge.

• Tomasello, M. (2018). The normative turn in early moral development. Human Development, 61, 248–263. https://doi.org/10.1159/000492802

• Woo, B. M., Tan, E., & Hamlin, J. K. (2023). Human morality is based on an early-emerging moral core. Annual Review of Developmental Psychology, 4, 41–61. https://doi.org/10.1146/annurev-devpsych-121020-023312