From an evolutionary perspective, morality is a form of cooperation. Cooperation requires individuals either to suppress their own selfinterest or to equate it with that of others. We review recent research on the origins of human morality, both phylogenetic (research with apes) and ontogenetic (research with children). For both time frames we propose a two-step sequence: first a second-personal morality in which individuals are sympathetic or fair to particular others, and second an agent-neutral morality in which individuals follow and enforce group-wide social norms. Human morality arose evolutionarily as a set of skills and motives for cooperating with others, and the ontogeny of these skills and motives unfolds in part naturally and in part as a result of sociocultural contexts and interactions.

In most research on the early ontogeny of sympathy, young children are presented with an overtly distressed person and their responses are observed. In the current study, the authors asked whether young children could also sympathize with a person to whom something negative had happened but who was expressing no emotion at all. They showed 18- and 25-month-olds an adult either harming another adult by destroying or taking away her possessions (harm condition) or else doing something similar that did not harm her (neutral condition). The "victim" expressed no emotions in either condition. Nevertheless, in the harm as compared with the neutral condition, children showed more concern and subsequent prosocial behavior toward the victim. Moreover, children's concerned looks during the harmful event were positively correlated with their subsequent prosocial behavior. Very young children can sympathize with a victim even in the absence of overt emotional signals, possibly by some form of affective perspective taking.

Young children help other people, but it is not clear why. In the current study, we found that 2-year-old children’s sympathetic arousal, as measured by relative changes in pupil dilation, is similar when they themselves help a person and when they see that person being helped by a third party (and sympathetic arousal in both cases is different from that when the person is not being helped at all). These results demonstrate that the intrinsic motivation for young children’s helping behavior does not require that they perform the behavior themselves and thus “get credit” for it, but rather requires only that the other person be helped. Thus, from an early age, humans seem to have genuine concern for the welfare of others.

Two studies investigated whether young children are selectively prosocial toward others, based on the others' moral behaviors. In Study 1 (N = 54), 3-year-olds watched 1 adult (the actor) harming or helping another adult. Children subsequently helped the harmful actor less often than a third (previously neutral) adult, but helped the helpful and neutral adults equally often. In Study 2 (N = 36), 3-year-olds helped an actor who intended but failed to harm another adult less often than a neutral adult, but helped an accidentally harmful and a neutral adult equally often. Children's prosocial behavior was thus mediated by the intentions behind the actor's moral behavior, irrespective of outcome. Children thus selectively avoid helping those who cause--or even intend to cause--others harm.

We investigated children's moral behaviour in situations in which a third party was harmed (the test case for possession of agent-neutral moral norms). A 3-year-old and two puppets each created a picture or clay sculpture, after which one puppet left the room. In the Harm condition, the remaining (actor) puppet then destroyed the absent (recipient) puppet's picture or sculpture. In a Control condition, the actor acted similarly but in a way that did not harm the recipient. Children protested during the actor's actions, and, upon the recipient's return, tattled on the actor and behaved prosocially towards the recipient more in the Harm than in the Control condition. This is the first study to show that children as young as 3 years of age actively intervene in third-party moral transgressions.