If you bail on an activity with a preschooler, you’d better have a good excuse.

That’s because, according to research published this week in the journal Child Development, children as young as three and a half years old understand and value the obligations that accompany joint commitments. The researchers found that children who abandon a cooperative activity for an apparently selfish reason tend to prompt more resentment from their peers than those who quit the task for another reason.

These findings do not just build on a growing body of research suggesting that the very young possess moral capabilities that are more sophisticated than scientists previously thought. They also suggest that the notion of shared obligation is in some ways fundamental to Homo sapiens, the only known animal to create social institutions.

“The kinds of joint commitments we are seeing here in the three-year-olds can be scaled up into legal contracts, in which we mutually pledge to hold up our end of the bargain,” says Margarita Svetlova, a visiting assistant professor at Duke University, who co-authored the study with colleagues from the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. “If you really want, you could scale it up to the social contract in general.”

Researchers at Max Planck ran an experiment in which 72 same-sex pairs of three-and-a-half-year-olds were asked to complete a task that required two people to pull a rope on an apparatus to retrieve a pair of marbles.

Members of each pair were randomly assigned the role of “subject” and “partner.” The researchers told the subjects that they would be working with the partner to obtain the marbles. But the partners were there to thwart the plan. Some were instructed to quit the task in exchange for an individual reward, so that they would appear selfish to the subject. Others were trained to use the apparatus in a way that didn’t work, so that they would appear incompetent. And for other partners, the machine was rigged so that they would “break” it.

The researchers found that the subjects reacted more strongly when the partner appeared to abandon the task for selfish reasons. When the partner appeared incompetent, the subject would tend to attempt to teach the partner how to pull the rope.

“We were amazed that three-year-olds only blamed their partner if she intentionally broke the rules of the cooperative game,” says Professor Svetlova. “They were fine with it if she was ignorant of the rules, and in fact in this case they taught her the rules.”

The subjects’ responses, when they inferred their partners’ underlying intentions and respond appropriately, are arguably “the kind of reactions that could be expected of a competent moral agent,” note the researchers in their paper.

“The fact that in this study they react differentially depending on why the partner failed in her role shows that they really understand what they are doing,” Svetlova says.

Humans begin cooperating very early in life. Studies indicate that children as young as 14 months of age tend to help strangers fetch objects that are out of reach, remove obstacles, and attempt to correct mistakes. Rewarding or verbally encouraging children doesn’t seem to increase helping behavior, and in some cases, rewarding kids actually decreases their motivation to help again. Many psychologists and biologists see these tendencies as a sign that evolution has endowed us with a predisposition to cooperate.

“We’re really not solitary individuals,” says Felix Warneken, a Harvard psychologist who studies altruism and cooperation in infants and young children but who did not participate in this study. “We depend on each other maybe more than any other species, maybe with the exception of eusocial insects,” like ants and most bees.

Viewed this way, it makes sense that a species as adaptable as our own would evolve an instinctive drive to collaborate. “We can basically survive in any part of the world because we’re able to learn from each other,” says Professor Warneken. “It’s not preprogrammed in us how to find food or how to protect ourselves from weather. This is all something we have to learn from each other.”

“When we run studies like this with chimpanzees,” he adds, “we do not see similar performance.”

The study’s authors also note that these findings may be of some practical use to parents and others who work with preschoolers.

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“One of the lessons for parents is that in many cases you would be a lot better off just letting kids work things out for themselves, even if that doesn’t produce the outcome you yourself would choose for them,” says Svetlova.

“They need to learn the consequences of their actions for their relations with their friends and peers, who, as we show in this study, are perfectly capable of reacting in a morally appropriate way.”