Not playing fair is a common squabble in the sandbox.

kids squabbling over a toy in a playground sandbox

Stanford scholar Lin Bian looks at how infants and toddlers rank moral principles of fairness and group loyalty. (Image credit: Getty Images)

Now, new research by a Stanford scholar provides an explanation for how infants and toddlers perceive these playground disputes, like how toys or cookies should be divvied up.

Lin Bian, a postdoctoral scholar of psychology at Stanford University, is lead author of a new study published Feb. 26 in Proceedings of the National Academy of Sciences that examines how infants and toddlers rank fairness versus supporting their own social group, which the researchers call ingroup support.

“Our work provides new evidence that infants’ reasoning is guided by principles of fairness and ingroup support and, for the first time, demonstrates that infants also follow a context-sensitive ordering of these principles,” Bian said. “When there is enough to go around, fairness is expected to prevail; when there is not enough to go around, however, ingroup support is expected to prevail.”

Favoritism versus fairness

While recent research has shown that infants possess an understanding of fairness and loyalty, never have psychologists pitted the two moral principles against each other, said Bian, who is currently working with Stanford psychology Professor Ellen Markman.

portrait of Lin Bian

Postdoctoral scholar Lin Bian is working with Stanford psychology Professor Ellen Markman. (Image credit: Yibing Bian)

To test how infants and toddlers respond when fairness and favoritism are put in opposition, Bian and her co-authors from the University of Illinois at Urbana-Champaign showed 1.5- and 2.5-year-olds various scenarios of resources being distributed between two social groups.

In each setup, infants and toddlers watched live interactions between three puppets from two animal categories.

In the first set of experiments, infants watched one puppet present a tray of identical cookies to the other two puppets, one from their own social group and another from outside the group (Bian used a monkey and a giraffe puppet). Bian found that when there were more cookies than puppets, infants expected all the puppets – regardless of species – to receive equal cookies.

However, when there were just enough cookies for the group, infants expected the distributing puppet to give all the cookies to their own social group. Group loyalty overrode fairness, said Bian, who noted that infants noticed when the distributor gave any of the cookies to the outgroup puppet.

The third experiment tested the same question with toddlers. Using toys instead of cookies, the group found that toddlers reacted much the same way as infants: They also expected fairness when there were as many toys as puppets but expected ingroup support when there were fewer toys than puppets. These findings show that beginning early in life, toddlers already have a sense of fairness.

First draft of morality

The study also offers a new understanding of what social and evolutionary psychologists call the “first draft” of morality.

Some scholars have suggested that over time, humans have gradually evolved a capacity for moral reasoning connected to their survival. This includes fairness and ingroup support, but also other expectations like avoiding harming others and deferring to authority.

“Our findings indicate that by the second year of life, children are already capable of sophisticated moral computations that take many factors into account,” Bian said. “This suggests that how we as humans reason about what is right and wrong is in part an evolved adaptation.”

On the practical side – like negotiating sandbox politics – Bian hopes that these findings can help parents understand what might have caused these disagreements to begin with.

Other coauthors include Stephanie Sloane and Renée Baillargeon of the University of Illinois Urbana-Champaign.

Media Contacts

Melissa De Witte, Stanford News Service: (650) 725-9281,