Babies Can Tell Fairness From Unfairness By 15 Months

Babies as young as 15 months have a basic sense of fairness and know the difference between equal and unequal sharing, according to a new study.

While previous studies reveal that 2-year-old children show a certain level of altruism by helping one another, and by 6 or 7 display a sense of fairness, researchers suspected those qualities could be apparent at an even younger age.

Jessica Sommerville, an associate professor of psychology at the University of Washington, said:

“Our findings show that these norms of fairness and altruism are more rapidly acquired than we thought. These results also show a connection between fairness and altruism in infants, such that babies who were more sensitive to the fair distribution of food were also more likely to share their preferred toy.”

Cooperative Behavior

Babies around 15 months old begin to show cooperative behaviors, such as spontaneously helping others.

“We suspected that fairness and altruism might also be apparent then, which could indicate the earliest emergence of fairness,” Sommerville says.

For the study, a 15-month old baby sat on a parent’s lap and watched two short videos of experimenters acting out a sharing task. In one video an experimenter holding a bowl of crackers distributed the food between two other experimenters.

They did the food allocation twice, once with an equal allotment of crackers and the other with one recipient getting more crackers.

The second movie had the same plot, but the experimenters used a pitcher of milk instead of crackers.

Then the experimenters measured as the babies, 47 in all who were tested individually, looked at the food distributions. According to a phenomenon called “violation of expectancy,” babies pay more attention when they are surprised.

Similarly, the babies spent more time looking if one recipient got more food than the other.

“The infants expected an equal and fair distribution of food, and they were surprised to see one person given more crackers or milk than the other,” Sommerville says.

Toy Sharing

To discover if the babies’ sense of fairness related to their own willingness to share, the researchers did a second task in which a baby could choose between two toys: a simple LEGO block or a more elaborate LEGO doll.

Whichever toy the babies chose, the researchers labeled as the infant’s preferred toy.

Then an experimenter who the babies had not seen before gestured toward the toys and asked, “Can I have one?” In response, one third of the infants shared their preferred toy and another third shared their non-preferred toy.

The other third of infants did not share either toy, which might be because they were nervous around a stranger or were unmotivated to share.

“The results of the sharing experiment show that early in life there are individual differences in altruism,” Sommerville says.

Comparing the toy-sharing task and the food-distribution task results, the researchers found that 92 percent of the babies who shared their preferred toy, the “altruistic sharers”, spent more time looking at the unequal distributions of food.

In contrast, 86 percent of the babies who shared their less-preferred toy, the “selfish sharers,” were more surprised, and paid more attention, when there was a fair division of food.

“The altruistic sharers were really sensitive to the violation of fairness in the food task,” Sommerville says.

Meanwhile, the selfish sharers showed an almost opposite effect.


Schmidt MFH, Sommerville JA (2011)
Fairness Expectations and Altruistic Sharing in 15-Month-Old Human Infants.
PLoS ONE 6(10): e23223. doi:10.1371/journal.pone.0023223

Image: By Kozuch CC BY-SA 3.0

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