Babies as young as 15 months old are more likely to help people who share the same ethnicity, a phenomenon known as in-group bias, or favouring people who have the same characteristics as oneself, scientists say.
The idea for the research came when a University of Washington researcher who studies how children develop social behaviours like kindness and generosity noticed something odd.
The 15-month-old infants in her experiments seemed to be playing favourites among the researchers on her team, being more inclined to share toys or play with some researchers than others.
"It's not like one experimenter was nicer or friendlier to the babies - we control for factors like that," said Jessica Sommerville, a UW associate professor of psychology.
She took a closer look at the data and realised that the babies were more likely to help researchers who shared the same ethnicity.
"At the time, about half of the research assistants in my lab were Asian-American and the other half were Caucasian, and most of the babies in our experiments are Caucasian. We know that by preschool, children show in-group bias concerning race, but results in infants have been mixed," she said.
She and her research team designed a new experiment to test how race and fairness - a social tendency that infants appear to notice - influence babies' selection of a playmate.
The findings, published in the journal Frontiers in Psychology, show that 15-month-old babies value a person's fairness - whether or not an experimenter equally distributes toys - unless babies see that the experimenter unevenly distributed toys in a way that benefits a person of the same race as the infant.
In the study, 40 white 15-month-old babies sat on their parents' laps while watching two white experimenters divide toys between recipients.
One experimenter divided the toys equally, and the other experimenter divided the toys unequally.
Later, when the babies had a chance to choose who to play with, 70 per cent of the time infants preferred the experimenter who distributed the toys fairly.
This suggests that when individuals are the same race as the infant, babies favour fair over unfair individuals as playmates.
In a second experiment, 80 white 15-month-old infants saw a fair and an unfair experimenter distribute toys to a white and to an Asian recipient.
Half the babies saw the unfair experimenter give more to the Asian recipient; and the other half of babies saw the experimenter give more to the white recipient.
When it came time to decide a playmate, infants seemed more tolerant of unfairness when the white recipient benefited from it.
"If all babies care about is fairness, then they would always pick the fair distributor, but we're also seeing that they're interested in consequences for their own group members," Sommerville said.