A breakthrough study has found that infants as young as 15-months-old are sensitive to fairness and can engage in altruistic sharing, meaning that they were concerned for the well-being of others at their own expense.

Previous research suggested that fairness and altruism may not emerge until early to mid-childhood.

"The current study provides the first evidence that by at least 15 months of age, human infants possess the rudiments of a sense of fairness in that they expect resources to be allocated equally when observing others,” said study author Jessica A. Sommerville from the University of Washington.

Researchers also found that 15-month-old infants had different types of personalities when sharing. Some kids paid more attention to unfairness while others paid more attention to equal sharing and suggested that such individual differences might have deep ontogenetic roots.

Researchers studied 47 babies. They played two types of videos of a person distributing crackers and milk to two people. They studied the reaction of babies in fair and unfair distributions. On average, the babies paid more attention to unequal sharing, but some were more surprised than others.

In a second test about sharing, researchers gave each infant the option to choose among two toys. After selecting a preferred toy, they gave infants the non-preferred toy as well and later asked them to share one of them.

One third of infants shared the preferred toy therefore called "altruistic sharers.” One third shared the non-preferred toy and were called "selfish sharers" and one third did not respond at all.

When the authors compared the sharing results with the video-watching results, they found that 92 percent of babies who shared their preferred toy were also the ones who were shocked by unfairness in the videos and were named "altruistic sharers."

Among those babies that shared the non-preferred toy, 86 percent were also shocked by equal sharing in the video called "selfish sharers."

"Altruists pay attention to normative (moral) issues of fairness, whereas selfish infants are interested in non-moral physical aspects of social interactions,” researchers wrote in the study published on October 7 in the journal Plos ONE.

Researchers believe these results shed light on the interdisciplinary debate for explaining how humans become cooperative beings.