Babies can distinguish between people based on their actions toward a third party, U.S. researchers say.

"Infants prefer an individual who helps another to one who hinders another, prefer a helping individual to a neutral individual, and prefer a neutral individual to a hindering individual," the Yale University psychology researchers report in the edition of Nature to be published Thursday.

Young babies choose characters who help others over those who hinder them, a U.S. study shows.
(CBC)

"The findings reported here constitute the first evidence that young infants' social preferences are influenced by others' behaviour towards unrelated third parties," they say. The findings show humans make social evaluations at a much younger age than previously thought.

Kiley Hamlin and colleagues tested groups of babies, either six or 10 months old, to see how they evaluated individuals based on how the individuals acted toward others.

They showed the babies a "climber," made of wood with large eyes glued on, trying to get up a hill. After two failures, another character — either a helper or a hinderer — would appear, and either push the climber up or down the hill.

The babies were then encouraged to reach for (choose) one or the other character. Of the 28 babies, 26 — all 12 younger children and 14 of 16 in the older group — reached for the helper, "indicating that they held distinct impressions of the two characters on the basis of their actions towards the climber," the study said.

Further experiments were used to ensure the babies weren't simply responding to perceptual differences but were making a social judgment, and to distinguish between a neutral character and a helper or hinderer.

The authors speculated that the ability to evaluate individuals by their social actions could be the basis of moral judgment.

The babies were unaffected, unrelated and therefore unbiased parties, yet they made a judgment about a social act, the study authors say. Because the babies are not involved with the situation, their judgment includes a crucial component of a genuine moral judgment, they say.

"The ability to judge differentially those who perform positive and negative social acts may form an essential basis for any system that will eventually contain more abstract concepts of right and wrong," the authors say.