The study was the work of Kiley Hamlin, a graduate student at Yale University in New Haven, Connecticut, and colleagues, and is published in the 22nd November issue of the journal Nature.
The researchers showed that babies aged 6 months and 10 months who observed a puppet show could tell the difference between the helpful and unhelpful character, even though the events did not affect them directly.
After watching the show, the babies showed a preference for the character that helped one of the puppets who was trying to climb a hill, and did not show a preference for the character that behaved unhelpfully by hindering the progress of the climber.
Hamlin said that:
"We knew that babies were socially skilled, but we weren't aware that they were so skilled that they could track people by their behavioural tendencies; how they might treat someone else."
The babies watched a puppet show where a coloured round wooden block with "googly eyes" tried to climb a steep hill with little success. There were two scenes: one where the climber puppet was helped by another "good Samaritan" puppet who gave him a friendly push up the hill, and another where an "evil" puppet shoved the climber down the hill.
After the puppet show that babies were given the opportunity to reach out for either the helpful puppet or the unhelpful puppet. Nearly all the babies reached for the helpful puppet. The researchers said this suggested that at least the babies were able to distinguish between the puppets. They also showed "some tendency towards the positive helper," said Hamlin, who added that:
"We were shocked by the strength of the responses. We thought infants would be sensitive to the behaviour of others, but didn't anticipate the extent of this."
The researchers said the effect was not so strong when they removed the eyes from the puppets, suggesting that the babies identified with them as characters.
They then performed a second experiment where the babies watched another puppet show where the climber appeared to "make friends" with either the helpful or the unhelpful puppet. The older babies spent more time watching the show when the climber approached the unhelpful character, as though this was more surprising to them.
Hamlin and colleagues concluded that: "These findings constitute evidence that preverbal infants assess individuals on the basis of their behaviour towards others. This capacity may serve as the foundation for moral thought and action, and its early developmental emergence supports the view that social evaluation is a biological adaptation."
The researchers said the results suggested that the older babies were able to make sophisticated conclusions about social interactions, attitudes and motives from observing the behaviour of others. While there was a lot of hearsay about parents knowing this, it had never been tested before, they said.
Speculating on their findings, the researchers suggested the ability to choose between "nice" and "nasty" people could be innate. Having a hard wired tendency to favour helpful over unhelpful people could confer positive social advantages to a growing child.
"Just by spending more time with positive people, they might get a different set of learning inputs than if they spent time with negative people, and over time you can see that could have a real influence on their development," said Hamlin.
"Social evaluation by preverbal infants."
J. Kiley Hamlin, Karen Wynn, & Paul Bloom.
Nature 450, 557-559 (22 November 2007)
Written by: Catharine Paddock