(HealthNewsDigest.com) - New Haven, Conn.- Infants as young as nine months old prefer individuals who punish those who are not like them, and this seemingly innate mean streak grows stronger in the next five months of life, a study by researchers at Yale University has found.

Babies, like adults, prefer individuals who like the same things they do. A new study reports that they want individuals who share their tastes to be treated well by others, but want those whose tastes differ from their own to be treated badly. The study of 200 nine- and 14-month-old infants was published online in Psychological Science, a journal of the Association for Psychological Science.

Psychologists have long known that people tend to like others who are like themselves. Social bonds form more easily among those who look the same, act the same, have the same interests, and are members of the same group. We deem people who are like ourselves to be more just, intelligent, and trustworthy, while we attribute negative qualities to those who are different from us.

But when do these attitudes arise?

In recent years, Yale's Karen Wynn, professor of psychology and cognitive science, has shown that even before their first birthday, infants too prefer individuals who share their own tastes in food or clothes. Wynn's research team introduced babies to two hand puppets that had expressed contrasting preferences (for example, one preferring green beans to graham crackers, the other preferring the crackers to the beans). Babies who themselves preferred the crackers were much more likely to reach for puppets that liked crackers.

Wynn and lead author, Kiley Hamlin, now of the University of British Columbia, wanted to know if infants' preference for similar individuals meant that they hold negative attitudes toward those who are unlike themselves. In the new study, the researchers introduced babies to a puppet with the same food preference as the baby and to a puppet with the opposite preference. They then introduced two new puppets: One was helpful and retrieved a dropped rubber ball. The other was mean and took the ball away.

As expected babies of both ages preferred the helper over the meanies when the puppet being assisted liked the same food they did. But the next finding surprised the researchers: When the puppet that dropped the ball did not share the babies' taste in food, the infants preferred the mean puppet to the helper. In other words: Babies prefer someone who is nice to an individual similar to themselves, but they also prefer someone who is mean to a dissimilar individual.

However, Wynn, said, the results do not necessarily show that babies are born with a mean streak.

"We were surprised - and more than a little chagrined - to find that babies actively prefer individuals who mistreat someone whose tastes differ from theirs," Wynn said. "But while our findings show that we may be built to dislike differences, we are also built to like similarities - and humans all around the world are similar in a multitude of ways."

It may be that the more similarities babies - and adults - recognize between themselves and others, the less they will want to see those others harmed, said Wynn. When no other information is given, babies appear to dislike someone who differs from them. Their attitude might change if they had more information, she said.

"We don't want to be too quick to generalize. My husband hates cheese, and I love cheese, and we get along just fine," Wynn said. "The interesting question to me is what kinds of information allow us to transcend superficial differences and build on our commonalities."

Additional authors on the study are Neha Mahajan, and Zoe Liberman. The research was supported by the National Science Foundation and the National Institutes of Health.

60 Minutes Video

http://www.cbsnews.com/video/watch/?id=50135408n 

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