Never has a human population been found that has no racial stereotypes. Not in other cultures or far-flung countries. Nor among tiny tots or people with various psychological conditions.

Until now.

Children with Williams syndrome, a rare genetic disorder that makes them lack normal social anxiety, have no racial biases. They do, however, traffic in gender stereotypes, said study researcher Andreas Meyer-Lindenberg of the University of Heidelberg in Germany.

Normally, children show clear preferences for their own ethnic group by the age of three, if not sooner, other research has shown.

And, indeed, the children in this study without Williams syndrome reliably assigned good traits, such as friendliness, to pictures of people the same race as themselves. When asked something negative, such as "which is the naughty boy," they overwhelmingly pointed to the other race.

Children with Williams syndrome, however, were equally likely to point to the white or black child as naughty or friendly.

While this study was done with white children, other research has shown that blacks and people of other races also think more highly of their own, Meyer-Lindenberg told LiveScience.

Williams syndrome is caused by a gene deletion known to affect the brain as well as other organs. As a result, people with Williams syndrome are "hypersocial," Meyer-Lindenberg told . They do not experience the jitters and inhibitions the rest of us feel.

"The whole concept [of social anxiety] would be foreign to them," he said.

They will put themselves at great peril to help someone and despite their skills at empathy, are unable to process social danger signals. As a result, they are at increased risk for rape and physical attack.

Nature or nurture?

While the first human population to demonstrate race-neutrality is missing critical genes, "we are not saying that this is all biologically-based and you can't do anything about it," Meyer-Lindenberg said.

"Just because there is a genetic way to knock the system out, does not mean the system itself is 100 percent genetic," he said.

The study does show, however, that racism requires social fear. "If social fear was culturally reduced, racial stereotypes could also be reduced," Meyer-Lindenberg said.

Despite their lack of racial bias, children with Williams syndrome hold gender stereotypes just as strongly as normal children, the study found. That is, 99 percent of the 40 children studied pointed to pictures of girls when asked who played with dolls and chose boys when asked, say, who likes toy cars.

The fact that Williams syndrome kids think of men and women differently, but not blacks and whites, shows that sex stereotypes are not caused by social anxiety, Meyer-Lindenberg said.

This may be because we learn about gender within "safe" home environments, while a different race is usually a sign of someone outside our immediate kin. (Studies to test this explanation, such as with racially-mixed families, have not yet been done.)

Racial biases are likely rooted in a general fear of others, while gender stereotypes may arise from sweeping generalizations, Meyer-Lindenberg said. "You watch mother make the meals, so you generalize this to everyone female."

In their heads

Due to the present study, we now know that "gender and race are processed by different brain mechanisms," Meyer-Lindenberg said, although those involved in gender are less understood.

Previous work has shown that in the brains of people with Williams syndrome, the amygdala — the emotional seat of the brain — fails to respond to social threats. While the amygdala itself is functionally normal, it is misguided by the pre-frontal cortex — the executive of the brain — to block all social anxiety.

This system is now thought to underlie racism, but it seems uninvolved in the formation of sex stereotypes.

Meyer-Lindenberg and colleagues are now using brain imaging to get a clearer picture of how racism and sexism are differentiated in the brain. The present study was published in the journal Current Biology.

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