The reaction to African-American faces was found to be weaker in people with racially diverse peers.
There's never been good reason to believe that human beings are naturally racist. After all, in the environment of human evolution--which didn't feature, for example, jet travel to other continents--there would have been virtually no encounters between groups that had different skin colors or other conspicuous physical differences. So it's not as if the human lineage could have plausibly developed, by evolutionary adaptation, an instinctive reaction to members of different races.
Nonetheless, people who want to argue that racism is natural have tried to buttress their position with evidence that racism is in some sense biological. For example: studies have found that when whites see black faces there is increased activity in the amygdala, a brain structure associated with emotion and, specifically, with the detection of threats.
Well, whatever power that kind of argument ever had--which wasn't much, since the fact that a psychological reaction has a biological correlate doesn't tell you whether the reaction is innate--it has even less power now. In a paper that will be published in the Journal of Cognitive Neuroscience, Eva Telzer of UCLA and three other researchers report that they've performed these amygdala studies--which had previously been done on adults--on children. And they found something interesting: the racial sensitivity of the amygdala doesn't kick in until around age 14.