Robert Kurzban thinks evolution offers hints to combat racism. Kurzban, an evolutionary psychologist at the University of California at Los Angeles, speculates that the primal impulse to spot allies prompted people to use race as a clue about allegiance. If other visual clues were better indicators, he says, people would pay less attention to race. He and his colleagues tested the idea by having volunteers watch videos showing conversations among groups of two African American men and two white men. Next, sentences were displayed alongside photos of the people who said them. At the end of the study, the volunteers were asked to match sentences with the speakers.

Volunteers initially mixed up the speakers mostly along racial lines. But in a second video, the speakers wore colored T-shirts that divided them into two teams. This time, volunteers confused statements between members of the same team more often than between members of the same race, evidently paying less attention now to skin color. It took just four minutes to erase racial categories, Kurzban says.