I think we're all very slightly racist by nature; we'd prefer more to be around people that look and act like us.
For example, let's say you took 4 people (2 men, 2 women) of each of the 'major' racial groups (white, black, Arabian, Asian, Indian, Hispanic, Native America), and showed them 100 pictures of people of both genders, of all ages and races, and then asked them for every picture, if they would like to befriend or be around that person. I bet you if they collected the data, every person would have approved of more pictures of people of their own race.