Whether it is a lack of interracial marriage, an anti-foreign bias in politics or a nativist desire to keep out immigrants, it's clear people naturally prefer people who are like them. Even Switzerland, usually seen as a bastion of tolerance, recently passed a Constitutional referendum banning the construction of Muslim minarets on mosques (the picture on the left is fear mongering propaganda from the campaign). I'm also not exempt from this trend. Most of my friends are white, twenty something, upper middle class, and college educated. I work hard to ensure my bias doesn't reach the classroom, but I think it is important to understand why these preferences exist. I believe the solution is the main point where my religious beliefs and economics background converge, human selfishness.
I believe people are totally depraved and rationally self-interested (or maybe this justifies our inherent extra selfishness). The Bible and other faiths say we should love or neighbor as a ourselves, assuming loving ourselves is the default. You don't have to teach children to be selfish, though sadly we do. So if we are our number one, then number two must be people who are like us. This is true racially, geographically (neighborhood, city, state, nation) and even within our social class. Not only is it easier to put ourselves in someone else's shoes who is like us, it is also more likely to be us in the future. My bet is that people from Boston were more sympathetic to 9/11 victims in New York or that people from Miami better understood the pain felt by Hurricane Katrina victims in New Orleans. There is even evidence we are nicer to the siblings that look like us. The good news is as the world becomes more connected we see how similar humans are all over the world, the less prejudice we there will be.