Does our writing reveal our prejudices?

The current presidential race reminds me of something I heard many years ago during a lecture given by a man who examines slave narratives in an attempt to determine authenticity. Before I reveal what I learned, let me point out what fired up this train of thought:

Barack Obama is frequently referred to as "a black man with a white mother." It is equally true that he is "a white man with a black father," yet he's never referred to in this manner. What does it say about us--or, more specifically, about the media--that Obama's degree of "blackness" is worthy of comment?

What the lecturer revealed about his research is this (and I'm over-simplifying): You can often determine an author's race by how he describes people. As writers, we tend to spend more effort describing those who are not like us.

I saw it in my own work and, once I realized I was doing it, have tried to avoid it.