Jon Mixon wrote in Have you ever been witness to racism?:

Racism is such a part of my daily existence that I only really notice it when:

1. It intensifies and name-calling or open hostility are present.

2. When it is absent, as when a person treats me like I'm another human being just as they are.

His answer made me pause.

2012 America still has a long way to go.

The Have you ever been witness to racism? page contains several other examples.

I don't know where it is, but I do remember some famous experiment conducted on 5 year olds that exposed them to a live play with people of many different races. In the surveys after, most of the kids didn't distinguish characters by race. That said, there may be something evolutionary in nature that kicks in as we age, yes partly shaped by environmental agents, but also natural, when we see others who do not resemble us. It's a complicated issue.

Racism, sexism, xenophobism, homophobism -- I've seen it all. It is definitely a learned behavior; it's a nurture v. nature experience; those nurtured in an environment tolerant or accepting of those kinds of behaviors, inevitability are probably to exhibit some form of them.

But you can absolutely believe I am a staunch racist in the pure definition of the word -- I believe in one human race, above all the other species. :)