It is easier for the brain to first quantify objects into pairs and then to differentiate them into opposing groups: right or wrong, lights or dark, Republican or Democrat, etc. This neural process of simplification and generalization is a form of biological stereotyping because it does not take into account individual differences and nuances. Once an oppositional dyad is created, the brain will then impose an emotional bias on each (root for favorite sports team and disparage the other). This includes people from different cultural, religious, and ethnic background. Unfortunately, this inborn us-versus-them mentality easily converts into racism. So it appears that bias in innate, prejudice is learned.