There is no cut and dried answer, but most experts believe that racism is perpetuated via culture and the attitudes/opinions of those in authority. Many are surprised when they travel outside of their own countries to find that the ethnic groups that act one way in their country, do not act that way in other countries. This would lead one to believe that it is culture that shapes not only the attitudes of those who develop racist tendencies and outlooks, but those to whom the prejudices are applied.
