Prejudice and racism reflect some of the negative aspects of group psychology. As they have caused enormous suffering across history, it is very important to understand how they work. Prejudice and racism both refer to a negative view of one group of people based solely on their membership in that group. Rupert Brown defines prejudice as a derogatory attitude, negative emotion, or discriminatory behavior toward members of an out-group because of membership in that out-group. Racism is a specific form of prejudice, involving prejudicial attitudes or behavior toward members of an ethnic group. The definition of race is somewhat variable, but commonly refers to an ethnic group originating on a specific continent, such as people of African, European, or Asian descent. Social psychologists have long been interested in the phenomenon of prejudice and have contributed much to our understanding of it.