Short answers, pulled from the story.
The word prejudice has been used since Middle English around the year 1300. Its roots lie in a Latin phrase meaning before judgment. This ancient etymology reveals the core mechanism of the concept as a decision made prior to experience.
Gordon Allport defined prejudice as a feeling, favorable or unfavorable, toward a person or thing prior to or not based on actual experience. He published this definition in his classic work The Nature of Prejudice in 1954. Allport claimed that prejudice is a natural and normal process for humans.
The first psychological research conducted on prejudice occurred in the 1920s. One article from 1925 which reviewed 73 studies on race concluded that the studies seemed to indicate the mental superiority of the white race. These studies led many psychologists to view prejudice as a natural response to races believed to be inferior.
Academics Thomas Pettigrew and Linda Tropp conducted a meta-analysis of 515 studies involving a quarter of a million participants in 38 nations. They found that three mediators are of particular importance for reducing prejudice. These mediators include enhancing knowledge about the outgroup, reducing anxiety about intergroup contact, and increasing empathy and perspective-taking.
The Robber's Cave experiment demonstrated that negative prejudice and hostility was created between two summer camps after sports competitions for small prizes. The hostility was lessened after the two competing camps were forced to cooperate on tasks to achieve a common goal. This experiment showed that competition for limited resources leads to increased negative prejudices and discrimination.
The justification-suppression model of prejudice was created by Christian Crandall and Amy Eshleman. This model explains that people face a conflict between the desire to express prejudice and the desire to maintain a positive self-concept. The conflict causes people to search for justification for disliking an out-group to avoid negative feelings.