The ability to distinguish friend from foe helped early humans survive, and the ability to quickly and automatically categorize people is a fundamental quality of the human mind. Categories give order to life, and every day, we group other people into categories based on social and other characteristics.

This is the foundation of stereotypes, prejudice and, ultimately, discrimination.

Definition of terms
A stereotype is an exaggerated belief, image or distorted truth about a person or group — a generalization that allows for little or no individual differences or social variation. Stereotypes are based on images in mass media, or reputations passed on by parents, peers and other members of society. Stereotypes can be positive or negative.

A prejudice is an opinion, prejudgment or attitude about a group or its individual members. A prejudice can be positive, but in our usage refers to a negative attitude.

Prejudices are often accompanied by ignorance, fear or hatred. Prejudices are formed by a complex psychological process that begins with attachment to a close circle of acquaintances or an "in-group" such as a family. Prejudice is often aimed at "out-groups."

Discrimination is behavior that treats people unequally because of their group memberships. Discriminatory behavior, ranging from slights to hate crimes, often begins with negative stereotypes and prejudices.

How do we learn prejudice?
Social scientists believe children begin to acquire prejudices and stereotypes as toddlers. Many studies have shown that as early as age 3, children pick up terms of racial prejudice without really understanding their significance.

Soon, they begin to form attachments to their own group and develop negative attitudes about other racial or ethnic groups, or the "out-group". Early in life, most children acquire a full set of biases that can be observed in verbal slurs, ethnic jokes and acts of discrimination.

How are our biases reinforced?
Once learned, stereotypes and prejudices resist change, even when evidence fails to support them or points to the contrary.

People will embrace anecdotes that reinforce their biases, but disregard experience that contradicts them. The statement "Some of my best friends are _____" captures this tendency to allow some exceptions without changing our bias.

How do we perpetuate bias?
Bias is perpetuated by conformity with in-group attitudes and socialization by the culture at large. The fact that white culture is dominant in America may explain why people of color often do not show a strong bias favoring their own ethnic group.

Mass media routinely take advantage of stereotypes as shorthand to paint a mood, scene or character. The elderly, for example, are routinely portrayed as being frail and forgetful, while younger people are often shown as vibrant and able.