We are social animals. Our ancestors lived in groups. They protected themselves in groups. They fed themselves in groups.

And so there's a very strong tendency to care about the group and to identify ourselves with the group. We call that our social identity.

What makes a group? Is it the country you were born in? The color of your skin? Those you are related to? A set of common beliefs?

Groups are everywhere. And when there are groups, there is something called prejudice.

Prejudice comes from the phrase to prejudge, and it refers simply to a positive or negative evaluation of another person based solely on their group membership.

There is positive prejudice. This is when someone makes a positive evaluation in favor of someone else within their own group. And then there is the negative form of prejudice, where a negative evaluation is made about someone in a different group.

Negative prejudice often leads to discrimination towards these individuals, who are thought of as the other. So where prejudice is an unjustifiable attitude toward a group and its members, discrimination is to engage in negative behavior.

Social psychologists usually talk about groups in terms of in groups and out groups. That is, members of groups that you're a member of and groups that you're not a member of.

The in group is us. The out group is them. It's we and they.

So my in group might be your out group and vice versa. And these things change over time.

We tend to treat in group members, or view in group members, very differently than out group members.

People tend to think that we, in our group, are diverse. They are all alike.

Groups have lots of positive functions. They are for protection. Groups typically are better at solving difficult problems of logic than individuals are, even highly talented members of those groups. But there's also a downside.

One negative repercussion of forming in groups is prejudice. Prejudice is an unjustified, often negative attitude.

Well, stereotyping typically involves a generalization, often an over-generalization, about members in a particular group. So it has to do with belief. Prejudice tends to be negative. Most definitions focus much more on that than any sense of prejudice serving a positive function.

But in the case of stereotyping, there can be cases in which you can actually have a positive stereotype. You might think about the elderly in terms of being very wise. You might think about certain ethnic groups as being very much pro-family, as thinking a lot about kids.

Experimentally, we see stereotypes arise very easily.

A classic example of prejudice between groups is the Robber's Cave Experiment, conceived by Muzafer Sherif in 1954.

Muzafer Sherif collected 22 young Oklahoma boys, brought them to a Boy Scout camp, separated them into two groups, and through a series of competitions with prizes for victory, created an in group and an out group. Two different groups that were at war with one another. It was sort of Lord of the Flies on a boys scale.

And they ransacked one another's campsites, they broke out into fights, food wars in the dining hall. And then Sherif did an interesting thing.

The researchers found that the best way to alleviate the intergroup hostility was to present a challenge that was too great for any one group to surmount.

They together helped get a stalled truck out of the mud. They did a variety of things like this together. And at the end of the time, they did in fact, become friends. Closed fists became open arms. And they rode home on the same bus singing songs together.

Prejudice is the most popular topic within social psychology. Most people who go into social psychology want to do something about prejudice.

One issue in studying prejudice is trying to define what it is. And we now know that all of our thinking, our memories, our perceptions, our attitudes exist at a conscious level and an unconscious level. There's explicit attitudes, for example, we have toward other people. But there's also implicit, automatic associations that we have with other people.

What is, in a sense, the new challenge is to deal with implicit forms of prejudice. Forms of prejudice that we're not necessarily aware of.

And so researchers have developed different instruments to measure the conscious explicit and the unconscious automatic attitudes. And one of the things they're teaching us is that to a large extent, we fly on autopilot. And only occasionally does consciousness do a manual override to enable us to override our automatic attitudes and prejudices.

Whether we see somebody in the dark shadows as holding a gun or a wrench may depend not on our thoughtful attitudes, but on our automatic associations between a person of a particular race and violence. And if we know that, then we can do some things to rein in our automatic associations and reactions.

Historically, prejudice has contributed to some of the worst problems of intergroup conflicts in history, and continues to do so to this very day. So within American culture certainly, the study of prejudice is not at all controversial. Everybody's sort of agreed we need to reduce prejudice. We need to reduce stereotyping, ultimately eradicate it, and we'd have a much better world.