It's human nature to want to categorize things.

We categorize all the time. Think about it. Even words are categories. Anything that has four legs, triangular ears, whiskers, and meows is a "cat".

John Stossel and Kristina Kendall explain this tendency to categorize in their article "The Psychology of Stereotypes": "Psychologists say we categorize -- or stereotype -- by age and race and gender, because our brains are wired to do so automatically." They also cite John Dovido, a professor of psychology at the University of Connecticut, who says, "When you're a social animal, you need to be able to distinguish who's a friend and who's a foe. You need to understand who's a member of your pack, who's a member of a different pack"

So categorization is useful, because we need to know what is dangerous and what is not. However, categorization can have a dark side. It can lead to stereotyping people, which can lead to prejudice. And this stereotyping begins at a young age. Stossel and Kendall explain this by telling of an experiment:

"'20/20' brought together three groups of kids and showed them pictures of two men -- one Arab, the other Asian.

When we asked the children which man they liked better, over and over, more kids said they preferred "the Chinese guy."

One child preferred the Chinese man "because he looks nicer and he has a smile on." But both men were smiling.

Several children weighed in on the Arab man's personality, basing their opinions on just seeing his picture. One child said, "I think he's weird." Another child said, "He's like the scary dude."

Next, "20/20" showed the kids pictures of a black man and white man. This time the pictures were different. Here were some of the comments the kids made about the photo of the black man.

One said, "He looks mean." Another referred to him as "FBI's Most Wanted." Another commented, "He looks like he's a basketball player."

When the white man's picture was shown, one child said, "He's nice." Another said, "I think he's nice except he might be mad about something."

The boy was probably picking up on something. The photo of a white man was of Oklahoma City bomber Timothy McVeigh. Admittedly, the pictures were a little bit different, but when we asked which man is a criminal, most kids pointed to the black man. When we asked which man was a teacher, most pointed to McVeigh. This is ironic because the black man pictured was Harvard University professor Roland Fryer."

It's disturbing to see that these prejudices get embedded in our minds at such a young age. Twice, these children judged the character of two individuals based merely on their race. Race, of course, is not at all an indicator of character. Yet, it was very natural for these children to assume it was.

Not only do people judge based on race, they have other biases and prejudices. Stossel and Kendall also described another experiment where people were shown to have biases against elderly people. The experiment used Harvard University's Implicit Association Test, which "is supposed to measure racial bias. The test flashes pictures of white and black faces and words like "evil" and "nasty," plus words like "joy" and "wonderful," and evaluates whether people associate different words with certain races.

The test is given quickly, so that test-takers don't have time to think consciously.

The test's designers say it can show whether or not you have a preference for anything -- skirts versus pants, Meg Ryan versus Julia Roberts.

"20/20" invited a group of Pace University students to take the test. They said they preferred Julia Roberts, and the test showed they did.

But when we told them the test results revealed other implicit biases, such as one against career women, the elderly, blacks, Arabs and gays, some students got defensive.

Researchers say the test shows what's really in your subconscious, with sometimes surprising results. Not just young people but old people, too, showed an overwhelming bias against the elderly.

"You wouldn't expect that old people would think that old is bad. But the elderly are every bit as negative about the idea of old age as much younger people are," said Anthony Greenwald, a professor of psychology at the University of Washington.

The researchers also found about half of the black people who took this test showed bias against blacks.

Greenwald says many people discover they have biases that they wish they didn't.

"I certainly don't want to think of myself as a racist. But these things are in my head, they show up on the test," said Greenwald

The findings of this experiment are really disappointing. Why do we have prejudices against certain people for things that are not bad and are just natural things, like age or race? Again, it seems to just be part of human nature to judge things as bad that shouldn't be judged at all. Greenwald's quote is very poignant. I wish I didn't have biases and prejudices against people for no good reason. But I do. We all do.

So what can we do?

It's hard to know how to go about solving this problem of categorizing people--judging people--based on race or any other physical attribute, especially since it is something deeply rooted in human nature. We all judge a person's character and/or personality based on appearances. Even if we know it's illogical, we do it. It comes naturally to us.

However, Stossel and Kendall make a great point in their article: "the biases in our head are only harmful if we act on them." Yes, I wish we didn't have these biases at all. But as long as we keep them in check, realizing they're just part of our human nature, the dark shadowy side none of us like--as long as we know that our prejudices are not true--as long as we still treat everyone with respect and kindness no matter what our biases are saying--then we're taking a huge step in the right direction.