Throughout the world, racial, cultural, and ethnic differences are used to place people into different categories. Once we categorize people in this way, we automatically assume that they have the essence of this category. For example, in 1994, Richard Herrnstein and Charles Murray wrote a book called The Bell Curve in which they documented racial differences in test scores. An implicit assumption of this book was that it was meaningful to classify people by race and that these racial categories reflected something essential about the people who were categorized.

How do racial categories develop? This issue was addressed in a paper by Marjorie Rhodes and Susan Gelman in a 2009 paper in Cognitive Psychology. They looked at two factors: age and cultural background. The participants in their study were primarily White. They came either from a mid-sized city that was politically liberal or from a rural area that was politically conservative. The participants ranged in age from 5-18.

The younger children played a game with a puppet. They were told that the puppet came from another place where they do some things wrong, but they do other things differently from the way we do them, but they are not wrong. After some practice with the game, children were shown an object or person and then were shown a second object or person and were told that the puppet thinks they are the same kind of thing and were asked whether they were right. For example, they might be shown a wolf and a lion and were told that the puppet thought that they were the same kind of thing. Over the course of the study, the puppet classified animals, and artifacts (like cars, forks, and dresses). The puppet also classified people based on and race.

The older kids did a similar task, but without the puppet. The oldest kids in this task (who were about 17) were asked these questions in a pencil-and-paper test.

So, what happened?

For simplicity, I'll just focus on the animal and racial categories. For the animals, kids of all ages tended to say that the puppet was wrong when it put together animals of different categories. That is, starting at age 5 and upward to age 17, children felt that it was not correct to put different animals in the same category.

The data for race were much more complex.

As an example, the participant might see a White girl and then an Asian girl and be told that the puppet thought that they were both the same kind of person.

The youngest children (5- and 7-year-olds) showed no strong preference for saying that the puppet was right or wrong when putting together people of different races. About half the time they said the puppet was right and half the time they said the puppet was wrong.

For the older children (10-year-olds and 17-year-olds), their answer depended on where they grew up. The older children who grew up in the politically liberal area said that it was correct to classify people from different races. Those who grew up in the politically conservative area said that it was incorrect to classify people from different races. That is, older kids from liberal environments had no problem with a category that involved people from different races, while older kids from a conservative environment thought it was wrong to classify people from different races in the same category.

The first thing to notice about these data is that the belief that race is a possible basis for classifying people emerges late. This observation is similar to what anthropologist Lawrence Hirschfeld has observed in his research.

The second thing to see is that beliefs about whether it is necessary to classify people based on their race depend on what other members of your culture suggest. You are much more likely to think it is necessary to classify people based on race if you grow up in a politically conservative environment than if you grow up in a politically liberal environment.

The reason that this type of classification matters is that classifying people into a group brings along the belief that the members of that group share some essential characteristics. Consistent with that, Rhodes and Gelman asked the 17-year-olds to fill out scales about how strongly they believe that members of the same race share deep underlying characteristics not shared by other races. Those kids who were most likely to think that it was necessary to classify people based on race were also the ones most likely to think that racial categories reflect something deeply similar about the members of that race.

For each of us, I think, it is worth reflecting on how likely we are to treat people differently because of the way we categorize them.