Social class is more than just how much money you have. It's also the clothes you wear, the music you like, the school you go to -- and has a strong influence on how you interact with others, according to the authors of a new article in Current Directions in Psychological Science, a journal of the Association for Psychological Science. People from lower classes have fundamentally different ways of thinking about the world than people in upper classes -- a fact that should figure into debates on public policy, according to the authors.

"Americans, although this is shifting a bit, kind of think class is irrelevant," says Dacher Keltner of the University of California-Berkeley, who cowrote the article with Michael W. Kraus of UC-San Francisco and Paul K. Piff of UC-Berkeley. "I think our studies are saying the opposite: This is a profound part of who we are."

People who come from a lower-class background have to depend more on other people. "If you don't have resources and education, you really adapt to the environment, which is more threatening, by turning to other people," Keltner says. "People who grow up in lower-class neighborhoods, as I did, will say,' There's always someone there who will take you somewhere, or watch your kid. You've just got to lean on people.'"

Wealthier people don't have to rely on each other as much. This causes differences that show up in psychological studies. People from lower-class backgrounds are better at reading other people's emotions. They're more likely to act altruistically. "They give more and help more. If someone's in need, they'll respond," Keltner says. When poor people see someone else suffering, they have a physiological response that is missing in people with more resources. "What I think is really interesting about that is, it kind of shows there's all this strength to the lower class identity: greater empathy, more altruism, and finer attunement to other people," he says. Of course, there are also costs to being lower-class. Health studies have found that lower-class people have more anxiety and depression and are less physically healthy.

Upper-class people are different, Keltner says. "What wealth and education and prestige and a higher station in life gives you is the freedom to focus on the self." In psychology experiments, wealthier people don't read other people's emotions as well. They hoard resources and are less generous than they could be.

One implication of this, Keltner says, is that's unreasonable to structure a society on the hope that rich people will help those less fortunate. "One clear policy implication is, the idea of nobless oblige or trickle-down economics, certain versions of it, is bull," Keltner says. "Our data say you cannot rely on the wealthy to give back. The 'thousand points of light' -- this rise of compassion in the wealthy to fix all the problems of society -- is improbable, psychologically."

The ability to rise in class is the great promise of the American Dream. But studies have found that, as people rise in the classes, they become less empathetic. Studies have also found that as people rise in wealth, they become happier -- but not as much as you'd expect. "I think one of the reasons why is the human psyche stops feeling the need to connect and be closer to others, and we know that's one of the greatest sources of happiness science can study," Keltner says.

The article is entitled, "Social Class as Culture: The Convergence of Resources and Rank in the Social Realm."