The rich really are different from the rest of us, scientists have found - they are more likely to commit unethical acts because they are more motivated by greed.

People driving expensive cars were more likely than other motorists to cut off drivers and pedestrians at a four-way-stop intersection in the San Francisco Bay Area, researchers at the University of California, Berkeley, observed. Those findings led to a series of experiments that revealed that people of higher socioeconomic status were also more likely to cheat to win a prize, take candy from children and say they would pocket extra change handed to them in error rather than give it back.

Because rich people have more financial resources, they're less dependent on social bonds for survival, the researchers reported Monday in Proceedings of the National Academy of Sciences. As a result, their self-interest reigns and they have fewer qualms about breaking the rules.

"If you occupy a more insular world, you're less likely to be sensitive to the needs of others," said study lead author Paul Piff, who is studying for a doctorate in psychology.

But before those in the so-called 99 percent start feeling ethically superior, consider this: Piff and his colleagues also discovered that anyone's ethical standards could be prone to slip if they suddenly won the lottery and joined the top 1 percent.

"There is a strong notion that when people don't have much, they're really looking out for themselves and they might act unethically," said Scott Wiltermuth, who researches social status at USC's Marshall School of Business and wasn't involved in the study. "But actually, it's the upper-class people that are less likely to see that people around them need help - and therefore act unethically."

In earlier studies, Piff documented that wealthy people were less likely to act generously than relatively impoverished people. With this research, he hoped to find out whether wealthy people would also prioritize self-interest if it meant breaking the rules.

The driving experiments offered a way to test the hypothesis "naturalistically," he said. Trained observers hid near a downtown Berkeley intersection and noted the makes, model years and conditions of bypassing cars. Then they recorded whether drivers waited their turn.

It turned out that people behind the wheels of the priciest cars were four times as likely as drivers of the least expensive cars to enter the intersection when they didn't have the right of way. The discrepancy was even greater when it came to a pedestrian trying to exercise a right of way.

There is a significant correlation between the price of a car and the social class of its driver, Piff said. Still, how fancy a car looks isn't a perfect indicator of wealth.

So back in the laboratory, Piff and his colleagues conducted five more tests to measure unethical behavior - and to connect that behavior to underlying attitudes toward greed.

For example, the team used a standard questionnaire to get college students to assess their own socioeconomic status and asked how likely subjects were to behave unethically in eight different scenarios.

In one of the quandaries, students were asked to imagine that they bought coffee and a muffin with a $10 bill but were handed change for a $20. Would they keep the money?

In another hypothetical scenario, students realized their professor made a mistake in grading an exam and gave them an A instead of the B they deserved. Would they ask for a grade change?

The patterns from the road held true in the lab - those most willing to engage in unethical behavior were the ones with the highest social status.

One possible explanation was that wealthy people are simply more willing to acknowledge their selfish sides. But that wasn't the issue here. When test subjects of any status were asked to imagine themselves at a high social rank, they helped themselves to more candies from a jar they were told was meant for children in another lab.

Another experiment recruited people from Craigslist to play a "game of chance" that the researchers had rigged. People who reported higher social class were more likely to have favorable attitudes toward greed - and were more likely to cheat at the game.

"The patterns were just so consistent," Piff said. "It was very, very compelling."

Piff, who is writing a paper about attitudes toward the Occupy movement, said that his team had been accused of waging class warfare from time to time.

"Berkeley has a certain reputation, so yeah, we get that," he said.

But rather than vilify the wealthy, Piff said, he hopes his work leads to policies that help bridge the gap between the haves and have-nots.

Acts as simple as watching a movie about childhood poverty seem to encourage people of all classes to help others in need, he said.