People are more likely to return a lost wallet with money inside than an empty wallet, concluded a group of international researchers who set out to test the tension between financial self-interest and honesty of people around the world.

To the surprise of researchers, people who found the wallets returned them more often when they had a small sum of money than if the wallets didn’t have any money at all—and returned the wallets even more often if they had nearly $100.

People on average returned 40% of wallets with no money in them but 51% of wallets with some money, according to a new paper published online in the journal Science on Thursday. The pattern held in 38 out of 40 countries where the study was conducted.

The findings run counter to a fundamental principle of classical economics and suggest that honesty, altruism and self-image can sometimes be more influential than economic self-interest.

“There’s this emphasis that money is what drives human behavior, and this paper is a beautiful, large-scale demonstration that people’s self-interest is really broader than just money,” said Kurt Gray, an associate professor of psychology at the University of North Carolina, Chapel Hill, who wasn’t involved in the study.