After polling people from 32 countries to learn how much they felt various feelings should be expressed openly, the authors found that emotional expressiveness was correlated with diversity. In other words, when there are a lot of immigrants around, you might have to smile more to build trust and cooperation, since you don’t all speak the same language.

People in the more diverse countries also smiled for a different reason than the people in the more homogeneous nations. In the countries with more immigrants, people smiled in order to bond socially. Compared to the less-diverse nations, they were more likely to say smiles were a sign someone “wants to be a close friend of yours.” But in the countries that are more uniform, people were more likely to smile to show they were superior to one another. That might be, the authors speculate, because countries without significant influxes of outsiders tend to be more hierarchical, and nonverbal communication helps maintain these delicate power structures.

So Americans smile a lot because our Swedish forefathers wanted to befriend their Italian neighbors, but they couldn’t figure out how to pronounce buongiorno. Seems plausible. But there’s also something very w i d e about the classic American grin. Why is it that Americans smile with such fervor?