It turns out that countries with lots of immigration have historically relied more on nonverbal communication—and thus, people there might smile more.
For a study published in 2015, an international group of researchers looked at the number of “source countries” that have fed into various nations since the year 1500. Places like Canada and the United States are very diverse, with 63 and 83 source countries, respectively, while countries like China and Zimbabwe are fairly homogenous, with just a few nationalities represented in their populations.
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.