Smiles are strange things. People use them when they are happy, yes, but also when they are uncomfortable, bored, anxious, or trying to be polite. Sometimes a smile has nothing to do with joy at all.

You've probably heard the claim that it takes more muscles to frown than to smile. It's usually framed as a feel-good reason to turn your frown upside down—less effort, more joy. But anatomically, the ...

Everybody everywhere smiles. Across all cultures, people smile. In fact, smiling may be an evolutionary throwback to the silent bared-teeth display of nonhuman primates. Although babies start smiling ...