Smiling, however, cannot be interpreted as preparation for birth but may be a reflex, Prof Campbell said. He added: "What's behind the smile, of course, I can't say, but the corners turn up and ...

But what if no one can see it? In a world of face masks, have we muted the power of a smile, a fundamental human expression? The Benefits of Smiling Smiling is touted as a natural stress reliever ...