The Origin of a Smile
To this day we're not quite sure how we came to smile that much. It's especially interesting subject in body language since the smile is something almost uniquely "our" thing. Other animals don't smile, at least not in the same context as we do (except for a few exclusions that are similar to our smile). We can say confidently that we're the only specie to hold so much meaning to such simple gesture of stretching the lips (it's argued that we have about 50 kinds of smiles!)