Here’s what Wikipedia says about a smile:
A smile is a facial expression formed by flexing those muscles……

Why, exactly, do humans smile?
This question puzzled anthropologists for hundreds of years.
The smile is instinctive, one of a thousand fascination cues we use to persuade others to connect with us. Yet from an evolutionary perspective, the smile makes no sense.

In the animal kingdom, retracting the mouth corners and baring teeth is a sign of aggression. Yet in humans, this same gesture signals openness.
{So why are humans different?}

* Humans have a hardwired connection between pitch of voice and facial expression. A simple experiment: Sing the highest note that you’re capable of, and notice how you raise your chin and eyebrows (almost like you’re cooing to a baby). Then, sing the lowest note. See how your chin and eyebrows lower, in a more aggressive expression?

The answer: Bigger animals have bigger mouths, and therefore lower vocal vibrations, which conveys dominance. Smaller animals have smaller mouth cavities, and their higher voices communicate friendliness or submission. It’s why a Rottweiler’s growl is more threatening than a Pomeranian’s.

When humans smile, we pull our cheek flesh back against our teeth, which makes our mouth cavity smaller, and raises the pitch of our voice. Presto, we sound friendlier essentially turning ourselves from a big animal into a smaller one. Smiling, anthropologists realized, began as a way to sound less threatening then evolved into a way to look more approachable.

The next time you become captivated by a person (or a brand or idea), without even realizing it, you’re most likely under the influence of the fascination triggers.

Sally Hogshead – is a speaker, brand consultant, and author of the upcoming book,␣FASCINATE: Your 7 Triggers to Persuasion and Captivation.