The human smile originates from the “fear grin”, observed in many primate species. Lacking verbal means to communicate, the smile acts a sign of submission towards a more dominant individual — a way of signalling non-threat or stress, preventing aggression and conflict within the group. The fear grin focuses on pulling back lips and the display of teeth.
In humans, this display of teeth has slowly transformed into our smile - a means to express positive emotions: happiness and friendliness.
A hundred years ago you weren’t supposed to smile in your portrait. Smiling was seen as a signal of lacking in morals… not being a person that could be taken seriously. Only people from the lower classes smiled.
Nowadays: Be happy, smile! Our smile is a gesture, an invitation to connect with us.
A smile can communicate everything from pure joy to bitter contempt. We smile when worried, nervous, or uncomfortable — when we want to appease the situation.
Sometimes the fear grin comes back.