Smile

A smile is a facial expression formed primarily by flexing the muscles at the sides of the mouth.

Among humans, a smile expresses delight, sociability, happiness, joy, or amusement.

Primatologist Signe Preuschoft traces the smile back over 30 million years of evolution to a "fear grin" stemming from monkeys and apes, who often used barely clenched teeth to portray to predators that they were harmless[2] or to signal submission to more dominant group members.

Many people in the former Soviet Union area consider smiling at strangers in public to be unusual and even suspicious behavior,[9] or even a sign of stupidity.

For example, Greg Rickford, a member of the Canadian Parliament told a female journalist to smile rather than answer the question she had asked.

[13] Cheek dimples are formed secondary to a bifid zygomaticus major muscle, whose fascial strands insert into the dermis and cause a dermal tethering effect.

As it travels anteriorly, it then divides with a superior bundle that inserts in the typical position above the corner of the mouth.

[22] While conducting research on the physiology of facial expressions in the mid-19th century, French neurologist Guillaume Duchenne identified two distinct types of smiles.

It is named after the now-defunct airline Pan American World Airways, whose flight attendants would always flash every passenger the same perfunctory smile.

For example, Barbary macaques demonstrate an open mouth display as a sign of playfulness, which likely has similar roots and purposes as the human smile.