Smile
A smile is a facial expression formed primarily by flexing the muscles at the sides of the mouth. Some smiles include a contraction of the muscles at the corner of the eyes, an action known as a "Duchenne smile". Smiles performed without the eye contraction can be perceived as "fake".
Among humans, smiling is an expression denoting pleasure, sociability, happiness, or amusement. It is distinct from a similar but usually involuntary expression of anxiety known as a grimace. Although cross-cultural studies have shown that smiling is a means of communication throughout the world, there are large differences between different cultures, with some using smiles to convey confusion or embarrassment.
Historical background
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. The smile may have evolved differently among species and especially among humans. Apart from Biology as an academic discipline that interprets the smile, those who study kinesics and psychology such as Freitas-Magalhaes view the smile as an affect display that can communicate feelings such as love, happiness, pride, contempt, and embarrassment.
