Smile

    SMILES ARE GOOD FACIAL EXPRESSION

A smile is a facial expression formed primarily by flexing the muscles at the sides of the mouth. It is believed it takes about 42 muscles to smile. 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 may be perceived as insincere.

Among humans, smiling is an expression denoting pleasure, sociability, happiness, joy 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 among different cultures, with some using smiles to convey confusion or embarrassment.
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, or to signal submission to more dominant group members. 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, glee, pride, contempt, and embarrassment. Also, other types of primates can express this gesture as a symbol of happiness and fun.
A smile seems to have a favorable influence upon others and makes one likable and more approachable. In the social context, smiling and laughter have different functions in the order of sequence in social situations:

Smiling is sometimes a pre-laughing device and is a common pattern for paving the way to laughter;
Smiling can be used as a response to laughter in the previous turn.
Smiling is a signaling system that evolved from a need to communicate information of many different forms. One of these is advertisement of sexual interest. Female smiles are appealing to heterosexual males, increasing physical attractiveness and enhancing sex appeal. However, recent research indicates a man's smile may or may not be most effective in attracting heterosexual women, and that facial expressions such as pride or even shame might be more effective. The researchers ignored the role of smiles in other sexual preferences.

As reinforcement and manipulation.

The influence of smiling on others is not necessarily benign. It may take the form of positive reinforcement, possibly for an underhand manipulative and abusive purpose.[