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Read my lips: New book explores a smile's subtleties

A smile is a "social magnet." We're drawn to this one, for sure.

A smile is much more than a cheerful expression, writes author Marianne LaFrance in her new book "Lip Service." The smile, she suggests, "is a social magnet, a trustworthiness meter, a device for diffusing anger, a patch for frayed interpersonal bonds, and a lubricant for keeping social ties in good working order."

Perhaps that's why turning the corners of the mouth upward is "the most instantly recognized facial expression." Whether discussing lop-sided grins, wolfish smirks, sinister sneers, or radiantly beaming, LaFrance, a Yale University psychology professor, delves into the science behind the smile and explains its affect on politics, work, relationships, and culture.

Although a smile often signals happiness, it can also convey a range of emotions from amusement and embarrassment to contempt and deception.

There are even gender differences in grinning: Studies suggest that on average girls and women smile more than boys and men.

One reason may be biological, says LaFrance. Researchers have found the primary smile muscle, known as the zygomaticus major, is thicker in gals than in guys. It's unclear whether women are born with a more well-endowed smile muscle so they use it earlier and often, or if the muscle bulks up from moving more.

A second explanation could be occupational: Women hold more service-industry jobs, as nurses, teachers, flight attendants, and wait staff, in which they may be required to do more smiling. (But there's some evidence that males in these professions smile the same amount as females. Perhaps both sexes recognize that smiling generates larger tips!)

A third reason is that girls are born with a more positive orientation to socialization. "It often falls to women to arrange the socal calendar, to reduce conflicts, and to care about other people's emotional lives," points out LaFrance.

Although smiles typically cast a positive glow, not all of them can be taken at face value: Smiles have a bright side -- a parent's delight at seeing baby's first smile -- and a dark side -- a two-faced smile in which the outward pleasantness camouflages a person's inner feelings.

There are other downsides to lifting your lips: "A smile can be a great mask," says LaFrance, and we can be easily taken in by one. Conartists often use a smile to get in our good graces and psychotics use it to seem charming. "Smiling is a method we use to get our way when other direct approaches don't work," LaFrance suggests.

Smiles can even be newsworthy: As surgeons perform more full facial transplants, one of their measures of success is the ability of the recipient to smile, which restores a vital part of human connection and communication.

Here are other interesting facts from the pages of Lip Service:

• Social psychologists regard a smile as the default facial expression for females and impassivity as the usual facial display for males.

• British smiles typically display both the upper and lower teeth, while Americans primarily expose their upper teeth.

• One study found that fake or deliberate smiles are on average 10 times bigger than geniune smiles, probably because fake ones are meant to be seen.

• In the US, the typical emoticon for happy is :-) and :-( for sad since Americans tend to focus on the lower part of the face to express emotion. But the Japanese pay attention to the eyes. So (^_^) means happy and (;_;) stands for sad or crying.