Smile. And the world smiles with you. Frown and your face drops and frightens children.

© JoshMak
According to body-language experts, if you don't smile much, over time, it will come out in your face. Without practice, smiling muscles weaken and wither. Bitterness, sadness and anger repositions the muscles and tissue into a "downturned smile" - this is where instead of smiling, a pouching at the corner of the mouth pulls your smile downward. This effect can be permanent and some people go scowling into oblivion.

Like everyone else who comes across this theory, I checked the sides of my mouth to see where my face stood. Obviously faces are made up in diverse ways, and smiling up or down doesn't necessarily mean anything. Then again maybe it does. Studies have shown that small children are instinctively afraid of the downturned smile and even adults exert caution around it.

Although it doesn't seem like psychologists recognize the phenomenon, plastic surgeons certainly have. You can now have your choice of Snap On Smiles, Botox Smiles and Smile Replacement surgeries where tendons are ripped and reattached, flesh is re-sculpted and various congealing substances are injected around the mouth. The specialists claim to be able to literally turn a frown upside down. So be as miserable as you want to be. For a bunch of cash, you can always get a reconstructed smile pasted back on your face.

"Over time," says Allan Pease, body-language expert and author of the Definitive Book of Body Language, "the face becomes a permanent record of emotions throughout one's own life. There's the old expression: 'After 40, your face is your fault,' but in fact it's even way before that."

Perhaps, what is disturbing about the surgical smile craze is there is an obvious natural solution to the problem of a gloomy face:

Smile more.

Smiling naturally exercises and draws up the smiling muscles. The downturned smile is easily corrected by leading a somewhat joyful life. But how? Whistle while you work? Sing in the shower. Join a cult?

An emerging field of science suggests that some of the most potent forms of joy aren't found inside people, they're found between people. The study of contagious behaviours, emotions you "catch" from others, has yielded insights into what people bring out in each other. When we think contagions, we usually think the common cold and SARS. But the human contagions of smiling, hugging and laughing are starting to get new attention.

A study published in November 2006, by a team of neuroscientists at the University College London, proved for the fist time something most of us probably already suspected - that laughter was contagious. However, it was perhaps a secondary finding that was more startling.

During the experiment, the scientists tested the brain's reaction to a variety of stimuli from laughter, to fear to disgust. Over the course of their study, they measured the contagiousness of the responses. What surprised the scientists was they had assumed negative triggers like fear or anger would produce the strongest response. After all, the entertainment industry - particularly TV, movies and videos games - and many politicians generally work from this assumption. But as they looked at brains lighting up under fMRI scans, it seemed like the neurological response to positive emotions was often greater in terms of brain real estate and effect. Contagious laughter was particularly dramatic. When laughter catches on, it sets off a cascade of chain reactions in a nearby person's brain that induces smiling, laughter and heart thumping. Although it was not the point of the experiment, the results were eye-opening.

"For example, if I hear someone scream in fear," explained lead researcher and cognitive neuroscientist Sophie Scott, "I might feel frightened but I might not actually start to scream. If I hear someone laugh, however, I would almost certainly start to smile. And when you look at it, the mirroring of behaviour that humans do is almost always strongly positive."

However, the dark side of this tendency has also become more apparent. Since the events of Sept. 11, there's been an increase in outbreaks of mass psychogenic illness. This is where a frightening event will cause a sudden panic and people actually develop symptoms of diseases or poisoning they probably don't have. This has happened when people smell mysterious substances on subways or buses and believe they've been poisoned or infected, although they haven't. Fear, like smiling, can produce deep involuntary responses.

Understanding how contagious behaviour works has a way of revealing what human beings are made of. For example, we are just starting to figure what natural smilers we are, possibly because we start very early. Conventional thinking has babies learning to smile a few months after birth, with serious doctors usually attributing the first smiles to "gas." In 2004, professor Stuart Campbell, at London's Create Health Clinic, used 4D scanning - a new form of ultrasound - to reveal that babies begin smiling in the womb.

"I've seen a smile on a fetal face as early as 18 weeks," he said in an interview. "You see them regularly at 24 weeks."

While Campbell wasn't sure what was instigating the smiles, whether the babies could be "catching" them from their mothers, the smiles were always contagious in reverse.

"When the mothers see images of their babies smiling in their wombs, they always begin to smile and laugh and beam. They're ecstatic."

Its early arrival may explain why few things are more contagious than smiling itself. Take the remarkable story of three smiling fat men stationed at the entrance to Mount Royal métro.

François Provost, who weights 280 pounds, leads a recently founded "fat guy awareness group," MÉGARS. To join, you have to be big, overweight and wear minimum Size 42 pants. The "mégas" as they're known decided to film a spontaneous meet and greet a couple weeks ago in Montreal. They stood smiling with their arms out at Mount Royal métro station. Perhaps it was because they were three jolly looking fat guys, but they were surprised at how much people smiled back at them.

There's an interesting explanation for this. A Swedish research team at Uppsala University demonstrated that smiling is often irresistible. Because smiling is triggered unconsciously, we'll smile back before we have a chance to think about it. To avoid smiling we have to work at it, which many people do. So when we come up the stairs and see three big guys smiling at us, most of us would smile.

But this is where it gets weird.

The 3 Men had a cameraman and were planning to produce a parody video of the Free Hugs campaign for their website. Free Hugs is an international movement launched in 2004 by Juan Mann, a young Australian who started hugging strangers at a crowded intersection in Sydney, causing a worldwide trend generated by the contagiousness of hugging and the infectiousness of YouTube.

"We were planning to pressure a few people into hugging us to show that people can love fat guys, too," he said.

Provost said what amazed them is they didn't need to pressure anyone. When people saw the big guys smiling, they just stepped up and hugged them, by the dozens.

"When people saw us they walked over to us and embraced us, often passionately," he said. " People ran up to us and hugged us, total strangers, just leapt into our arms," he said. "It went a little crazy."

Crazy indeed. Right in the square in front of the métro, the mégas set off some kind of hug riot. I've seen the video, and people are leaping into their arms. What started as a bit of a parody turned into a humbling love fest for the big men, who ended up hugging over 400 Montrealers.

"It was everyone, young and old, male and female, anglo and franco," said Provost. "A woman hugged me and said, I just lost my mother and I have no family left. You holding me has made me feel so much better."

While the mégas are still stunned by what happened their experience has intriguing echoes in the science of contagious behaviours.

"Many people told us we made their day," said mégas member Daniel Lafond, "but they made our day."

Author and University of Virginia psychology professor Jonathan Haidt believes there are powerful physiological implications to contagious behaviour. Haidt himself invented the entirely new term "elevation" to explain a physical sensation produced when we witness acts of kindness and "moral beauty."

Elevation is felt as a sudden warmth in the centre of the chest.

"Psychologists have conducted a great deal of research on the negative moral emotions, which people feel when they witness acts of cruelty, injustice, and impropriety. Yet little is known about the positive moral emotions," Haidt says.

Haidt told me in an interview that he got the idea from one of America's founding fathers, Thomas Jefferson. Jefferson once wrote a letter noting that he experienced a physical "dilation" of the chest and an "elevated" sense while considering acts of "moral beauty."

People might experience elevation when they see a family reunited on the news, when an old woman is rescued - or possibly when they unexpectedly get a hug.

In fact, this ability to produce a bonding hormone right out of the centre of our chests might explain the curative effects of hugging. Studies show that women who are hugged more often have a lower risk of heart disease. It may be that hugging itself trips a powerful nerve with chest-to-chest contact.

If you don't believe me, try politely hugging someone right now. You should notice a touch of heat in the centre of the chest. That would be the beginning of elevation.

Haidt credits the vagus nerve, which goes from the brain stem down the middle of the chest and into the heart with producing the effect. A stimulated vagus nerve causes a surge in oxytocin, a natural love hormone that has been shown to bond mothers to children and lovers together in a euphoric glow. At the prompting of the nerve, the thymus gland and the heart synthesize oxytocin, possibly helping explain why so many feel that virtue literally emanates from the heart.

But what happened to the big men at the spontaneous hug fest?

I asked Provost whether he remembered any physical sensation.

"Yes. I felt a warm feeling, in my heart," he said.

I apologized for medicalizing, but asked more specifically where the feeling was?

"Actually, it was in the centre, the very centre of my chest," he said.

Elevation has three principal physical effects. First would be a warmth in the centre of the chest, second a tightening of the throat, and third a tearing of the eyes often accompanied by a smile. These could only be triggered by one thing, our friend the vagus, as only this nerve wires all of these reactions. Haidt sent me his latest research on elevation where he goes farther, demonstrating that nursing mothers lactate when they witness elevation.

While the big men don't recall lactating, something else did happen.

"I was on the verge of tears," said the 280-pound Provost.

"So was I," said his mégas-partner Daniel Lafond. "The whole time."

I asked Lafond whether he remembers anything happening in his neck.

"My throat tightened," he said.

What I like about the Theory of Elevation is it suggests we are naturally turned on by goodness. Our basic decency comes to us easily, naturally and physically, without need for excessive moralizing and rationalizing.

"I feel so lucky," said Provost, " to live in a country where I could just go up and hug total strangers."

I described the scene to professor Haidt.

"That's elevation," he said. "Elevation is very contagious. Probably part of it was these guys could see each other being moved and they were just swept up."

Without moralizing or rationalizing too much, there may be a lesson here. The reason smiling is so potent is that it reaches across the divide between people and connects us unconsciously and involuntarily. Scientists are beginning to discover that the contagious involuntary behaviours can bring out the best in us. We're just built that way. So, even if we want to be whiny grumps, our bodies want to hug, smile and laugh with people. We just need to get out of the way.

While the jury is still out on whether we're wired more positively than negatively, what may matter more is that we can affect that wiring. The more positive we are, by the law of contagion, the more positivity we get back, and the more positive we may become. Although they didn't go looking for it, the big guys found love where they didn't expect it, between strangers, and that experience left the mégas literally smiling for hours.

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10 things that make you smile - naturally and involuntarily

1. Small children.

2. Contagious laughter.

3. Elevation (see story).

4. Good jokes.

5. Hugging.

6. Meeting and greeting people.

7. Holding hands.

8. Remembering good times.

9. Just for Laughs gags.

10. Being smiled at.