For God's sake don't say cheese

The old problem still haunts Labour. Not Europe, not the unions, but the smile, Tony Blair's instinctual, toothsome grin. The problem is, there are as many ways to read a smile as there are to read a manifesto.

Smiles are powerful things. Where would Jack Nicholson be without his demonic grin, or Claudia Schiffer without her radiant 1000-watt blast? Smiling gets people to do things for us. Babies recognise and respond to smiles at six weeks, and we go on responding to them until the end.

However, the fact that Tony Blair's smile is still seen as a turn-off in some quarters reveals just how complicated this apparently simple action is. One researcher has estimated that there are 18 different sorts of smile, and of those only one is the warm, genuine one that makes us feel good.

Humans are intensely social animals and we have evolved all sorts of complex behaviours to help us survive more efficiently in groups: laughter and smiling is one of them. "Laughter occurs when people are comfortable with one another. The more laughter, the more bonding within the group," says Mahadev Apte, a cultural anthropologist at Duke University in Durham, North Carolina.

But laughter isn't just a matter of being in with the in-crowd. We also laugh when we are embarrassed or socially uncomfortable. The reason for this, suggests Lawrence Mintz, a cultural historian at the University of Maryland, is that laughter also acts as a way of appeasing someone more powerful. If you feel you've committed a social gaffe - you are dressed up at a party when everyone else is dressed down - one way to stop people laughing at you is to get them to laugh with you.

So here already are two conflicting messages around laughter and smiling: "we're together" - obviously a good one for Blair - but also "I'm not a threat" - not such a good one for a leader. One of the ways these differences are conveyed is by subtle differences in the way our facial muscles work, and because spotting them is important, humans are good at it.

Research has shown that when it comes to feelings, the left side of the face is more expressive than the right, especially when the emotion is a fake. A genuine emotion tends to affect both sides of the face equally, but when the feelings are phoney there tends to be more activity on the left. A politician who gives a lopsided grin in response to a tricky question from the audience means that he probably isn't nearly so "pleased you asked me that" as he claims.

The reason that faking a grin is so tricky is that some of the muscles involved aren't under our conscious control. This shows up dramatically with stroke victims who have damage in the part of the left brain that controls the muscles on the right side of their faces. Ask them to smile and only one side moves. But make them laugh and their spontaneous smile appears as normal on both sides of the face.

A real smile needs two sets of muscles: one around the mouth, called the zygomatic, which you can choose to move like a finger, and another around the eyes, called the orbicularis, which only respond to genuine emotion. Politicians and actors can learn to fake it, but when a smile isn't heartfelt we talk about something being cold around the eyes.

Our obsession with putting on a smiling public face may reek of insincerity, but it is probably also a tribute to our democracy. For our ancestors, smiling and laughing was not really the done thing - particularly not for men (and it usually was men) of influence. The Earl of Chesterfield, for instance, advised his son in 1748 that "There is nothing so illiberal and so ill-bred as audible laughter", while Plato thought that the main reason for laughing was to make fun of the weak and those less fortunate than you.

This goes back to the idea of smiling as an appeasing gesture, something that has been studied by Professor Marianne LaFrance, a psychologist at Boston College, USA. "Often smiling is 'low power' behaviour - something that people who aren't holding all the cards do when dealing with the people who are."

But again it is more complicated than that, and the culture can change what a smile means. There is a theory, put forward by Dean Foster, director of Berlitz language schools' cross-cultural division in New York, which says that smiling gets less frequent the further east you go. This starts in America, where constant social smiling is the norm; in Western Europe we are a bit cooler, and in Russia it is fairly uncommon to smile with strangers.

Certainly the whole business of smiling gets even more complicated elsewhere. In Asia, Foster says, people smile when they're embarrassed, when whatever you did was somehow over the top - too much or too weird. In Japan, a smile accompanied by a quick sucking-in of air is "really a sign of disapproval that means the person you're talking to is very frustrated with what's been said."

What Tony Blair needs to be working on is what researchers call the Duchenne smile, named after the 19th-century French neurologist who identified it. It is the only one of 18 smiles identified by the leading researcher into facial expressions, Professor Paul Ekman at the University of California, San Francisco, which can stimulate that part of the brain that controls pleasant feelings.

"The key markers of the Duchenne smile that readily distinguish it from all others," Ekman has said, "are the crow's-feet wrinkles around the eyes and a subtle drop in the eye-cover fold so that the skin above the eye moves down slightly toward the eyeball." When you think of it that way, it's amazing any of us is co-ordinated enough to pull it off.

Surprisingly, however, this is not the smile to use if you are trying to plead with a policeman to let you off a speeding charge, or the boss to overlook that glaring error in your report. Professor LaFrance set up one experiment in which the subjects were meant to decide on a punishment for someone who might have cheated on an exam. The possibly guilty party flashed the judges various types of smiles - a full-blown Duchenne, a false or social one not involving the eyes, a miserable smile, or a neutral expression. The one that reduced punishment best was the false one. Professor LaFrance's theory is that it is because that's the one we see most often.

So with such a range of possible wrong smiles, it is perhaps not surprising that some people are picking up the wrong message from Tony Blair's grin, especially since there is probably growing tension between his bright grin and the fact that he is obviously a ruthless party operator.

However if he can't do anything about his own smile at this stage, there is still hope for him. What he needs to do is to get others, specifically newscasters, to do some smiling for him. An intriguing American study suggested that Peter Jennings, the anchorman of the American network ABC, may have influenced the result of the 1984 and 1988 presidential elections more than he thought. It was not a matter of anything he said; it was, rather, his facial expressions. He smiled more often when Reagan was seen or mentioned on air during the 1984 campaign, and again whenever Bush came up in the 1988 elections. Post-election analysis revealed that those viewers who tuned in to Jennings were more likely to vote for the facially favoured candidates than were voters who tuned in to other stations.

The effect is definitely there, according to research psychologist Carolyn Copper. In a controlled experiment involving simulated newcasts in a congressional election, she demonstrated that newscasters could indeed influence viewer attitudes toward candidates with nothing more than a smile. It's true that a newscaster's smiles can lead viewers to see that candidate as more likeable, but only when the viewers prefer the candidate to start with.