Smiles are recognised worldwide as a sign of friendliness, warmth, lack of hostility, trust and likeability,and they are one of the strongest emotional triggers we have. They are contagious. If you see someone smile, it is difficult not to smile back. If you doubt this, try a simple exercise on your next lunch break. Go into a series of shops or other outlets and smile at the people who serve you. Approach them with a serious face and speak to them. Then flash a big smile and note how many smile back. You will be amazed.

Smiles are one of the first things a baby learns to do because of this contagion. Young apes and monkeys have a significant advantage over their human counterparts, in that they can cling to their mothers’ fur to ensure close contact. But babies can’t do this, so they need signals that will make the mother want to stay close. Crying can attract her attention, but something is needed to make her want to stay when she arrives – a friendly smile.

While other species of primate do bare their teeth in a nonpthreatening way (expressions such as scowls and grimaces tend to pull the lips forward, but frightened ones pull them back; in the animal world, frightened = nonthreatening = friendly), we are the only species to have a ‘friendly’ smile where the corners of the mouth are turned upwards as well as pulled back.

When people put on a ‘false’ smile where the teeth are exposed but the eyes are cold, it is transparently obvious. Genuine smiles have three elements:

• The mouth. This lengthens as its corners move out and up, usually displaying the upper teeth. Although different people smile in different ways, showing the bottom teeth is sometimes a sign that the smile is false, as the lips have been ‘forced’ apart too far.
• The eyes. The lower eyelids become slightly raised, with wrinkles below them. Crow’s feet crease the skin at the corners.
• The cheeks. These rise and bulge, sometimes enough to narrow the eyes, and emphasize the crow’s feet and nose-to-mouth wrinkles.

For example, the smile below on Tony Blair’s wife Cherie looks false. The sides of the mouth have been pulled apart showing the bottom teeth, but there is no upward curve, no cheek bulging and no expression whatever in the eyes.

Now compare the two smiles from her husband. At first glance they may seem similar, but they aren’t.
The first is a genuine smile. The corners of the mouth are slightly turned up, the eyes are crinkled, and the lower eyelids are raised. The second, although similar, gives a different impression. The teeth are still exposed in his trademark grin, but the corners are pulled back to expose the teeth, not up (there is no fold halfway up the cheek), the lower teeth are exposed as the bottom lip is forced down and the eyes appear uninvolved.

I believe this is one reason Blair’s ‘trustworthy’ factor plummeted over the last two years of his time in power– too often his smiles appeared ‘pasted on’ just for the benefit of the camera.

Now compare the two smiles below from former New York Mayor Rudi Giuliani and President Bush:

Rudi Giuliani’s seems natural, genuine and unforced, primarily because the eyes are fully involved. It looks like he wouldn’t be able to switch it off easily. George Bush Jnr’s on the other hand, seems forced because it is more like the fleeting, easy-to-assume but just as easy-to-drop, tight-lipped smile we might get from a bank clerk.

Some people are natural smilers, others are not. If you conjure up a mental image of someone (let’s say a politician) it will be an amalgam of all the images you have seen and mentally stored of that person. If you are used to seeing them smiling, the image will be too, and vice versa.

Smilers include Rudi Giuliani, Tony Blair and Italian premier Silvio Berlusconi. Non-smilers would include UK ex-Prime Minister Gordon Brown,  Russian Premier Vladimir Putin, German Chancellor Angela Merkel and ex-French President  Jacques Chirac (the latter two permanently look as if their pets have just died – having said that, you probably would as well if you had to govern France. As President de Gaulle famously once said, ‘How can you govern a country which has 246 types of cheese?’).

Some people have a naturally hang-dog expression, where the corners of their mouths are permanently pulled downwards. When done as a ’one-off’ it shows that the person is angry, depressed, bored, unhappy or tense.
However, if a person tends to feel like this throughout their life, their face can set like that permanently (when your gran said ‘don’t do that – your face will set like that’, she was right).

Research has shown that such people are liked less, receive less eye contact and are avoided in the street. So if you’re a non-smiler by nature, simply be aware that the stress of speaking in public will probably mean that you will forget to smile at all, so you need to put more effort into it.

If you’re reading from notes, put a smiley face at the top of each page to remind yourself.