WE would be lying if we said wed never done it: told an untruth to defend or promote ourselves, to spare someones feelings or to ease a difficult situation. We teach our children never to do it. Yet the strange thing about lying is that, unlike stealing, murder this a moral crime we all commit on a regular basis. We lie by saying, 'Im fine thanks when were feeling miserable; we lie by saying, 'What a beautiful baby while inwardly marvelling at its resemblance to an alien - and everyone has faked enthusiasm for someone elses cooking.Not only do we constantly make exceptions to the rule against lying; sometimes we approve of it. If a doctor tells a bereaved husband that his wife died instantly in a car crash, rather than the truth - that she spent her last minutes suffering horrific pain - we applaud his compassion. We call the lies we like 'white lies, but if we are asked to define precisely what makes a lie white, we soon get lost in contradictions. In recent years, a growing number of academics have been investigating the complex role of lying in our lives. What they have discovered turns much of our thinking about lying on its head. When I started to research this topic I imagined the human tendency to lie was a design flaw. In fact, it has driven the evolution of our species. I took lying to be a sign of mental instability; I discovered that good liars tend to be better-balanced people. I learned that self-deception can lead to success at work and happier relationships. Lying is not a perversion of our nature, its central to it. The abilities to knowingly deceive and to detect deception are human and play a part in our relationships. We are all born liars - but when do we truly start to lie? Between the ages of two and four, childrens lies are usually told to avoid punishment. Very young children tend not to be good at lying. MO Then, at around the age of four, something changes. Psychologists have identified that somewhere between the ages of three-and-a-half and four-and-a-half, children learn how to lie with much greater skill and enthusiasm. Lying is hard. Children who lie well must be able to recognise the truth, conceive of an alternative, false but coherent story and juggle those two versions in their mind, while selling the alternative reality to someone else - all the time bearing in mind what the other person is likely to be thinking and feeling. It is wondrous that a child of four should be able to do this - if you catch your three-year-old in a well-told lie, be impressed - but dont congratulate them. In the story of Snow White, the Queen - Snow Whites wicked stepmother - repeatedly fools our heroine by disguising herself as a harmless peasant. When Snow White accepts her seemingly kind offer of a delicious apple, the Queen attacks her. At the moment Snow White opens the door to the Wicked Queen, she believes she is opening the door to a peasant woman, not her stepmother. Her reason for believing this seems obvious to us, as it does to four year-olds. We know that Snow White didnt see what weve seen and that forms part of the drama. However, children under three tend not to enjoy Snow White. They are unable to grasp that Snow White has been misled because they dont understand the concept of different people believing different things. Of course, until they grasp that point, its impossible to think about deceiving anyone. Theres no point in telling a lie if everyone believes the same thing. Dr Victoria Talwar, assistant professor of child psychology at McGill University in Montreal, has used a well-established experiment, the Peeking Game, to show the slight difference age makes to lying. After meeting the researcher and playing a few games to establish a relationship, the child is introduced to a guessing game. He is asked to face the wall. The researcher brings out a toy and the child is asked to guess what it is from the sound it makes (a police car, a crying doll) and then a deliberately baffling one, such as a cuddly cat that makes no noise while at the same time opening a musical greeting card. The child is stumped. Then the researcher makes an excuse to leave the room and warns the child not to peek. Children invariably turn around a few seconds after the door is closed. The researcher returns and asks for the childs answer. When they give it triumphantly, the researcher asks if he peeked. Generally, three-year-olds confess, whereas a majority of children aged four lie and say they did not. By the time they are six, 95 per cent of children tell this lie - wherever they are from in the world. The number of lies told by children-tends to spike among those aged four as they exercise their amazing new powers, but it usually declines during their first school years, as the child receives social feedback. They learn that the benefits of lying (self-defence or getting something they want) come at a hefty price. They find that if they lie too much, teachers and friends lose faith in their credibility and they become unpopular. The majority of children learn not to lie instinctively, but a few remain impervious to it. Persistent lying in older children is usually the sign of a deeper malaise. If a child is lying habitually after the age of seven, she will probably continue to do so for years to come, even into adulthood. According to Professor Nancy Darling of Oberlin University, Ohio, who specialises in the moral development of older children, lying is a 'self-reinforcing activity. If a lie works to get a child out of trouble, she might try it again. Professor Kang Lee of the University of Toronto and director of the Institute of Child Study says: 'The time to catch a liar is before eight years of age. The question of how children learn not to lie is as interesting as how they learn to lie in the first place. Most childrens lies are told to stay out of trouble rather than to manipulate others, and punishing these dodges too vigorously can trap children into a cycle of dishonesty. Prof Darling says: 'If you walk into a room to find your five-year-old with milk spattered everywhere and ask, Did you do that? youre inviting them to lie. If you say, Ah, you spilt the milk. Lets clean it up, shes less likely to lie. If she still does, its best to laugh it off - while making it clear you know shes lying. Theres no point telling her off because she lied. If a child feels their character is constantly under assault - or if they live with the threat of punishment for lying - they will build a shield of deceit around themselves. And as for adults, theres no settling the debate as to when it is right or wrong. We are, after all, born liars.