Revealed at last: Why boys will be boys and girls will be girls

It's the gene that explains feminine intuition. It's the gene that explains why you can persuade a group of adolescent men to attack a machine-gun emplacement. It's the gene that explains why New Men are made, not born.

Its effects may be subtle, but a team of British scientists is quite certain that they have tracked it down to the X chromosome - one of the two sex chromosomes.

The discovery marks the first time that behavioural differences between sexes have been pinpointed to a single location on one chromosome. Its implications are far-reaching. Professor David Skuse, who led the research at the Institute of Child Health, said: "It may imply that we need to think seriously about providing more structured social education for boys, compared to girls."

He emphasised that the gene is not a "gene for criminality", or for misbehaviour - though it may explain why boys can more easily be persuaded to behave badly: they are less able to see that their behaviour is errant.

Both men and women have the gene - but it is only "switched on" in women. Its effect is to make them responsive to others and able to recognise social norms without prompting.

"Feminine intuition comes about by observing non-verbal behaviour," said Professor Skuse. "It has a genetic origin. It's nothing to do with hormones. Boys aren't poor at this because of testosterone. It's because of the X chromosome."

Such a definite sexual split in the allocation of a gene would have to have an evolutionary advantage for both genders. Professor Skuse said: "While girls pick up social skills from those around them, boys are a blank slate to be written upon. The question is, why is it advantageous for males to be socially insensitive? We don't know for sure.

"It could mean that it's easier for a dominant male in a tribe to recruit them to a hunting party - or even for war. I don't think many young women would be prepared to go into the face of guns like young men did at Gallipoli. And being less empathic makes it easier to go out and kill somebody."

But he did have some reassuring words. "This finding does not mean that men are incapable of learning social skills. But it does mean they have to be taught them."

New Men, therefore, can only occur through education - they aren't born to the role.

Like all other genes, this one instructs the body to make a single protein, which has not yet been identified. But Professor Skuse doubted that we will ever be able to bottle feminine intuition. The protein seems to affect the brain, probably during the embryo stage.

The conclusions, reported today in the science journal Nature, emerged from interviews with parents of children who have a rare genetic condition known as Turner's Syndrome. Normally, men have an X chromosome (inherited from their mother) and a Y chromosome (from their father); women have two X chromsomes, each inherited from their parents. Turner's Syndrome, which only affects females, is caused by faulty cell division before conception, and leaves them with a single X chromosome rather than two because the egg or sperm fails to deliver an X chromosome.

Girls with the syndrome are usually of normal intelligence, but they frequently struggle to learn social behaviour such as recognising non- verbal signals.

Psychological tests on 80 girls with this condition found that the effect was more marked in those who had received their single X gene from their mothers. In those whose X gene came from their father, the lack of social skills was less marked.

This is because of a process called "imprinting": when two copies of a gene are inherited, only one will function. The "intuition" gene is turned off in the father's cells - but turned on, or imprinted, in his sperm. By contrast, the gene is turned off in the mother's egg cells - meaning that under normal circumstances a male cannot inherit feminine intuition.

The chromosomes pictured at the left come from a woman - because the sex chromosomes are both Xs (circled). The other set comes from a man, because it includes the X and Y sex genes (circled, right): you must have a Y gene to be male. Though both sexes have the "intuition" gene, located somewhere near the centre of the X chromosome, it only functions in women.

Men carry a silent copy of the gene, which they can pass to their daughters - who receive a working version. The gene was pinpointed by interviewing and testing women with a rare genetic disorder called Turner's Syndrome. They have a single X chromosome, inherited from their mother or father.

Photographs: Science Photo Library