Strong woman? Chances are you'll have a boy

A mother's personality and lifestyle may determine whether she has a boy or a girl. Women who are dominant, assertive and confident are up to five times more likely to have a boy than women who consider themselves timid, inhibited and shy, according to a new book.

And higher levels of female testosterone production in response to stress and pressure may well be the reason why dominant women tend to have boys, according to the research.

"Individual differences between women in the amount of testosterone appear to underlie both the potential to behave in a dominant way and the potential to conceive male infants," claims Dr Valerie Grant, the author of Maternal Personality, Evolution and the Sex Ratio. "I think it is most likely that there is a rise in testosterone under stress in females and this is the ... cause of skewed sex ratios."

The theory is supported by casual observation of some high-profile women. Beginning at the top, the Queen has three sons and one daughter, and Diana Princess of Wales had two sons. Indira Gandhi, the Indian prime minister who was assasinated in 1984, had two sons, Sanjay and Rajiv, while Cherie Blair QC has two sons and one daughter.

Harriet Harman, the social security secretary, has two boys and one girl, and fellow Labour MP Diane Abbott has one son. Majorie Scardino, the new chief executive of Pearson, has two boys and one girl, while actresses Patrica Hodge and Prunella Scales both have two sons, as do fashion designer Vivienne Westwood and broadcaster Jenni Murray.

"The more dominant a woman is, compared with other women, the more likely it is that she will conceive a male infant. Women who score in the top 20 per cent for dominance are five times more likely to conceive a male infant than women at the other end of the scale," says Dr Grant.

Traditionally, the sex of a baby has always been believed to be determined by whichever sperm wins the race to fertilise the egg.

But if the sex of a child was solely down to such pure chance, the numbers of boys and girls being born should even out over time. In fact, there are 105 boys born for every 100 girls, and at certain times the excess of boys soars even higher.

According to the theory of maternal dominance, the reason why more boys are born during and after wars is not because of divine intervention to replace dead men, but because women are in more dominant positions while men are away fighting - and, therefore, more likely to have raised testosterone levels.

In women, testosterone production is associated withadrenal glands which are involved in the body's response to stress. The maternal domination theory is that secretion of testosterone in women increases under stress and the hormone levels affect the uterus, having a "gatekeeping" role over which sperm gets to the egg.

"Thus, although X and Y sperm are produced in equal numbers by the male, the chances of either one or the other actually fertilising an individual woman's ovum may not be equal at all," says Dr Grant, lecturer in behavioural sciences at the University of Auckland, whose book is published by Routledge later this month.

Dr Grant believes the theory of maternal dominance fits well with the high birth rates of boys during wars, epidemics and other times of stress.

"In times of war, when, in the absence of their men, women are required to take over male roles, there is a temporary shift in average dominance. For a short time these social changes mean that there is a rise in dominance and its hormonal underpinnings, which is likely to be further accentuated by the rise in female testosterone during times of long-term stress. With this increase, some women who were close to the hormone threshold for conceiving male infants, tip over it. Hence the temporary rise in male births."

She adds: "War, famine, disease, captivity and overcrowding cause the kinds of stress that produce raised sex ratios."

Dr Grant says women who have children of both sexes can be explained by life changes: "Most women are moderately dominant, but life events and other environmental influences will change the levels of dominance from time to time and result in their conceiving infants of both sexes," she says.

Maternal dominance theory holds that a woman's personality indicates whether she conceives a boy or a girl. The sex of the inf ant may depend on which sex she is most suited to raise.