How mothers dominate family life

Research, published in New Scientist, suggests testosterone levels could be the key.

And the magazine also suggests mothers-in-law really can be bad for your health with historical research which shows babies were more likely to die if their father's mothers were around.

New Zealand researchers used an internet questionnaire to assess the dominance of a mother-to-be's personality.

Women were asked to choose from a list of 64 adjectives, such as proud, free, bored, awed and arrogant.

Among them were 13 words linked with high levels of dominance.

On average, women ticked three of these words.

Gender selection

But Dr Valerie Grant, a reproductive scientist from the University of Auckland found those who ticked over eight of the key words had an 80% chance of having a boy.

She carried out further research, which showed those women who scored highly in the tests also had high levels of testosterone.

Dr Grant told New Scientist: "People everywhere have it ingrained in them that the father's big contribution process is the sex of the offspring."

But she believes women control gender selection to produce babies whose sex suits them, pointing to the commitment they have to make to the conception, nurturing and raising of offspring.

She added: "I think the evidence that the male has anything to do with it is very flimsy."

Flesh and blood

In separate research, a study of German peasants living in the 18th and 19th centuries found that having the father's mother around doubled a baby's chance of dying.

Researchers from Germany's Giessen University believe this could be because the mother-in-law could not be sure the child was her own flesh and blood, whereas the mother's mother could.

Other studies have shown that the presence of paternal grandmothers may a less beneficial effect on a child's health - but this is the first to show a negative effect.

The researchers looked at church registers to obtain birth and death data for low-income families in the Krummhörn region of northern Germany.

They found if the maternal grandmother was alive when the baby was between six and 12 months old, it was 79% more likely to survive than if she was dead.

Eckart Voland, who led the research, said this could be because they help with weaning the baby.

But if the father's mother was alive, the baby was half as likely to survive as they would have if their grandmothers were dead.

Destabilising

Dr Voland suggested the explanation for the difference could be that a man's mother might be suspicious over the baby's paternity in the strict religious society they studied.

The harassment of the mother might then impact on the child's care.

But Harold Euler, an expert in the evolution of family relationships at Kassel University in Germany said the grandmother may want to destabilise the relationship, so her son can go on to meet new women.

"The son can also get grandchildren by having sexual relations with other women," he said.