Analysis

Winnipeg Free Press - PRINT EDITION

Your job influences the sex of your children

By: Robert Alison

Posted: 10/13/2009 1:00 AM | Comments: 0

If you want male offspring, be engaged in an appropriate male-type profession. New research shows that parents who have alpha-male jobs are much more likely to have sons; those in stereotypically female jobs are more likely to have daughters.

So far, the genetics of the link between profession and offspring gender is not understood. But researchers suggest that offspring gender reflects the "brain types" of one or both parents.

Although maleness or femaleness in humans is determined by genetic factors, new studies show that environmental and social influences can contribute. Research at the University Medical Centre in The Netherlands indicates some environmental or social variables are capable of "silencing female meiotic sex chromosomes".

In turtles, crocodiles, alligators, some lizards and birds, the sex of offspring is determined by the temperatures at which eggs incubate, says Jeffrey Lovich of the U.S. Geological Survey. Higher temperatures tend to produce male embryos.

"Selection should favour 'environmental sex determination (ESD)' over 'genetic sex determination (GSD)' when the developmental environment differentially influences male vs. female fitness," researchers at Iowa State University and the University of Sydney confirmed in a recent report.

Studies by Satoshi Kanazawa of the London School of Economics shows a disproportionate number of parents with Type-S brains produce sons; Type-E brains tend to produce daughters.

Researcher Griet Vandermassen of Ghent University has explained that Type-S brains tend to occur in people who excel in "systemizing," or figuring things out. Type-E brains tend to occur in people who are skilled at "empathasizing" (assessing through one's personality, especially feelings). Males most often have Type-S brains; females have Type-E brains.

"Brain types are heritable and they affect boys and girls differently," the researchers conclude.

"That is why systemizing parents tend to produce more sons, empathizing parents produce more daughters.

"When one or the other or both parents have Type-S brains, the couple is expected to produce more sons; when one or both have an excess of empathasizing skills, the couple is expected to produce more daughters," the researchers report.

In Canada, the overall human sex ratio is .98 males for every female; 1.06 males per female at birth. But Type-S parents produce 140 sons per 100 daughters; Type-E parents produce 135 daughters per 100 sons.

Type-S professions include: engineers, mathematicians, auditors, physicists, chemists and scientists. Type-E professions include: nurses, dieticians, therapists and teachers.

Studies show that engineers and others in the Type-S professions are most likely to have sons, whereas nurses and others in the Type-E professions are more likely to have daughters.

Preliminary data suggest other factors are involved in determining offspring sex. A disproportionately large number of tall parents produce sons; shorter parents more daughters. Violent fathers are much more likely to produce sons.

Promiscuous parents are likely to have sons. Beautiful parents more often have daughters.

Scientists speculate that Type-S brains were more adaptively advantageous to ancestral males; Type-E brains were more beneficial to ancestral females. Social and environmental factors tended to favour one type or the other and ultimately influenced sex ratios in human populations.

Robert Alison has a PhD in zoology and is based in Victoria, B.C.

Republished from the Winnipeg Free Press print edition October 13, 2009 A13

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