Baby sex ratios linked to latitude

New Scientist ^ | 26 APRIL 02 | editorial staff

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Baby sex ratios linked to latitude

00:01 26 April 02
Emma Young

People living in southern Europe have more male children than those in the north - but the latitude link is reversed in North America. The findings rebut suggestions that temperature variations could explain altered sex ratios at different distances from the equator.


Victor Grech and his team at St Luke's Hospital, in Malta used data from the World Health Organization to compare the male to female birth ratio in Europe and North America over 50 years.


They split the continents into three separate bands: southern Europe, central Europe and Nordic countries; and Mexico, the US and Canada. They found that in Europe, significantly more boys were born in southern Europe, such as Greece and Spain. This confirmed the findings of a smaller study conducted by the team in 2000.

"And this fits with an earlier German study that plotted male and female births, and found more males when the conception date was in the hottest months," Grech says. "But then we looked at North America, and the ratio was inverted, with significantly more males born in Canada. That really foxes me."

Environmental toxins

Just over 51 per cent of all babies born worldwide are males, according to the accepted average. The ratio of male to female births identified by Grech's team was slightly lower than predicted in all countries, but varied from one to another.


Between 1950 and 1999, the team found a shortfall of about 200,000 boys in central Europe, compared with 12,744 in southern Europe. In Mexico, the shortfall for the period between 1958 and 1997 was 521,789, compared with 21,993 in Canada. When population size was controlled for, the differences were statistically significant.


Research shows the average ratio of male to female births over the past 50 years has been decreasing worldwide. Some scientists think male embryos may be more susceptible to environmental toxins. Recent research has also shown that parents who smoke heavily around the time of conception are more likely to have female children.

Plant explosion

"I honestly haven't got a clue about what is behind our findings," Grech says. "But it is possible that exposure to environmental toxins such as dioxins could be involved."


The number of baby boys born to people living in the Italian town of Seveso declined dramatically after an explosion at a herbicide plant in 1976 released high quantities of dioxins into the air, he points out.

"We now need to breakdown the data and look at trends over time - that might indicate whether exposure to environmental toxins accounts for the results," Grech says.


Journal reference: British Medical Journal (vol 324, p 1010)


00:01 26 April 02

[Jeff Chandler]

There can only be two possible explanations for this phenomenon: global warming, or the occupation of the West Bank

[Jeff Chandler]

Or Enron. That makes three.