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Girl or Boy?Which One Do You Wish?

IN FOCUS: A question of sex

Many animals, such as some lizards and crocodiles, have the sex ratios of their offspring determined by external factors such as temperature. Somewhat bizarrely, the female of one species of bird even determines whether it has more sons or daughters based on the colour of its mate’s head. Now it appears that this kind of environmental factor might have a small influence on the sex ratios of humans too.

A clever new study took data found online in the CIA’s World Factbook (a very handy resource if you’ve never used it before…) and used it to compare the gender ratio of babies in 202 countries from all over the planet. What it found was intriguing: significantly more girls are born in the planet’s tropical nations than those further north or south.

Already we knew that slightly more boys are born than girls, thought to be because a larger number of young men perish through disease or violence than young women (the established figure has been 51.5% male births). But the new study shows this is wrong. It found that, in fact, 51.1% of newborns in tropical countries are male, compared to 51.3% for countries in cooler regions. The differences sound small but add up to thousands fewer boys in those tropical nations each year.

The researchers behind the study are at a loss to explain the mechanism for the difference. But the findings raise an interesting question – could it actually be possible to influence the sex of our offspring by altering our environment? Other research is already seeming to back this up: last year a study found that eating high calorie food prior to conception, especially breakfast cereals, could boost the chance of giving birth to a boy.


April 4, 2009 - Posted by | 1

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