Why are more girls than boys born in the Tropics and what does it mean?





Aristotle once suggested that the sex of a child was determined by the ardour of the man at the time of insemination, whereas other ancient Greek philosophers thought that it had something to do with the left and right sides of the body.

Two millennia later, an 18th-century French surgeon writing under the pseudonym of Procope Couteau took up the idea and advised men wishing to have baby boys to cut off their left testicle – a procedure no more painful than extracting a tooth, he said.

In more recent times, prospective parents wishing for either a boy or a girl have been offered all manner of remedies and food supplements to affect the sex of a baby. But none of these folk recipes – even those involving crystals under the bed – has been able to alter the fundamental biology that determines the 50:50 sex ratio.

A study published yesterday, however, has revealed a new twist to an ancient story. Scientists have found that the probability of giving birth to a baby girl rather than a baby boy increases significantly the nearer the mother lives to the equator. Conversely, the higher the latitude – and the further away from the equator – the greater the chances of a woman having a baby boy.



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