Women who have multiple sex partners 'preserve humanity'

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PROMISCUOUS women who have children by different men could help prevent humanity from becoming extinct, scientists claimed yesterday.

A study has shown that women who have multiple sexual partners reduce the risk of replicating a genetic quirk that means they are more likely to have only daughters.

A study by the Universities of Exeter and Liverpool contends that if all women had children with just one partner, a male- destroying chromosome could be reproduced and spread until humanity eventually became 100 per cent female, precipitating its extinction.

It claims that having multiple partners reduces the spread of a sex-ratio distortion (SR) chromosome that would lead to all-female offspring.

The SR chromosome has the effect of killing all the "male" Y chromosomes before fertilisation.

Polyandry, the practice of females having multiple partners to protect the future of the species, is common in the animal kingdom. Scientists believe that its occurrence has several benefits, including ensuring reproductive success and conferring more variation in traits to female's offspring, which would have a wider benefits for the health of a species' pack, hive or family.

The new research is the first to suggest that female humans should also have more than one man to safeguard our future.

The research was published in the journal Current Biology. One of the study's authors, Professor Nina Wedell, said: "Polyandry is a widespread phenomenon in nature, but it remains something of an enigma for scientists.

"This study is the first to suggest it could save a population from extinction."

Tom Price, another author on the paper, added that while the research spoke to all reproducing creatures, the complex nature of humans made it harder to apply in hard and fast terms.

The sex of a child is determined by X and Y chromosomes – a woman is XX and a man is XY.

But some men also carry the SR chromosome and when a human egg is fertilised, the SR kills the Y – producing a female baby.

That female will now also carry the SR gene, meaning any sons she has will also have SR chromosomes and will father only females.

But by having multiple partners – some of whom will not have the SR chromosome – the female can help ensure her descendants are males and females. The new research says monogamy means the sex ratio distortion chromosome will be passed down more often – eventually leading to an all-female population.

Experts carried out the experiment by studying fruit flies – which share 60 per cent of human genes. Some given some multiple partners and others were restricted to one mate each.

Over 15 generations, five of the 12 populations that had been monogamous died out because of a lack of males.