“One of the oldest questions in evolutionary biology is – why does sex exist when it uses up so much time and energy?”


Two answers come to mind; reproduction and pleasure.

Some may go as far as saying it is therapeutic and good for the health but ‘reproduction and pleasure’ are the two likeliest answers.

Scientists at the University of Stirling in Scotland sought more understanding of the phenomenon of sexual intercourse.


The team of experts took an innovative approach to test for the costs and benefits of sex.

What they discovered was that sex can help the next generation resist infection.

Using the waterflea, an organism that can reproduce both ways – clonally and sexually – researchers found that sexually produced offspring were more than twice as resistant to infectious disease as their clonal sisters.


Stuart Auld, a doctor at the Faculty of Natural Sciences, said: “Sex explains the presence of the peacock’s tail, the stag’s antlers and the male bird of paradise’s elaborate dance.

“But if a female of any of these species produced offspring on her own, without sex, her offspring should come to dominate, while the other females watch the redundant males fighting and dancing. So, why are we not surrounded by clonal organisms?

“By comparing clonal and sexual daughters from the same mothers, we found sexually produced offspring get less sick than offspring that were produced clonally.

“The ever-present need to evade disease can explain why sex persists in the natural world in spite of the costs.”


“But sex needs to be over twice as efficient as cloning to outweigh its costs. If sex is to be favored by natural selection, a sexual mother needs to either produce twice as many offspring as an asexual mother, or produce offspring that are twice as good.”

The study has been published in the Proceedings of the Royal Society B.

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