There are many excellent reasons to have sex, although scientifically speaking, getting jiggy is a very costly way to produce offspring. Not only does it use up a lot of energy, but it is also horribly inefficient, requiring two consenting adults to produce just one baby. However, researchers from Stirling University may have finally solved the mystery of why most animals continue to reproduce sexually rather than asexually, by discovering that it boosts successive generations’ resistance to parasites.
Sex is not entirely ubiquitous throughout the natural world, as many species – such as bacteria and bananas – reproduce by cloning themselves, therefore requiring just one parent. This asexual method confers several benefits, not least of which is the fact that it produces an entirely female population, with every individual able to reproduce.
In contrast, organisms that reproduce sexually end up with half their population being male, none of whom are able to actually give birth, which means sexual colonies are only able to grow at half the speed of asexual ones.
To figure out why so many species insist on having sex, researchers conducted an experiment using the water flea, which, unlike most creatures, is able to reproduce both sexually and asexually.
The team collected both clonal and sexual offspring and exposed them to parasites that had infected the fleas’ parents. Results, which are published in the Proceedings of the Royal Society B, showed that sexually produced offspring were twice as resistant to infection as those that had been produced asexually.
This is because clonal offspring are genetically identical to their single parent, which means that parasites that have evolved to infect the parental generation are equally infectious to all subsequent generations.
However, sexual reproduction introduces genetic mixing, leading to variations among offspring so that future generations can out-evolve the parasites of their parents.
In a statement, lead author Stuart Auld explained that “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.”
So, if ever the human race becomes threatened by an apocalyptic infectious disease, our best bet may be to shag our way out of trouble.