Why Sex Evolved

Scientists are curious people.

Some scientists are trying to determine why sex evolved.  Early life forms had to reproduce somehow, and presumably did so by natural cloning.  At some point in the past, however, sex entered the picture, and now, although some plant and even animal species that still exist reproduce without sex — bananas, starfish, and Komodo dragons are examples — sex has become the dominant method of reproduction.

Scientists wonder why.

7-water-flea-laguna-designGet your mind out of the gutter for a moment.  It’s a fair question, because scientists point out that sexual activity takes time and energy, frequently involves elaborate rituals — dating alone can be both expensive and time-consuming — and is therefore a lot less efficient than cloning.  Organisms that reproduce through cloning (which, incidentally, are entirely female, males not being needed) presumably could reproduce much more rapidly and easily than organisms that used the sexual approach.  As one scientist, Dr. Stuart Auld of the Faculty of Life Sciences of the University of Stirling, put it:  “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?”

Sex, fighting, dancing, and redundant males.  What could be more interesting than that?

Dr. Auld and his colleagues came up with an ingenious approach to trying to test why sex might have evolved.  They found an organism that reproduces both through cloning and through sex, the common water flea, and they compared offspring of the same mothers that were produced through cloning to those produced through sex.  They found that the sex-produced offspring were much more resistant to disease and parasites than their cloned sisters.  Sex evidently allows the genetic material to be mixed up and also shared, and organisms that use the sex route therefore get an advantage in avoiding illness.

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

So there you have it.

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