Study: Sex exists because of parasites


Here's a weird bit of biology. A new study suggests that parasites might be responsible for the existence of sex as we know it. According to, biologists at Indiana University have determined that:

"Although sexual reproduction between two individuals is costly from an evolutionary perspective, it is favored over self-fertilization in the presence of co-evolving parasites. Sex allows parents to produce offspring that are more resistant to the parasites, while self-fertilization dooms populations to extinction at the hands of their biological enemies."

Basically, that's a long-winded way of saying that we have a little worm called Caenorhabditis to thank for all our sexual exploits. Otherwise we'd be doomed to a sexless existence (and an all-female species).This is a rare occasion when we can actually attribute a parasite for making our lives a lot more fun.

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Commentarium (6 Comments)

Jul 11 11 - 2:13pm

I'm sure that this was just copied from the poorly written HuffPo article, but C. elegans is not a parasite, and definitely didn't 'cause' sexual dimorphism in humans. It's just a harmless nematode that lives in rotting vegetative material and feeds off of bacteria. It's been used as a model organism for genetic studies since the 70s, and was chosen for this study because the species consists of males and self-fertilizing hermaphrodites -- meaning that the scientists could study both cross- and self- fertilization in the same species.

Jul 11 11 - 5:12pm
Sean Matthews

Um, there are overwhelming theoretical arguments in favour of sexual reproduction in terms of rapid evolution of fitness. Sexual reproduction appeared for approximately the same reason (viewed from a very abstract perspective) that boulders roll downhill. You don't need a parasitic worm to do it.

Jul 11 11 - 7:26pm

Just because there are two separate DNAs doesn't mean at all that the offspring will be more parasite resistant. What about the fact that sex itself could contribute to the spread of said parasite? This is a poorly correlated hypothesis.

Jul 11 11 - 10:35pm

Gah. The worm isn't parasitic.

Here's a fairly good write-up of the actual paper. Please read this before passing judgment on the validity of the experiment (which was based off of existing research, had multiple controls, and puts forward a convincing argument for parasitism being ONE important factor in the evolution of sexual reproduction.)

Nov 20 11 - 6:36am

Stay with this guys, you're helping a lot of peploe.

Nov 20 11 - 12:30pm

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