Parasites and sex typically aren't two things you want to think about together, but according to new research parasites might be responsible for sex as we know it.
PhysOrg reports that Indiana University biologists have affirmed the "Red Queen hypothesis" -- the idea that human beings reproduce through sex because we're, well, keeping up with the parasites, the ones that threaten to potentially harm us.
The hypothesis gets its name from a line in Lewis Carroll's Through the Looking Glass: "It takes all the running you can do, to keep in the same place."
The idea is that sexual reproduction via cross-fertilization keeps host populations one evolutionary step ahead of the parasites, which are coevolving to infect them. It is within this coevolutionary context that both hosts and parasites are running (evolving) as fast as they can just to stay in the same place.
It's likely news to anyone who isn't a biologist, but sex apparently doesn't make evolutionary sense. Discover explains that sexual reproduction requires splitting a species into two sexes, only one of which can produce offspring.
From an evolutionary perspective, that process is much more work for a species. It's much easier to have self-fertilization where a female can trigger her own eggs to develop into embryos, no sperm necessary -- thus a female only species is all that's produced, because that's all that's needed. Theoretically, self-reproduction should be widespread throughout species and sex should be rare.
According to the paper published today in Science, we can thank a tiny worm called Caenorhabditis elegans for forcing evolution to require a partner for reproduction. Without those little guys, life would probably be quite a bit more boring and we'd be a species of only women -- it's up to you to decide whether or not that's a good thing.