It seems we may have parasites to thank for the existence of sex as we know it. Indiana University biologists have found that, although sexual reproduction between two individuals is costly from an evolutionary perspective, it is favored over self-fertilization in the presence of coevolving 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.
The July 8 report in Science, “Running with the Red Queen: Host-Parasite Coevolution Selects for Biparental Sex,” affirms the Red Queen hypothesis, an evolutionary theory who’s name comes from Lewis Carroll’s Alice in Wonderland text: “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.
“The widespread existence of sex has been a major problem for evolutionary biology since the time of Charles Darwin,” said lead author Levi T. Morran. Sex does not make evolutionary sense, because it often involves the production of males. This is very inefficient, because males don’t directly produce any offspring. Self-fertilization is a far more efficient means of reproduction, and as such, evolutionary theory predicts that self-fertilization should be widespread in nature and sex should be rare. However, as we all know, this is not the case.
The Red Queen Hypothesis provides one possible explanation for the existence of sex.