Sex might seem like one of those little gifts from evolution. But it's
pretty inefficient from an evolutionary perspective. It'd be much easier
to reproduce if you could do away with finding the right member of the
opposite sex to help you create the next generation. So why did evolution
come up with sex?
Biologists have hypothesized that one driving force might have been
parasites. Now scientists have had a chance to test that theory. Asexual
reproduction leads to clones. Being genetically identical, clones are also
weak in the same ways, and thus more likely to all succumb to a parasite.
But sex keeps shuffling the genetic deck.
Well, there's a snail common in New Zealand lakes that does both-some
populations have sex and some reproduce asexually. So researchers spent
10 years monitoring the two populations, and the number of parasites
living off both groups. As expected, cloned snails that were plentiful
at the beginning of the study suffered big losses as they became infected
with parasites. But the sexual snail populations remained stable, results
published in the journal American Naturalist. So, next time you're feeling
sexy, thank a parasite.