Thank a parasite

I considered giving my post a longer title. “Thank a parasite for the existence of sex.” But aside from my dislike of long titles, I didn’t want to give in the temptation to write a title including a word that would probably drive up the hits on my blog considerably, at least for a day or two. I certainly welcome new readers, but I figured the shorter title you see is more likely to get the sort of readers who would appreciate my blog than the longer one I was considering.

In either the short or long form, that line is a direct quote from an article I just read. I first came across the topic in an article by Matt Ridley in the Wall Street Journal. I’m currently reading a book by Matt Ridley, whose writing I became interested in after reading a previous article by him in the WSJ. Naturally I was interested in reading more by him – especially when the article’s title began with the words “Why sex?”

So what do parasites have to do with sex? Well, there are apparently ways that parasites can be passed from one sexual partner to another (I’ll let you Google the topic if you want details), but that’s not what these articles are about. This is about why so many creatures create the next generation through sexual reproduction, rather than by cloning, which is asexual. As cloning is far more efficient in terms of the numbers produced, and evolution assumes that all current life forms descended from those that reproduced by cloning, the question arises as to how life forms producing sexually could have produced the numbers required to win against the asexual competitors in their ecological niches.

Even if you don’t believe evolution is a plausible explanation for the development of species, it is still an interesting question why some species reproduce sexually, some asexually, and some can do it either way, depending on conditions. The two competing theories for why sexual reproduction developed, I learned from Ridley’s article, are both based on the fact that genes are remixed with each new generation of sexual reproduction, whereas the genome remains the same with cloning.

The one that Ridley favors, called the Red Queen Theory, says that the genome needs to keep changing to stay ahead of parasites, which also keep adapting to take advantage of weaknesses in the host. An alternate theory says that the mixing of genes is to get rid of damaging mutations. New research, while not conclusive, strongly supports the Red Queen Theory. This article gives further details on the research.

As one of the researchers explained when asked how he got interested in this topic, “As for being interested in the topic of sex, who isn’t?”


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