Sickness All Around

The LoomBy Carl ZimmerAug 9, 2005 7:39 AM


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I've got two stories in tomorrow's New York Times about getting sick. One is about malaria. I've always been fascinated by how parasites can manipulate their hosts for their own ends, and much of my book Parasite Rex is dedicated to explaining how this creepy remote control works. I've come across many new examples from time to time. Now a new study shows that the parasite that causes malaria can alter us humans to turn us into good mosquito bait. As with most stories about life, this one is ultimately about evolution—in this case, how parasites repeatedly have evolved ways to boost their own reproductive success by manipulating hosts like us. I've never gotten malaria (knock on wood), but I have just experienced the subject of my second piece: appendicitis. Three weeks ago I got appendicitis, and if I lived 150 years ago my appendix would have probably ruptured and I'd have died. Fortunately, I got to the hospital without a hitch and had a straightforward operation to get the appendix out. Once the anesthesia cleared from my head, I began mulling how odd it was that I was born with an organ so exquisitely suited to failure and so useless to me. The manipulations of the malaria parasite are remarkable adaptations, but the appendix is, to a great extent, an maladaptation. In the article, I offer some of the ideas scientists have had about how we all ended up with an appendix, but there was one interesting take on the appendix that I didn't have room to include in my story. Evolutionary biologists Randolph Nesse and George Williams wrote an article a few years back in Scientific American, in which they argued that all things being equal, natural selection should favor mutations that made the appendix dwindle away to nothing. So why isn't it gone? Perhaps if the appendix got even smaller than it is now, it would become even more prone to appendicitis and cause more deaths. Natural selection, in other words, has reached a dead end. It's an interesting idea, but it would take a study of thousands of people—measuring their appendix and seeing who does or doesn't get appendicitis—to test it. Perhaps some philanthropist will get appendicitis some day and decide to drop a few million bucks to figure out how exactly we all got stuck with this peculiar little time bomb.

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