Why Do We Get Allergies?

The more you think about sickness and health, the trickier it gets to draw a clean line between them. We tend to think of ourselves as being prepared by nature for a good life. If we can just keep bacteria and viruses from killing us, and avoid walking into open elevator shafts, we’ll live a long, healthy life.

But we are actually the products of evolution, and evolution can’t give us perfect health. It has endowed us with powerful immune systems, thank you very much. And it has endowed us with quick reflexes that can, in some cases, keep us out of open elevator shafts. But evolution doesn’t automatically march to perfection. It stops short, leaving us with grave imperfections.

We have lots of defenses against cancer, for example, but they weaken as we get old. That’s a recipe for heartbreak in millions of families. But in the game of evolution, that’s a winning formula. Natural selection strongly favors defenses against cancer that threaten our ability to survive to adulthood and have kids. But if we die of cancer at age sixty, our kids are well on their way, carrying out genes down to the next generation.

This evolutionary perspective could change the way we think about our health in many ways. Take allergies. They affect millions of people, causing everything from hay fever to anaphylactic shock. One of the world’s leading immunologists, Ruslan Medzhitov, is convinced that allergies are actually adaptations we use to defend ourselves from noxious chemicals. As awful as allergies can get, we wouldn’t want to live without them.

I’ve written a profile of Medzhitov. It appeared today originally in Mosaic, but it’s now propagating through the Internet. You can also find it on Ars Technica, Discover, Gizmodo, Digg, and elsewhere. Check it out at the outlet of your choice. And good luck this pollen season!