The Evolution of Allergies

Immunobiologist Ruslan Medzhitov said he was recently discussing evolutionary medicine with fellow Yale professor Stephen Stearns, and Stearns told him that patients often like evolutionary explanations for their ailments. "It helps them with the 'why me' question," Medzhitov said.

Medzhitov is known for his pioneering work on the so-called innate immune system, for which many think he should have shared a recent Nobel Prize. Now he's turned his attention to the evolutionary roots of allergies. This week he's lead author on a Nature paper that could help Higgs and other allergy sufferers with that "why me" question. Allergies are not just a malfunction of the immune system, he said. They may also reflect an evolutionary battle between us and the many species that surround us.

The standard theory holds that allergy evolved as a mechanism to help us and other mammals fight parasitic worms, he said. He proposed that allergic symptoms also evolved to help animals to avoid venoms and other noxious chemicals in the environment.  Most allergy symptoms function to either expel something or make us run the other direction, he said.  We humans vary in how strongly we react and what we react to, but it's all part of a system for keeping us from being damaged by toxins and irritants.

He offers a possible explanation for why severe allergies are on the rise – we're increasingly living in enclosed spaces. For most of our evolutionary history, people weren't exposed to peanut dust in an airplane cabin, or to dust mites in a bedroom. Now, however, we live in enclosed spaces where there's no turning away. Higgs suffers from skin rashes that have been diagnosed as allergies. The veterinarians put him on a diet of hydrolyzed protein to no avail. They shaved his fur and scratch tested his skin but got no definitive answers. He's fine with the occasional anti-inflammatory steroid pill. He was probably fine when he lived out in the alley, but he has no desire to return.