THERE’S A FOREST NOT FAR FROM MY HOME where I like to take my kids. They swing on vines, balance on fallen trees and turn rocks. They look, prod and then gather or catch much of what they find. When they’re done, we all sit down in a patch of grass on top of a hill and watch clouds drift by. During these times, I hope that my kids are getting covered by bacteria and other microorganisms.
For this approach, some might consider me a bad parent. After all, as far back as the 1800s, Louis Pasteur and other scientists developed what would later be called the germ theory of disease: the then-revolutionary idea that microbes, by invading our bodies, are the cause of many human diseases. Since then, this theory—by spawning behaviors such as hand washing and drugs that now cure many illnesses—has saved millions, perhaps billions, of lives.
In recent years, however, I’ve come to believe that the germ theory leaves out a lot. My new thinking stems from the findings of scientists working in several different fields of biology. Independently, these biologists have all come to a similar conclusion: Many animal species, even those we tend to think of as dangerous or disgusting, are beneficial to our health.
Some discoveries are old. A small cadre of scientists has long known that many microorganisms that inhabit our bodies and our homes are necessary for a healthy life. Get rid of them and we would die. Without microbes, for example, our digestive systems would stop functioning.
But more recent research suggests that microbes also are needed for the immune system to operate properly. In a number of studies going back to the 1980s, microbiologists and public health workers have found that rural children are less likely to develop allergies than are urban children, a discovery that has been attributed to the fact that country kids, through frequent contact with soil and animals, are exposed to a larger number and diversity of bacteria and other microbes than are city kids. Known as the hygiene hypothesis, the idea is that exposure to microbes is necessary for a child’s immune system to develop. Take away some of the bugs, or even change their composition, and a host of allergic and autoimmune disorders seem to become more common.