When humans evolved, they did so in close proximity to nature. Homeostatic set points in their bodies reached normal levels based upon the interaction between anatomy and environment. When you change the environment in which humans live drastically, those set points start to vary from normal, and chronic disease may result. One of the components of nature that we were immersed in through our evolutionary history was dirt, and in particular soil. We sat in it. It coated many of our foods. We slept next to it. It got on our hands and feet, and into our mouths. It was our companion.

Today, we have very little interaction with soil, or even dirt. Many of us have been convinced that dirt is a terrible thing. We now wash our hands regularly, even compulsively. We have been convinced by corporate marketers to buy product after product to protect us from these threats in dirt. We think of bacteria as horrible invaders. We avoid touching each other for fear of spreading bacteria. Hand shakes have been replaced with elbow bumps. This thinking permeates our culture. And, it does nothing to take into account the beneficial role of soil and bacteria in human health.

 

Some scientists, however, are starting to investigate this. In one study, human cancer patients being treated with the bacteria Mycobacterium vaccae which is omnipresent in soil unexpectedly reported increases in their quality of life. Following up on these results, a team looked closely at the brains of mice treated with this bacteria. They found that treatment with M. vaccae activated a group of neurons that produce the brain chemical serotonin. The lack of serotonin in the brain is thought to contribute to depression in people; thus M. vaccae's effects on the behavior of mice may be due to increasing the release of serotonin in parts of the brain that regulate mood. In another study, treatment of mice with a 'friendly' bacteria normally found in the soil altered their behavior in a way similar to that produced by antidepressant drugs.

What does this mean for an autistic child? Don’t be afraid of taking them outside; in fact, do so all the time. If they get dirty, great. They may be getting a dose of bacteria that they need. I am  not telling you to make them eat dirt, but this reinforces the concept that they should spend a lot of time outside playing on the ground, like the children from whom they descended. They are not fragile beings that need to be kept indoors, protected from the dangers of the world. This type of existence only worsens their condition.