Every creature on earth has their own microbial community . This internal ecology determines how we digest food and resist disease and can even affect behavior or how often mosquitoes bite us. Rob Knight, a microbial ecologist, has concluded that microbes are as critical as the brain–they make each of us who we are.

“The three pounds of microbes [we carry] may be more important for some health conditions than every gene in our genome,” Knight says. We share 99.9% of our DNA with the people around us, but our microbes share only 10% similarity. The diversity in our microbial communities is astonishing and can help us differentiate health based on our genetic makeup from our health based on the way in which we developed as children. Knight explains that children born in C-sections are more susceptible to allergies and obesity. Children who are born vaginally, however, gain protective microbes from the birth canal that help protect them.

The three pounds of microbes we carry may be more important for some health conditions than every gene in our genome.

Knight and his team at the University of Minnesota have discovered that manipulating unseen microbial world has the ability to cure such diseases as inflammatory bowel disease, obesity, and even possibly make strides against autism and depression. Through a series of experiments in which they shared different kinds of microbes among lean and obese mice, they discovered that weight gain can be passed on via microbes in two ways. First, they could change the way the body digests food. But they could also change a mouse’s behavior: Different microbes made some mice eat more food. Knight’s conclusion: microbes can affect mammalian behavior and also dictate how the body responds to certain functions.

Another surprising discovery was that antibiotics might actually be degrading our microbial ecosystems. Children who receive antibiotics in the first six months of their life, says Knight, are more likely to become obese. “What we do early on,” he explained, “may have a profound impact on the gut microbial community.”

Knight’s most recent project is called American Gut, an initiative to map the unique microbe makeup of individuals around the country to discover how our lifestyle and diet affect our health. But his discoveries have already unfurled exciting possibilities in understanding our bodies. This “microbial GPS” has the potential to transform human health from the early stages of life onward.