Many of us were taught that microbes—and bacteria in particular—were dangerous pathogens, and the safest thing human beings could do was create a sterile, bacteria-free environment. But in fact microbes are absolutely essential to human health, the health of the soil, and to pretty much all life on earth. Dr. Emeran Mayer is a gastroenterologist, executive director of the G. Oppenheimer Center for Neurobiology of Stress and Resilience, and the director of the UCLA Microbiome Center. And he’s author of the new book, The Gut-Immune Connection. We talk about how the human microbiome functions, how it's stressed by the standard American diet (SAD) and lifestyle—and the deep interconnections between the human gut and the destruction of the soil microbiome by intensive chemical agriculture. And yes, there are good solutions—if we have the knowledge and will to make them happen.