Our health, body shape, mood and even our evolution are determined by the unseen life forms that swarm throughout our bodies. There are worms in your bowels, bacteria in your mouth, fungi in your lungs and even viruses in your DNA. The combined genetic information of all these bugs is more than 150 times greater than our own genes. Their cells outnumber our own by 10 to 1. This collective menagerie is called the microbiome, and in a very real sense, it is the making of us all. Though they have evolved with us over millennia, in recent years we have been drastically changing our relationship with our internal microbes, bombing them with antibiotics and an unhealthy diet. The consequence of this war on our bugs is an epidemic of disease. This episode looks at the battleground within our bodies and the remarkable new science that is changing our views about health and disease.