"You are just 10% human. For every one of the cells that make up the vessel that you call your body, there are nine impostor cells hitching a ride. You are not just flesh and blood, muscle and bone, brain and skin, but also bacteria and fungi. Over your lifetime, you will carry the equivalent weight of five African elephants in microbes. You are not an individual but a colony. Until recently, we had thought our microbes hardly mattered, but science...