In Bloom, researcher and science writer Jeff Leach finds himself sitting around a campfire in a dry creek bed high in the rugged mountains of northern Namibia, wondering if the tribesmen on the other side of the fire, whom he had traveled 8,000 miles and to the farthest reaches of the world to find, held in their guts the microbial clues to some of the world"s most devastating diseases. Modern humans are 99.9 percent similar genetically, but the genetic content of the trillions of microbes living on and in our bodies, our microbiome, can differ by as much as 90 percent. Like a precious family heirloom, our initial population of bacteria is handed down to us from our mother during birth. This founding population soon outnumbers our own cells ten to one, making us more microbe than mammal?a veritable superorganism?and plays a critical role in our health throughout life. Just how critical is now being revealed by an explosion in powerful molecular techniques that are providing an unprecedented glimpse into the part microbes play in conditions as diverse as diabetes, cancer, obesity, autoimmune diseases, heart disease, and more. In Bloom, Leach delves deep into our evolutionary past and traces forward the ecological, technological, and cultural events that have shaped the codevelopment of humans and our microbes. Modern lifestyle choices are dramatically impacting the health of our primal microbiome and, as a result, contributing to, or outright causing, many diseases. By looking backward to better understand the seasonal landscape that nurtured a normal?that is, healthy?microbiome, we just might find the clues to evolve ourselves into a better, disease-free future.