For centuries, people in the West, believing themselves to hold God-given dominion over nature, thought too much of humanity and too little of microbes to believe they could take us down. When nineteenth-century scientists finally made the connection, life-saving methods to control infections and contain outbreaks soon followed. The next big break came with the birth of the antibiotic era in the 1930s. And yet, less than a century later, the promise of the antibiotic revolution is already receding due to years of overuse. Is our self-confidence getting the better of us again? So Very Small follows the thread of human ingenuity and hubris across centuries—along the way peering into microscopes, spelunking down sewers, visiting army hospitals, traipsing across sheep fields, and more—to show how we came to understand the microbial environment and how little we understand ourselves. Levenson traces how and why ideas are pursued, accepted, or ignored—and hence how human habits of mind can, so often, make it terribly hard to ask the right questions.