The spread of Covid-19, and the world's response to it, has its roots in many different histories: the history of trade, travel, and globalization; the history of medicine and public health; the history of governance and how citizens respond to it. This month, historian Donald Worster puts the pandemic in the deep history of human interaction with the natural world, especially agriculture.  He argues that Covid-19 is part of a long pattern of unintended consequences that result when humans have transformed the environment and the other species around us.