Joe Roman reveals how ecosystems are sculpted and sustained by animals eating, pooping, and dying—and how these fundamental functions could help save us from climate catastrophe. If forests are the lungs of the planet, then animals migrating across oceans, streams, and mountains—eating, pooping, and dying along the way—are its heart and arteries, pumping nitrogen and phosphorus from deep-sea gorges up to mountain peaks. This book takes readers on an exhilarating and enlightening global adventure, revealing the remarkable ways in which the most basic biological activities of animals make and remake the world—and how a deeper understanding of these cycles provides us with opportunities to undo the environmental damage humanity has wrought on the planet we call home.