David Quammen explores island biogeography—the study of how species distribute themselves across isolated habitats—as both scientific discipline and lens for understanding extinction. He travels to islands around the world, from Madagascar to Tasmania to Indonesia, meeting the scientists who study their unique creatures and the creatures themselves: lemurs, Komodo dragons, birds that have forgotten how to fly. Quammen explains how islands serve as natural laboratories for evolution, producing species found nowhere else, and how the same isolation that enables this diversification makes island species vulnerable to extinction when humans arrive. He traces the intellectual history of the field, from Darwin and Wallace through the mathematical models of Robert MacArthur and E.O. Wilson to contemporary applications for conservation biology. The book's argument is that habitat fragmentation is turning the whole world into islands—isolated patches of wilderness surrounded by human-dominated landscape—and that island biogeography predicts the results: species loss proportional to habitat loss. Quammen writes with the narrative skill that makes his science journalism compelling, combining adventure travel, intellectual history, and ecological science into a work that entertains while alarming. The book remains relevant decades after publication, its warnings about fragmentation and extinction confirmed by subsequent research. Readers will understand why islands matter and what their fates predict about life on a planet increasingly shaped by human hands.