Wilson opens the book by discussing the nature of humans, a discussion he returns to throughout the book. Humans are the product of millions of years of both biological and cultural evolution. We are “magnificent in imaginative power and exploratory drive, yet yearning to be more master than steward of a declining planet” (1). The planet is facing several serious issues, most of which are due to human activity, including a too large and growing human population, a declining supply of fresh water, polluted seas and atmosphere, and climate change. These issues have already caused extinctions of species and radically transformed Earth. Due to the global nature of these issues, humans are reaching “a point of no return” (2) at which we will not be able to reverse the planetary threat of mass extinction.

Wilson also outlines the main proposal of Half-Earth, which forms a trilogy with Wilson’s previous books The Social Conquest of Earth and The Meaning of Human Existence to argue that humans have become “the architects and rulers of the Anthropocene epoch” (2). Current conservation strategies, which focus on the most threatened species and habitats, will not prevent a mass extinction event. Wilson proposes the following goal: Preserve at least half of Earth’s surface (land and water) to save its biodiversity.