On the southern edge of the Sahara in Fongoli, Senegal, lives a group of remarkable chimpanzees that could hold clues to how we became human. The Fongoli chimps live at the very limits where chimps can survive, having adapted to the extreme heat and dryness of the savanna woodlands. For years, these chimps were elusive ghosts, rarely seen. NATURE traces the remarkable 25-year story of how American anthropologist Jill Pruetz and local chimp expert Dondo Johnny Kante got so close to the Fongoli chimps to uncover unique behavior, including hunting with spears, sheltering in caves, digging wells, and reading fire. Seeing into their secret lives and recording extraordinary new behaviors shine a light on our own evolutionary past and fundamentally change how we think about ourselves.