Humans are the only mammals to truly walk on two, rather than four legs—but why, and how, exactly, did we take our first steps? And at what cost? Bipedalism has its drawbacks: giving birth is more difficult and dangerous; our running speed is much slower than other animals; and we suffer a variety of ailments, from hernias to sinus problems. Taking a seven-million-year journey to the origins of the human lineage, paleoanthropologist Jeremy DeSilva shows how upright walking was a gateway to many of the other attributes that make us human—our technological abilities, thirst for exploration, and use of language—laying the foundation for our species' traits of compassion, empathy, and altruism.