In industrialized nations, our sedentary lifestyles have led to skyrocketing rates of obesity and diseases like diabetes. The answer, we are told, is exercise - voluntary physical activity for the sake of health. However, most of us struggle to stay fit, and we are plagued by misconceptions and anxieties about it. Drawing on over a decade of research, Lieberman shows that, in fact, we evolved to be physically active but not to exercise. Offering illuminating insights from evolutionary biology and anthropology, he explains why and how exercise can promote health, debunks myths about sitting, speed, strength and endurance, and points the way towards how we can be more physically active in the modern world.