“Then, in a blink of the eye, we invented the modern postindustrial world. Suddenly some of us can take it easy 24/7 in ways unimaginable to earlier generations. Instead of walking, carrying, digging, running, and throwing, we sit for most of the day in ergonomically designed chairs, stare at screens, and press buttons. The only catch is we still inherited our active ancestors’ thrifty genes that rely on physical activity to grow, maintain, and repair our bodies. Incessant sitting combined with modern diets and other novelties thus contributes to evolutionary mismatches, defined as conditions that are more common and severe today than in the past because our bodies are poorly adapted to novel environmental conditions.3 The twenty-first-century world, of course, is not without extraordinary benefits. Today, nearly seven billion of us live longer and healthier lives than most of our Stone Age forebears ever did, many of us enjoying comforts beyond the imaginations of pharaohs and emperors of yore. But just as we never evolved to cope with jet lag or guzzle gallons of soda, we never evolved to be persistently physically inactive.”