In this book the author, a Harvard evolutionary biologist presents an account of how the human body has evolved over millions of years, examining how an increasing disparity between the needs of Stone Age bodies and the realities of the modern world are fueling a paradox of greater longevity and chronic disease. It illuminates the major transformations that contributed key adaptations to the body: the rise of bipedalism; the shift to a non-fruit-based diet; the advent of hunting and gathering, leading to our superlative endurance athleticism; the development of a very large brain; and the incipience of cultural proficiencies. The author also elucidates how cultural evolution differs from biological evolution, and how our bodies were further transformed during the Agricultural and Industrial Revolutions. While these ongoing changes have brought about many benefits, they have also created conditions to which our bodies are not entirely adapted, the author argues, resulting in the growing