Why do gazelles have legs and not wheels? Why is all life based on carbon rather than silicon? Why do humans have eyes on the front of their heads? And beyond earth, would life - if it should exist - look like our own? The puzzles of life astound and confuse us like no other mystery. An astrophysicist once conceded that even the smallest insect is far more complex than either an atom or a star. But in this groundbreaking new account of the process of evolution, Professor Charles Cockell reveals how nature is far more understandable and predictable than we would think. Refining Darwin's theory of natural selection, Cockell puts forward a remarkable and elegant account of why evolution has taken the paths it has. The key is understanding how fundamental physical laws constrain nature's direction and form at every turn. From the animal kingdom to the atomic realm, he shows how physics is the true touchstone for understanding life in all its extraordinary forms. Provocative and captivating, this book will fundamentally change how you view the world.