The human body is a machine whose many parts – from the microscopic details of our cells to our limbs, eyes, liver and brain – have been assembled in fits and starts over the four billion years of our history.
But scientists are still puzzling over why we evolved into this particular form. Why do humans uniquely have a chin, for example? And why, relative to body weight, is a human testicle triple the size of a gorilla’s but a fifth of that of a chimpanzee? As I show in my new book, The Tree of Life, we are still searching for the answers to many of these “why” questions. But we are starting to find answers to some of them.
