A human being is a mammal. Most of us appreciate that at some level. But what does it mean to have more in common with a horse and an armadillo than with a sparrow, gecko or T. Rex? Why do only mammals have hair, mammary glands and three bones in their middle ears? I, Mammal is a personalised quest to understand what it means to be a mammal, exploring the different traits that uniquely define them. From their particular sexual anatomy through to their burgeoning brains, via milk, parenting and warm blood, each chapter provides a potted history of how each mammalian feature evolved and of how scientists came to understand it. Entwined are tales of how different mammals live with these traits everyday, exploiting them in ways that enable them to adapt and survive. Gradually, an animal emerges - a mammal. A type of creature whose biology runs throughout the human experience.