This book is an exploration of what morality means, and what animals can teach us about it. Wild elephants walking along a trail stop and spontaneously try to protect and assist a weak and dying fellow elephant. Laboratory rats, finding other rats caged nearby in distressing circumstances, proceed to rescue them. A chimpanzee in a zoo loses his own life trying to save an unrelated infant who has fallen into a watery moat. The examples above and many others, argues the author, show that our fellow creatures have powerful impulses toward cooperation, generosity, and fairness, even morality. Yet it is commonly held that we Homo sapiens are the only animals with a moral sense, that we are somehow above and apart from "the animals." This book forces us to reexamine what the author calls our "Darwinian narcissism", and it shows the profound connections, the moral continuum, that link humans to many other species. The author shows how much animal behavior follows principles embodied in humanity's ancient moral codes, from the Old Testament rules as expressed in the Ten Commandments to the New Testament principles of attachment through cooperation, kindness, and empathy. Understanding the moral lives of animals offers new insight into our own.