Almost 200 million human beings, mostly civilians, have died in wars over the last century, and there is no end of slaughter in sight. The Most Dangerous Animal asks what it is about human nature that makes it possible for human beings to regularly slaughter their own kind. It tells the story of why all human beings have the potential to be hideously cruel and destructive to one another. Why are we our own worst enemy? The book shows us that war has been with us---in one form or another---since prehistoric times, and looking at the behavior of our close relatives, the chimpanzees, it argues that a penchant for group violence has been bred into us over millions of years of biological evolution. The Most Dangerous Animal takes the reader on a journey through evolution, history, anthropology, and psychology, showing how and why the human mind has a dual nature: on the one hand, we are ferocious, dangerous animals who regularly commit terrible atrocities against our own kind, on the other, we have a deep aversion to killing, a horror of taking human life. Meticulously researched and far-reaching in scope and with examples taken from ancient and modern history, The Most Dangerous Animal delivers a sobering lesson for an increasingly dangerous world.