In a world increasingly dominated by human beings, the survival of other species becomes more and more questionable. In this brilliant book, Paul Shepard offers a provocative alternative to an "us or them" mentality, proposing that other species are integral to humanity's evolution and exist at the core of our imagination. This trait, he argues, compels us to think of animals in order to be human. Without other living species by which to measure ourselves, Shepard warns, we would be less mature, care less for and be more careless of all life, including our own kind.