From the combination of strength and sensitivity of an elephant's trunk to the life-saving camouflage of an ant-mimicking beetle, the living world is populated by creatures that seem miraculously designed for the lives they lead. But these complex and brilliantly effective features cannot have come about by undirected chance. That would be equivalent to scaling the sheer face of the mountain of improbability. The only way to explain seemingly designed objects is by slow, gradual evolution - inching cumulatively, almost infinitely slowly by the standards of human history, up the gentle paths on the far side of Mount Improbable.

Richard Dawkins guides the reader through the spectacular mountain passes of the natural world. We are led through the silken world of spiders; we are shown how wings gradually sprouted on the bodies of flightless animals; we see how a fig is a garden for its own teeming population of insects; and we learn how the eye has evolved no less than forty times independently. And through all of it runs the thread of DNA, the molecule of life, responsible for its own destiny on an unending pilgrimage through geological time.