The towering cliffs of Mount Improbable can never, it seems, be climbed. In Richard Dawkins's remarkable new book the heights of Mount Improbable represent the combination of perfection and improbability that is epitomized in the seemingly "designed" perfection of living things. 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 in a single leap. 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. 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 the fig is a garden for its own teeming population of insects; and we learn that the eye has evolved no less than forty times independently. And through it all runs the thread of DNA, the molecule of life, responsible for its own destiny on an unending pilgrimage through geological time.