John and Mary Gribbin, authors of In Search of Schrodinger's Cat and The Hole In the Sky, join forces to unfold the origins and evolution of humankind, set against the background of dramatic changes in climate. Some scientists believe it was climatic change, a catastrophic cooling of the globe, that brought an end to the era of the dinosaurs and opened up new opportunities for mammals, including our ancestors, and forced one kind of mammal, a woodland ape, out of the forests of Africa and on the road to intelligence. John and Mary Gribbin attempt to show that the origin of human intelligence is intimately connected with the series of ice ages that the world experienced during the Plio-Pleistocene epochs.