The Cambrian explosion is the "big bang" of evolution--a period of less than five million years during which life on Earth rapidly developed both armaments and defenses. Animals suddenly became both hunters and the hunted, and the number of animal groups with hard body parts mushroomed from three to 38. But why did the explosion happen when it did? Ground-breaking and accessible, this book unravels the evidence demonstrating that this was the period when the eye evolved, leading to an evolutionary scramble for survival.