In the geological record, there are five major mass extinctions--the "Big Five." The most famous happened at the end of the Cretaceous Period, when the dinosaurs and two-thirds of all marine animal species were wiped out, opening the door for the age of mammals and the rise of Homo Sapiens. Using this example as a springboard, David M. Raup leaps into an egaging discussion of the theories, assumptions, and difficulties associated with the science of species extinction. Woven is along the way are stories of the trilobite eye, tropical reefs, flying reptiles, and the fate of the heath hen on Martha's Vineyard, a very modern extinction.