We are currently in the midst of the most sweeping wave of extinctions since the one that did in the dinosaurs, according to the authors. This time, man is the cause, as well as the potential victim. What distinguishes this book from the many others on the subject is that at its best it offers more than the usual bromides and bleak statistics. The editors have compiled six chapters ranging from engrossing to clichÃ‰-ridden, each written by a different expert on extinction. In one of the more absorbing sections, paleontologist David Jablonski notes there is some evidence that mass extinctions of the past did not occur at random intervals but rather regularly, approximately every 26 to 28 million years, Jablonski's research suggests a highly unorthodox View of the way evolution works: that many evolutionary turnovers have been driven by mass extinctions and have not necessarily been for the better. In another interesting chapter, Ghillean T. Prance of the New York Botanical Garden examines one of the gravest present problems, the destruction of tropical forests, which are extremely rich in unique plants and animals. Two scientists with the US Department of Interior describe what species have already been lost here in North America. An official of the American Association of Zoological Parks and Aquariums outlines the formidable physical, ethical and financial impediments to efforts to transform zoos into temporary refuges and breeding grounds for disappearing species. A useful, if uneven and somewhat technical, addition to the literature on extinction.