EXTINCTION

In a well-organized overview of a vital subject, Stefoff surveys extinctions since the earth began, especially discussing theories about the several periods of ``mass extinctions,'' then going on to show how man-caused extinctions differ in both causes and effects from earlier cataclysms, covering the pressures exerted on environments and preservation efforts. She deals evenhandedly with issues like how to balance the survival of animal species and the real needs of their human neighbors, and with the debate over using triage to target species to be saved. A bit dry but, overall, lucid, well researched, and thought- provoking. Many useful b&w photos of varying quality plus an eight-page color section; international list of conservation organizations and US government agencies; bibliography; glossary; index. (Nonfiction. 11+)