From a leading paleontologist, a book (not a catalogue) to complement a show: the American Museum of Natural History's first ""issues"" exhibition, opening this spring in New York City, with curator Eldredge in charge. The theme is familiar to Eldredge (Reinventing Darwin, 1995, etc.) fans and environmentalists worldwide. In the author's dramatic words, the planet has undergone five major extinctions since life began--and we now face a sixth, the product of our own actions. The book sets out to answer four questions: What is biodiversity? Why should we care about it? What precisely threatens it? And what can we do to stem the tide? The answers are played out in terms of the twin ""modes"" that influence life: evolution and ecosystems. Interestingly, Eldredge begins with a close-up view of territory he knows well: Botswana, home to the Eden-like Okavango River delta, as well as the nearby dry Kalahari region. Vagaries of climate (recent drought), population increases, cattle-raising, abandonment of the local hunter-gatherer lifestyle for agriculture--these are among the major threats to the survival of the ""big hairies,"" as well as numerous others, including a species of termites that plays a unique role in the ecosystem. The book's remaining sections celebrate global biodiversity, allowing Eldredge to indulge in picking his favorites across the flora and fauna (nicely illustrated). The value of diversity addresses esthetics as well as the need to ensure variation for evolution to play upon, not to mention the potential for new sources of drugs and other useful goods. As for stemming the tide, the message is control, control, control (of excesses, land use, population) and empowerment of women and of local peoples to utilize local resources wisely--messages often heard but little heeded. In a book that's part rhapsody, part sermon, Eldredge once more may be addressing a choir of believers. One can only hope that the throngs attending the exhibition absorb and act on the message.