Humans, the Harvard University entomologist Edward O. Wilson has observed, have an innate--or at least extremely ancient--connection to the natural world, and our continued divorce from it has led to the loss of not only "a vast intellectual legacy born of intimacy" with nature, but also our very sanity. In The Diversity of Life, Wilson takes a sweeping view of our planet's natural richness, remarking on what on the surface seems a "almost all the species that ever lived are extinct, and yet more are alive today than at any time in the past." (Wilson's elegant explanation is a scientific education in itself.) This great variety of species is, of course, threatened by habitat destruction, global climate change, and a host of other forces, and Wilson revisits his oft-stated call for the protection of wilderness and undeveloped land, noting that "wilderness has virtue unto itself and needs no extraneous justification." We should, he continues, regard every species, "every scrap of biodiversity," as precious and irreplaceable, without attempting to quantify that regard with utilitarian measures such as "bio-economics." In short, Wilson offers with this book a simple, workable environmental ethic that extends the work of Aldo Leopold and other conservationists. A remarkably productive and influential scientist, Wilson is also a fine writer, and his survey of biodiversity makes for welcome and instructive reading. --Gregory McNamee