In this companion to the PBS television series Nature, science writer Shreeve diligently examines the lives of six large ""earthlings""--polar bears, tigers, elephants, gorillas, wolves, and marsupials. Tapping the vast research efforts of such notables as George Schaller and the late Dian Fossey, Shreeve explores everything from the methods employed by these animals to find food and mate, to the environments they inhabit, their means of territory marking and defense, the types of social bonds they form, and, ultimately, their role in the larger ecosystem. The text features a plethora of fascinating natural history facts. We learn, for example, that the howl of the wolf, an extremely social carnivore, can be heard by other members of the species as far as 140 miles away; that elephant herds, who feed and travel together for their lifetime, grieved when a family member dies; and that a gorilla group is utterly dependent on the wisdom of the mature ""silverback"" male. But there's more here. Most of the species discussed are endangered--mainly as a result of man's destruction of their habitats (tearing down of rainforests for logging; slash-and-burn agricultural techniques) and predatory habits (poaching, hunting)--and this is brought home again and again by Shreeve. The potentially devastating consequences to man of the loss of massive numbers of not only animal but also plant species are also made evident. ""A large mammal nearing extinction,"" says Shreeve, ""is probably a sign that an ecosystem is suffering some deeper distress farther down in its workings."" A most worthy accompaniment (with glorious color photographs) to the Nature programs, and an eloquent appeal for greater human responsibility toward the environment and our cohabitants of the planet.