Blending paleontology and environmentalism, MacLeish (The Gulf Stream, 1988) explores the nature of America as it was before Europeans arrived. After briefly sketching the variety and complexity of the indigenous human societies (whalers in the Pacific Northwest and mound builders in Ohio, as well as the more familiar denizens of plains and forest), the author jumps backward in time to an ice-covered continent on which no human had ever set foot. South of the glaciers lived an astonishing variety of now-vanished creatures: mammoths, saber-toothed cats, camels, giant beavers, ground sloths, and predatory flightless birds. At some point -- at least 15,000 years ago, possibly 50,000 or more -- human beings arrived, and the continent began to change. How much of the loss of Pleistocene fauna was caused by hunting is a matter of debate, but MacLeish's point is clear: Human beings have always had an impact on their world. Plant life also changed, most obviously in the domestication of such crops as corn, squash, beans, and other staples of Indian agriculture. After a simplistic look at Europe on the eve of the discovery of America, the author traces the impact of colonization not only on the native population (hit hardest by diseases to which it had no resistance), but on an ecology that seemed at first to offer boundless riches. He traces the rise of the lumber industry, the conversion of the prairies into farmland, the arrival of a voracious consumer society. Finally, he tries to see what the future may offer, finding no easy solutions for the unsettling possibilities posed by population growth and environmental degradation. MacLeish occasionally descends to facile Europe-bashing, but he has a noteworthy ability to place modern issues in the broad context of geological time. Unusually rewarding for readers who want to see beyond the familiar and the comfortable.