Until the middle of the present century Mongolia was little affected by man, in the sense of interference with and distortion of the natural environment. In 1918 the population of this 600,000-square-mile country was only 640,000, with 9.6 million domestic animals. (The comparable figures today are 1,300,000 and 23.4 million). Thanks to this lack of interference and the protective measures of the Mongolian People's Republic, Mongolia still has some of the rarest of the world's mammals, notably wild horse and camel, Gobi bear and Asian wild ass. The most threatened of them is the Przewalski horse, which some scientists think is extinct. But the two authors believe that it survives in small numbers. They urge the need for large reserved areas where livestock, which compete for the horses' grazing and water, can be eliminated.