While terrestrial life in the mountains flourished during the continent’s climatic swings, aquatic life fared equally well. Within Great Smoky Mountains National Park live some 70 species of fish. Contrast this with the number in Shenandoah National Park in the Blue Ridge of Virginia, which has only about 25 species. Why so many in the Smokies? The answer parallels the situation for plants and terrestrial animals: diversity of environments and plenty of time. All the streams of the Smokies lie within the Tennessee River drainage, which is part of the Mississippi River drainage. The Tennessee River has more species of fish than any other river in North America, because of its many environments (lowland, plateau, and mountain); the vastness of the Mississippi drainage; its existence for many millions of years; and its Pleistocene history. During glacial periods many species of fish were forced southward by ice and cold glacial water. The Tennessee River system offered them a refuge just as Southern Appalachian coves offered a refuge for plants. Even the Mississippi itself was a less favorable haven because it received most of the meltwater. In the headwaters of the Tennessee, the streams of the Smokies thus benefit from their contact with an ancient, relatively undisturbed river system. Within the park, stream environments range from cold and fast to comparatively cool and slow, with large, deep pools. While most of the present plant and animal species of the Smokies have ranges that extend far beyond these mountains, and while many of these have spread here from other areas of origin, a few are restricted solely to the Smokies. This suggests that they may have evolved here. One such plant is Rugel’s groundsel, a member of the Composite family that grows to about 28 centimeters (11 inches) high and bears large, cylindrical clusters of tiny golden flowers. This plant, abundant in the park’s spruce-fir forests, has not been found outside the Smokies. This suggests that it evolved in the Southern Appalachians and that after the last glacial period, when connection with other sections of spruce-fir forest was broken, it persisted or survived only in the Smokies. By comparison, the Fraser fir, though most abundant in the Smokies, also occurs north to southwestern Virginia on the highest mountains, indicating that it evolved at some earlier, colder time when spruce-fir forest was more nearly continuous. The red-cheeked salamander, a striking creature, is probably the sole vertebrate found exclusively in the Smokies. Many other species of salamanders, however, are restricted to parts of the southern end of the Appalachians and probably evolved there, where the cool, wet climate and diverse topography provide ideal conditions for this group of animals. How many other species of plants and animals evolved in the region and subsequently spread far beyond this point of origin we can only conjecture. Natural History Sampler