A mustang is the free-roaming horse of the North American west that first descended from horses brought to the Americas by the Spanish. Mustangs are often referred to as wild horses, but there is debate over terminology. Because they are descended from once-domesticated horses, they can be classified as feral horses.In 1971, the United States Congress recognized that "wild free-roaming horses and burros are living symbols of the historic and pioneer spirit of the West, which continue to contribute to the diversity of life forms within the Nation and enrich the lives of the American people." In the 21st century, mustang herds vary in the degree to which they can be traced to original Iberian horses. Some contain a greater genetic mixture of ranch stock and more recent breed releases, while others are relatively unchanged from the original Iberian stock, most strongly represented in the most isolated populations.The free-roaming mustang population is managed and protected by the Bureau of Land Management (BLM). Controversy surrounds the sharing of land and resources by the free-ranging mustangs with the livestock of the ranching industry, and also with the methods with which the federal government manages the wild population numbers. A policy of rounding up excess population and offering these horses for adoption to private owners has been inadequate to address questions of population control, and many animals now live in temporary holding areas, kept in captivity but not adopted to permanent homes. Advocates for mustangs also express concerns that the animals may be sold for horsemeat. Additional debate centers on the question of whether mustangs—and horses in general—are a native species or an introduced invasive species. Many methods of population management are used, including the adoption by private individuals of horses taken from the range.