The Wild Horse (Equus ferus) is a member of the Horse genus and was found in Europe and Asia. Two species or subspecies (taxonomy is debated) survived into modern times: The Tarpan or Eurasian Wild Horse (Equus ferus ferus), and the Przewalski's Horse or Mongolian Wild Horse (classification disputed, either Equus ferus przewalskii or Equus caballus przewalskii). The Tarpan became extinct in 1875. The Przewalski's Horse is still found today, though it is an endangered species and was considered extinct in the wild, with roughly 1500 animals protected in zoos around the world. However, a small breeding population is in the process of being reintroduced in Mongolia."Przewalski's Horse," Smithsonian National Zoological Park, accessed June 25, 2006 As of 2005, a cooperative venture between the Zoological Society of London and Mongolian Scientists has resulted in a free-ranging population of 248 animals in the wild."An extraordinary return from the brink of extinction for worlds last wild horse" ZSL Living Conservation, December 19, 2005.

The Przewalski is not merely a feral horse; it has never been successfully domesticated. It also has notable biological differences from the domestic horse: unlike domesticated horses, which have 64 chromosomes, the wild horse has 66 chromosomes. However, the offspring of Przewalski and domestic horses are fertile, possessing 65 chromosomes.The American Museum of Natural History When Is a Wild Horse Actually a Feral Horse?

Other species of wild horses were once indigenous to North America, populating the continent before and during the Ice Age. Approximately 10,000 years ago, horses in the Western Hemisphere migrated to Eurasia across the Bering land bridge, and fanned out from Siberia to the rest of Asia, Europe, and the Middle East. What horses remained behind became extinct in North America. There are two competing theories about why this happened. One theory holds that climate changes associated with the end of the last Ice Age caused the extinction of the horse, the mammoth and other large land animals. Another theory holds that newly-arrived humans hunted horses to extinction. It is also possible that it was a combination of both factors. "Ice Age Horses May Have Been Killed Off by Humans" National Geographic News, May 1, 2006.

When Europeans reintroduced the horse to the Americas, beginning with the arrival of the Conquistadors in the 15th century, some horses escaped and formed feral herds known today as Mustangs. By 1900, there were 2 million feral horses in America. Their major predators, such as the mountain lion, were significantly depleted by human hunting and fur-trapping, and for more than a century their biggest enemy has been humans. Although the Free-Roaming Horse and Burro Protection Act of 1971 halted practices such as shooting Mustangs from airplanes and rounding them up for slaughter, the population today is still quite reduced. The limited acreage available on wild horse refuges in the western United States today now supports a present day number of about 25,000.

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