Wild horse

The Wild Horse (Equus ferus or Equus ferus caballus) is a member of the Horse genus that currently is native only in Asia. The true wild horse is not merely a feral horse like the Mustang; a true wild horse species is one that was never successfully domesticated.

Two species or subspecies (taxonomy is debated) of wild horses survived into modern times: The Tarpan or Eurasian Wild Horse (Equus ferus ferus), once native to Europe and Asia, and the Przewalski's Horse or Mongolian Wild Horse (classification disputed, either Equus ferus przewalskii or Equus przewalskii), native to Central Asia and the Gobi Desert. The Tarpan became extinct in captivity in the Ukraine in 1918 or 1919. The Przewalski's Horse is still found today, though it is an endangered species and for a time was considered extinct in the wild. Roughly 1500 animals are protected in zoos around the world, and today, a small breeding population has been reintroduced in Mongolia. 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.

The Przewalski 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.

Other species of wild horses were once indigenous to North America, as well, populating the continent before and during the last Ice Age. Approximately 10,000 years ago, some 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 several 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. A third holds that the newly arrived humans brought a biological factor which caused the demise of horses and other large ungulates in the Americas. It is also possible that it was a combination of factors.