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This article is about the species Equus ferus, which includes both never-domesticated "wild" horse subspecies and the domesticated 'Equus ferus caballus. For "wild", meaning free-roaming horses descended from domesticated ancestry, see feral horse. For other uses, see Wild Horses.
The wild horse (Equus ferus) is a species of the genus Equus, which includes both the domesticated horse subspecies as well as the undomesticated Tarpan and the Przewalski's Horse. The Tarpan became extinct in the 19th century, and the Przewalski's Horse was saved from the brink of extinction and reintroduced successfully to the wild. The most likely ancestor of the domestic horse was the Tarpan, which roamed the steppes of Eurasia at the time of domestication.[1][2][3][4][5] Since the extinction of the Tarpan, attempts have been made to reconstruct the phenotype of the Tarpan, resulting in horse breeds such as the Konik and Heck horse. However, the genetic makeup and foundation bloodstock of those breeds is substantially derived from domesticated horses, and therefore these breeds possess domesticated traits. The term "wild horse" is also used colloquially to refer to free roaming herds of feral horses such as the Mustang in the United States, the Brumby in Australia, and many others. These feral horses are untamed members of the domestic horse subspecies (Equus ferus caballus), and should not be confused with the two truly "wild" horse subspecies.
[edit] Subspecies and their historyE. ferus had several subspecies. Three survived into modern times:[6]
These are the only two never-domesticated "wild" groups that survived into historic times.[7] However, other subspecies of Equus ferus may have existed and could have been the stock from which domesticated horses are descended.[7] [edit] Przewalski's HorsePrzewalski's Horse occupied the eastern Eurasian steppes, perhaps from the Urals to Mongolia, although the ancient border between Tarpan and Przewalski distributions has not been clearly defined. Przewalski's Horse was limited to Dzungaria and western Mongolia in the same period, became extinct in the wild during the 1960s, but was re-introduced in the late 1980s to two preserves in Mongolia. Although researchers such as Marija Gimbutas theorized that the horses of the Chalcolithic period were Przewalski's, more recent genetic studies indicate that Przewalski's Horse is not an ancestor to modern domesticated horses. 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 Przewalski's Horses are protected in zoos around the world. A small breeding population has been reintroduced in Mongolia.[8] 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.[9] Przewalski's Horse has some biological differences from the domestic horse; unlike domesticated horses and the Tarpan, which both have 64 chromosomes, the Przewalski's Horse has 66 chromosomes due to a Robertsonian translocation. However, the offspring of Przewalski and domestic horses are fertile, possessing 65 chromosomes.[10] [edit] Evolution and taxonomyMain article: Evolution of the horse The horse family Equidae and the genus Equus evolved in North America, before the species moved into the Eastern Hemisphere. Studies using ancient DNA as well as DNA of recent individuals, shows the presence of two closely related horse species in North America, the Wild Horse and the "Stilt-legged Horse;" the latter is taxonomically assigned to various names. [4] [11] Currently, three subspecies that lived during recorded human history are recognized.[6] One subspecies is the widespread domestic horse (Equus ferus caballus),[6] as well as two wild subspecies, the recently-extinct Tarpan (Equus ferus ferus) and the endangered Przewalski's Horse (Equus ferus przewalskii).[2] [3] [6] Genetically, the pre-domestication horse, Equus ferus ferus, and domesticated horse, Equus ferus caballus, form a single homogeneous group (clade) and are genetically indistinguishable from each other.[4][11][12] [13] The genetic variation within this clade shows only a limited regional variation, with a notable exception of the Przewalski's Horse.[4][11][12][13] The Przewalski's Horse has several unique genetic differences that distinguishes it from the other subspecies, including 66 instead of 64 chromosomes,[2] [14] unique Y-chromosome gene haplotypes, [15] and unique mtDNA haplotypes. [16] Besides genetic differences, osteological evidence from across the Eurasian wild horse range, based on cranial and metacarpal differences, indicates the presence of only two subspecies in post-glacial times, the Tarpan and the Przewalski's Horse.[7] [17] [edit] Scientific naming of the speciesAt present, the domesticated and wild horses are considered a single species, with the valid scientific name for the horse species being Equus ferus. The wild Tarpan subspecies is Equus ferus ferus, the Przewalski's Horse is Equus ferus przewalski, and the domesticated horse is Equus ferus caballus.[18] The rules for the scientific naming of animal species are determined in the International Code of Zoological Nomenclature, which stipulates that the oldest available valid scientific name is used to name the species. Previously, when taxonomists considered domesticated and wild horse two subspecies of the same species, the valid scientific name was Equus caballus Linnaeus 1758 [19], with the subspecies labeled Equus caballus caballus (domesticated horse), Equus caballus ferus Boddaert, 1785 (tarpan) and Equus caballus przewalskii Poliakov, 1881 (Przewalski's Horse). However, in 2003, the International Commission on Zoological Nomenclature decided that the scientific names of the wild species have priority over the scientific names of domesticated species, therefore mandating the use of Equus ferus for the horse, independent of the position of the domesticated horse. [edit] Difference from feral horses Main articles: Feral horse and feral Horses that live in an untamed state but have ancestors who have been domesticated are not truly "wild" horses; they are feral horses. For example, when Europeans reintroduced the horse to the Americas beginning in the late 15th century, some horses escaped and formed feral herds, the best-known being the Mustang. The Australian equivalent to the Mustang is the Brumby, descended from horses strayed or let loose in Australia by English settlers.[20] There are isolated populations of feral horses in a number of places, including Portugal, Scotland, and a number of barrier islands along the Atlantic coast of North America from Sable Island off Nova Scotia, to the Shackleford Banks of North Carolina. While these are often referred to as "wild" horses, they are not truly "wild" in the biological sense of having no domesticated ancestors. [edit] Status unclearIn 1995, British and French explorers discovered a new population of horses in the Riwoche Valley of Tibet, unknown to the rest of the world, but apparently used by the local Khamba people. It was speculated that the horse might be a relic population of wild horses,[21] but testing did not reveal genetic differences with domesticated horses,[22] which is in line with news reports indicating that they are used as pack and riding animals by the local villagers.[23] These horses only stand 12 hands (48 inches, 122 cm) tall and are said to resemble the images known as "horse no 2" depicted in cave paintings alongside images of the Przewalski's horse.[22] [edit] See also[edit] References
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