Domestication of The Horse - Predecessors To The Domestic Horse

Predecessors To The Domestic Horse

A 2005 study analyzed the mitochondrial DNA (mtDNA) of a worldwide range of equids, from 53,000 year old fossils to contemporary horses. Their analysis placed all equids into a single clade, or group with a single common ancestor, consisting of three genetically divergent species: Hippidion, the New World stilt-legged horse, and the true horse. The true horse, which ranged from western Europe to eastern Beringia, included prehistoric horses and the Przewalski's Horse, as well as what is now the modern domestic horse, belonged to a single Holarctic species. A more detailed analysis of the true horses grouped them into two major clades. One of these clades, which seemed to have been restricted to North America, is now extinct. The other clade was broadly distributed from North America to central Europe, north and south of Pleistocene ice sheets. It became extinct in Beringia around 14,200 years ago, and in the rest of the Americas around 10,000 years ago. This clade survived in Eurasia, however, and it is from these horses which all domestic horses appear to have descended. These horses showed little phylogeographic structure, probably reflecting their high degree of mobility and adaptability.

Therefore, the domestic horse today is classified as Equus ferus caballus. No genetic originals of native wild horses currently exist, other than the never-domesticated Przewalski's Horse. The Przewalski has 66 chromosomes, however, as opposed to 64 among modern domesticated horses, and their Mitochondrial DNA (mtDNA) forms a distinct cluster. Genetic evidence suggests that modern Przewalski's horses are descended from a distinct regional gene pool in the eastern part of the Eurasian steppes, not from the same genetic group that gave rise to modern domesticated horses. Nevertheless, evidence such as the cave paintings of Lascaux suggests that the ancient wild horses that some researchers now label the "Tarpan subtype" probably resembled Przewalski horses in their general appearance: big heads, dun coloration, thick necks, stiff upright manes, and relatively short, stout legs.

The horses of the Ice Age were hunted for meat in Europe and across the Eurasian steppes and in North America by early modern humans. Numerous kill sites exist and many cave paintings in Europe indicate what they looked like. Many of these Ice Age subspecies died out during the rapid climate changes associated with the end of the last Ice Age or were hunted out by humans, particularly in North America, where the horse became completely extinct.

Classification based on body types and conformation, absent the availability of DNA for research, once suggested that that there were roughly four basic wild prototypes, thought to have developed with adaptations to their environment prior to domestication. There were competing theories, some argued that the four prototypes were separate species or subspecies, while others suggested that the prototypes were physically different manifestations of the same species. However, more recent study indicates that there was only one wild species and all different body types were entirely a result of selective breeding or landrace adaptation after domestication. Either way, the most common theories of prototypes from which all modern breeds are thought to have developed suggests than in addition to the so-called Tarpan subtype, there were the following base prototypes:

• The "Warmblood subspecies" or "Forest Horse" (once proposed as Equus ferus silvaticus, also called the Diluvial Horse), which evolved into a later variety sometimes called Equus ferus germanicus. This prototype may have contributed to the development of the warmblood horses of northern Europe, as well as older "heavy horses" such as the Ardennais.
• The "Draft" subspecies, a small, sturdy, heavyset animal with a heavy hair coat, arising in northern Europe, adapted to cold, damp climates, somewhat resembling today's draft horse and even the Shetland pony.
• The "Oriental" subspecies, (once proposed as Equus agilis) a taller, slim, refined and agile animal arising in western Asia, adapted to hot, dry climates, thought to be the progenitor of the modern Arabian horse and Akhal-Teke.

Only two never-domesticated "wild" groups survived into historic times, Przewalski's horse (Equus ferus przewalski), and the Tarpan (Equus ferus ferus). The Tarpan became extinct in the late 19th century and Przewalski's horse is endangered; it 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. Other subspecies of Equus ferus appear to have existed and could have been the stock from which domesticated horses are descended.