Domestication of the horse
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There are a number of theories regarding the domestication of the horse. Although horses appeared in Paleolithic cave art as early as 30,000 BC, these were truly wild horses and were probably hunted for meat; how and when horses became domesticated is less clear. The clearest evidence of use of the horse as a means of transport is c. 2000 BC. However, the Kurgan hypothesis, which sets the domestication of horses in the Ukraine at approximately 4000 BC, is gaining ever more evidence and is becoming widely accepted.
Attempts to date domestication by genetic or morphological analyses rests on the assumption of a separation of the genotype or phenotype of the domesticated and the wild populations. Such a separation has doubtlessly taken place in historical times, but dates based on such methods can only ever result in an estimation of the latest possible date for domestication without excluding the possibility of an unknown period of significant gene-flow between wild and domestic populations (which will occur naturally as long as the domesticated population is kept within the habitat of the wild population).
The date of the domestication of the horse depends to some degree on one's definition of "domestic." All horse populations retain the ability to revert to a feral state, and all feral horses are of domestic types; that is, they descend from ancestors that escaped from man. The domestic horse is Equus caballus. Its wild ancestor was Equus ferus. No genetic originals of native wild horses currently exist, other than the never-domesticated Przewalski's Horse.
 Predecessors to the domestic horse
The Ice Age featured a number of subspecies of Equus ferus, a controversial term used to describe the wild prototype of Equus caballus, which were hunted for meat on the tundra and steppes by early modern men. Numerous kill sites exist and many cave paintings in Europe tell us what they looked like. The main problem for students of horse domestication is many early subspecies were apparently hunted out by humans, particularly in North America, where the horse became completely extinct.
There is a theory that there were four basic "proto" horses that developed with adaptations to their environment prior to domestication. There are competing theories, some arguing that the prototypes were separate species, others suggesting that the prototypes were physically different manifestations of the same species.  Other theories hold that there was only one wild species was domesticated and all different body types were entirely a result of selective breeding.
Either way, the most common theories of multiple wild subspecies from which other types are thought to have developed suggests the following base prototypes:
- The "Warmblood subspecies" or "Forest Horse" (Equus ferus silvaticus, also called the Diluvial Horse), thought to have evolved into Equus ferus germanicus, and which 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, 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
- The "Tarpan subspecies," dun-colored, sturdy animal, the size of a large pony, adapted to the cold, dry climates of northern Asia, the predecessor to the Tarpan and Przewalski's Horse as well as the domesticated Mongolian horse.
Only two truly "wild" groups survived, Przewalski's horse and the Tarpan. The Tarpan became extinct in the 19th century and Przewalski's is endangered and until recently was considered extinct in the wild. Although researchers such as Gimbutas theorized that the horses of the Eneolithic 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 not yet known to modern science may have existed. Scholars refer to these unknown animals as "caballine", meaning that they are not Equus caballus, but are ancestral to it.
Even though horse domestication was widespread in a short period of time, it is still possible that domestication began with a single culture, which passed on techniques and breeding stock. The earliest domestication is most likely to have occurred in the 8000 BC - 5000 BC window. It is possible that the two "wild" subspecies remained when all other groups of "wild" horses died out because all others had been, perhaps, more suitable for taming by humans and the selective breeding that gave rise to the modern domestic horse.
How could those horses possibly have survived in Europe after 8000 BC, the approximate date of their extinction in the Americas? The most probable answer is that humans, having hunted out the feral herds, kept horses as livestock. If that is true, one might speak of "domestic horses" dating from 8000 BC. Scholars are currently looking for convincing evidence for this theory.
Recent genetic studies by a team headed by C. Vila, using the DNA of frozen fossil horse feet found in the Alaskan permafrost, dating from 28,000 to 12,000 BP, identified 77 mares who were ancestral to today's Equus caballus, from different times and places. Vila concluded that horses were widely domesticated over Eurasia and that the horse taming technology passed between different cultures.
 Archaeological evidence
Incontrovertible evidence of domestication comes from archaeological finds of human artifacts connected with horses:
- depictions of horses used as mounts or draught animals
- equipment such as bits or other types of horse tack
- horse remains in archaeological context, particularly horses interred in human graves or showing other signs of ceremonial burial.
Studies of morphological features of existing animals compared to those of fossil remains (frozen remains, other preserved remains, and sub-fossils) led to the hypothesis that horses were domesticated in one small area of the great steppes of Eurasia, perhaps around the mid 5th millennium. The earliest archaeological evidence of domestication are bone bits and horse remains in human graves found in the eneolithic (5th millennium) Samara culture at the middle Volga. Interestingly, this same culture is suggested to correspond to the Proto-Indo-Europeans in the Kurgan hypothesis.
It remains for archaeology to find and excavate the sites that will tell us what happened. In historical times, the use of horses is nearly a diagnostic of Indo-European culture in the diaspora phase. It is certainly one if hardly the only way to account for the rapid spread of the Kurgan culture and the ease with which it seems to have gotten the upper hand over Pre-Indo-European cultures. For the most part, the forest-steppe region and the plains of Asia remain archaeologically unexplored, leaving room for future discoveries.
The earliest evidence of horse domestication spreading outside regions that encompassed the wild horse's natural habitat is found in early depictions of horses as draught animals in the Ancient Near East, dating to ca. 1800 BC. These images showed harnessed horses controlled with nose rings, as was also the practice with the onagers (Equus hemionus) native to the Near East; horses controlled in such a manner could draw chariots in processions, but not in battle. Widespread introduction of the horse to the Near East coincides with the turmoil of the Kassite period from ca. 1600 BC.
The first evidence of domesticated horses in China dates to the late Bronze Age Yin Dynasty, and evidence for introduction to the Indian Subcontinent (see History of the horse in South Asia) and Northern Europe (see Trundholm sun chariot) date to about the same period.
 Genetic evidence
More recently, a comparative study of mitochondrial DNA (mtDNA) from living and fossil horses suggests that horses were domesticated in many places, at many times.
Evolutionary biologists at Uppsala University in Sweden studied mitochondrial DNA from 191 pedigreed horses, including examples of historical English and Swedish breeds considered "primitive," and one breed derived from animals imported to Iceland by the Vikings. They also obtained DNA samples from the Przewalski's horse. They compared these samples with fossil DNA from leg bones of horses that have been preserved in the Alaskan permafrost for more than 12,000 years and with other samples from 1000- to 2000-year-old archaeological sites in southern Sweden and Estonia.
This analysis showed that the modern horses had almost as much genetic variation as samples of fossil horses. By contrast, similar analyses of mitochondrial DNA had shown that modern individuals from cattle, sheep, water buffalo, and pig breeds are much less genetically diverse than their ancient forbears. Thus, it appears that a large number of wild lineages were involved in the domestication of the horse, many more than in any other domestic mammal, and suggests that the domesticated horse had ancestors in many places. This probably means either that domestication occurred in many areas or that the gene pool of the domesticated population was continuously refreshed from that of the wild population by new captures.
These studies also indicate that the equine matrilineal most recent common ancestor (the mt-mrca) clearly predates the domestication of the horse. On the other hand, the patrilineal most recent common ancestor (the Y-mrca) may be more recent.
 Location and time of domestication
The time of domestication is also difficult to establish, and here again there seem to be several competing theories. One claim is that evidence at several sites shows equine tooth wear that only could result from the friction of a bit against the molars, indicating captive animals--though not necessarily domesticated ones. Sites include Dereivka, a Ukrainian settlement site (circa 4500–3500 BC), and sites identified as the Botai culture, dated 3500–3000 BC in the northern steppes of Kazakhstan, east of the Ishim River. Not all molars at the sites showed bit wear: one theory argues that the horses with bit wear were cult animals and were kept as objects of veneration. Another theory suggests that there would be a large population of equines in the area; some would be captive and others would remain wild. The captive animals would be used to hunt the wild individuals; only the captive animals would show bit wear.
Another camp resists this evidence of domestication altogether because there are no skeletal changes that provide incontrovertible proof that the horses were actually domesticated—that is, bred in captivity—and not merely tamed. A species cannot be said to be truly domesticated until it will reliably breed in captivity. Marsha A. Levine, one of the foremost researchers in this field, points out that traditional peoples world wide (both aboriginal hunter-gatherers and horticulturists) routinely tame individuals from wild species, typically by hand-rearing infants whose parents have been killed.
Levine's model of horse domestication starts with individual foals being kept as pets while the adult horses were slaughtered for meat. Foals are relatively small and easy to handle. Horses, being herd animals, need companionship to thrive, and the modern data show that foals can and will bond to other domestic animals to meet their intimacy needs. Levine envisions horses being repeatedly made into pets over time, preceding the great discovery that these pets could be ridden or otherwise put to work.
The traditional scenario, in which the horse would have been domesticated in one isolated locale in the 5th millennium BC, is not without some serious anthropological puzzles. On one hand, logic suggests that horses would have been ridden long before they were driven. But it is also far more difficult to gather evidence of this, as the materials required for riding—simple hackamores or blankets--would not survive as artifacts, and other than tooth wear from a bit, the skeletal changes in an animal that was ridden would not necessarily be particularly noticeable. Evidence of horses being driven is much stronger.
As Levine points out, the unequivocal date of domestication and use of the horse as a means of transport is circa 2000 BC, the date of the Sintashta chariot burials in the southern Urals. However, shortly thereafter, the expansion of the domestic horse throughout Europe was little short of explosive. In the space of possibly 500 years, there is evidence of horse-drawn chariots in Greece, Egypt, and Mesopotamia. By another 500 years, the horse-drawn chariot had spread to China.
 Driving versus riding
A difficult question is if domesticated horses were first ridden or driven. While the most unequivocal evidence shows horses first being used to pull chariots in warfare, there is strong, though indirect, evidence for earlier uses.
For the proposition that horses were ridden before being driven, David W. Anthony, one of the co-founders of the Institute for Ancient Equestrian Studies, wrote (Anthony, 1998):
- "The Dereivka stallion exhibits bit wear made by a hard bit - perhaps bone. The amount of wear would have required at least 300 hours of riding with a hard bit, according to our experiments. If the deposit containing the stallion skull and mandible dates to about 4000 BC, as Brown, Telegin and I would argue, it pre-dates the invention of the wheel. If the bit wear at Dereivka precedes the introduction of wheeled vehicles, it probably resulted from riding. The bit wear at Dereivka is the earliest evidence for the use of horses as transport animals anywhere in the world. "
In addition, as the modern hackamore demonstrates, horses can also be ridden without a bit by using rope and other evanescent materials to make equipment that fastens around the nose. So the absence of unequivocal evidence of early riding in the record does not settle the question.
On the other hand, others debate the issue, arguing that evidence of bit wear does not necessarily correlate to riding. Some theorists speculate that a horse could have simply been led by placing a bit in the mouth, connected to a lead rope, and leading the animal while pulling a primitive wagon or plow. Since oxen were usually relegated to this duty in Mesopotamia, it could be guessed that early plows might have been attempted with the horse, and a bit may indeed have been significant as part of agrarian development rather than as warfare technology.
 Horses in ancient warfare
- Main Article: Horses in warfare
Horses in the Bronze Age were relatively small by modern standards, which led some theorists to believe the ancient horses were too small to be ridden and so must have been driven. Herodotus' description of the Sigynnae, a steppe people who bred horses too small to ride but extremely efficient at drawing chariots, illustrates this stage.
The Iron Age saw the rise of mounted cavalry as a tool of war, as evidenced by the notable successes of mounted archer tactics used by various invading equestrian nomads such as the Parthians. Over time, the chariot gradually become obsolete.
The horse of the Iron Age was still relatively small, perhaps 12.2 to 14.2 hands high or 1.27 to 1.47 meters, measured at the withers. This was shorter overall average height than modern riding horses, which range from 14.2 to 17.2 hh (1.47 to 1.78 meters). However, small horses were used successfully as light cavalry for many centuries. For example, Fell ponies, believed to be descended from Roman cavalry horses, are comfortably able to carry fully grown adults (although with rather limited ground clearance) at an average height of 13.2 hands (1.37 m). Likewise, the Arabian horse is noted for a short back and dense bone, and the successes of the Muslims against the heavy mounted knights of Europe demonstrated that a 14.2 hand horse can easily carry a full-grown human adult into battle.
Mounted warriors such as the Scythians, Huns and Vandals of late Roman antiquity, the Mongols who invaded eastern Europe in the 7th century through 14th centuries AD, the Muslim warriors of the 8th through 14th centuries AD, and the American Indians in the 16th through 19th centuries each demonstrated effective forms of light cavalry.
- ^ [http://www.imh.org/imh/kyhpl1b.html#xtocid2243616 "A Chronological History of Humans and Their Relationship With the Horse" from International Museum of the Horse, web site, accessed February 8, 2007
- ^ Bennett, Deb. Conquerors: The Roots of New World Horsemanship. Amigo Publications Inc; 1st edition 1998. ISBN 0-9658533-0-6
- ^ Budiasky, Stephen. The Nature of Horses.
- ^ Note that the Sumerian term for "horse" is derived from that for "donkey", ANŠE.KUR.RA 𒀲𒆳𒊏, literally "mountain donkey", indicating introduction of the horse to the plains of Mesopotamia from Anatolia or Persia.
- ^ This association has occasionally inspired descriptions of the Kassites as equestrian nomads.
- ^ Vilà et al., 2001
- ^ Lindgren et al. (2004); note that also in human genetics, "Y-Adam" is considerably younger than "mt-Eve".
 See also
- Horses in warfare
- Medieval horses
- Horse sacrifice
- Equestrian nomad
- Evolution of the Horse
- list of horse breeds
- horse training
- horse breeding
- horse tack
- horse teeth
 Additional References
- Anthony, David W. (1998). The opening of the Eurasian steppe at 2000 BC. In The Bronze Age and Early Iron Age Peoples of Eastern Central Asia, ed. Victor H. Mair, vol. 1. (Journal of Indo-European Studies Monograph 26). Washington, D.C.: The Institute for the Study of Man.
- Lindgren, G., Backström, N., Swinburne, J., Hellborg, L., Einarsson, A., Sandberg, K., Vilà, C., Binns, M. & Ellegren, H. (2004) Limited number of patrilines in horse domestication. Nature Genetics 36: 335-336.
- Vilà, C, Leonard, JA, Götherström, A, Marklund, S, Sandberg, K, Lidén, K, Wayne, RK, and Ellegren, H. (2001). Widespread origins of domestic horse lineages. Science 291: 474-477.