There are a number of theories regarding the domestication of the horse. Although horses began appearing in cave art as early as 30,000 BCE, these were truly wild horses, and were probably hunted for meat; how and when they became domesticated is less clear.
Older theories (pre-1999)
Before the common use of DNA in such research, anthropologists and evolutionary biologists had to content themselves with studying features of existing animals and comparing them to preserved specimens from the past–frozen remains, other preserved remains, and fossils. For horses, the data led to the hypothesis that horses were domesticated in one small area, perhaps around 4600 BCE on the grassland steppes of Eurasia.
Theories from DNA 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 mtDNA from 191 pedigree horses (Vil et al., 2001), including primitive English and Swedish animals and one breed derived from animals imported to Iceland by the Vikings. They also obtained DNA samples from a Przewalski’s horse, a small Mongolian equine thought by some to be a sister species to the original wild horses. 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.
The mtDMA analysis showed that the modern horses had almost as much genetic variation as samples of fossil horses. By contrast, similar mtDNA analyses had shown that modern individuals from cattle, sheep, water buffalo, and pig breeds are much less genetically diverse than their ancient forbears. This would suggest that horses, unlike the other domestic animals studied, had ancestors in many places, implying that domestication occurred in many areas.
Investigations by professor Hans Ellegren et al., Sweden, publicated i Nature Genetics 2004 has revealed that all horses, Big and small, probably descend from one single stallion. These investigations were performed on chromosome Y. On the other hand similar investigations showed that there are at least a hundred different maternal ancestors. The conclusion ought to be that mankind early understood the importance of breeding good stallions since they can produce much more foals than a mare can. This fact is even today of big importance in breeding.
The Equivocal evidence: When and Where domestication occurred
The when is also difficult to establish, and here again there seem to be several camps. One claim is that evidence at several sites shows equine tooth wear that only could appear from the friction of a bit against the molars. Sites incluke Dereivka, a Ukrainian settlement site (circa 4500-3500 BCE), and the Botai culture, dated 3500-3000 BCE in the northern steppes of Kazkhstan, east of the Ishim River. One idea is that the horses with bit wear were part of the religion, and were kept as objects of veneration; this is clearly the beginning of domestication. Another idea is that there would be a large population of equines in the area; some would be domesticated and others would be still-wild. The domesticated individuals would be used to hunt the wild individuals; only the domesticated individuals would show bit wear.
Another camp resists this evidence because there’s no proof that the horses were actually domesticated, as opposed to merely tamed. Marsha A. Levine, one of the foremost researchers in this field, points out that traditional peoples (aboriginal hunter-gatherers and horticulturists) world-wide tame individuals from wild species, typically by hand-rearing infants whose parents have been killed. A species cannot be said to be truly domesticated until it will reliably breed in captivity.
Levine’s model of horse domestication starts with individual near-infant horses (foals) being captured as their mothers 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 made into pets happening repeatedly over time, until the great discovery that these pets could be put to work.
The horse may have been domesticated in one isolated locale 4500 BCE. But as Levine points out, the unequivocal date of domestication and use as a means of transport is circa 2000 BC, the Sintashta chariot burials. 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-pulled chariots in Greece, Egypt, and Mesopotamia. By another 500 years, the horse-pulled chariot had spread to China.
What came first, riding or driving?
The real question for a given time and locale is: which came first, domestication of the horse or the invention of the wheel?
Ancient or early-domesticated horses were relatively small by modern standards, perhaps 12.2 to 14.2 hands high (see horse for explanation of hands) or 1.27 to 1.47 meters, measured at the shoulder. The small stature of these horses, compared to modern riding horses of 15.2 to 17.2 hh (1.6 to 1.8 meters), lead theorists to believe the ancient horses were too small to be ridden and so must have been driven.
However, this does not necessarily tarry with the strength of equivalent modern breeds; 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.
Undoubtedly, our understanding of early horse domestication will continue to evolve, and continue to be hotly debated.