Domestication of the horse

It is not entirely clear how, when or where the domestication of the horse took place. Although horses appeared in Paleolithic cave art as early as 30,000 BCE, these were wild horses and were probably hunted for meat. The clearest evidence of early use of the horse as a means of transport is from chariot burials dated c. 2000 BCE. However, an increasing amount of evidence began to support the hypothesis that horses were domesticated in the Eurasian Steppes in approximately 3500 BCE. Discoveries in the context of the Botai culture had suggested that Botai settlements in the Akmola Province of Kazakhstan are the location of the earliest domestication of the horse. However, Taylor and Barrón-Ortiz (2021) argue that Botai findings only reflect intensive exploitation of wild horses—possibly involving some level of management, herding, or seasonal capture—but not full domestication in the way we see in later horse-using societies. Warmuth et al. (2012) pointed to horses having been domesticated around 3000 BCE in what is now Ukraine and Western Kazakhstan. The evidence is disputed by archaeozoologist Williams T. Taylor, who argues that domestication did not take place until around 2000 BCE.

Genetic evidence indicates that domestication of the modern horse's ancestors likely occurred in an area known as the Volga–Don, in the Pontic–Caspian steppe region of eastern Europe, around 2200 BCE. From there, use of horses spread across Eurasia for transportation, agricultural work, and warfare. Scientists have linked the successful spread of domesticated horses to observed genetic changes. They speculate that stronger backs (GSDMC gene) and increased docility (ZFPM1 gene) may have made horses more suitable for riding.

The date of the domestication of the horse depends to some degree upon the definition of "domestication". Some zoologists define "domestication" as human control over breeding, which can be detected in ancient skeletal samples by changes in the size and variability of ancient horse populations. Other researchers look at the broader evidence, including skeletal and dental evidence of working activity; weapons, art, and spiritual artifacts; and lifestyle patterns of human cultures. There is evidence that horses were kept as a source of meat and milk before they were trained as working animals.

Attempts to date domestication by genetic study or analysis of physical remains rest on the assumption that there was a separation of the genotypes of domesticated and wild populations. Such a separation appears to have taken place, but dates based on such methods can only produce an estimate of the latest possible date for domestication without excluding the possibility of an unknown period of earlier 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).

Whether one adopts the narrower zoological definition of domestication or the broader cultural definition that rests on an array of zoological and archaeological evidence affects the time frame chosen for the domestication of the horse. The date of 4000 BCE is based on evidence that includes the appearance of dental pathologies associated with bitting, changes in butchering practices, changes in human economies and settlement patterns, the depiction of horses as symbols of power in artifacts, and the appearance of horse bones in human graves. On the other hand, measurable changes in size and increases in variability associated with domestication occurred later, about 2500–2000 BCE, as seen in horse remains found at the site of Csepel-Haros in Hungary, a settlement of the Bell Beaker culture.

Use of horses spread across Eurasia for transportation, agricultural work and warfare. Horses and mules in agriculture used a breastplate type harness or a yoke more suitable for oxen, which was not as efficient at utilizing the full strength of the animals as the later-invented padded horse collar that arose several millennia later.

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: the South American Hippidion, the North American New World stilt-legged horse, and Equus, the true horse. The true horse included prehistoric horses and the Przewalski's horse, as well as what is now the many breeds of modern domestic horses, belonged to a single Holarctic species.

The true horse migrated from the Americas to Eurasia via Beringia, becoming 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.