The origins and spread of domestic horses from the Western Eurasian steppes

Domestication of horses fundamentally transformed long-range mobility and warfare1. However, modern domesticated breeds do not descend from the earliest domestic horse lineage associated with archaeological evidence of bridling, milking and corralling2–4 at Botai, Central Asia around 3500 bc3. Other longstanding candidate regions for horse domestication, such as Iberia5 and Anatolia6, have also recently been challenged. Thus, the genetic, geographic and temporal origins of modern domestic horses have remained unknown. Here we pinpoint the Western Eurasian steppes, especially the lower Volga-Don region, as the homeland of modern domestic horses. Furthermore, we map the population changes accompanying domestication from 273 ancient horse genomes. This reveals that modern domestic horses ultimately replaced almost all other local populations as they expanded rapidly across Eurasia from about 2000 bc, synchronously with equestrian material culture, including Sintashta spoke-wheeled chariots. We find that equestrianism involved strong selection for critical locomotor and behavioural adaptations at the GSDMC and ZFPM1 genes. Our results reject the commonly held association7 between horseback riding and the massive expansion of Yamnaya steppe pastoralists into Europe around 3000 bc8,9 driving the spread of Indo-European languages10. This contrasts with the scenario in Asia where Indo-Iranian languages, chariots and horses spread together, following the early second millennium bc Sintashta culture11,12.

Dairying enabled Early Bronze Age Yamnaya steppe expansions

During the Early Bronze Age, populations of the western Eurasian steppe expanded across an immense area of northern Eurasia. Combined archaeological and genetic evidence supports widespread Early Bronze Age population movements out of the Pontic–Caspian steppe that resulted in gene flow across vast distances, linking populations of Yamnaya pastoralists in Scandinavia with pastoral populations (known as the Afanasievo) far to the east in the Altai Mountains1,2 and Mongolia3. Although some models hold that this expansion was the outcome of a newly mobile pastoral economy characterized by horse traction, bulk wagon transport4–6 and regular dietary dependence on meat and milk5, hard evidence for these economic features has not been found. Here we draw on proteomic analysis of dental calculus from individuals from the western Eurasian steppe to demonstrate a major transition in dairying at the start of the Bronze Age. The rapid onset of ubiquitous dairying at a point in time when steppe populations are known to have begun dispersing offers critical insight into a key catalyst of steppe mobility. The identification of horse milk proteins also indicates horse domestication by the Early Bronze Age, which provides support for its role in steppe dispersals. Our results point to a potential epicentre for horse domestication in the Pontic–Caspian steppe by the third millennium bc, and offer strong support for the notion that the novel exploitation of secondary animal products was a key driver of the expansions of Eurasian steppe pastoralists by the Early Bronze Age.

Rethinking the evidence for early horse domestication at Botai

Despite its transformative impact on human history, the early domestication of the horse (Equus caballus) remains exceedingly difficult to trace in the archaeological record. In recent years, a scientific consensus emerged linking the Botai culture of northern Kazakhstan with the first domestication of horses, based on compelling but largely indirect archaeological evidence. A cornerstone of the archaeological case for domestication at Botai is damage to the dentition commonly linked with the use of bridle mouthpieces, or “bit wear.” Recent archaeogenetic analyses reveal, however, that horse remains from Botai are not modern domesticates but instead the Przewalski’s horse, E. przewalskii—warranting reevaluation of evidence for domestication. Here, we compare osteological traits hypothesized to have been caused by horse transport at Botai with wild Pleistocene equids in North America. Our results suggest that damage observed in Botai horse teeth is likely generated by natural disturbances in dental development and wear, rather than through contact with bridle equipment. In light of a careful reconsideration of the mid-Holocene archaeological record of northern Eurasia, we suggest that archaeological materials from Botai are most effectively explained through the regularized mass harvesting of wild Przewalski’s’ horses—meaning that the origins of horse domestication may lie elsewhere.

The Evolutionary and Historical Foundation of the Modern Horse: Lessons from Ancient Genomics

The domestication of the horse some 5,500 years ago followed those of dogs, sheep, goats, cattle, and pigs by ∼2,500–10,000 years. By providing fast transportation and transforming warfare, the horse had an impact on human history with no equivalent in the animal kingdom. Even though the equine sport industry has considerable economic value today, the evolutionary history underlying the emergence of the modern domestic horse remains contentious. In the last decade, novel sequencing technologies have revolutionized our capacity to sequence the complete genome of organisms, including from archaeological remains. Applied to horses, these technologies have provided unprecedented levels of information and have considerably changed models of horse domestication. This review illustrates how ancient DNA, especially ancient genomes, has inspired researchers to rethink the process by which horses were first domesticated and then diversified into a variety of breeds showing a range of traits that are useful to humans.

High genetic diversity of ancient horses from the Ukok Plateau

A growing number of researchers studying horse domestication come to a conclusion that this process happened in multiple locations and involved multiple wild maternal lines. The most promising approach to address this problem involves mitochondrial haplotype comparison of wild and domestic horses from various locations coupled with studies of possible migration routes of the ancient shepherds. Here, we sequenced complete mitochondrial genomes of six horses from burials of the Ukok plateau (Russia, Altai Mountains) dated from 2.7 to 1.4 thousand years before present and a single late Pleistocene wild horse from the neighboring region (Denisova cave). Sequencing data indicates that the wild horse belongs to an extinct pre-domestication lineage. Integration of the domestic horse data with known Eurasian haplotypes of a similar age revealed two distinct groups: the first one widely distributed in Europe and presumably imported to Altai, and the second one specific for Altai Mountains and surrounding area.

Local origin or external input: modern horse origin in East Asia

Background Despite decades of research, the horse domestication scenario in East Asia remains poorly understood. Results The study identified 16 haplogroups with fine-scale phylogenetic resolution using mitochondrial genomes of 317 horse samples. The time to the most recent common ancestor of the 16 haplogroups ranges from [0.8–3.1] thousand years ago (KYA) to [7.9–27.1] KYA. With combined analyses of the mitochondrial control region for 35 extant Przewalski’s horses, 3544 modern and 203 ancient horses across the world, researchers provide evidence for that East Asian prevalent haplogroups Q and R were indigenously domesticated or they were involved in numerous distinct genetic components from wild horses in the southern part of East Asia. These events of haplotypes Q and R occurred during 4.7 to 16.3 KYA and 2.1 to 11.5 KYA, respectively. The diffusion of preponderant European haplogroups L from west to East Asia is consistent with the external gene input. Furthermore, genetic differences were detected between northern East Asia and southern East Asia cohorts by Principal Component Analysis, Analysis of Molecular Variance test, the χ2 test and phylogeographic analyses. Conclusions All results suggest a complex picture of horse domestication, as well as geographic pattern in East Asia. Both local origin and external input occurred in East Asia horse populations. And besides, there are at least two different domestication or hybridization centers in East Asia.

Turning Points in Horse Breeding in the Eurasian Steppes and the Near East

This article discusses the pivotal points in horse domestication on the Eurasian steppes and the Near East in the 5th to 2nd millennia BC, from the initial time and place of the domestication of horses to the emergence of various types of horse harnesses. On the basis of 5th and 4th millennia BC Eurasian horse-headed scepters, the means for handling horses are reconstructed. Six types of head harnesses are described, and their evolution is traced from simple muzzles (type 1) and more complex ones (types 2 and 3) to those supplemented with drop nosebands (type 4) and snaffl e (type 5) and non-snaffl e bridles (type 6). A unique 3rd millennium BC document—an Elamite clay tablet from Susa, listing horse farms, has made it possible to assess the structure of each farm, and evaluate the size of the domestic horse population in Elam. Training techniques of chariot horses were described by the “master horse trainer Kikkuli of Mitanni”. These techniques were further developed by the proto-Indo-Aryans on the Eurasian steppes in the early 2nd millennium BC, and became known to the Hittites and Assyrians via the Mitanni horse breeders. On the basis of the Rigveda, the type and exterior of those swift horses with which the Indo-Aryans spread over Asia are characterized.