The cradle of horse domestication has been identified by researchers, who pinned down the Western Eurasian steppes, especially the lower Volga-Don region, as the homeland of modern domestic horses.
Domestication of horses fundamentally transformed long-range mobility and warfare, bringing about huge changes to the human way of life.
The earliest horse lineage associated with archaeological evidence of bridling, milking and corralling was at Botai, Central Asia, around 3500 BC, but molecular-based tested has shown that modern domesticated breeds do not descend from these horses. The Botai horses instead show links with the Przewalski’s horse.
Other longstanding candidate regions for domestication, such as Iberia and Anatolia, have also recently been challenged.
So, where were modern horses first domesticated, and by whom? When did they conquer the rest of the world? And how did they supplant the myriad of other types of horses that existed at that time?
Fresh research led by paleogeneticist Ludovic Orlando, of the French National Centre for Scientific Research, shows that horses were first domesticated in the Pontic-Caspian steppes, in the northern Caucasus, before conquering the rest of Eurasia within a few centuries.
The ground-breaking international study, reported in the journal Nature, involved a team of 162 scientists specialising in archaeology, palaeogenetics and linguistics.
“We knew that the time period between 4000 to 6000 years ago was critical but no smoking guns could ever be found,” Orlando said.
The study team therefore decided to extend its investigation to the whole of Eurasia by analysing the genomes of 273 horses that lived between 50,000 years ago and 200 BC.
The results were compared with the genomes of modern domestic horses, revealing a remarkable new picture.
They showed that although Eurasia was once populated by genetically distinct horse populations, a dramatic change had occurred between 2200 BC and 2000 BC.
“The horses living in Anatolia, Europe, Central Asia and Siberia used to be genetically quite distinct,” explained Dr Pablo Librado, first author of the study.
Then, a single genetic profile, previously confined to the Pontic steppes in the North Caucasus region, began to spread beyond its native region, replacing all the wild horse populations from the Atlantic to Mongolia within a few centuries.
Genetic evidence also points to an explosion in horse numbers at the time, with no equivalent in the last 100,000 years, Orlando added. “This,” he said, “is when we took control over the reproduction of the animal and produced them in astronomic numbers.”
Interestingly, scientists found two striking differences between the genome of this horse and those of the populations it replaced. The genetic evidence showed people were breeding for more docile behaviour and a stronger backbone.
The researchers suggest that these characteristics ensured the animals’ success at a time when horse travel was becoming global.
The study also reveals that the horse spread throughout Asia at the same time as spoke-wheeled chariots and Indo-Iranian languages. However, the migrations of Indo-European populations, from the steppes to Europe during the third millennium BC could not have been based on the horse, as its domestication and diffusion came later. This demonstrates the importance of incorporating the history of animals when studying human migrations and encounters between cultures, the researchers said.
Before domestication, horses clustered into four geographically defined groups. One cluster included Equus lenensis, a lineage identified in northeastern Siberia from the Late Pleistocene to the late fourth millennium BC.
A second group covered Europe, including Late Pleistocene Romania, Belgium, France and Britain, and the region from Spain to Scandinavia and Hungary, the Czech Republic and Poland during the sixth-to-third millennium BC.
The third cluster comprised the earliest known domestic horses from Botai and the Przewalski’s horses, and extended to the Altai and Southern Urals during the fifth-to-third millennium BC.
Finally, modern domestic horses, dubbed DOM2, formed a cluster that was centered on the Western Eurasia steppes, but not further west than the Romanian lower Danube, south of the Carpathians, before and during the third millennium BC.
By around 2200 BC to 2000 BC, the typical DOM2 ancestry profile appeared outside the Western Eurasia steppes in Bohemia, the lower Danube and central Anatolia, before spreading across Eurasia shortly afterward, eventually replacing all pre-existing lineages.
The research also solved the mysterious origins of the tarpan horse, which became extinct in the early 20th century. The tarpan came about through the mixing of horses native to Europe and horses closely related to DOM2.
Discussing their findings, the study team said their work resolves longstanding debates about the origins and spread of domestic horses.
“Whereas horses living in the Western Eurasia steppes in the late fourth and early third millennia BC were the ancestors of DOM2 horses, there is no evidence that they facilitated the expansion of the human genetic steppe ancestry into Europe, as previously hypothesized.”
There may have been some early horse management and herding practices by the Yamnaya people and those of the Botai culture in Central Asia, but these remained localized practices within a sedentary settlement system.
“The globalization stage started later, when DOM2 horses dispersed outside their core region, first reaching Anatolia, the lower Danube, Bohemia and Central Asia by approximately 2200 to 2000 BC, then Western Europe and Mongolia soon afterward, ultimately replacing all local populations by around 1500 to 1000 BC.
“This process first involved horseback riding, as spoke-wheeled chariots represent later technological innovations, emerging around 2000 to 1800 BC in the Trans-Ural Sintashta culture,” the researchers said.
“The weaponry, warriors and fortified settlements associated with this culture may have arisen in response to increased aridity and competition for critical grazing lands, intensifying territoriality and hierarchy.
“This,” they said, “may have provided the basis for the conquests over the subsequent centuries that resulted in an almost complete human and horse genetic turnover in Central Asian steppes.”
The authors said their results have important implications for mechanisms underpinning two major language dispersals.
“DOM2 dispersal in Asia during the early-to-mid second millennium BC was concurrent with the spread of chariotry and Indo-Iranian languages, whose earliest speakers are linked to populations that directly preceded the Sintashta culture,” they said.
Chariotry and improved horse breeds (including chestnut coat colouration) both linguistically and genetically transformed Eurasian Bronze Age societies globally within a few centuries after about 2000 BC.
The study was directed by the the Centre for Anthropobiology and Genomics of Toulouse (CNRS/ Université Toulouse III – Paul Sabatier) with help from Genoscope (CNRS/CEA/Université d’Évry). The French laboratories Archéologies et sciences de l’Antiquité (CNRS/Université Paris 1 Panthéon Sorbonne/Université Paris Nanterre/Ministère de la Culture), De la Préhistoire à l’actuel: culture, environnement et anthropologie (CNRS/Université de Bordeaux/Ministère de la Culture) and Archéozoologie, archéobotanique : sociétés, pratiques et environnements (CNRS/MNHN) also contributed, as did 114 other research institutions throughout the world.
The study was primarily funded by the European Research Council (the Pegasus project) and France Genomique (the Bucéphale project).
Librado, P., Khan, N., Fages, A. et al. The origins and spread of domestic horses from the Western Eurasian steppes. Nature (2021). https://doi.org/10.1038/s41586-021-04018-9