University of Copenhagen: Origin of domestic horses finally established

Horses were first domesticated in the Pontic-Caspian steppes, northern Caucasus, before conquering the rest of Eurasia within a few centuries. These are the results of a study led by paleogeneticist Ludovic Orlando. The study is published in Nature on 20 October 2021.

By whom and where were modern horses first domesticated? 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? This long-standing archaeological mystery finally comes to an end thanks to a team of 162 scientists specialising in archaeology, palaeogenetics and linguistics.

A few years ago, Ludovic Orlando’s team looked at the site of Botai, Central Asia, which had provided the oldest archaeological evidence of domestic horses. The DNA results, however, were not compliant: these 5500-year-old horses were not the ancestors of modern domestic horses. Besides the steppes of Central Asia, all other presumed foci of domestication, such as Anatolia, Siberia and the Iberian Peninsula, had turned out to be false.

“We knew that the time period between 4,000 to 6,000 years ago was critical but no smoking guns could ever be found” says CNRS research professor Orlando.

The scientific team, therefore, decided to extend their study to the whole of Eurasia by analysing the genomes of 273 horses that lived between 50,000 and 200 years BC. This information was sequenced at the Centre for Anthropobiology and Genomics of Toulouse (CNRS/Université Toulouse III – Paul Sabatier) and Genoscope2 (CNRS/CEA/Université d’Évry) before being compared with the genomes of modern domestic horses. This strategy paid off: although Eurasia was once populated by genetically distinct horse populations, a dramatic change had occurred between 2000 and 2200 BC.

“That was a chance: the horses living in Anatolia, Europe, Central Asia and Siberia used to be genetically quite distinct” notes Dr Pablo Librado, first author of the study.

Then, a single genetic profile, previously confined to the Pontic steppes (North Caucasus)3, began to spread beyond its native region, replacing all the wild horse populations from the Atlantic to Mongolia within a few centuries.

“The genetic data also point to an explosive demography at the time, with no equivalent in the last 100,000 years” adds Pr Orlando. “This is when we took control over the reproduction of the animal and produced them in astronomic numbers.”

But how can this overwhelming popularity be explained? Interestingly, scientists found two striking differences between the genome of this horse and those of the populations it replaced: one is linked to a more docile behaviour and the second indicates a stronger backbone. The researchers suggest that these characteristics ensured the animals’ success at a time when horse travel was becoming “global”.

Horse domestication was a game changer
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 BC4 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.

“This study is of great importance for understanding the significant cultural changes that took place in the early third millennium BC in northern Europe, including Denmark. The emergence of new material culture has been associated with the introduction of steppe related ancestry, the Indo-European language, and horse domestication. With this study we are able to show that migrations from the steppe in the early third millennium BC didn’t include domesticated horses as these were introduced c. 1000 years later in the earliest Bronze Age,” says University of Copenhagen archaeologist Rune Iversen. He adds:

“The invention of horse-drawn chariots was a huge advancement and a game changer in warfare. Living in a world where the fastest way of moving was running or paddling dugout canoes, horses and chariots changed everything.”

His colleague, linguist Guus Kroonen, says the new genetic study is supported by the historical linguistic evidence:

“By analyzing horse aDNA from the relevant periods we were able to test a popular linguistic hypothesis on the spread of the Indo-European languages in an entirely new way. An old view is that, around 5.000 years ago, Indo-European-speaking groups arrived from the eastern European steppes on horseback and brutally subjugated more peaceful, farming societies. This cross-disciplinary study challenges that narrative.”

The aDNA from the samples we helped collect for this study shows no indications that steppe groups took their horses with them. A review of the linguistic evidence supports this, Guus Kroonen adds:

“All of the oldest Indo-European languages share the same word for ‘horse’, derived from Proto-Indo-European *h₁ekʷos. However, no corresponding word exists for ‘to ride’. If Indo-European speakers became involved in domesticating steppe horses, they therefore likely only did so for their meat and milk. When Indo-European groups started spreading to Europe, they took their languages with them, but they didn’t come on horseback nor did they arrive in wagons pulled by horses.”

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