Farmer and horse herd

Giddy-up: origins of the domestic horse uncovered

The modern domestic horse is beloved worldwide as a favoured pet or an aid in the busy work of tending crops and livestock. But scientists looking to untangle the messy evolutionary roots of the modern horse have often been frustrated by false lines of inquiry.

Now, a new study in the journal Nature has revealed that horses were first domesticated in the Pontic-Caspian steppes in the northern Caucasus, a region spanning Europe and Asia between the Black Sea and the Caspian Sea, before coming to dominate the rest of Eurasia within a few centuries.

Horses running in the steppes of Inner Mongolia, China. July 2019.Credit: Ludovic Orlando.

The discovery was made by a team of 162 scientists across the disciplines of archaeology, linguistics and palaeogenetics, led by Ludovic Orlando of the French National Centre for Scientific Research (CNRS).

Previously, Orlando’s team had investigated the oldest-known remains of domestic horses at a site belonging to the Botai culture that persisted in Kazakhstan between 3700 BC and 3100 BC.

These domesticated horses were thought to be the potential progenitors of all modern horses, but the team’s DNA analysis revealed that they were not the ancestors of modern horses, but were the progenitors of Przewalski’s horse, a species of feral Mongolian horse once thought to be 100% wild.

Foiled in their quest for modern equine origins, the team looked at other potential candidates, including Anatolia, Siberia and the Iberian Peninsula.

Horse mandible excavated from the Ginnerup archaeological site, Denmark, June 2021. Image credit: Lutz Klassen, East Jutland Museum.

“We knew that the time period between 4000 to 6000 years ago was critical, but no smoking guns could ever be found,” says Orlando. 

To solve the puzzle, the team extended its search to the whole of Eurasia, sequencing the genomes of 273 horses that lived between 50,000 BC and 200 BC, and comparing the results with modern domestic horses.

The research revealed a smoking gun: while Eurasia was once roamed by various, genetically distinct horse populations, a shift occurred between 2000 BC and 2200 BC.

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

Horses running in the steppes of Inner Mongolia, China. July 2019.Credit: Ludovic Orlando.

Then a single, genetically distinct species, previously confined to the Pontic steppes of North Caucasus, began to spread beyond its native region, all but replacing 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 Orlando. “This is when we took control over the reproduction of the animal and produced them in astronomic numbers.”

Crucially, the researchers identified critical genes in this ancestral horse species that may have made it favourable to humans looking for an animal for transport and freight. One was a gene associated with higher docility, and another was associated with a stronger backbone – characteristics that may have made them a popular choice, and ensured their evolutionary success through domestication.

Even more tantalisingly, the researchers found that the horse spread throughout Asia almost in step with the spread of spoke-wheeled carriages and Indo-Iranian languages, suggesting an association between these ancient people and the domestication of what would become the modern horse.