For thousands of years, the grassy plains of Europe and Asia were home to a mosaic of genetically distinct horse lineages. But a single lineage galloped ahead to overtake and replace all the other wild horses. This domesticated lineage became the horse of our modern imagination: slender legs, a muscular back and a mane that shimmers in the wind.
For decades, scientists had tried to sleuth out when and where modern horses were first domesticated but had yet to find the smoking hoof they needed.
Now, in a paper published Wednesday in the journal Nature, scientists have finally solved the mystery. After collecting and sequencing 273 ancient horse genomes, a team of 162 authors concluded that modern horses were domesticated around 4,200 years ago in steppes around southern Russia, near where the Volga and Don rivers intersect.
This new paper comes as close as currently possible to solving the mystery of the origins of the domestic horse, according to Peter Heintzman, a paleogenomics researcher at the Tromso campus of the Arctic University of Norway, who was not involved with the research. “It’s a monumental effort,” Dr. Heintzman said, noting that they collected a “wall of data” from “hundreds of horses.”
Ludovic Orlando, a paleogeneticist and research director of the Center for Anthropobiology and Genomics of Toulouse in France and an author on the paper, has toiled over this question for a decade.
In recent years, scholars homed in on a Botai settlement in the Kazakh steppes that was brimming with horses’ bone fragments and clay pots that were lined with what appeared to be mare’s milk. This was the earliest archaeological evidence of horse domestication, and seemed promising as the birthplace of modern horses.
But in 2018, a team of researchers including Dr. Orlando sequenced the genomes of the horse bones at Botai. To the researchers’ surprise, the Botai horses did not give rise to modern horses, but were instead the direct ancestors of Przewalski’s horses, a stocky lineage originally thought to be the last wild horses on the planet. They revealed Przewalski’s were not wild after all, but instead the feral descendants of domestics. So the puzzle of the origins of modern horses remained unsolved. “Every time I was expecting something, it was wrong,” Dr. Orlando said.
He said that to solve the mystery, “we decided to be exhaustive and really look everywhere.”
Everywhere, in this case, meant across Eurasia. Starting in 2016, Dr. Orlando collected samples across the region from archaeological collections and new digs, essentially every ancient horse bone they could get their hands on.
To preserve the remains for the future, the researchers drilled tiny holes into the ancient horses’ inner ears, teeth and other bones to retrieve tiny samples.
As the researchers gradually mapped the horse genomes across time and space, the picture became sharper. A little over a year ago, they were able to pinpoint the precise location: the Volga-Don region in what is now Russia.
With such a gargantuan data set, the researchers ended up answering additional horsy historical details. They found modern horses had two stark genetic differences from other ancient lineages — one gene linked to docility and another to a stronger backbone — which may have facilitated the animals’ spread.
Domestic horses transformed human history, allowing people to travel great distances and develop new technologies of warfare. “Everyone wanted the horse,” Dr. Orlando said.
Accordingly, the paper’s genetic findings “constitute major advances in our understanding of the human societies which bred these horses,” said Pauline Hanot, a postdoctoral researcher at the French National Centre for Scientific Research who was not involved with the research.
The study also knocked down ideas about horses’ role in earlier human history. For instance, one pre-existing theory suggested a pastoralist people called the Yamnaya were able to migrate on horseback in massive numbers into Europe around 5,000 years ago. But the new genetic map found no evidence; the researchers point out oxen, not horses, could have been the driving factor of their expansion.
The new paper also reveals domestic horses spread across Eurasia along with the Bronze Age Sintashta culture, which possessed spoke-wheeled chariots, around 3,800 years ago.
After taming all of this horse data, Dr. Orlando has taken on a new hobby: He started taking riding lessons.
Like all other humans, he rides domestic horses — descendants of the ancient animals that galloped in southern Russia.
“I would not dare approach a Przewalski’s horse,” Dr. Orlando said. “They kill wolves. I am not that fast of a runner.”