One of the most stubborn mysteries in prehistory has finally been reined in. A massive study of ancient DNA has revealed where horses were domesticated: around 2200 BC on the steppes of central Eurasia, near the Volga and Don rivers in what is now Russia.
“Finally, we find where and when horses were domesticated,” says at Paul Sabatier University in France.
The domestication of horses was a crucial event because it revolutionised travel and warfare. Horses can carry riders and pull wheeled vehicles, enabling people to journey far faster than before.
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However, despite decades of effort, it hasn’t been possible to pin down where this event happened. That is partly because domestic horses are about the same size as their wild ancestors and don’t look significantly different – unlike most domestic animals. That means looking at ancient horse bones cannot tell us when the shift happened. “You don’t have an obvious smoking gun,” says Orlando.
As recently as two years ago, there were as many as five locations that were serious candidates for the site of domestication, says at the University of Michigan in Ann Arbor. They range from what is now Spain in western Eurasia to what is now Mongolia in the east.
To resolve the mystery, Orlando teamed up with dozens of researchers to compile 273 genomes of ancient horses from all over Eurasia, plus 10 genomes from modern domestic horses. Most of the ancient horses had been carbon-dated, so their ages were known.
The DNA from the modern domestic horses was most similar to that of ancient horses once living on the steppes of western Eurasia, in the region where the Volga and Don rivers flow from north to south and drain into the inland Caspian Sea. “This is a region of about 500 kilometres east to west,” says Orlando, and a little smaller from north to south.
The ancestral group of horses had separated from other horse populations by around 3000 BC. Then, after about 2200 BC, what was a small population of modern-like horses in the Volga-Don region exploded: both in numbers and in range. Within a few centuries, horses with similar genetic make-up were found as far afield as Europe, Anatolia and what is now Kazakhstan.
The implication is that horses were domesticated in the Volga-Don region in the centuries before about 2200 BC, says Orlando. The domestic horses proved so useful that they rapidly spread all over Eurasia.
In September, Ventresca Miller and her colleagues published a study of the proteins preserved on people’s teeth, revealing that . “The genomic data that they present really aligns well with the proteomics data that we’ve been analysing,” says Ventresca Miller. “Now we have sort of irrefutable evidence that horses were domesticated in this locale.”
It is less clear exactly why horses were domesticated in the first instance. They have three main uses: carrying people on their backs, pulling wheeled vehicles and as food – both milk and meat. Which came first?
Ventresca Miller’s work suggests that the first domestic horses were a source of milk. “Dairying and domestication kind of are going hand in hand,” she says.
However, Orlando says the spread of horses around Eurasia was probably driven by transport. In Europe, there is evidence of horseback riding, while in eastern Asia they seem to have been used to pull chariots with spoked wheels. Furthermore, the team identified alterations to two genes. One, ZFPM1, may have led to more docile horses, but the other, GSDMC, may have strengthened horses’ backs and thus enabled riding.
One possibility is that dairying fuelled the initial domestication, and then riding and chariots fuelled the spread of domestic horses. “That’s a really easy narrative to understand,” says Ventresca Miller. For that reason, she is suspicious of it. “I’m guessing that it’s a lot more complicated.”
Nature
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