People have relied on the modern horse to plow fields, charge into battle and traverse long distances for millennia. Horses have transformed human societies with every stride. But scientists have struggled to answer the seemingly simple of question of when and where these animals were domesticated.
It took an international team of more than 160 scientists to pinpoint the origins of the modern horse's domestication: between 4,200 and 4,700 years ago near the Volga and Don Rivers in southwestern Russia. The team reported their findings this week in the journal Nature.
The researchers collected samples from 273 ancient horses that once lived across Europe and Asia between 50,000 and 200 B.C.E. Using DNA sequencing, the team created a genetic map that allowed them to trace the horses' lineages. They found four separate lineages, but the one most closely related to modern horses originated in the Volga-Don region, reports Genelle Weule for ABC in Australia.
Their genetic map also revealed that up until about 2,000 B.C.E., horse populations across Europe and Asia were genetically diverse. But within just a few centuries thereafter, the level of variation plummeted, and all domestic horses could be traced back to the population in the Volga-Don region, reports Jonathan Lambert for Science News.
This likely happened when people living in the Volga-Don region began breeding wild horses for domestication and traveled with them to faraway places. Soon enough, this lineage took over Europe and Asia. It happened "almost overnight," researcher Ludovic Orlando, a molecular archaeologist at the Centre for Anthropobiology and Genomics of Toulouse in France, tells Rebecca Dzombak for National Geographic. "This was not something that built up over thousands of years."
"As they expanded, they replaced all the previous lineages that were roaming around Eurasia," he says. The horse we know today "is the winner, the one we see everywhere, and the other types are sort of the losers."
Genetic sequencing also identified two key genes in the modern horse's ancestors that are linked to greater docility and an improved weight-bearing ability, which could explain why they became so prolific, reports Sabrina Imbler for the New York Times.
Breeders likely selected for "two really good factors not [previously] present in any horse," Orlando tells Science News. "That created an animal that was both easier to interact and move with."
This study also throws a wrench in previous front-running theories. For example, it was thought that the Yamnaya people migrated westward into Europe around 5,000 years ago on horseback. It was a monumental migration that transformed European ancestry, Ann Gibbons reported for Science in 2017. But this study says otherwise—the Yamnaya must have migrated on oxen instead of horses, since horses weren't domesticated until around 4,000 years ago, according to the Times.
The researchers offer an alternate theory: domestic horses made their way across Europe—and started replacing other lineages—during the expansion of the Sintashta culture. This happened around 3,800 years ago during the Bronze Age when horse-drawn chariots rolled in hordes of people, the Times reports.
"The history of humans is wrapped up in horse DNA," Kate Kanne, an archaeologist at the University of Exeter in the U.K., tells National Geographic. "It tells the story of both our species."