The moment domesticated horses changed the course of human history is now revealed

Horses are shown running in the steppes of Inner Mongolia, China.

(CNN)The domestication of horses changed the course of human history, but scientists have tried for years to figure out when and where this crucial event happened. Now, evidence from a new study using DNA analysis suggests horses were first domesticated 4,200 years ago in the steppes of the Black Sea region, part of modern-day Russia, before spreading across Asia and Europe in the centuries that followed.

It has been incredibly difficult to pin down when and where horse domestication occurred because it's a less obvious shift than that seen with animals like domesticated cattle, which experienced a change in size. Instead, the researchers had to work off of indirect evidence, such as tooth damage that suggested the wearing of bridles or even horse symbolism across cultures, said lead study author and paleogeneticist Ludovic Orlando, research director at the French National Center for Anthropobiology & Genomics of Toulouse for University of Toulouse--Paul Sabatier in France.
"Tracing human activity in the archaeological record is a difficult task, and even more difficult when it comes to reconstructing ancient relationships with horses, from which we often have only fragmented material, like horse bones, available to study," said study coauthor William Taylor, an assistant professor and curator of archaeology at the University of Colorado Museum of Natural History.
    With this latest study, an international team of scientists collected and sequenced genomes from the remains of 273 ancient horses found across Europe and Asia and compared them to the DNA of modern horses to determine their origin.
      The study published Wednesday in the journal Nature.
      All modern domestic horses can be traced to ancestors from 4,200 years ago.

      Critical window for horse domestication

      Previous research suggested that the original home of domesticated horses was at the Botai site, in what today is northern Kazakhstan, in Central Asia, because it provided the oldest archaeological evidence of these animals. But DNA told a different story. The Botai horses, which lived 5,500 years ago, could not be traced to modern domestic horses. Other potential origin sites in Anatolia, Siberia and the Iberian Peninsula didn't pan out, either.
        Orlando and his team knew that the time period between 4,000 and 6,000 years ago was a critical window for investigating when horses became domesticated due to the dating of ancient horse remains, "but no smoking gun could ever be found," he said.
        The researchers broadened the search to provide a bigger picture, studying DNA from ancient horses that lived between 50,000 BC and 200 BC. When this was compared with modern domestic horse DNA, the team was able to pinpoint a time and place.
        "Horse domestication was an absolute lightning strike in human history, leading to incredible, widespread, and lasting social transformations all across the ancient world," Taylor said. "Horses were an order of magnitude faster than many of the transport systems of prehistoric Eurasia, allowing people to travel, communicate, trade and raid across distances that would have previously been unthinkable."

        The spread of domestic horses

        Eurasia was once