Scientists uncover origins of horse riding from human remains

As anyone who has ever ridden a horse knows, riding a horse is hard on the body, but does it change the way your skeleton looks?

The answer is “complicated,” according to archaeologists at the University of Colorado Boulder, who in a new study drew on a wide range of evidence, from medical studies of contemporary horse-riding peoples to skeletal records spanning thousands of years.

The researchers concluded that horse riding can indeed leave a mark on the human skeleton, including by subtly changing the shape of the hip joint, but these changes alone cannot clearly tell whether people have ridden horses over their lifetimes. Many other activities, such as sitting for long periods of time, can also change human bones.

“There are very few examples in archaeology where you can unequivocally link specific activities to skeletal changes,” said Lauren Hossek, lead author of the study and assistant professor in the Department of Anthropology at the University of Colorado Boulder.

She and her colleagues reported their findings September 20 in the journal Science Advances.

The findings could have implications for researchers studying the origins of when humans first domesticated horses, and may also call into question a long-standing theory in archaeology known as the Kurgan hypothesis.

The first rider

The research goes to the center of a long-standing debate in archaeology, said William Taylor, a co-author of the new study and curator of archaeology at the University of Colorado Museum of Natural History.

He explained that the oldest and most indisputable evidence of human use of horses as transportation comes from the region around the Ural Mountains in Russia, where scientists have found horses, bridles and chariots dating back about 4,000 years.

But the Kurgan hypothesis, which emerged in the early 20th century, argues that humans and horses were closely related much earlier. Proponents believe that around the 4th millennium BCE, ancient people living in the Black Sea region known as Yamnaya first began riding horses across Eurasia. In the process, they may have spread primitive versions of the languages ​​that would later evolve into English, French, and other languages.

“Much of our understanding of both the ancient and modern world hinges on when people began using horses for transportation,” Taylor says. “For many decades there has been the idea that the distribution of Indo-European languages ​​is somehow linked to the domestication of the horse.”

Recently, scientists have pointed to the Yamnaya culture, dating back to around 3500 BCE, as key evidence supporting the Kurgan hypothesis: the ancient skeletons show signs of wear, likely from horse riding.

Hips can lie

But in their new study, Hosek and Taylor argue that it’s not quite that simple.

Hosek has spent a lot of time poring over human bones to learn about the past. He explained that skeletons aren’t static, but can change shape and move throughout a person’s life. For example, pulling on a muscle can cause a reaction where the muscle attaches to the bone. In some cases, bones can become porous or develop raised ridges.

But reading such cues is ambiguous at best. The hip joint is one example.

Horsek noted that when you bend your leg at the hip for long periods of time, such as when you’re horseback riding, the ball-and-socket of your hip joint can rub against one end. Over time, this rubbing can make the round socket of your hip joint more elongated and oval-shaped. But other activities can also cause similar elongation, he said.

Archaeological evidence shows that oxen, donkeys, and even wild asses were used for transportation in parts of Western Asia centuries before humans domesticated the horse. Ancient people likely yoked these beasts of burden to pull carts or smaller chariots (similar to chariots).

“Over time, this repeated intense pressure in a bent position can cause changes to the skeleton,” Hosek said.

For example, she has seen similar changes in the skeletons of 20th-century Catholic nuns, who didn’t ride horses but traveled long distances in carriages across the American West.

Ultimately, Hossek and Taylor say, human remains alone aren’t enough to pinpoint when humans first started riding horses, at least with the science currently available.

“Human skeletons alone are not enough evidence,” said Horsek, “We need to combine it with evidence from genetics, archaeology, and the study of horse remains.”

Taylor added that this situation does not bode well for the Kurgan hypothesis.

“None of this evidence, at least at present, suggests that the Yamnayans kept domestic horses.”