As anyone who has spent time in the saddle knows, horseback riding can be hard on the body. But can it change the way your skeleton looks?
The answer, according to archaeologists at the University of Colorado at Boulder, is complicated. In a new study, the team drew on a wide range of evidence, from medical studies of modern horsemen to records of human remains spanning thousands of years.
The researchers concluded that horseback riding can, in fact, leave a mark on the human skeleton, for example by subtly altering the shape of the hip joint. But those kinds of changes alone can’t definitively reveal whether people have ridden horses during their lifetime. Many other activities, including sitting for long periods of time, can also transform human bones.
“In archaeology, there are very few cases where we can unequivocally link a particular activity to skeletal changes,” said Lauren Hosek, senior author of the study and an assistant professor in the Department of Anthropology at CU Boulder.
She and her colleagues reported their findings on September 20 in the journal Scientific advances.
The findings may have implications for researchers studying the origins of when humans first domesticated horses, and also cast doubt on a long-standing theory in archaeology known as the Kurgan hypothesis.
The first riders
The research is at the center of one of the long-standing debates in archaeology, said William Taylor, co-author of the new study and curator of archaeology at the CU Museum of Natural History.
He explained that the oldest and most incontrovertible evidence that humans used horses for transport comes from the Ural Mountains region of Russia. There, scientists have discovered horses, bridles and chariots dating back some 4,000 years.
But the Kurgan hypothesis, which emerged in the early 20th century, holds that the close relationship between humans and horses began much earlier. Its proponents believe that around the fourth millennium BCE, ancient humans living near the Black Sea, called the Yamnaya, began galloping across Eurasia on horseback. In the process, the story goes, they may have spread an early version of the languages that would later evolve into English, French and others.
“Much of our understanding of the ancient and modern world depends on when people began using horses for transportation,” Taylor said. “For decades, there has been an idea that the distribution of Indo-European languages is somehow related to the domestication of the horse.”
Recently, scientists have pointed to human remains from the Yamnaya culture dating to around 3500 BCE as a key piece of evidence supporting the kurgan hypothesis. These ancient people, the group argued, showed evidence of wear and tear on their skeletons that likely came from horseback riding.
Hips can lie
But in the new study, Hosek and Taylor argue that the story is not so simple.
Hosek has spent a lot of time studying human bones to learn lessons about the past. He explained that the skeleton is not static, but can change shape over a person’s lifetime. If a muscle is pulled, for example, a reaction can occur where the muscle attaches to the underlying bone. In some cases, the bone can become more porous or raised ridges can form.
However, interpreting such clues can be confusing at best. The hip joint is one example.
Hosek noted that when the legs are bent at the hip for long periods, including during long horseback rides, the ball-and-socket joint and hip socket can rub together along an edge. Over time, that rubbing can cause the round socket of the hip bone to elongate further, or take on an oval shape. But, he said, other activities can cause the same kind of elongation.
Archaeological evidence shows that humans used cattle, donkeys, and even wild asses for transport in parts of western Asia centuries before horses were domesticated. Ancient people likely harnessed these beasts of burden to pull carts or even smaller two-wheeled vehicles that resembled war chariots.
“Over time, this intense, repetitive pressure from that type of pushing in a flexed position could cause skeletal changes,” Hosek said.
She has observed similar changes, for example, in the skeletons of 20th-century Catholic nuns. They never rode horses, but they did take long carriage rides across the American West.
Ultimately, Hosek and Taylor say human remains alone cannot be used to date when people first began riding horses, at least not with the science currently available.
“Human skeletons alone will not be sufficient evidence,” Hosek said. “We need to combine that data with evidence from genetics and archaeology, and also by analyzing horse remains.”
Taylor added that the outlook does not look encouraging for the Kurgan hypothesis:
“At least for now, none of these lines of evidence suggest that the Yamnaya people kept domestic horses.”