Hips do lie? Study draws doubt about the first humans to ride horses

BOULDER, Colo. —What inspired early humans to first ride a horse? Rather than build a time machine to ask our ancestors, archaeologists are studying changes in human skeletons to discover the world’s first equestrians. However, researchers from the University of Colorado Boulder say what they’re finding is only adding to this mystery.

At the center of this research is the fact that horseback riding transforms human bones, creating slight changes to the shape of the hip joint.

“In archaeology, there are vanishingly few instances in which we can tie a particular activity unequivocally to skeletal changes,” says Lauren Hosek, lead author of the study and an assistant professor in the Department of Anthropology at CU Boulder, in a media release.

However, the recent study published in Science Advances complicates a popular theory on the origins of horseback riding, known as the Kurgan hypothesis.

The exact time humans domesticated horses has been debated for many years. Some scholars, based on the remains of horse skeletons, bridles, and chariots in the Ural Mountains of Russia, argue the earliest use of horses was 4,000 years ago.

Meanwhile, the Kurgan hypothesis argues horses were domesticated much sooner. This theory estimates that horse riding began around the fourth millennium B.C. with the Yamnaya tribe living near the Black Sea — roughly 6,000 years ago. Their horse riding would take them across Eurasia and possibly spread a primitive language that would later develop into English, French, and more.

“A lot of our understanding of both the ancient and modern worlds hinges on when people started using horses for transportation,” adds William Taylor, a curator of archaeology at CU Boulder’s Museum of Natural History. “For decades, there’s been this idea that the distribution of Indo-European languages is, in some way, related to the domestication of the horse.”

Some of the strongest evidence for the Kurgan hypothesis is the remains of the Yamnaya, which date to about 3,500 B.C. Their skeletons showed wear and tear that aligned with skeletal changes one would see from horse riding.

In the new study, the authors examined the skeletons from ancient human bones and found that some clues linking the hip joint changes in the Yamnaya tribe to horseback riding may be due to other factors.

When you flex your legs at the hip like during long horse rides, the ball and socket of the hip joint can rub together along one edge. According to Hosek, this continuous rubbing can lengthen or make the round socket of the hip joint more oval-shaped. However, other activities can produce the same effect.

Archaeologists have uncovered evidence suggesting humans used cattle, donkeys, and wild asses for transportation in western Asia centuries before the alleged domestication of horses. Similar to a chariot, people probably harness these animals to pull carts or transport themselves.

“Over time, this repetitive, intense pressure from that kind of jostling in a flexed position could cause skeletal changes,” Hosek explains.

A similar change in the hip joint is seen among the skeletons of 20th-century Catholic nuns. These women rarely rode horses but took long carriage rides across the American West.

The study reveals flaws in the Kurgan hypothesis, and the authors suggest that researchers need to do more than study skeletal changes to pinpoint an exact date when humans tamed horses.

“Human skeletons alone are not going to be enough evidence,” Hosek emphasizes. “We need to couple that data with evidence coming out of genetics and archaeology and by looking at horse remains, too.”

The debate is still ongoing, but at least for now, it looks like the Yamnaya people weren’t the first horse riders after all.