WASHINGTON, May 19 — Modern humans have lighter bones than our hunter-gatherer ancestors, and researchers said Monday that may be due to the rise of agriculture and a corresponding fall in our mobility, rather than urbanization, nutrition or other factors.
The discovery, reported in the U.S. journal Proceedings of the National Academy of Sciences, was based on a study of the bones of hundreds of humans who lived during the past 33,000 years in Europe.
"There was a lot of evidence that earlier humans had stronger bones and that weight-bearing exercise in modern humans prevents bone loss, but we didn't know whether the shift to weaker bones over the past 30,000 years or so was driven by the rise in agriculture, diet, urbanization, domestication of the horse or other lifestyle changes," lead author Christopher Ruff, professor of the Johns Hopkins University, said in a statement.
"By analyzing many arm and leg bone samples from throughout that time span, we found that European humans' bones grew weaker gradually as they developed and adopted agriculture and settled down to a more sedentary lifestyle, and that moving into cities and other factors had little impact."
The research focused on Europe because it has many well-studied archeological sites, Ruff said, and because the population has relatively little genetic variation, despite some population movements, which meant that any changes observed could be attributed more to lifestyle than to genetics.
They took molds of bones from museums' collections and used a portable X-ray machine to scan them, focusing on two major bones from the legs and one from the arms.
"By comparing the lower limbs with the upper limbs, which are little affected by how much walking or running a person does, we could determine whether the changes we saw were due to mobility or to something else, like nutrition," Ruff said.
When they analyzed the geometry of bones over time, the researchers found a decline in leg bone strength between the Mesolithic era, which began about 10,000 years ago, and the age of the Roman Empire, which began about 2,500 years ago. Arm bone strength, however, remained fairly steady.
"The decline continued for thousands of years, suggesting that people had a very long transition from the start of agriculture to a completely settled lifestyle," Ruff said. "But by the medieval period, bones were about the same strength as they are today."
That meant mechanization and urbanization had less effect on bone strength than the rise of agriculture, they said.
Ruff noted that Paleolithic-style bones are still likely achievable, at least for younger humans, if they recreate to some extent the lifestyle of their ancestors, notably doing a lot more walking than their peers.
He cited studies of professional athletes that have demonstrated how lifestyle is written in our bones.
"The difference in bone strength between a professional tennis player's arms is about the same as that between us and Paleolithic humans," he added. (PNA/Xinhua)