Evolution constantly adapts organisms to their environment and activities and humans are no exception. Recent research by physical anthropologists shows that modern human skeletons only evolved into their lightly built form around 12,000 years ago, with some human populations only showing the shift over the last 8,000-9,000 years.
The study involved high-resolution imaging of bone joints from modern humans and chimpanzees, which were then compared to fossils of extinct human species. The study shows proto-humans and humans had heavy bone density until a notable decrease modern human bone density beginning around 10,000 BC.
Shift to sedentary agricultural lifestyle connected to evolution of lighter bone structure
The new research published in the Proceedings of the National Academy of Sciences on Monday also notes a greater decrease in the density of the legs/hips than in that of the arms/shoulders, suggesting that the transformation is likely related to the shift from a foraging lifestyle to a sedentary agricultural one that occurred around the same time. The anthropologists theorize that the bone density of the legs, hips and pelvis of humans gradually decreased as the agricultural lifestyle did not require as much walking and running.
Statements from researchers
“Despite centuries of research on the human skeleton, this is the first study to show that human skeletons have substantially lower density in joints throughout the skeleton, even in ancient farmers who actively worked the land,” said Brian Richmond, a study author and a research professor at George Washington University.
“Our study shows that modern humans have less bone density than seen in related species, and it doesn’t matter if we look at bones from people who lived in an industrial society or agriculturalist populations that had a more active life. They both have much less bone density,” explained Habiba Chirchir, lead author of the paper and a postdocresearcher at the Smithsonian Institution’s National Museum of Natural History. “What we want to know now is whether this is an early human characteristic that defines our species.”