Researchers studying changes in bone density in humans over the millennia believe that changes in our skeletons have to do with our evolutionary shift from foraging lifestyle to a more sedentary way of life. That's the focus of discoveries written up today in the Proceedings of the National Academy of Science, and shared with Boing Boing by the Smithsonian’s National Museum of Natural History:
Recent modern humans have a relatively ‘lightly’ built skeleton compared to chimpanzees and extinct human species, and it is still unknown when during human evolution this unique feature first appeared. Habiba Chirchir et al. examined the density of trabecular, or ‘spongy’, bone throughout the skeleton of modern humans and chimpanzees, as well as in fossils of extinct human species spanning several million years. They found that the upper and lower limbs of recent modern humans are ‘lightly’ built compared to those of modern nonhuman primates, pre-Holocene modern humans, and extinct human species. Rather than representing a consistent gradual shift towards ‘lighter’ skeletons, bone density remained high throughout human evolution until it decreased significantly in recent modern humans. The ‘lightly’ built skeletons of modern humans evolved late in our evolutionary history, and the decrease in bone density was more marked in lower limbs than in upper limbs, suggesting that it might have been driven by changes in mobility. The decrease in bone density in recent modern humans is consistent with a reduction in mobility in recent human populations, which may have been linked to a shift from a foraging lifestyle to a more sedentary one, the authors suggest.
Read the paper: "Recent origin of low trabecular bone density in modern humans" [Proceedings of the National Academy of Science, PNAS; image: Reuters]