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Lighter Bone, Weaker Skeleton of Modern Humans Due to Sedentary Lifestyle

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In a study published in the Proceedings of the National Academy of Scientists, it is being suggested that humans gained weaker bone structures after evolving from a hunter-gatherer lifestyle some thousands of years ago. It also didn't matter if a person was from an agriculturalist population or an industrialized society; both still featured less bone density.

Lead author Habiba Chirchir and colleagues sought to figure out the difference in bone density between non-human primates and humans across thousands of years of the history of evolution. Utilizing comparative high-resolution imaging, they compared ancient and more recent samples of human bones from hunter-gatherers and farmers found in present-day Illinois in the United States to hominid species believed to be the ancestors of humans and chimpanzees. Specifically, the trabecular structure of the bone, the spongy part of the bone found in arm joints, ankles, knees and hips were used.

"Trabecular bone has much greater plasticity than other bone, changing shape and direction depending on the loads imposed on it," said Dr. Colin Shaw from the University of Cambridge, who has also done similar research, adding that the structure can change in form, capable of going from as thin as pin to plate-like in strength.

He added that the trabecular structure similar in all population samples, except in those from hunter-gatherers, where the spongy part of the bone actually had more than air. Researchers put this thickening in the trabecular structure as a result of constant strain on the bone, damaging the bone mesh which prompts it grow back thicker and stronger. The constant strain means the spongy part of the bone kept growing thicker and stronger throughout life until peak strength is achieved.

With low trabecular density mostly showing in recent modern humans and in parts of the body like the ankles, knees and hips, researchers deduced that this change has to do with a shift in lifestyle, going from hunting and gathering to something more settled.

Given the results of the study, researchers want to spread the word about strengthening bones early in life to help offset some of the effects of aging. Take hip fractures, for instance. Bone loss is natural when a person ages but builds enough bone strength early in life and it may never drop to a point that will easily give way to fractures.

Aside from Chirchir, other authors for the study include: Brian Richmond, Bernhard Zipfel, Kristian Carlson, Jean-Jacques Hublin, Christopher Ruff and Tracy Kivell.

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