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Human Bones Lighter, More Fragile with the Switch from Foraging to Farming

Dec 23, 2014 10:50 AM EST
Over thousands of years of evolution, human bones have become much lighter and more fragile with the switch from foraging to farming, according to new research. [Pictured: Members of the Ju:'hoansi tribe foraging in North-Western Namibia, who still live by the hunter-gatherer lifestyle.]
(Photo : Stephan C. Schuster, Penn State University)

While it would seem that moving from the hunter-gatherer lifestyle to an agricultural existence was largely beneficial, its impact on our skeletons presents a different argument. Over thousands of years of evolution, human bones have become much lighter and more fragile with the switch from foraging to farming, according to new research.

About 7,000 years ago, bone mass was approximately 20 percent higher in foragers - comparable in strength to modern orangutans - whereas just 6,000 years later farmers from the same region had lighter and more breakable bones.

And since the rise of agriculture humans have become more and more sedentary, with obesity a major issue in modern culture today. That's not to say that it's impossible for us to gain back orangutan-like strength in our bones, but we no longer undergo enough frequent and intense stress like our hunter-gatherer ancestors did to reach this optimal level.

"Contemporary humans live in a cultural and technological milieu incompatible with our evolutionary adaptations. There's seven million years of hominid evolution geared towards action and physical activity for survival, but it's only in the last say 50 to 100 years that we've been so sedentary - dangerously so," co-author Dr. Colin Shaw, from the University of Cambridge, said in a statement.

Reported in the journal PNAS, the researchers x-rayed samples of femur bones from four distinct archaeological human populations representing mobile hunter-gatherers and sedentary agriculturalists, all living within the same region of the United States. They focused on the trabecular bone at the top of the femur that connects to the pelvis, which is one of the most load-bearing bone joints in the body. Bone analysis revealed that while the trabecular structure was more or less the same in all studied populations, the "spongy" mesh part of the bone - which allows for flexibility - was denser in hunter-gatherers.

"Trabecular bone has much greater plasticity than other bone, changing shape and direction depending on the loads imposed on it; it can change structure from being pin or rod-like to much thicker, almost plate-like. In the hunter-gatherer bones, everything was thickened," Shaw explained.

The daily intense physical activity of foragers made their bones stronger and more weight-bearing, and thus less prone to hip fractures, for example.

Researchers ruled out diet differences and changes in body size as possible causes for this biological shift, concluding that physical activity is the root cause of degradation in human bone strength across millennia.

On a side note, while hunter-gatherers had extremely strong bones compared to our farming relatives, earlier hominids from around 150,000 years ago had even stronger bones than they did.

"Something is going on in the distant past to create bone strength that outguns anything in the last 10,000 years," Shaw added.

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