Human bones became weaker about 12,000 years ago

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FRANCE: Two studies suggest that during human evolution, our bones became weaker when we switched from being hunter-gatherers to farmers, about 12,000 years ago. Both studies, published in the journal Proceedings of the National Academy of Sciences. During that transition, humans became less physically active, which resulted in a gradual reduction in bone density – our bones became lighter and weaker.
It is already known that human bones are weaker than those of our ancestors, but it was previously unknown why. However, recently, researchers have focused on trabecular bone, which can be found at the ends of joint bones, and, in certain bones, is less dense than in those of our ancestors. In the first study, researchers took scans of primates’ hand bones, including humans and chimps, to compare the difference in trabecular bone density.
The difference was somewhat stark. Human ancestors, from chimpanzees to Neanderthals to early homo sapiens, were found to have greater bone density than modern humans. Chimps had 50-75% more, and some hominids had 100% more.
The change started to come about during the late Pleistocene or early Holocene periods, when agriculture started to become important to human society, and the evolutionary need for stronger, denser bones became less important. Speaking to Smithsonian, the study’s co-author, Habiba Chirchir explained that the change came from the lower amount of physical activity.
“What we think is going on is that humans were becoming less active, more sedentary. People were adopting farming, domesticating animals. That reduction in physical activity is what’s resulted in this light skeleton”.
The second study focused on the density of trabecular bone in the hip joint of four ancient groups in ancient Illinois, two agricultural groups, and two who were hunter-gatherers. The study found that the forager groups had thicker, denser, and more compact trabecular bone in their hips than the agricultural groups. The agricultural group’s diets were not lacking, both consuming a broad range of foods, thus suggesting that the difference in physical activity, not diet, is the primary factor behind the differences.