The shift to farming and more sedentary lifestyles over the time is the reason why modern humans have more fragile bones, reveals a new study.
The comparatively light bone structure of modern humans compared to early human species and other modern primates may be due to the modern abandonment of the constant physical activity that was inherent in the life of early hunter gathers.
The most plausible explanation, he said, is that a lack of constant physical activity causes the bone in the head of the femur, the long bone in the thigh, to become thinner and lighter than that found in more mobile populations or modern primates such as chimpanzees, gorillas and orangutans.
The other two possible explanations, that humans and nonhuman primates have different bone structure because of genetics, with humans evolving to a lighter, more gracile structure, or that the large joint surfaces required for upright, two-legged movement decrease the strain on bone and therefore the development of strong bones, do not appear to be true.
Ryan, working with Colin N. Shaw of the University of Cambridge, UK, looked at the hip joint to determine which of the three possible explanations was likely.
The researchers found that the agriculturalists had significantly lower bone mass than the foragers. However, the bone characteristics of the more mobile foragers overlapped with those of the nonhuman primates.
This knowledge might aid in prevention of osteoporosis and hip fracture in the elderly.
The study is published in the Proceedings of the National Academy of Sciences.