A new study claims that human bones used to be stronger but had evolved to become lighter to match people's sedentary agricultural lifestyle.
The sedentary lifestyle became the most common way of life across the world. Scientists believe that the transition occurred between 8,000 and 5,000 B.C. when humans learned to domesticate animals and cultivate plants instead of hunting and gathering them.
Brian Richmond of the American Natural Museum of Natural History and his colleague Habiba Chirchir of George Washington University examined the bone density of human skeletons that date back as far as 12,000 years to determine the impact of the lifestyle change to human evolution.
"Despite centuries of research on the human skeleton, this is the first study to show that human skeletons have substantially lower density in joints throughout the skeleton, even in ancient farmers who actively worked the land," said Richmond in a museum press release.
The researchers used high-resolution computed tomography and microtomography to analyze the bones, limbs and joints of modern humans then compared them to chimpanzees and fossil hominins.
The analysis revealed that the human bones have lighter bone density compared to chimpanzees and the hominins. The difference is more notable in the hip, knee and ankle.
"Much to our surprise, throughout our deep past, we see that our human ancestors and relatives, who lived in natural settings, had very dense bone. And even early members of our species, going back 20,000 years or so, had bone that was about as dense as seen in other modern species," Richmond said.
The findings of the study provide another insight to explain the reason modern humans are more prone to osteoporosis, a medical condition that causes the bones to become brittle and weak. According to the National Osteoporosis Foundation, about 54 million Americans age 50 and above have osteoporosis.
The study was published in the Dec. 22 issue of the Proceedings of National Academy of Sciences.
