The weakening of the human bones is often attributed to modern and sedentary lifestyles but it appears that the spread of farming should instead be blamed as to why the bones of modern humans are not as strong as those of their forebears.

Scientists have long been aware that our hunter-gatherer ancestors possessed stronger bones compared with humans today. Unfortunately, they have difficulty identifying when this change happened.

Now, a new research involving samples of bones of hundreds of humans who lived over the past 33,000 years has revealed that the start of agriculture and the reduction in mobility during the Neolithic period marked the decline in the strength of human bones.

"Results strongly implicate declining mobility as the specific behavioral factor underlying these changes," the researchers wrote in their study. "Mobility levels first declined at the onset of food production, but the transition to a more sedentary lifestyle was gradual, extending through later agricultural intensification."

The new study, which was published in the PNAS on May 18, provides insight on the changes that has made modern humans vulnerable to osteoporosis, which is characterized by thinning and brittle bones.

Christopher Ruff, from Johns Hopkins University School of Medicine, and colleagues looked at bone samples from more than 1,800 people who lived in Europe between 11,000 to 33,000 years ago during the Paleolithic period to the 20th century and found that the biggest change in bone strength occurred when hunter-gatherers adopted agriculture.

They found that the shift to more settled and permanent living arrangements resulted in dramatic changes in human skeletons. The study, however, has shown that the bones of Homo sapiens remained relatively similar since this time.

"By analyzing many arm and leg bone samples from throughout that time span, we found that European humans' bones grew weaker gradually as they developed and adopted agriculture and settled down to a more sedentary lifestyle, and that moving into cities and other factors had little impact," Ruff said.

The researchers said that achieving Paleolithic-style bones is still possible for younger humans if they engage in activities that mimic our ancestors' lifestyle such as by walking more. Ruff noted that studies have shown that the difference in the strength of the bones in a professional tennis player's arms is almost the same as those of modern humans and those who lived during the Paleolithic era.

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