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 Scientists analyzed the remains of Europeans who lived at various
times over the past 33,000 years and found the more stationary
lifestyle afforded by farming - not the rise of cities or changes in
diet - appears to have led to thinner, more brittle bones in modern
humans, compared to our “caveman” ancestors.
"There was a lot of evidence that earlier humans had stronger bones
and that weight-bearing exercise in modern humans prevents bone
loss, but we didn't know if the shift to weaker bones was driven by
the rise in agriculture, or by other causes like diet or
urbanization," said Dr. Christopher Ruff, director of the Center for
Functional Anatomy and Evolution at Johns Hopkins Medical Center in
Baltimore who led the study published May 18 in the Proceedings of
the National Academy of Sciences.
Past research has found that load-bearing play and exercise in
childhood, paired with adequate calcium and vitamin D, is the best
way to build strong bones for a lifetime.
Ancient humans, however, had denser bones at any age compared to
modern counterparts. To understand when and why that difference
arose, Ruff and colleagues examined long bones in the legs and arms
from 1,842 individuals who lived during the Paleolithic to Neolithic
eras of hunting and gathering in Europe, often known as the Stone
Age, as well as during the Roman empire, Medieval times, the
Industrial Revolution and the 20th century.
They X-rayed the bones, and made silicone putty molds of the bone
surface. Then they did a computer analysis of the data to help
pinpoint the moment in human history that coincided with a
structural shift to thinner bones.
Bone strength started declining in the femur and tibia bones of the
leg about 7,000 years ago in the Neolithic period, as rudimentary
farming practices began to take hold, and continued until about
2,000 years ago in the Roman period, the analysis found.
"The decline continued for thousands of years, suggesting that
people had a very long transition from the start of agriculture to a
completely sedentary lifestyle," Dr. Ruff said. "By the medieval
period, bones were about the same strength that they are today."
Changes in the humerus bone in the upper arm were smaller and less
consistent.
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Looking at both the upper and lower body, and showing a greater
reduction in bone strength in the lower limb, "rules out a change
like less protein or less calcium in the diet," said Dr. Steven
Churchill, an evolutionary anthropologist at Duke University in
Durham, North Carolina, who provided some of the Stone Age data but
was not involved in the study.
In the legs, researchers also found that strength related to
front-to-back motions associated with running or walking long
distances declined more dramatically than strength linked to
side-to-side motions tied to bending, lifting and pivoting.
The findings only apply to Europeans, the study team notes, and they
cannot say whether the same pattern of changes occurred in other
parts of the world.
Given how much more sedentary lifestyles have become since Roman
times, it's surprising that the bones of 20th century humans didn't
become even weaker as technology enabled even less exertion in daily
life, Dr. Simon Mays, a human skeletal biologist at English Heritage
in Portsmouth and visiting lecturer at the University of Southampton
in the U.K., said by email.
Mechanization has risen particularly in the past 50 years, said
Mays, who wasn't involved in the study. "I wonder whether improved
nutrition in the 20th century has led to thicker bones, canceling
out any bone-thinning effects of increased sedentism."
SOURCE: http://bit.ly/1FmhSKX
Proc Natl Acad Sci 2015.
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