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NELL GREENFIELDBOYCE
i
Farming helped fuel the rise of civilizations, but it may also have given us less robust bones.
Leemage/UIG via Getty Images
Compared to other primates and our early human ancestors, we modern humans have
skeletons that are relatively lightweight — and scientists say that basically may be
because we got lazy.
Biological anthropologist Habiba Chirchir and her colleagues at the Smithsonian's
National Museum of Natural History were studying the bones of different primates
including humans. When they looked at the ends of bones near the joints, where the
inside of the bone looks almost like a sponge, they were struck by how much less dense
this spongy bone was in humans compared to chimpanzees or orangutans.
"So the next step was, what about the fossil record? When did this feature evolve?"
Chirchir wondered.
Their guess was that the less dense bones showed up
Our Skulls Might
Have Evolved To
Withstand Blows
To The Face
a couple million years ago, about when Homo
erectus, a kind of proto-human, left Africa. Having
lighter bones would have made it a lot easier to
travel long distances, Chirchir speculated.
But after examining a bunch of early human fossils, she realized their guess was
wrong. "This was absolutely surprising to us," she says. "The change is occurring much
later in our history."
The lightweight bones don't appear until about 12,000 years ago. That's right when
humans were becoming less physically active because they were leaving their nomadic
hunter-gatherer life behind and settling down to pursue agriculture.
A report on the work appeared Monday in the Proceedings of the National Academy of
Sciences, along with a study from a different research group that came to much the
same conclusion.
Those researchers looked at the bones of people in
more recent history who lived in farming villages
Golden Arches:
Human Feet More
Flexible Than We
nearly a thousand years ago, and compared them to
Thought
the bones of people who had lived nearby, earlier, as
foragers.
The bones of people from the farming communities were less strong and less dense
than those of the foragers, whose measured bone strength was comparable to
similarly-sized nonhuman primates.
"We see a similar shift, and we attribute it to lack of mobility and more sedentary
populations," says Timothy Ryan, an associate professor of anthropology at Penn State
University. "Definitely physical activity and mobility is a critical component in
building strong bones."
© 2014 npr