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And now a reminder about our place in the world. We modern humans have skeletons that are relatively lightweight, especially when we compare ourselves to other primates and our earlier human ancestors. Some new research suggests that we have this kind of bone structure basically because we got lazy. NPR's Nell Greenfieldboyce explains.
NELL GREENFIELDBOYCE, BYLINE: Habiba Chirchir works at the Smithsonian's National Museum of Natural History. She and some colleagues were recently studying the bones of different primates, including humans. In particular, they were looking 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.
HABIBA CHIRCHIR: So the next step was, what about the fossil record? When did this feature evolve?
GREENFIELDBOYCE: Their guess was that it showed up a couple million years ago. That's when Homo erectus, a kind of proto-human, left Africa. Chirchir speculated that having lighter bones would have made it a lot easier to travel long distances. But after examining a bunch of early human fossils, she realized their guess was wrong.
CHIRCHIR: This was absolutely surprising to us. The change is occurring much later in our history.
GREENFIELDBOYCE: The lightweight bones don't appear until about 12,000 years ago.
CHIRCHIR: And why is this happening at this time?
GREENFIELDBOYCE: She thinks it could be that humans were becoming less physically active. They were leaving their nomadic hunter-gathering life behind and settling in one place.
CHIRCHIR: So many things occurred in human history, from agriculture and settlements to city states, the use of farming equipment.
GREENFIELDBOYCE: A report on the work appears 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 who lived in farming villages nearly a thousand years ago and compared them to the bones of people who'd lived in nearby earlier as foragers. The bones of the foragers were stronger and more dense. Nell Greenfieldboyce, NPR News.
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