Image courtesy of © AMNH/J. Steffey and Brian Richmond
By Charles Q. Choi
The relatively lightly built skeletons of modern humans developed late in evolutionary history, and may have been the result of a shift away from a nomadic lifestyle to a more settled one, according to a new study.
These findings may shed light on modern bone conditions such as osteoporosis, the scientists said.
Bone is one of the strongest materials found in nature. Ounce for ounce, bone is stronger than steel, since a bar of steel of comparable size would weigh four or five times as much. In another comparison, a cubic inch of bone can in principle bear a load of 19,000 lbs. (8,620 kilograms) or more — roughly the weight of five standard pickup trucks — making it about four times as strong as concrete.
Still, modern humans have a relatively lightly built skeleton compared with those of chimpanzees — the closest living relatives of humans — as well with those of extinct human lineages.
“Throughout our skeleton, our joints are about three-quarters to one-half as dense as those of our early human ancestors and those of other modern primate species,” study co-author Brian Richmond, curator of human origins at the American Museum of Natural History in New York City, told Live Science. “That raises the question of when this happened in humans.”
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