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Tuesday, March 19, 2024
March 19, 2024

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Study: Thumb bones in prehumans make them more like us

The Columbian
Published:

WASHINGTON — Some of our tree-swinging prehuman ancestors may have been a bit more like us than previously thought, thanks to a tiny section of their thumbs.

One key attribute that separates humans from other animals is our opposable thumb, and the way parts of the thumb are structured to allow for a strong yet precise grip that fostered advanced use of tools. It’s what allows us to throw items more precisely, pick guitars and turn a key.

And now, thanks to high-tech tools of our own, scientists have found that a couple million years ago, one of our prehuman ancestors had the same human-defining precision grip, even though researchers think of them as little more than upright walking apes, according to a study published recently in the journal Science. That supports earlier evidence that the small-brained Australopithecus africanus fashioned early tools.

“It forces us to revisit how we think (the entire prehuman genus) made a living,” said study lead author Matthew Skinner of the University of Kent in the United Kingdom. “It could be evidence of our greater reliance on tools.”

This is the oldest evidence of prehumans using hands to manipulate items, said Brian Richmond, human origins curator at the American Museum of Natural History in New York, who wasn’t part of the study.

This species, not technically part of the Homo family, roamed South Africa between 2 and 3 million years ago. A similar prehuman species of hominids, typified by the famed Lucy fossil, lived in East Africa.

“These are some very primitive creatures overall,” Richmond said. “Basically, they would have more or less been like upright walking great apes. We wouldn’t think of them as very human, but this makes them a little more human than we thought.”

Skinner and colleagues at the Max Planck Institute in Germany built their own high-resolution micro CT scanner and container that they shipped to museums in Africa to scan the tiny parts of the thumbs of fossils that can’t be moved out of their home countries.

They focused on a small part of the base of the thumb underneath the fleshy pad of muscle, finding a wear pattern in bone that is similar to what is seen in humans from frequent activity, but not seen in chimpanzees and other apes, Skinner said.

This is not an inherited pattern but one that develops with continued use of the precision grip, Skinner said. It’s similar to how tennis star Roger Federer’s right arm has grown, through use, to be significantly bigger than his left, he said.

And that grip, Richmond said, “is one of the hallmarks of humankind.”

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