Thumb bones in pre-humans make them more like us, study says

AP News
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Posted: Jan 22, 2015 2:01 PM

WASHINGTON (AP) — Some of our tree-swinging pre-human 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 determined that a couple million years ago one of our pre-human 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 Thursday in the journal Science. That supports earlier but controversial evidence that the small-brained Australopithecus africanus fashioned early tools.

"It forces us to revisit how we think (the entire pre-human 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 pre-humans using hands to manipulate items, said Brian Richmond, human origins curator at the American Museum of Natural History in New York. He wasn't part of the study but praised it as important.

This species, not technically part of the Homo family, roamed South Africa between 2 and 3 million years ago. A similar pre-human 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 we have 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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Online:

Journal Science: http://www.sciencemag.org

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Seth Borenstein can be followed at http://twitter.com/borenbears