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MU researcher helps change view of human evolution

Thursday, February 10, 2011 | 3:08 p.m. CST; updated 9:53 a.m. CST, Friday, February 11, 2011
This fourth metatarsal from Australopithecus afarensis is a key piece of evidence for the early evolution of the uniquely human way of walking. Carol Ward, an MU researcher in the department of pathology and anatomical sciences at the MU School of Medicine, and colleagues from Arizona State University are studying the 3.2 million-year-old foot bone discovered in Hadar, Ethiopia.

COLUMBIA — Researchers, including one from MU, have discovered that early humans walked fully upright much earlier than scientists previously thought.

The team studied a fossilized foot bone in Ethiopia that is at least 3 million years old and determined that human ancestors had arches in their feet, which allowed them to stand and move on two legs.

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That means researchers can begin to pinpoint when human ancestors abandoned swinging in trees for walking on the ground.

“It’s the first one ever discovered,” said Carol Ward, a professor in the department of pathology and anatomical sciences at MU's School of Medicine, and one of the team's primary researchers.

“It’s an important bone because it gives us information about the structure of the foot. It may be one reason our ancestors were so successful.”

Ward, along with William Kimbel and Donald Johanson, co-authors from Arizona State University, will publish their findings Friday in the journal Science.

Evidence from the findings could exchange the classic image of hunched-back apes for one similar to modern humans who were capable of walking and even running as we do today.

The existence of arches in early human feet strongly supports the premise that humans walked much earlier, Ward said, although the researchers cannot give an exact date.

The fundamental difference between human feet and ape feet is that humans' are stiff, providing stability and shock absorption when we move. An ape's foot is more flexible, so it can grasp branches easily. Evidence of arches in the fossilized bone proved to researchers that our human ancestors evolved at a faster rate than was previously understood.

The bone, which was unearthed in Ethiopia 10 years ago, is a fourth metatarsal, located on the outside of the foot. The shape of the bone is clear evidence of arches in early human feet, according to the findings.

“This bone could only exist in an arched foot,” said Jeremy DeSilva, an anthropologist at Boston University, who has read the study.

The quest to fill an evolutionary gap began in 2000 when the research team found the foot bone in an Ethiopian desert.

The Hadar region of Ethiopia has produced more than 370 fossils. Arguably the two most important specimens to come from the region belonged to “Lucy” and “Ardi.” Both human ancestors are the most complete fossil skeletons from their time periods.

Donald Johanson, a member of the current research team, originally uncovered “Lucy” in 1974. She is dated to around 3.2 million years ago, and “Ardi” lived roughly 4.5 million years ago.

The fossilized bone that led to the latest findings belongs to the same species as “Lucy,” Australopithecus afarensis.

After it was removed from the field in 2000, the foot bone was cleaned using dental drills and brushes. Casts were made, and the original packed away in the National Museum of Ethiopia.

It remained there for several years with hundreds of other bones from the region. Political upheaval in the country forced researchers to wait before studying the original fossils again.

It wasn't until 2008 that Ward, Kimbel and Johanson could return to their research.

It had been assumed “Lucy” and her relatives held onto some tree-climbing characteristics while living on the ground. The research team's discovery supports a primarily ground-dwelling species instead.

“This has been a debate within the anthropological community for decades,” Ward said, “partly because we haven’t had the right bones preserved in the fossil records. This foot bone really shows that these were indeed ground-walking animals.”

Scientists largely commended the study as the best skeletal evidence for early arches to be found yet, calling it consistent with fossilized footprints found in Tanzania that indicate similar arches.

“A big step in evolution is abandoning trees as sources of refuge and resources,” Kimbel said.

Anthropologist William Jungers of Stony Brook University in New York said researchers “made the case, successfully,” that the arches described in the study are human-like.

“I think there is still sufficient evidence to support that this species still took advantage of the trees,” Jungers said.

Longer, more curved toes and fingers useful for climbing trees have been found from the same species. Along with shorter legs and longer arms, these fossils support the theory of some residual form of tree-climbing.

“These are not apes, but they’re not people either,” Jungers said.

“An animal with poor locomotion like that would have been eaten by leopards,” DeSilva said. “If this species was primarily on the ground, as I think it was, it raises the interesting question of how they survived for so long.”

MU researcher Ward is currently studying fossils in South Africa.


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Comments

Gregg Bush February 10, 2011 | 6:14 p.m.

This is a fantastic story! Good work, Matthew.

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