Researchers Reconstruct Oldest Known Human Ancestor

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An international team of more than 70 scientists, including UC Berkeley professors, announced yesterday the reconstruction of skeletal remains of the oldest known ancestor of modern humans.

Nicknamed Ardi, the 4.4-million-year-old partial female skeleton of Ardipithecus ramidus was constructed by the Middle Awash Project, which was co-directed by Tim White, UC Berkeley professor of integrative biology.

The announcement followed years of excavation, study and reconstruction that began with the first discovery of the hominid 17 years ago in Ethiopia. A report on the project's findings is slated to be released Friday.

White has previously been recognized for the discovery of what was previously the oldest-known hominid, the 3.2-million-year-old Lucy, who was discovered in 1974 near the location Ardi was found.

Leslea Hlusko, UC Berkeley associate professor of integrative biology who participated in the study, said the discovery sheds further light on the process by which human evolution diverged from that of chimpanzees.

"All the evidence we had before suggested that our common ancestor was quite chimpanzee-like," she said. "(But)with Ardipithecus, we now see that the earliest member of our lineage wasn't chimpanzee-like at all."

She added that the discovery of Ardi suggests that while humans and chimpanzees share a common ancestor approximately six to eight million years ago, the two quickly evolved much differently.

While Ardi had big toes ideal for grasping, suggesting her natural aptitude for climbing tall trees, she also walked on two feet and had small canine teeth in contrast to modern chimpanzees.

The canine difference suggests that even at this stage in evolution,

hominids had already been monogamous, Hlusko said.

"The males were standing upright in order to carry back food to the females and this is very different from what chimpanzees (do)," she said. "A combination of small canines with being able to stand up and carry things suggest that the males were provisioning the females and that this would be an evidence of pair bonding."

Sediment found in the excavation area indicates that the fossils were not transported by water from other areas.

The fact that the sediment and the fossils were found in the same area has allowed the researchers to better ascertain the habitat in which Ardipithecus ramidus lived, Hlusko said. The surrounding area was a woodland inhabited by antelopes, monkeys and rats, whose fossils were also discovered at the site, she said.

Such a discovery may disprove another evolutionary theory that says human ancestors started walking on two feet in order to adapt to a savannah environment, Hlusko said.

She said the announcement of the reconstruction of the 4.4 million-year-old fossil remains is already likely to stoke scientific debate for years to come until the story of human evolution is better understood.

"With Ardi, and with this publication out there for all the scientists to study, we'll see years and years and years of debate of what the anatomy means," Hlusko said. "And we need to find more fossils, and hopefully even older ones, to test the hypotheses that are now posed by the Ardi skeleton."


Contact Paul Edison at [email protected]

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