Discovery in Ethiopia casts light on human origins

WASHINGTON Fri Oct 2, 2009 11:20am EDT

1 of 7. Digitally rendered composite foot of the 'Ardi' partial skeleton released to Reuters on October 1, 2009. The skeleton of an early human who lived 4.4 million years ago shows that humans did not evolve from chimpanzee-like ancestors, researchers reported on Thursday. In a special issue of Science, an international team of scientists has for the first time thoroughly described Ardipithecus ramidus, a hominid species that lived in what is now Ethiopia.

Credit: Reuters/Science/AAAS/Handout

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WASHINGTON (Reuters) - The skeleton of an early human who lived 4.4 million years ago shows that humans did not evolve from chimpanzee-like ancestors, researchers reported on Thursday.

Instead, the missing link -- the common ancestor of both humans and modern apes -- was different from both, and apes have evolved just as much as humans have from that common ancestor, they said.

The researchers stressed that "Ardi" may now be the oldest known hominid, but she was not the missing link. "At 4.4 million years ago we found something pretty close to it," said Tim White of the University of California Berkeley, who helped lead the research team.

They described the partial skeleton of a female representative of Ardipithecus ramidus. The hominid species lived 4.4 million years ago in what is now Ethiopia.

The 4-foot (1.2 meter) tall creature is a million years older than "Lucy" -- the skeleton of another species called Australopithecus afarensis that is one of the best-known pre-humans.

Genetics suggest that humans and our closest living relatives, the chimpanzees, diverged 6 million to 7 million years ago, although some research suggests this may have happened 4 million years ago.

"Ardi" is clearly a human ancestor and her descendants did not grow up to be chimpanzees or other apes, the researchers report in the journal Science.

She had an ape-like head and opposable toes that allowed her to climb trees easily, but her hands, wrists and pelvis show she strode like a modern human and did not knuckle-walk like a chimp or a gorilla.

"People have sort of assumed that modern chimpanzees haven't evolved very much, that the last common ancestor was more or less like a chimpanzee and that it's been ... the human lineage ... that's done all the evolving," White said.

But "Ardi" is "even more primitive than a chimpanzee," White said.

So chimps and gorillas do not knuckle-walk because they are more primitive than humans -- they have evolved this characteristic that helps them live in their forest homes.

White, Berhane Asfaw of Rift Valley Research Service in Addis Ababa and a large team analyzed all the bones of Ardi and found she might have been more peace-loving than modern chimpanzees. She does not have the long, sharp canines that chimps use to fight, for instance.

And males and females have similar-sized teeth, suggesting more equality than seen among modern apes.

But her brain, while small, is positioned in a way more similar to that of Australopithecus and modern humans, suggesting more human-like visual and spatial perception.

(Editing by David Morgan)

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