Oldest human ancestor revealed

WASHINGTON — A 4-foot-tall female nicknamed Ardi, who lived 4.4 million years ago in Africa, has replaced Lucy as the earliest best known ancestor of the human species.

Ardi's nearly complete skeleton is 1 million years older than Lucy's, pushing back the point when hominids — prehuman primates — are known to have split from the evolutionary line that led to chimps and gorillas, an international team of scientists said Thursday.

"Ardi is not a chimp. It's not a human. It's what we used to be," said paleontologist Tim White, an authority on human evolution at the University of California, Berkeley. White and his colleagues spent 15 years recovering and studying Ardi's bones before Thursday's announcement, sponsored by the journal Science.

Ardi is named for her genus and species, Ardipithecus ramidus, a distant cousin of Lucy's line, Australopithecus afarensis.

The discovery sheds new light on human evolution during a previously little-known epoch. Scientists think humans and apes descended from a "last common ancestor," an even-more primitive primate that lived 7 million to 9 million years ago.

Ardi isn't the last common ancestor, White said, but "it's the closest we've come to the last common ancestor."

A few older hominid skulls and teeth have been discovered, but nothing as complete as Ardi or Lucy.

The first of Ardi's bones, a single tooth, was discovered in 1992, not far from where Lucy's skeleton was buried in the fossil-rich Afar Rift of Ethiopia. Later, more than 100 other pieces, including bits of a skull, hand, foot and pelvis, were eased out of the volcanic soil and reassembled.

The remains of 35 other individuals, plus birds, animals and plants, also were found there.

White called the project to assemble Ardi, which eventually involved 47 scientists from 10 countries, "a scientific mission into the very deep past. ... It was like discovering a time capsule from a period and place we knew nothing about."

The older skeleton reverses the common wisdom of human evolution, said anthropologist Owen Lovejoy, an evolutionary biologist at Kent State University in Ohio.

Rather than humans evolving from an ancient chimplike creature, the new find provides evidence that chimps and humans evolved from some long-ago common ancestor — but each evolved and changed separately along the way.

"This is one of the most important discoveries for the study of human evolution," said David Pilbeam, curator of paleoanthropology at Harvard's Peabody Museum of Archaeology and Ethnology.

Ardi's hands, feet, pelvis and teeth are more like the bones of modern humans than of chimpanzees or gorillas. For example, her pelvis is modified for walking upright on the ground and for climbing trees.

"Ardi was not a knuckle-walker [like apes]," Lovejoy said. But she probably couldn't have outrun the smaller, more advanced Lucy.

"If Ardi and Lucy had a race, Lucy would win handily," Lovejoy said.

Ardi was a woodland creature, with a small brain, long arms and short legs. Her discovery disproves the earlier theory that prehumans learned to walk when they came down from trees to live on open savannas, White said.

She probably ate fruit, berries, mushrooms, birds, bats and mice and other small mammals, judging by her teeth and the remains found where she was discovered. Scientists can tell she was female because of the shape of her canine teeth and her pelvis.

The Afar Rift is a large basin created when the Arabian peninsula split off from Africa millions of years ago. The breakup also produced the Red Sea and the Gulf of Aden. Afar is often called "The Cradle of Humankind," because so many hominid remains have been found there.

Ardi was the subject of 11 scientific papers published in the new issue of the journal Science.