Researchers Find Earliest Human Ancestor

July 11, 2001 -- Teeth and bone fragments from the oldest fossil ever found in the human family tree reveal that our ancestors walked on two legs more than 5 million years ago and perhaps even millions of years earlier, a team of international scientists announced today.

Fossilized remnants of the animal, classified as Ardipithecus ramidus kadabba, indicate it was about the size of a modern chimpanzee, says Yohannes Haile-Selassie, a graduate student from the University of California, Berkeley that made the find along with colleagues.

The fossil was found in the desert of central Ethiopia in an area that has been one of the most fertile areas for early human-like fossils in the world. The layers of volcanic soil around the fossil date to between 5.2 and 5.8 million years ago.

"It is the earliest hominid," Haile-Selassie told Reuters. "We are pushing back the hominid record by more than a million years."

Small Pieces of the Human Tree

The hominid family tree includes all creatures, living and extinct, that are more closely related to humans than to chimpanzees. Molecular studies have suggested that the lineages that evolved into humans and chimpanzees diverged from a common ancestor around 5.5 to 6.5 million years ago.

The new fossil is tantalizingly close to when that divergence might have occurred, scientists say, suggesting that the split of the two lineages may have occurred earlier than research has indicated.

In Thursday's issue of the journal Nature, scientists report of scant remains from the fossil: teeth, part of a jawbone, hand, arm and collar bones, as well as one toe bone. The bones represent at least five individuals of the new species, researchers say.

The toe bone was a crucial part of the find, Haile-Selassie said in a news release.

"Its toe bone is like that of a bipedal animal," he said. The bone suggested it was a member of a group of human-like animals that scientists call hominids, which walked on two legs.

Were Some Apes Also Bipedal?

Walking on two legs has long been thought of as a hallmark of the human family tree, Henry Gee says in an article that accompanies the study in Nature. But the trait might have also belonged to other, closely related animals.

Because scientists are finding older and older fossils that appear to have been upright walkers, researchers might eventually find traces of extinct lineages of ape were also bipedal. That, says Gee, could change how we think about the human family tree.