International team of researchers spent 17 years piecing together a detailed picture of 4.4 million-year-old bones
Her bones were so fragile some of them crumbled when they were touched. Her skull had been flattened and parts of her skeleton had been broken into more than 100 pieces.
Still, researchers working in northeastern Ethiopia knew they had made a stunning discovery in 1994 when they uncovered a cranium, lower jaw, teeth, pelvis and leg, ankle and foot bones of a hominid who had lived 4.4 million years ago, more than a million years earlier than the famous Lucy.
After a challenging and painstaking reconstruction, an international team of scientists revealed Thursday why Ardipithecus ramidus, nicknamed Ardi for short, is a far more revolutionary discovery than her younger relative.
The team describe Ardi and her world in 11 papers in Friday’s edition of the journal Science. At a press conference in Washington Thursday, the lead scientists explained how her fragile bones offer evidence to overturn entrenched hypotheses on what our ancestors looked like, how they behaved and where and why early humans first walked upright.
We were never knuckle walkers like chimps and gorillas.
“That kind of locomotion never occurred in the human line,” says C. Owen Lovejoy, an evolutionary biologist at Kent State University in Ohio.
Reconstructed lateral view of the skeleton of ARA-VP-6/500 (Ardi).
It has been assumed for years that early humans looked like chimps, our closest living relatives. Now, scientists have a strange new face to paste in the family album, one with flatter features than a chimp and a more upright head.
Ardi is not a common ancestor between chimps and humans, but because she dates to not long after the two lines diverged the scientists say her fragile bones suggest we never looked like chimps. This also suggests the chimp line has undergone radical changes of its own.
As well, the find challenges current thinking on where early humans began to walk upright, on two legs. It couldn’t have been on African savannas, as has long been hypothesized, because Ardi lived in the forest. Her long, opposable big toes would have grasped branches and helped her climb, but would have made running on the ground awkward.
Lucy, the best known member of the species Australopithecus afarensis, was already a full-time upright walker, so offered no clues as to how early humans moved from the trees to the ground, says Dr. Lovejoy. Ardi’s strange feet and pelvis show how she was able to straddle the two worlds, and live both on the ground and in the trees and find food in both, eating plants, insects and maybe small mammals.
The researchers say they are expecting debate over their conclusions. But the implications for the social history of the human may prove to be the most controversial element of the Ardi story.
She had small canine teeth, and the scientists found other small canines belonging to males of her species.
Typically, says Dr. Lovejoy, apes and monkeys with big canines use them as weapons, but Ardi and her ilk probably had a social structure without strong male-male conflicts.
Frans de Wall, an Atlanta-based primatologist who was not involved in the project, says the discovery challenges the assumption in anthropology that our last common ancestor was a killer.
“The idea in anthropology is that last common ancestor is the chimp, a fighter and killer, so we have been doing it for 6 million years and chimps have been doing it for 6 million years,” Dr. de Waal said in an interview.
“If the last common ancestor was not a chimp, then the story changes and it opens up whole new ways of thinking about the human evolutionary story.”