By Rob Waters
Oct. 1 (Bloomberg) — The 4.4 million-year-old skeleton nicknamed “Ardi” by scientists who found her remains in Ethiopia show the earliest known ancestor of humans was a lot more like us than chimps or apes.
The 4-foot-tall Ardi was more than 1 million years older than the best-known human ancestor, “Lucy,” whose remains were found 75 kilometers (46 miles) away. Ardi, from Ardipithecus ramidus, walked on two feet and lived in groups where males cooperated rather than fought and females chose mates based on the size of their fangs, according to an analysis published today in the journal Science.
Ardi’s bones, discovered in the Afar Rift of Ethiopia and described in today’s report, challenge previous assumptions that when humans and apes split into separate species millions of years ago, the ancestor they shared was a lot like a chimpanzee.
“The common ancestor was not like a chimpanzee,” said Andrew Hill, an anthropologist at Yale University in New Haven, Connecticut, who wasn’t involved in the research. “There were some good reasons we made that assumption, but it’s wrong.”
Some of the most compelling evidence of the divergent evolutionary paths humans and apes have taken is that the upper canine teeth of Ardi’s male peers were smaller than those of chimps.
“In Ardipithecus, the canine is no longer a weapon,” said Owen Lovejoy, an evolutionary biologist at Kent State University in Kent, Ohio, who led the team’s anatomical analyses. “So there has been an enormous social transformation from heavily male-male conflict to virtual elimination of conflict. The males are cooperative.”
‘Lucy’ Not Oldest
The excavation and analysis of the remains of Ardi and her peers were conducted by a team of 47 scientists from 10 countries. Previously the earliest known pre-human remains were those of Lucy, a member of the genus Australopithecus afarensis.
Ardi helps fill a gap in the evolutionary history of humans, said Tim White, a paleontologist at the University of California, Berkeley, and the project’s co-director. “There’s been a tendency to view chimpanzees as the presumed stand-in for what the last common ancestor of both apes and humans looked like,” said Lovejoy. “This fossil changes that view completely.”
The report consists of 11 articles providing details of Ardi’s skull, hands, arms, pelvis and feet, and discussing how they illuminate the origin of humans and the evolution of behavior.
Finger Bone
Berhane Asfaw, an anthropologist with the Rift Valley Research Service in Addis Ababa, Ethiopia, was walking with his colleague Yohannes Haile-Selassie in November 1994 when Haile- Selassie found the first fragment of Ardi, a half of a finger bone.
Haile-Selassie blurted out “It’s a hominid,” recalled Asfaw, the project’s co-director, in a telephone interview from Addis Ababa yesterday, using the scientific name given to modern humans and their now-extinct ancestors. Haile-Selassie is now curator of physical anthropology at the Cleveland Museum of Natural History.
“Then the whole crew converged on the area and we crawled on the surface like a baby on hands and knees” searching for additional bones, he said. In the coming months, they found dozens of bones scattered over an area of 10 to 15 meters (33 to 49 feet).
Lovejoy did an analysis on 145 teeth they found, including canines from as many as 21 individuals.
Not ‘Dagger-like’
They found Ardi’s group had teeth quite different from the “dagger-like” canines in male chimps and gorillas, Lovejoy said in a telephone interview yesterday. “Male gorillas use their canines to threaten and fight with other males and are usually successful in excluding all but one other male from the group.
As a result, gorillas live in groups with a dominant male, sometimes a subordinate male, and up to 12 females, Lovejoy said. Male chimpanzees stake out turf for their clan, patrol it, and keep unrelated males from entering, he said. Invading outsiders can be killed.
In Ardipithecus, male and female canines differ little in size and the male canine has been “dramatically feminized” with a shape like a diamond instead of a sharp point, the report found.
Lovejoy theorizes that canines shrunk in males as a result of evolutionary pressure from females choosing mates with smaller fangs who were less aggressive.
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