Bickering Over Old Bones

For a couple of geezers, the two rivals are really going at it. In one corner stands the official champion, Ardipithecus ramidus, discovered in 1994 in the barren Ethiopian badlands by paleoanthropologist Tim White of the University of California, Berkeley, and his team. At 4.4 million years old, ramidus is the current holder of the title "oldest human ancestor." In the other corner glares the scrappy challenger, Orrorin tugenensis, excavated last year from ancient strata in Kenya. His French discoverers say the 6 million-year-old guy deserves the "oldest ancestor" crown, but Orrorin's pedigree is controversial, and he has been snubbed by many anthropologists like an arriviste at a social-register tea. Not ones to grow complacent, the ramidus team last week boosted their man's claim of ancestral primacy. Scouring the same arroyos and escarpments that held the original ramidus, Berkeley grad student Yohannes Haile-Selassie found 11 fossils that seem to represent an older ramidus clan, 5.2 to 5.8 million years old. Belonging to five individuals, they're "the earliest definitive evidence of the hominid" family, says Haile-Selassie--our oldest human relatives, ancestral not to chimps but to us alone.

The latest find is called Ardipithecus ramidus kadabba ("basal family ancestor"). His appearance remains a mystery: with neither a skull nor intact limb bones to guide them (only a toothy jawbone, hand and foot bones, fragmentary arm bones and collarbone), all scientists can tell is that he was the size of today's chimps, Haile-Selassie reports in the journal Nature. He found the first fossil on Dec. 16, 1997, as he walked across ancient sediments exposed by erosion. The jawbone "was sitting on the surface, waiting for some lucky guy to pick it up, and it turned out to be me!" he said by e-mail to NEWSWEEK from Ethiopia.

Kadabba dates from when human ancestors and chimp ancestors went their separate evolutionary ways, 6.5 to 5.5 million years ago. It was, as they used to say, missing-link time, and by age alone kadabba might be either chimp or human. His teeth, however, show traits shared exclusively by every member of the family of man, says White, not by any chimps. His toe bone is even more revealing. A telltale slanted surface at the rear joint is characteristic of bipedal walkers who push forward by leaving the front part of the foot on the ground and lifting the heel, explains Haile-Selassie. Walking erect is one of the key achievements (maybe the key achievement) distinguishing humans from chimps.

If kadabba is the first member of the human family, then Eden was a forested upland where active volcanoes erupted from fractures in the land and underwater in lakes, where primitive elephants, rhinos, horses, rats and monkeys roamed. Yet paleo-dogma says that the savanna, not the forest, was the birthplace of humanity, as climate change turned forests to grasslands and evolutionary pressure split the ape lineage into the hairy ones who stayed in the forest and the naked ones who roamed the savanna. With kadabba, says Haile-Selassie, that theory is "down the drain."

While scientists figure out what to replace it with, they can engage in a favorite sport: dissing each other's fossils. Orrorin ("original man") is having the worst time of it. Soon after Martin Pickford of the College de France and Brigitte Senut of the National Museum of Natural History in Paris unearthed him, they concluded that he was bipedal and thus the earliest human. Critics say Orrorin might be the earliest chimp, or possibly ancestral to both. To call Orrorin a hominid, says Bernard Wood of George Washington University, you "have to rewrite human evolutionary history." Senut retorts that kadabba was no biped; its toe-bone slant was instead "a climbing adaptation." Those are the kinder exchanges. Anthropologists accuse Pickford of collecting fossils illegally, but he has the permits to disprove them. He sued fossil maven Richard Leakey for false arrest after being jailed in Kenya for allegedly collecting without those permits (Leakey denies all involvement). Pickford's book about Leakey is subtitled "Master of Deceit."

Will we ever find our oldest direct ancestor? Apes from 5 or 6 million years ago so resemble each other that we may never know which begat chimp and which begat man. Complicating things even more, our family tree is so bushy "there is not a single line from ape to angel," says anthropologist Donald Johanson of the Institute of Human Origins. Still, it would be nice to know where the lines begin.

Comments