Fossil find may steer evolution theory in new direction

By WILLIAM McCALL, Associated Press

(March 21, 2001 5:04 p.m. EST http://www.nandotimes.com) - Scientists have discovered a 3.5 million-year-old skull in Kenya that may force them to revise anthropology textbooks and drop the fossil nicknamed "Lucy" from the line of human ancestors.

The skull was identified by Meave Leakey, a member of the famed fossil-hunting Leakey family. She said it is about the same age as Lucy but appears to be a completely different and previously unknown species, with a more human-like face.

Researchers named the species Kenyanthropus platyops, or "flat-faced man of Kenya."

Leakey said the chances are 50-50 that this species - and not Lucy's species, Australopithecus afarensis - was an early direct ancestor of humans. That means anthropologists may have to rethink the human evolutionary tree.

"We've always assumed Lucy was our ancestor, and now we need to re-evaluate that idea," Frank Brown, a University of Utah geologist who helped date the site.

The skull was found by researchers at the National Museums of Kenya in 1998-99 along the shores of Lake Turkana. Lucy's bones were found in Ethiopia in 1974.

An analysis of the more recently discovered skull was published in Thursday's issue of the journal Nature.

Leakey said the species represented by the new skull could have been an ancestor of modern humans, or it could have been an evolutionary dead end. At the same time, she said, the same could apply to Lucy.

And she acknowledged that researchers still could easily find a third possible ancestor from that period because of the great number of fossil discoveries being made in Africa.

Leakey and her husband, Richard, who is known for his work as a Kenyan wildlife activist, have made a series of fossil discoveries in East Africa, following in the footsteps of Richard Leakey's parents, Louis and Mary Leakey.

The Kenya skull has distinct qualities that appear to separate it from Lucy's species, Leakey and her colleagues reported. She said one of the most striking things about the skull is how human its face looks.

Andrew Hill, a Yale anthropologist, said the skull has the unusual combination of a large, flat face and small teeth, compared with the generally big teeth and a different facial structure for Lucy. Hill said differences in teeth and jaw structure suggest different diets led to evolutionary changes.

"You have to look for dietary reasons they're separated like this, as perhaps an environmental adaptation to different regions at about the same time," Hill said.

Although Leakey believes the skull represents a genus - a grouping that includes related species - that is separate from Lucy's Australopithecus, another researcher said it also could just be a subcategory of Lucy's species or a related but different species within her genus.

"I think that's the most controversial part of this paper, the claim that it's a new genus," said Tim White, an anthropologist at the University of California at Berkeley. "If you think of a family tree with a trunk, we're talking about two trunks, if they're right."

Leakey said it was not surprising to find evidence that ancient forerunners of humans diverged along separate evolutionary paths around Lucy's time. "The fact we haven't seen it before is more a lack of evidence, I believe," she said.

In a commentary accompanying the study, George Washington University anthropologist Daniel Lieberman said the skull adds to the confusion about the human evolutionary tree. But he said it also adds to evidence that there were several human-like species between 2 million and 3.5 million years ago that adapted well to different environments.

He noted that the skull's discovery, made during field work sponsored by the National Geographic Society, is among a series of fossil finds over the past 15 years that have nearly doubled the number of recognized human-like species.

"To those of us who are interested in reconstructing the evolutionary history of our species, these discoveries have been fun, if a little bewildering," Lieberman said.