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Monday, October 14, 2002

By Byron Spice, Post-Gazette Science Editor

It's an exciting time for anthropologists. And a contentious time.

	Maeve Leakey

On one hand, the number of fossils of early hominids -- the scientific name for the family of humans -- has jumped markedly in recent years, along with claims of entirely new genera and species of hominids.

"The evidence, in general, is staggering," said Maeve Leakey, the current standard-bearer for the famed Leakey family of paleoanthropologists. While human evolution once was seen as a straightforward progression of species, one after another, to modern humans, it now appears far more complicated. Many different, but now extinct, species of hominids appear to have coexisted in our prehistory -- so many that the human family tree now looks more like a tangled bush.

At the same time, arguments about what all these new fossils really are -- and what defines a hominid -- are growing fiercer. Last week, rival groups of researchers traded jabs in the journal Nature over whether a fossil that one team claims is the earliest known human ancestor is a hominid or an ape.

	About Leakey's talk Maeve Leakey will discuss "The Search and Discovery of Our Earliest Ancestors" at 7 p.m. Thursday in the Carnegie Music Hall, Oakland. Tickets are $15 and may be purchased by calling 412-394-3353 or on the Internet at www.proartstickets.org.

"There's been an incredible diversity of names added to the human family tree," said K. Christopher Beard, curator of vertebrate paleontology at the Carnegie Museum of Natural History. Arguments now center on which ones are truly new species and which ones are really hominids.

"What is not debatable," he added, "is that a good proportion of the new names do document new species."

"It's very exciting," said Leakey, who will discuss the emerging evidence of early hominids during a public lecture Thursday at the Carnegie Museum of Natural History.

She added to the excitement last year when she announced the discovery of a new genus and species of hominid, Kenyanthropus platyops, or "flat-faced man of Kenya." The 3.5-million-year-old skull that her team unearthed near the western shore of Kenya's Lake Turkana would have coexisted with Australopithecus afarensis, the human ancestor best known as the fossil "Lucy."

	Top: Kenyanthropus platyops, a new genus and species of hominid whose discovery was announced last year by Maeve Leakey. (National Museums of Kenya) Bottom: The Toumai skull is the subject of squabbling among scientists about whether its lineage is human or ape.

In July, a team led by the French paleontologist Michel Brunet announced what may be the earliest known hominid, a fossil his team recovered from the desert of Chad. That claim was particularly startling because its age -- 6 to 7 million years old -- places it very near the time when molecular DNA analysis suggests hominids branched off from chimpanzees and other primates.

"I really think it is one of the most important finds yet," Leakey said last week in a telephone interview from Nairobi, Kenya, where she is on the staff of the National Museums of Kenya.

The size and shape of the fossil skull is ape-like, but the face and teeth appear amazingly similar to modern humans for a species that supposedly had only just diverged from the apes.

But Leakey said the human-like features are not quite so surprising when you think about it. "People automatically expected that it would appear more ape-like" because of its age, she said. But it's a mistake to think that apes are necessarily primitive. "They have evolved for six million years" since diverging from hominids.

Jeffrey Schwartz, a University of Pittsburgh anthropologist who has personally examined the vast majority of all existing human fossils, said it's also a mistake to assume that early hominids would necessarily resemble chimpanzees, the species that genetically is closest to humans. Genetic similarity, he contended, does not always equate with physiological similarity.

Last week in Nature, a group of anthropologists including Brigette Senut of the Natural History Museum in Paris, argued that the Chad fossil is not a new genus and species of hominid -- Sahelanthropus tchadensis -- as Brunet claimed, but a female gorilla or chimp. Among other criticisms, they said the fossil showed indications that it did not routinely walk upright on two legs. Walking like a human, they contended, is a critical part of being human.

Brunet, noting that Senut last year had made her own controversial claim of finding an early hominid, replied that his critics had made mistakes in describing his fossil and had failed to prove that it was a gorilla.

One of the problems with all of these claims, Schwartz said, is that scientists are becoming increasingly reticent about showing their fossils to other investigators. Traditionally, scientists have been expected to make available those fossils that are the basis for identifying a species, but many have recently begged off, claiming their reports of new genera and species are only "preliminary," he added.

"Brunet won't allow anyone to see [the Chad fossil]. When you ask him to see it, he won't even answer your email," he said.

Leakey "has really been a good example in the field" for her willingness to cooperate with other researchers, Schwartz said. Though he hasn't yet seen the Kenyanthropus platyops fossil, he was allowed to photograph her previous finds for his current project -- a set of scientific volumes that include photographs and consistent descriptions of all human fossils.

"On one level, this rash of discoveries is very exciting," Schwartz said. "But then the question is, what are they?" Though the debate seems to get nastier and nastier, it is forcing greater consideration of basic questions, such as what defines a hominid, he added.

Leakey, born Maeve Epps in London in 1942, is the second wife of Richard Leakey, who in turn is the son of the late Louis and Mary Leakey, who began searching for human fossils in Africa seven decades ago. With Richard Leakey no longer involved in field work, Maeve Leakey and their daughter, Louise, have been carrying on the Leakey fossil-hunting tradition.

Kenyanthropus was discovered near the western shore of Lake Turkana. Leakey said her team has recently returned to the eastern shore, a rich source of human fossils discovered by her husband in 1967. "It's been over 20 years since any serious survey work has been done there," she said.