May 12, 2000
Fossil Signs of First Human Migration Are Found
By JOHN NOBLE WILFORD


In a discovery with profound implications for the study of early human
history, scientists digging in the republic of Georgia have found
1.7-million-year-old fossil human skulls that show clear signs of African
ancestry and so may represent the species that first migrated out of Africa.

The two relatively complete skulls, being described today in the journal
Science, begin to put a face, in a sense, to the ancestors who responded to
opportunity and necessity by leaving Africa and spreading out over much of
the rest of the world. Many paleoanthropologists hailed the discovery as a
major advance in their field, and said the skulls were probably the most
ancient undisputed human fossils outside Africa.

"It's the first good physical evidence we have of the identity of the first
emigrants out of Africa," said Dr. Ian Tattersall, a paleontologist and
evolutionary biologist at the American Museum of Natural History in New York
City.

The international discovery team, led by Dr. Leo Gabunia of the Georgia
National Academy of Sciences, concluded that the age and skeletal
characteristics of the skulls linked them to the early human species Homo
ergaster, who lived from 1.9 million to 1.4 million years ago and who some
researchers think is the African version of Homo erectus. The specimens were
said to bear less resemblance to the typical Asian Homo erectus.

"We suggest that these hominids may represent the species that initially
dispersed from Africa and from which the Asian branch of H. erectus was
derived," the discoverers said in their report.

The findings contradicted the theory that human ancestors left Africa soon
after they invented better stone axes and other tools of what archaeologists
call the Acheulean culture. The more than 1,000 stone tools found in the
sediments with the two skulls were all pre-Acheulean, crudely chipped cobbles
that had been made since human ancestors began knapping stone tools about 2.5
million years ago.

The earliest tools of the Acheulean style did not appear in Africa until 1.6
million years ago, and about 100,000 years later outside Africa, in Israel.
By contrast, the discovery team reported, the tools found with the Georgian
skulls resembled tools found in the Olduvai Gorge of Tanzania and dated at
about 1.8 million years.

So it was not technology, but biology or environment, that presumably set
human ancestors off on their migrations, scientists now say.

Dr. Susan C. Anton, a paleoanthropologist at the University of Florida who
was a member of the discovery team, said that by this time human ancestors
had become more carnivorous and their diets pushed them to expand their home
range to match the wider ranges of the animals they preyed on.

"With the appearance of Homo, we see bigger bodies that require more energy
to run, and therefore need these higher quality sources of protein as fuel,"
Dr. Anton said of the adaptation to meat-rich diets.

As long as early human ancestors had smaller bodies and brains, Dr.
Tattersall said, they lived mainly on plants and confined themselves to a
limited range at the edge of forests, not too deep in or too exposed far out
on the savanna. Once they had stronger bodies and high-protein meat diets,
they were able to spread out geographically and ecologically.

Dr. Alan Walker, a paleoanthropologist at Pennsylvania State University who
specializes in searching for human fossils in Kenya, said he agreed with the
interpretation of the Georgian skulls. "The new fossils look exactly like
early Homo skulls from Kenya," Dr. Walker said.

He said the implications of the new findings for human dispersal from Africa
supported an idea he and his wife, Dr. Pat Shipman, an anthropologist,
proposed in 1989. They suggested that once the more apelike
australopithecines evolved into the genus Homo and became carnivorous, they
were forced to expand their home territory.

"Herbivores are restricted to where the plants are that they eat," Dr. Walker
said. "Carnivores are not so restricted. Meat is meat, and you often have to
travel far to find it."

The two skulls were uncovered last summer at Dmanisi, on a slope of the
Caucasus Mountains 55 miles southwest of Tbilisi, the Georgian capital. At
the same site in 1991, paleontologists found a jawbone of what was identified
as a Homo erectus. Finding the craniums -- one of a young adult male and the
other of a female adolescent -- has seemed to quiet skeptics who had disputed
the jawbone dating.

The discovery team included scientists from France, Germany and the United
States, as well as Georgia. Dr. Carl C. Swisher 3rd of the Berkeley
Geochronology Center in California determined the approximate age of the
skulls by geochemical and paleomagnetic analysis of the sediments and the
presence of small rodent bones of a well-established age that were found with
the human fossils.

Dr. Philip Rightmire, a specialist in Homo erectus at the State University of
New York at Binghamton, said he was impressed by the new discovery's
implications for "a pretty quick, really wholesale dispersal of these people,
along with other animals," from the time the new species emerged in East
Africa.

There is fossil evidence that by the time the individuals the Dmanisi skulls
belonged to were living in Georgia, others of their species had already
traveled as far east as Java in southeast Asia.

Unlike some scientists, Dr. Rightmire classifies the African ergaster
together with the Asian erectus in the same species. To him and many others,
they are regional variants of the same species.

Other scientists, often referred to as "splitters" and including discoverers
of the Georgian skulls, look at the same fossils and see distinct species in
Africa and Asia, with the Dmanisi fossils much more closely related to its
African roots.

In their report, the discoverers said, "The Dmanisi site suggests a rapid
dispersal from Africa into the Caucasus via the Levantine corridor,
apparently followed by a much later colonization of adjacent European areas."

It was somewhat surprising, the discoverers said, to find that the Dmanisi
fossils bore so little similarity to later European lineages.

Being close to the boundary between Europe and Asia, Georgia might have been
a crossroads of dispersal to the west in Europe as well as to southern and
eastern Asia.

Scientists said the discovery left unchanged current interpretations of the
origin of anatomically modern humans in Africa some 100,000 years ago

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