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Coastal clues suggest new direction for worldwide spread of early humans


Long before sushi bars spread through Deep Ellum, early humans were already shucking their own seafood.

Homo sapiens probably enjoyed his shellfish raw, even in the days before wasabi. At one spot, along Africa's Red Sea coast, he left behind remains of such a feast.

In a fossilized coral reef in Eritrea, scientists have uncovered fragments of crabs, clams, oysters and scallops. Nearby lie stone axes and obsidian blades, presumably used to pry apart the seafood delicacies.

"We found the tools but not the toolmakers," said Robert Walter, a geologist at the Centro de Investigacion Cientifica y Educacion Superior de Ensenada (Center for Scientific Research and Higher Education of Ensenada) in Mexico.

But the question of the toolmakers' identity is key. Dating techniques show that the reef is 125,000 years old, placing it squarely in the time frame when modern H. sapiens was evolving, many scientists think. So the axes and blades could have been made by some of the earliest modern humans.

The discovery also suggests a path by which H. sapiens may have traveled - the coast. Paleoanthropologists don't agree on where or when H. sapiens first appeared, but many believe he arose in Africa and then spread across continents. Under that scenario, the new findings could suggest that early humans used the Red Sea coastline to guide their northward migration, Dr. Walter said.

A team of researchers, led by Dr. Walter and including two Texas scientists, found the tool-riddled reef during expeditions in 1997 and 1999. By publishing their results last week in the journal Nature, they have found themselves in the middle of paleoanthropology's hottest debate - the origin of our species.

Reactions to the Nature paper were sharply mixed.

"If they're right, then they've got something that destroys most arguments about modern humans," said Richard Klein of Stanford University. That's because some of the newfound tools appear to be of a primitive technology that should have disappeared by 125,000 years ago, before H. sapiens arose, he said.

But Ofer Bar-Yosef, of Harvard University's Peabody Museum of Archaeology and Ethnology, said the survival of this tool technology wasn't surprising. The Eritrea research "fits pretty well within the general picture we already had," he said.

One rare point of agreement is that our genus, Homo, probably got its start in Africa some 2.3 million years ago. Several species of Homo appeared, then disappeared, over several million years. The big question is when, and where, the first examples of modern humans - H. sapiens - appeared.

Many researchers support the "out of Africa" hypothesis, which holds that modern humans originated in Africa between 200,000 and 100,000 years ago, then spread to Europe, Asia and Australia. Others support an idea called "multiregionalism," which holds that H. sapiens arose separately on different continents, their ancestors having left Africa much earlier.

The out-of-Africa idea is boosted by the fact that the oldest known bones of H. sapiens are found only in Africa, from about 115,000 years ago. The species isn't found outside of Africa until roughly 90,000 to 100,000 years ago, in Israel.

Eritrea lies at a crossroads for understanding the timing of early human migration, Dr. Walter said. Anyone moving out of Africa could take either a coastal route, along the Red Sea, or an inland one, perhaps along the Nile Valley. Yet few early human fossils have turned up in Eritrea. In fact, only one ancient human bone is known from the country, a 1 million-year-old fossil skull uncovered just south of the newfound reef.

As a geologist, Dr. Walter studies the kind of rocks in which human fossils might appear. In January 1997, he and his team were driving a rough coastal road in Eritrea when it got dark and began to rain. The group was forced to camp on the nearest open flat spot. In the morning, as the scientists were breaking camp, the marine biologist in the group discovered that the flat spot was actually a fossil coral reef.

Coral after coral lay exposed in the air, peppered with stone tools, blades and the occasional animal bone.

"It was one of the most amazing experiences of my life," said Dr. Walter.

Today, the reef lies just inland from the Gulf of Zula, but 125,000 years ago it was underwater. The climate then was relatively warm, and sea level was about 15 feet higher. Tools and food remains were claimed by the sea and embedded in the coral.

When global temperatures dropped, the polar icecaps grew, locking up more seawater as ice. Sea level fell, leaving behind exposed coral reefs like a bathtub ring around the ocean, Dr. Walter said.

Life at the beach would have been great, he noted.

The early humans had plenty of shellfish to harvest from the reef environment. The humans also apparently butchered big land animals, like elephant and hippopotamus, that wandered down to the shore. Freshwater springs - of which there is yet no evidence - might have provided respite from the salty Red Sea water.

"I suspect we're seeing the early stages of anatomically modern humans adapting to this coastal marine environment," said Dr. Walter.

It's not surprising that humans would live by the coast, pointed out Christopher Stringer, a paleoanthropologist at the Natural History Museum in London. Other sites - such as the Klasies River Cave in South Africa and Vanguard Cave in Gibraltar - show how people exploited food and other marine resources just a few tens of thousands of years later.

But the Eritrean site could shed light on exactly where people were at a crucial point in human evolution, said team member Dick Buffler of the University of Texas' Institute for Geophysics.

"That's a very exciting aspect that expands our thinking," he said.

H. sapiens must have traveled from Africa to Australia by 60,000 years ago, as ancient human burials there show. Migrating along the coast might have provided an easy alternative to trekking inland, through wildly varying environments of desert, savannah, mountains and so on, Dr. Stringer noted.

"It doesn't mean they were migrating, but it certainly would provide an easy way for them to migrate," he said. "If you can live on the coast in the Red Sea, you can live on the coast in Arabia and in India."

But none of this is very surprising, said Dr. Bar-Yosef. Few anthropologists would argue that the coastal route is any less likely than an inland one.

To Dr. Klein of Stanford, the oddest aspect of the reef discovery is that some of the stone tools appear very primitive. Their technology reaches back a quarter-million years in history; by 125,000 years ago, such axes had mostly disappeared from use, replaced by more modern blades, he said.

While some critics consider the tools the biggest puzzle of the Eritrean site, others question the toolmakers' identity.

"It's silly to think we know who made these tools," said Milford Wolpoff, an anthropologist at the University of Michigan and a prominent critic of the out-of-Africa theory. Certainly, the toolmakers could be H. sapiens, he said - but that doesn't prove they were in the early stages of moving out of Africa.

Fortunately, the Eritrea project is in its early stages, said Dr. Walter, with much more work to do and interpretations to re-evaluate. His group plans to return to the site soon, with archaeologists and other specialists to help document the human artifacts.

Dr. Buffler predicted the team would find many more tools, and even the bones of early H. sapiens.

"They're there," he said. "They're just waiting to be found."
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