New tests show bones are earliest of humans

Skulls dug up in Ethiopia in 1967 push back the birth of modern man 35,000 years

February 17, 2005|By Dennis O'Brien | Dennis O'Brien,SUN STAFF

Researchers taking a second look at skull fragments in an Ethiopian museum have made a startling discovery: They're the oldest remains of modern human ever found.

Tests on two partial skulls unearthed from wind-swept rock formations on opposite sides of Ethiopia's Omo River show that both are 195,000 years old - which pushes back the earliest known date for the emergence of modern humans by 35,000 years.

In a report published today in the journal Nature, researchers say their new age estimates are based on dating techniques far more precise than those available when paleontologist Richard E. Leakey and colleagues unearthed the skulls in 1967.

The findings also lend real-life support to recent DNA studies suggesting that modern humans, or Homo sapiens, emerged from older hominids about 200,000 years ago.

"It's great stuff," said Daniel Lieberman, a Harvard anthropologist who was not affiliated with the study. "I was incredibly excited when I heard about this."

Anthropologists often learn something new from artifacts discovered years ago.

In 2003, similar tests on three skulls found in 1977 in northern Ethiopia showed they were 160,000 years old, which made them the previous record holder.

Members of that earlier team say they don't feel upstaged by today's findings.

"What's important is what is to be learned here," said F. Clark Howell, a paleoanthropologist at the Laboratory for Human Studies at the University of California at Berkeley, who worked in Ethiopia for 11 years.

Researchers originally estimated that the Omo River remains were 130,000 years old.

That made them less important at the time than the search for more ancient hominids, said geologist Frank Brown, a co-author of the study who worked on the original project in the 1960s.

DNA evidence

Anthropologists are more focused these days on finding fossils that confirm the DNA evidence that dates the arrival of modern humans to about 200,000 years ago, Brown said. But he said that wasn't a priority in the 1960s.

"No one was interested in that piece of human evolution that seems to have blossomed with these genetic studies of the past 20 years," he said.

Researchers originally visited the site to track down fossils of ape-like precursors to humans that lived millions of years ago.

"We were looking for things that were maybe 2 million years old, things that would tell us about our more ancient ancestors," said Brown, dean of the College of Mines and Earth Sciences at the University of Utah.

The skull fragments were discovered in the deepest of four layers of fine-grained sediment in rock formations exposed by centuries of flooding, wind and erosion.

Experts disagreed

Fossils from one individual, identified as Omo 1, include some leg and arm bones.

Another skull, known as Omo 2, was found two miles away, and at the time, some experts believed it was the remains of an earlier, more primitive being.

But for years, experts disputed the ages of the skulls, which have been kept at the National Museum of Ethiopia in Addis Ababa.

Those disagreements prompted the study that proved just how old they are.

The researchers made four trips to Ethiopia beginning in 1999. There they used photographs and field notes compiled by Leakey's team to locate the sites where the fragments were found.

Their analysis showed the skulls came from two individuals who lived at about the same time.

The more primitive skull could have belonged to someone from a different but related human group, indicating that diverse types of hominids lived in proximity at the time, the researchers said.

Precise technology

The fragments were dated using a mass spectrometer equipped with lasers that measured isotopes formed by radioactive decay in the pumice of volcanic ash mixed in with sediment where the skulls were buried.

Such precise technology was unavailable in the 1960s.

Researchers also dated the sediments by comparing them with sediments that washed into the Mediterranean from Ethiopia during periods of known prehistoric flooding.

"There were periods of intense rainfall that washed into the Nile out of Ethiopia, and so you have these gummy layers of sediment left over," said John Fleagle, a researcher from Stony Brook University and co-author of the study.

Studies of fossil remains often take years, with delays caused by lack of research funding and problems getting into war-torn regions.

Visits to the Omo site were restricted for more than 15 years because of civil unrest in Ethiopia. "There was a military government in the 1980s, and access was limited," Fleagle said.

More questions

The study was funded by the National Science Foundation, the Leakey Foundation, the National Geographic Society and the Australian National University. Ian McDougall, a geochronologist at the Australian National University, was the lead author.

Fleagle said the findings raise questions about the lives of the hunter-gatherers who once inhabited Ethiopia's vast savannas and the tools available to them.

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