by Lee Bowman
Scripps Howard News Service
February 17, 2005
These findings, reported Thursday in the journal Nature, roll back the debut of anatomically modern humans by as much as 50,000 years over previous estimates and raise new questions of just when the "sapiens" ("thinking") part of "Homo sapiens" came into play.
When paleontologist Richard Leakey first found the fossilized bones in 1967 among rock formations along the Omo River in Ethiopia, they were thought to be 130,000 years old.
There were two sets of remains: Omo 1, which featured part of a skull and some skeletal bones; and Omo 2, with a more complete skull but no other bones. Neither has a complete face.
More recently, University of California-Berkeley paleoanthropologist Tim White found similar fossil remains dated to 160,000 years old at a different site in Ethiopia's Afar region.
Teams led by Ian McDougall, a geologist at the Australian National University in Canberra returned to the Omo site four times between 1999 and 2003, and found the area examined by Leakey. They obtained more parts of Omo 1, including part of a femur (upper leg bone) that fit a section found in 1967. They also found animal fossils and stone tools and studied the ancient layers of river sediment in which the fossils were found.
The new research dated mineral crystals found in volcanic ash layers above and below the sediments that contain the early human bones and concluded they are far older than a 104,000-year-old layer of ash, and very close in age to a layer of ash laid down 196,000 years ago.
"It pushes back the beginning of anatomically modern humans," said geologist Frank Brown, a co-author of the study and dean of the University of Utah's College of Mines and Earth Sciences.
While it had been thought that Omo 2 had more primitive characteristics, co-author John Fleagle, an anthropologist at New York State's Stony Brook University, said the two individuals lived within a few hundred years of each other at the site and that they were either members of overlapping populations, or that the features of Omo 2 represent natural variation within the species.
Brown said the earlier emergence of Homo sapiens "is significant because the cultural aspects of humanity appear much later in the (fossil) record, only 50,000 years ago, which would mean 150,000 years of Homo sapiens without cultural stuff, such as evidence of eating fish, of harpoons, of anything to do with music, needles, even (advanced) tools, except for stone knife blades."
Human ancestors used stone tools as far back as 2.5 million years ago, but sophisticated flaking methods for knives, spear and arrowheads didn't show up until modern man was well-established in Africa. Some recent finds in southern Africa suggest humans were making jewelry and advanced art as long ago as 90,000 to 100,000 years ago, but the artifacts are few in number and their context and symbolism uncertain.
"There is a huge debate in the archaeological literature regarding the first appearance of modern aspects of behavior," Fleagle said. "They only appear as a coherent package about 50,000 years ago, and the first modern humans that left Africa between 50,000 and 40,000 years ago seem to have had the full set.
"As modern human anatomy is documented at earlier and earlier sites, it becomes evident that there was a great time gap between the appearance of the modern skeleton and 'modern behavior,' " Fleagle said.
He also pointed out that the new dates strengthen arguments that modern humans arose exclusively in Africa, rather than rising spontaneously at several locations around the world.
And, the new dates for the fossils match almost exactly the timing of modern human's ascent set by recent genetic studies that plotted the age of our species based on the extent of variations in genes found in people around the world.
On the Net: www.nature.com
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