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Oldest bones of our species
identified, researchers say
Posted Feb. 16, 2005
Courtesy the University of Utah, Nature
and World Science staff
A new study has identified what may be the oldest known bones of our species, which suggest humans roamed Africa about 195,000 years ago, researchers say.
This indicates there was a great time lag between when our species evolved and when it started “acting” modern, around 50,000 years ago, the scientists add.
The bones themselves are no new discovery. They were found in 1967 near Kibish, Ethiopia, but
were originally thought to be about 130,000 years old. A new analysis indicates they’re much older, which “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.
The research journal Nature is publishing the study in its Feb. 17 issue. Brown conducted the research with Ian McDougall of Australian National University in Canberra, and John Fleagle of New York state’s Stony Brook University.
“These are the oldest well-dated fossils of modern humans (Homo sapiens) currently known anywhere in the world,” the scientists wrote in a summary of the study. The previously oldest-known human bones are thought to be about 160,000 years old, they said.
Brown said pushing the emergence of Homo sapiens from that time period back to about 195,000 ago, give or take 5,000 years, shows there
was a major time lag between the origin of the species and the time we developed a true culture.
“The cultural aspects of humanity in most cases appear much later in the record – only 50,000 years ago,” Brown said. This “would mean 150,000 years of
Homo sapiens without cultural stuff,” such as evidence of eating fish, of harpoons, anything having to do with music, needles and tools, he said.
“This stuff all comes in very late, except for stone knife blades, which appeared between 50,000 and 200,000 years ago, depending on whom you believe.”
Fleagle added: “There is a huge debate in the archeological literature regarding the first appearance of modern aspects of behavior such as bone carving for religious reasons, or tools (harpoons and things), ornamentation (bead jewelry and such), drawn images, arrowheads. 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.’”
The study moves the date of human skulls found in the Kibish rock formation back from 130,000 years to a newly determined date of 195,000 years
ago. Some of the fossils, from an individual known as Omo I, look like bones of modern humans, but others are from a more primitive cousin named Omo II.
In addition to the cultural question, the researchers said, the earlier date for humanity’s emergence is important for other reasons. First, it makes the dates in the fossil record agree almost exactly with the dates suggested by genetic studies for the origin of our species, Fleagle said.
“Second, it places the first appearance of modern Homo sapiens in Africa many more thousands of years before our species appears on any other continent. It lengthens that gap. … Finally, the similar dating of the two skulls indicates that when modern humans first appeared there were other contemporary populations [Omo II] that were less modern.”
In 1967, a team of paleontologists led by Richard Leakey traveled to the rock
formation, along the Omo River in southernmost Ethiopia. They found parts of the skull, arms, legs, feet and the pelvis of Omo I, and the top and back of the skull of Omo II. Brown was working nearby at the time and got to see the site and fossils.
“Anthropologists said they looked very different in their evolutionary status,” Brown recalls. “Omo I appeared to be essentially modern Homo sapiens, and Omo II appeared to be more primitive.”
In 1967, the fossils were dated as being 130,000 years old. But scientists doubted the accuracy of their dating technique, which was based on the decay of radioactive uranium-238 in oyster shells from a rock layer near the skulls. Because radioactive elements decay at known rates, one can estimate the age of objects containing them,
but the technique involves some uncertainties.
Fleagle says no scientist has suggested Omo II is anything other than Homo
sapiens. Now that the new study confirms Omo I and Omo II are the same age – living within a few hundred years of each other about 195,000 years ago – some anthropologists suggest “maybe it [Omo II] isn’t so primitive after all,” Brown says.
McDougall, Brown and Fleagle and other researchers returned to Kibish between 1999 and 2003. They identified sites where Omo I and Omo II were found in 1967, and obtained more of Omo I, including part of the femur (upper leg bone) that fit a piece found in 1967. The
Nature study includes initial results from those expeditions.
The fossil record of human ancestors may go back 6 million years or more. The genus
Homo, a group which includes Homo Sapiens, arose at least 1.8 million years ago when human-like primates called australopithecines evolved into human ancestors known as
Homo habilis. Brown says the fossil record of humans is poor from 100,000 to 500,000 years ago, so Omo I is significant because it now is well dated.
Omo I and Omo II were buried in the bottom portion of the Kibish Formation, a series of deposits laid down by floods of the ancient Omo River at the mouth of Lake Turkana.
The researchers examined the rate of decay of radioactive forms of the element argon in the rocks. The average age estimate is around 196,000 years, they said. This agrees almost exactly with an age arrived at by another technique, they added, which involves dark rock layers on the Mediterranean seafloor deposited when the Nile River flooded. The study found that the groups of rock layers of the Kibish formation were laid down at the same time as the these dark layers formed 195,000 years ago. “It is pretty conclusive,” said Brown.
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