Scientists have identified the remains of the oldest known modern humans. They are nearly 200,000-year-old skulls from Ethiopia, dating back almost to the time when modern people evolved in Africa from earlier beings. The date means they are more than 40,000 years older than what anthropologists thought were the oldest human remains. Experts say the finding provides new information about early humans who roamed the earth.
The two skulls were originally excavated from near Kibish, Ethiopia, in 1967 by a team, including world renowned archaeologist Richard Leakey. Earlier scientific dating estimated them to be about 130,000 years old. But even at that age, they were not the oldest known modern humans. That distinction fell to other relics from Ethiopia estimated to be about 160,000 years old.
Now, a new analysis of the Kibish River skulls using new dating techniques puts their age at just under 200,000 years, confirming that they are the oldest known examples of human species.
Paleontologists believe modern humans, called Homo Sapiens, developed from more primitive humans between 200,000 and 250,000 years ago. They are thought to have then migrated out of Africa after developing modern skills, such as hunting, spear making and cave painting about 40,000 to 165,000 years ago.
But study co-author John Fleagle of New York State's Stony Brook University says the new dating of the bones suggests that our ancient ancestors may have learned these skills at an earlier time.
"What this shows is that there were modern humans in Africa nearly 200,000 years ago," he explained. "So there's a huge amount of our history that is essentially African and almost three-quarters of our history took place in that continent, and much of that record is still present in our genetics today."
The Kibish skulls were discovered 38 years ago at the bottom of the rocky layers of dried sediments of a lake washed back and forth from the Mediterranean for thousands of years. Among the layers of river sediments are occasional deposits of volcanic ash from ancient eruptions, which encased the relics. It was an analysis of those sediments that was used in determining the age of the bones.
What convinced the scientists that the date is correct is corroborating evidence from the Mediterranean seafloor. Layers of Mediterranean sediments washed from the Ethiopian lake during ancient floods corresponded exactly in age to the lake deposits.
University of Utah geologist Frank Brown played a key role in figuring out the age of the relics.
"We think this is absolutely wonderful that we actually have correlations between the deep sea and a big system on land in the middle of the African continent," he said, "because we can see the climatic effect on deposition in southern Ethiopia and northern Kenya."
Experts say there is little information about the fossil record of humans from 100,000 to 500,000 years ago. They say modern human remains found throughout Africa have been hard to date, which is why the latest finding is so important.
Curiously, one of the skulls appears more primitive than the other, despite the similarity in age. John Fleagle at Stony Brook University says it could mean there were contemporary groups of different, perhaps slightly less modern Homo Sapiens, or there was natural variation within one population.
"This is not unusual. At many of the sites where people have found early modern humans, there seems to be a diversity of morphologies [shapes] there," he said.
The variation in the skulls is one issue anthropologists like Christopher Stringer of the Natural History Museum in London are trying to resolve.
"What's interesting, I think now, is that it opens up the question of did modern humans originate just in one area? East Africa certainly is leading the way in a sense now in all of east Africa as being the place that has the earliest remains of modern humans," he said. "So, was that in fact an area of origin, or were we picking up a bit of the story in this region. I don't think we know that yet."
Details of the aging of the fossils are published this week in the journal Nature.