Two skulls unearthed in Ethiopia may be the oldest known human fossils, dating from the dawn of modern humanity 195,000 years ago, a new analysis shows.
In research made public Wednesday, scientists recalculated the age of the two skulls, discovered in 1967, concluding that they were about 30,000 years older than any other human fossils.
The antiquity of the skulls makes them the only reliable record of a time when anatomically modern humans first appeared among more primitive species in the evolutionary incubator of Africa.
In resolving the age of the fossils, however, the dating experts highlighted a deeper mystery of human evolution that the bones by themselves could not answer: the gap between the advent of modern human anatomy and the awakening of the mind 50,000 to 150,000 years later.
"If it was anatomically modern, why wasn't it culturally modern?" asked geologist Frank Brown at the University of Utah, who helped recalibrate the age of the fossils.
Overwhelming archeological evidence of art, advanced tool use, music and other tokens of modern intelligence first appeared in Europe about 50,000 years ago, many experts believe. A small but growing number of scholars argue that they see earlier, more gradual signs of evolving modern behavior in Africa, starting about 150,000 years ago.
The re-dating of the skulls "goes directly to the issue of the origin of our own species and timing of that event," said anthropologist Philip Rightmire at Binghamton University in New York.
The two skulls, one slightly more primitive in appearance, have puzzled researchers since their discovery in 1967 a few miles apart along the Omo river near Kibish, in southern Ethiopia. They were thought then to be about 130,000 years old, but the dating was uncertain at best.
Experts have argued ever since over the age of the relics, called Omo I and Omo II, and whether they were remains of one human species or two. The features of Omo I, with a more sizable brain case, appear more delicate and modern than those of its companion.
Scientists led by Brown, dean of the University of Utah's College of Mines and Earth Sciences, and geologist Ian McDougall at the Australian National University in Canberra re-dated the skulls by analyzing mineral crystals in volcanic ash layers above and below the siltstone sediments that contained the two sets of bones. They determined the age by examining the rate of decay of unstable isotopes of the element argon in the rocks, according to their report in the current issue of the journal Nature.
