Born in Africa_ The Quest for the Origins of Human Life - Martin Meredith [82]
But further research at Berkeley confirmed the initial results. A sample of 189 people, including 121 Africans from six sub-Saharan regions, suggested a common mitochondrial-DNA ancestor in Africa between 166,000 and 249,000 years ago. A Harvard University team, using different mitochondrial tests, produced a date of 220,000 years ago. One study of the complete mitochondrial genome, albeit from only two humans, pointed to an origin date of 176,000 years ago. All the genetic evidence indicated a founding population that lived in Africa in the vicinity of 200,000 years ago. In similar studies, scientists tracking the Y chromosome, a parcel of DNA inherited only through the male line, came up with much the same result.
The fossil evidence to support the theory, however, was sparse. It amounted to little more than odd fragments of bone found in a variety of locations, difficult to date. The most interesting items were finds made in 1967 by Richard Leakey’s Omo team when exploring the banks of the Kibish River in southern Ethiopia. These included a partial skull and skeleton known as Omo I and a second skull, Omo II, both dated at about 130,000 years old but clearly identifiable as Homo sapiens.
A few researchers during the 1970s argued that Omo I—a male—was a far more likely ancestor for the Cro-Magnons than the Neanderthals. Omo I had a higher and rounder skull and a bigger chin than any Neanderthal, and his skeleton suggested he had a taller and lighter frame. A study by Michael Day and Chris Stringer published in 1982 claimed not only that the Omo skeleton belonged to an early modern human but that it possibly came from the ancestral stock of all living humans. Fossil fragments from sites in South Africa—Klasies River and Border Cave—also pointed to modern-looking humans living there as far back as 100,000 years ago. But otherwise, field evidence to support the idea of an African origin was still meagre.
Two subsequent events dramatically changed the picture. In 1997, members of Tim White’s Middle Awash Research Group, exploring a site near the Afar village of Herto, on the Bouri Peninsula, found three fossilised skulls—two adults and a child—which clearly belonged to Homo sapiens. Like modern humans, the adults had small faces tucked under capacious braincases, making the facial profile vertical. The cranial volume of one of them was 1,450 cubic centimetres—large even for modern humans. But the skulls did not provide an exact match: They were slightly larger and longer and their brow ridges were more pronounced, echoing features seen in Homo rhodesiensis /heidelbergensis. Because of the differences, White’s team classified the Herto specimens as a subspecies of sapiens, calling it sapiens idaltu, an Afar word for ‘elder’. White described idaltu as ‘a population that is on the verge of anatomical modernity but not yet fully modern’. The dates were stunning. All three fossils had been found sandwiched between two volcanic layers that were reliably dated to about 160,000 years ago.
The next revelation came when geologists revisited the site in southern Ethiopia where Richard Leakey’s team had found Omo I and II to ascertain a more exact age for the fossils by using advanced dating techniques. Their conclusion, published in Nature in 2005, was that the fossils dated back to 195,000 years ago.
Geneticists added their own flourish. A team from the University of Maryland, led by Sarah Tishkoff, reported in 2003 that genetic analysis of more than 600 living Tanzanians showed that they belonged to one of the oldest known human DNA lineages in the world. The Tanzanians came from fourteen different tribes and four linguistic groups; these included the Sandawe, who speak a ‘click’ language; the Burunge and Gorowaa, who migrated to