Jan 12, 2007
A 36,000-year-old skull from South Africa provides the first fossil evidence that modern humans left Africa 70,000 to 50,000 years ago to colonize Eurasia, new research suggests.
"Up until a few years ago, this was largely just a theory based on some genetics," said Ted Goebel, an anthropologist at Texas A&M University who was not involved in the study.
"We're beginning to accumulate evidence from archaeology, from genetics, from physical anthropology that support this model or theory that modern humans spread out of Africa … 60,000 or 70,000 years ago," he said.
Scientists today can only theorize about how anatomically modern humans, who appeared in East Africa by 195,000 years ago, spread across the continent to the Middle East, Asia, Australia, and Europe.
The mystery endures in large part due to the scarcity of human fossils in sub-Saharan Africa dating to 70,000 to 15,000 years ago, Goebel says.
The "out of Africa" theory holds that modern humans left East Africa only relatively recently, pushing into southern Africa, the Middle East, Eurasia, and Australia sometime between 70,000 to 50,000 years ago.
This theory is bolstered not only by this latest discovery but also by a separate find in Russia, in which human teeth and artifacts have been dated to around the same age as the South Africa skull.
The results of both discoveries appear in the current issue of the journal Science.
The skull study was led by Frederick E. Grine, an anthropologist and anatomist at Stony Brook University on Long Island, New York.
The fossil was originally unearthed from a riverbed near Hofmeyr, South Africa, in 1952 but was never accurately dated.
Grine says he first spotted the skull on a bookshelf in a colleague's office in Cape Town, South Africa, and was struck by its similarities to the skulls of the first modern humans found in Europe.
This inspired him to reexamine the skull.
Unable to date it via traditional radiocarbon techniques, Grine sent sand grains pried from the skull's braincase to colleagues at England's Oxford University.
There study co-author Richard Bailey and colleagues used advanced optical and uranium-dating techniques to determine when quartz crystals in the sand were last exposed to sunlight.
The answer—36,000 years ago—gave them the age of the skull.
A study co-author, Katerina Harvati of Germany's Max Planck Institute for Evolutionary Anthropology, then compared the skull to those of Neandertals, members of present-day ethnic groups, and European humans from the Late Ice Age (from about 35,000 to 11,500 years ago).
Grine says the skull bore surprisingly little resemblance to Khoe-San, also known as Bushmen, who have occupied South Africa for at least 15,000 years.
"Indeed [the skull's] closest affinities were to people from Europe [from the Late Ice Age]," he said.
"This would indicate to me that the skull is very similar to what we would have seen in eastern Africa at the same time."
"In other words, when I look at this skull, it looks like the most recent common ancestor of all modern people."
In a related Science commentary, Goebel, of Texas A&M, wrote, "Here is the first skull of an adult modern human from sub-Saharan Africa that … can speak to the relationship of early moderns from Africa and Europe."
Discovery in Russia
In the second Science study, archaeologist Mikhail V. Anikovich and a team of scientists shed light on the possible routes taken by humans after they left Africa.
The team investigated an array of human teeth and artifacts found on the Don River, about 250 miles (400 kilometers) south of Moscow, and dated them to around 45,000 years ago.
Modern humans are believed to have spread into central and western Europe about 40,000 years ago.
Anikovich's finding suggests that humans may have migrated to Eastern Europe slightly before settling the central and western regions of the continent.
"It's surprising to find [modern humans] showing up so early in one of the coldest and driest parts of mid-latitude Europe," said study co-author John Hoffecker, an archaeologist at the University of Colorado at Boulder.
"It is perhaps the last place we would expect some recent immigrants from the tropical zone to be occupying," he added.