January 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.
(See an interactive map of early human migration.)
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.
Skull Analysis
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.
Common Ancestor
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.
(Read related story about Bushmen: "'Python Cave' Reveals Oldest Human Ritual, Scientists Suggest" [December 22, 2006].)
"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.
http://news.nationalgeographic.com/news/2007/01/070112-africa-skull_2.html
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