Eden? Maybe. But Where ’s the Apple Tree?
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Fri May 1 17:45:48 UTC 2009
May 1, 2009
Eden? Maybe. But Where’s the Apple Tree?
By NICHOLAS WADE
Locations for the Garden of Eden have been offered many times before,
but seldom in the somewhat inhospitable borderland where Angola and
Namibia meet. A new genetic survey of people in Africa, the largest of
its kind, suggests, however, that the region in southwest Africa
seems, on the present evidence, to be the origin of modern humans. The
authors have also identified some 14 ancestral populations. The new
data goes far toward equalizing the genetic picture of the world,
given that most genetic information has come from European and Asian
populations. But because it comes from Africa, the continent on which
the human lineage evolved, it also sheds light on the origins of human
“I think this is an enormously impressive piece of work,” said Alison
Brooks, a specialist on African anthropology at George Washington
University. The origin of a species is generally taken to be the place
where its individuals show the greatest genetic diversity. For humans,
when the new African data is combined with DNA information from the
rest of the world, this spot lies on the coast of southwest Africa
near the Kalahari Desert, the research team, led by Sarah A. Tishkoff
of the University of Pennsylvania, said in this week’s issue of
Dr. Brooks, who spent many years in the area, said that it had some
trees but that it also had deep sand and was not particularly
garden-like. The area is a homeland of the Bushmen or San people,
whose language is distinguished by its many click sounds. But the San
in the past might not have been restricted to where they are now, she
said. The San are thought to have once occupied a much larger area,
one that probably stretched from southern Africa up the east coast to
as far as present-day Ethiopia.
Since the geneticists’ calculations refer to people, not geography,
the San — and therefore the site of greatest human diversity — might
have been located elsewhere in the past. Christopher Ehret, an expert
on African languages at the University of California, Los Angeles, and
a member of Dr. Tishkoff’s team, has detected traces of words borrowed
from click languages in East African languages. This suggests that
proto-Khoisan, the inferred ancestral language of all click-speakers,
may have originated in East Africa, Dr. Brooks said.
The language of the first modern humans may have undergone a very
early branching, Dr. Ehret said, with the Khoisan click languages on
one branch and the other three language groups of Africa —
Nilo-Saharan, Niger-Kordofanian and Afroasiatic — on the other branch.
Clicks are difficult to pronounce fluently and with a single exception
no click languages are known outside Africa.
Another finding of the Tishkoff-Ehret team is that African languages
tend to be highly correlated with the genetics of their speakers, a
finding that helps indicate cases of language replacement. The various
Pygmy groups in Africa, the team has found, show distant genetic
relationships to the San and other click-speakers, suggesting the
pygmies, too, once spoke Khoisan languages but have now adopted those
of their neighbors.
Another instance of a mismatch between language and genetics concerns
the Luo, an ethnic group in Kenya to which President Obama’s father
belonged. The Luo speak a Nilo-Saharan language and are thought of as
a people of Sudanese origin, but genetically they have a heavy mixture
of Bantu speakers’ genes, Dr. Tishkoff said.
Dr. Tishkoff’s team has also calculated the exit point from which a
small human group — maybe a single tribal band of 150 people — left
Africa some 50,000 years ago and populated the rest of the world. The
region is near the midpoint of the African coast of the Red Sea.
Dr. Tishkoff and her colleagues found that the 14 ancestral African
populations they detected are now highly mixed, with the exception of
the Bantu speakers.
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