|
by Brian Vastag
July 26, 2012
from
TheWashingtonPost Website
Neanderthal-type species once roamed Africa, DNA
shows.
There's
only one way the foreign DNA could have made it
into modern
human populations.
"We're
talking about sex," said Joshua Akey of the
University of Washington, whose lab identified
the foreign DNA
in three
groups of modern Africans.
The human family tree just got another - mysterious - branch, an
African "sister species" to the heavy-browed Neanderthals that once
roamed Europe.
While no fossilized bones have been found from these enigmatic
people, they did leave a calling card in present-day Africans:
snippets of foreign DNA.
There's only one way that genetic material could have made it into
modern human populations.
"Geneticists like euphemisms, but
we're talking about sex," said Joshua Akey of the University of
Washington, whose lab identified the foreign DNA in three groups
of modern Africans.
These genetic leftovers do not resemble
DNA from any modern humans. The foreign DNA also does not resemble
Neanderthal DNA, which shows up in the DNA of some modern Europeans,
Joshua Akey said.
That means the newly identified DNA came
from an unknown group.
"We're calling this a Neanderthal
sibling species in Africa," Akey said.
He added that the interbreeding likely
occurred 20,000 to 50,000 years ago, long after some modern humans
had
walked out of Africa to colonize
Asia and Europe, and about the same time Neanderthals were waning in
Europe.
Akey said that present-day Europeans show no evidence of the foreign
DNA, meaning the mystery people were likely confined to Africa.
The find offers more evidence that for thousands of years,
modern-looking humans shared the Earth with evolutionary cousins
that later died out. And whenever the groups met, they did what came
naturally: They bred.
The once controversial idea that humans mated with other species is
now widely accepted among scientists. In fact, hominid hanky-panky
seems to have occurred wherever humans met others who looked kind of
like them.
In 2010, researchers from the
Max Planck Institute for Evolutionary
Anthropology in Germany announced finding Neanderthal
DNA in the genomes of modern Europeans.
Heavyset people whose thick double brows, broad noses and flat faces
set them apart from modern humans, Neanderthals disappeared 25,000
to 30,000 years ago.
Another mysterious group of extinct people known as
the Denisovans - recently
identified from a finger bone in Siberia - also left some DNA in
modern Pacific Islanders.
And while modern humans and the newly found "archaic" Africans might
be classified as distinct species, they managed to produce viable
offspring. Likewise, donkeys and horses, lions and tigers, and
whales and dolphins can mate and make babies.
"They had to be similar enough in
appearance to anatomically modern humans that reproduction would
happen," said Akey.
But with no fossils in hand, it's
impossible to say what these people looked like.
One thing is clear:
This enigmatic group left its DNA
all across Africa.
The researchers found it in the
forest-dwelling pygmies of central Africa and in two groups of
hunter-gatherers on the other side of the continent: the
Hadza and
Sandawe people of Tanzania.
Starting a decade ago, a team led by
Sarah Tishkoff of the
University of Pennsylvania drew blood from five individuals in each
of the three groups. Using the latest genetic technology, Tishkoff
spent $150,000 to read, or sequence, the DNA of these 15 people.
The research was reported Wednesday in the journal Cell.
"This is very cutting-edge
population genetics work," said geneticist Spencer Wells, a
National Geographic explorer.
"This 'whole genome' analysis the team performed is really
revolutionizing our understanding of human history. It's an
exciting time to be in the field, but it's difficult to
interpret all the new data."
Wells said the oldest modern human
skull, found in Ethiopia, dates to 195,000 years ago. For more than
150,000 years, then, humans shared the planet with cousin species.
Despite all the amorous advances, though, only one group survived:
us.
|