The DNA doesn't match modern humans or
Neanderthals, two species
that lived in that area around the same time — 30,000 to 50,000 years
ago.
Instead, it suggests the Siberian species lineage
split off from the branch leading to moderns and Neanderthals a million
years ago, the researchers calculated. And they said that doesn't seem
to match the history of human ancestors previously known from fossils.
So the Siberian species may be brand new, although
the scientists cautioned that they're not ready to make that claim yet.
Other experts agreed that while the Siberian species
may be new, the case is far from proven.
"We really don't know," said Ian Tattersall of the
American Museum of Natural
History in New York, who wasn't involved in the new research.
But "the human family tree has got a lot of
branchings. It's entirely plausible there are a lot of branches out
there we don't know about."
The discovery "is like many new finds," said Eric
Delson of Lehman College of the City University of New York, who didn't
participate in the new work. "You say, `I think this is different, but
I'm not sure.' And then you look for more material and you try to make
better comparisons."
The researchers, who say the Siberian species is not a
direct ancestor of modern-day people, hope further genetic analysis
will show if it's a new species. Some experts are skeptical about
whether such analysis will resolve that.
In any case, the finding emphasizes that quite unlike
the present day, anatomically modern humans have often lived alongside
their evolutionary relatives, one expert said.
"We weren't alone," said Todd Disotell of New York
University, who was familiar with the new work. "When we became modern,
we didn't instantly replace everybody. There were other guys running
around who survived quite well until very, very recently."
Just last month, other researchers used DNA analysis
to show the
genetic
diversity still present in residents of Africa, the cradle of the
human race. And another project produced the first genome of an
ancient human — a man who
lived in Greenland some 4,000 years ago.
The new work, published online Wednesday by the
journal Nature, is reported by Johannes Krause and Svante Paabo of the
Max Planck Institute for
Evolutionary Anthropology in Leipzig, Germany, and others.
They describe mapping DNA from what appeared to be a
youngster's pinkie finger bone, which had been recovered in 2008 from
Denisova Cave in
Altai
Mountains of southern Siberia. They showed how it differed from
DNA of 54 modern-day people and six
Neanderthals.
Their analysis indicated the Siberian species last
shared a
common ancestor
with modern humans and Neanderthals about 1 million years ago. That in
turn suggested there was a previously unrecognized migration out of
Africa around that time, they said.
The work decoded the complete set of DNA from
mitochondria, the power plants of cells. That's different from the
better-known DNA that comes from cell nuclei and determines things like
eye color. Paabo said the researchers are working to decode
nuclear DNA from the
Siberian species. That will reveal whether it was closely related to
Neanderthals or today's humans, and answer questions like whether it
interbred with Neanderthals or ancestors of modern-day people, he said.
Without a completed analysis of the nuclear DNA, "we
are not saying this is a new species," Paabo said, although he said
that's a likely possibility.
Rick Potts, director of the
Smithsonian Institution's
Human Origins
Program, said the Siberian find might represent
Homo heidelbergensis or
Homo erectus. And even
analysis of the Siberian species' nuclear DNA won't show if it's
distinct from those ancestors, he said.
As for the study's suggestion of a migration out of Africa about a
million years ago, Potts said there's already evidence of one or two
migrations around that time.
The finger bone recovered from the Siberian species is not enough for a
fossil-to-fossil comparison with other ancient species to show whether
it's a new species, Delson said.
He suspects it might be a descendant of Homo erectus that's already
documented in some fossil remains in northern Africa and Europe.
Scientists are still trying to figure out how many species of the Homo
grouping those bones represent and what name or names to attach to them,
he said.
Disotell said the new creature could be an early version of
Homo antecessor, a
forerunner of Neanderthals and modern humans known from fossils in
Spain. Or, he said, it could be a new species. In fact, the eventual
decision could hinge mostly on the philosophical question of just how
different a creature has to be to be declared a new species, he said.
Potts said that in the new work, "what we're seeing is a really, really
interesting distant echo of the DNA history of
human evolution.... This
is an amazingly powerful technique that these guys have. This is going
to be a growth industry in the study of human evolution."
David Mikael Taclino
Inyu Web Development and Design
Creative Writer
