“Now there’s a third group that’s neither
Neandertal nor modern human.” — DAvi D Reich
Genes reveal mysterious group of
hominids as Neandertal relatives
10 mm
By Laura Sanders
Neandertals need to make
room for a new member
in the early human family.
By sequencing the full
genome of a girl’s fossil finger bone found in a Siberian
cave, researchers conclude
that a distinct group of early
hominids living in central
Asia about 40,000 years
ago was closely related
to the Neandertals. Data
from the finger and a molar
tooth found in the cave also show that,
like Neandertals, the mysterious group
interbred with modern humans, in this
case leaving behind a genetic legacy in
modern-day Melanesians of Papua New
Guinea and Bougainville Island.
Reported December 23 in Nature,
the work underscores the fluidity of
human evolution and hints that even
more groups are waiting to be uncov-
ered, says paleoanthropologist Milford
Wolpoff of the University of Michigan
in Ann Arbor, who was not involved in
the research. “We’re just scraping the
outside of what’s probably a much more
complex picture.”
Even a year ago, evidence suggested
that modern humans spread through-
out the world in a single migration out of
Africa that wiped out any genetic traces
of other early hominids. But the new
study suggests that the lineage of mod-
ern humans is much more intertwined.
The presence of the ancient group’s
genes in modern-day humans suggests that
it was once widespread throughout Asia.
“This was a place where Neandertals and modern humans were already
known to be living, right in this region,”
says study coauthor David Reich of the
A fossilized molar tooth (shown) and finger bone
offer evidence for a distinct group of early humans.
Broad Institute of MIT and Harvard in
Cambridge, Mass. “Now there’s a third
group that’s neither Neandertal nor
modern human.”
He and his colleagues call the group
“Denisovans,” after the Denisova Cave in
southern Siberia where the finger bone
and tooth were found.
Last year, researchers studied the
mitochondrial DNA from the finger
bone (SN: 4/24/10, p. 5), leading them
to conclude that the girl belonged to a
group that split from the line leading to
modern humans roughly a million years
ago, well before the Neandertal-human
split about 270,000 to 440,000 years ago.
But mitochondrial DNA, a small loop of
genetic material inherited only through
the female line, isn’t as informative as
the DNA packed into cells’ nuclei. So
Reich and his colleagues decided to catalog the finger’s nuclear DNA.
Comparison of the ancient Denisovan genome with that of Neandertals,
whose genome was completed in 2010
(SN: 6/5/10, p. 5), suggests a much closer
relationship than shown by the mitochondrial DNA. A big surprise came,
too, from comparing the Denisovan DNA
with modern-day humans’: DNA samples
from Melanesians carried about 4 to
6 percent of the Denisovan genome.
“It indicates there was gene flow from
Denisovans into modern humans,”
Reich says.
Such a Denisovan genetic stamp
isn’t found in other modern human
populations, suggesting a unique interbreeding event in Melanesian history
that probably took place after a similar
genome mingling between Neandertals
and non-African modern humans.
The study is one of the first examples
of genetic data defining a new ancient
group. “This is kind of a topsy-turvy
world, where now we’re starting from
the genome and going from there to
learn about a new group,” Reich says.
While details about the Denisovan
girl’s life are lacking, her cave may have
been a busy place: Artifacts suggest that
modern humans and Neandertals lived
in close proximity in the region. Mitochondrial DNA thought to belong to a
Neandertal turned up in a site about 100
kilometers away from Denisova Cave.
Mitochondrial DNA studies of the
molar tooth found in the cave show that
it belonged to another Denisovan individual, not to the owner of the finger
bone. The large and unusually shaped
tooth is presumed to be an upper molar
from a young adult. It’s “like nothing
we’ve ever seen before,” Reich says.
But some disagree about the importance of the tooth. Anthropologist Erik
Trinkaus of Washington University in St.
Louis says that the tooth is almost identical to one from a hominid called Oase
2, which he says is “an unquestionable
early modern human.” Reich contends
that the tooth from Oase 2 was likely to
be diseased, and therefore not useful
for comparisons.
For now, details about the Denisovan
group’s appearance and culture remain
unknown. “All we have is this tooth, and
this finger bone and this incredibly informative genome,” Reich says. But after
this new group’s debut, he hopes more
Denisovan bones will start to turn up.
