The photograph shows the view
from Denisova cave in Siberia, the only place where fossils of Neanderthals and
Denisovans have been found together. Credit MPI-EVA for this photograph and BBC
News for this story.
To truly know who you are
you must know your origins
Once upon a time a very / very
/ very long time ago, two early humans of different ancestry met at a cave in
Russia.
Some 50,000 years later,
scientists have confirmed that they had a daughter together. DNA extracted from
bone fragments found in the cave show the girl was the offspring of a
Neanderthal mother and a Denisovan father.
The discovery, reported in
Nature, gives a rare insight into the lives of our closest ancient human
relatives. Neanderthals and Denisovans were humans like us, but belonged to
different species.
"We knew from previous
studies that Neanderthals and Denisovans must have occasionally had children
together," says Dr. Viviane Slon, researcher at the Max Planck Institute
for Evolutionary Anthropology (MPI-EVA) in Leipzig, Germany. "But I never
thought we would be so lucky as to find an actual offspring of the two groups."
Present-day, non-African humans
have a small proportion of their DNA that comes from Neanderthals. Some other
non-African populations, depending on where they live, also have a fraction of
their DNA that comes from an Asian people known as Denisovans. The fact the
genes have been passed down the generations shows that interbreeding must have
happened.
However, the only known site
where fossil evidence of both Denisovans and Neanderthals has been found is at
Denisova cave in the Altai Mountains of Siberia. And very few -- less than 20
-- so-called archaic humans (those belonging to species other than our own,
Homo sapiens) have had their genomes sequenced.
"Out of this very little
number we find one individual that has half-and-half mixed ancestry," Dr.
Slon told BBC News. When other studies are taken into account, "you start
to get a picture that over all of our evolutionary history humans always mixed
with each other."
The cave was inhabited by a
hermit, Dionisij (Denis), in the Eighteenth Century and was named after him. In
the 1970s, Soviet scientists discovered paleoarcheological remains in the cave
that led to further explorations. So far, 22 strata have been identified, with
archeological artifacts that cover the time from Dionisij back to about
125,000–180,000 years ago.
Neanderthals and Denisovans are
known to have overlapped in time in Eurasia. The two groups lived until about
40,000 years ago; Neanderthals in the west and Denisovans in the east. As
Neanderthals migrated eastwards, they may have encountered Denisovans at times,
as well as early modern humans.
"Neanderthals and
Denisovans may not have had many opportunities to meet," says Svante
Pääbo, director of MPI-EVA. "But when they did, they must have mated
frequently -- much more so than we previously thought."
The girl's story has been
pieced together from a single fragment of bone found in the Denisova cave by
Russian archaeologists several years ago. It was brought to Leipzig for genetic
analysis.
"The fragment is part of a
long bone, and we can estimate that this individual was at least 13 years
old," says Bence Viola of the University of Toronto.
The researchers deduced that
the girl's mother was genetically closer to Neanderthals who lived in western
Europe than to a Neanderthal individual who lived earlier in Denisova Cave.
This shows that Neanderthals migrated between western and eastern Europe and
Asia tens of thousands of years before they died out. Genetic tests also
revealed that the Denisovan father had at least one Neanderthal ancestor
further back in his family tree.