20 THE SCIENTIST | the-scientist.com
XING GAONOTEBOOKremains have been found in a cave in
northern China, suggesting that the peo-
ple who made the tools were not Deniso-
vans, Neanderthals, or another relative,
but belonged to our species. Thus, the
finding appears to push back the date of
Homo sapiens presence in one of Earth’s
harshest environments.
Ye t the study raises more questions
than it answers. For one, if the ancientblade-makers really were Homo sapiens,
were they the ancestors of today’s Tibet-
ans, or a people who later vanished from
the plateau? Rasmus Nielsen, a genet-
icist at the University of California,
Berkeley, who led the study that identi-
fied the Denisovan origins of EPAS1 but
was not involved in the current study,says that work on ancient DNA indi-
cates that two key altitude-coping genes
did not come under selective pressure
in the Tibetan genome until around
4,000 years ago, or even later, making
it unlikely that Tibetans’ ancestors had
settled at high altitudes many millennia
before that. But without human remains
at the site, “what these people were, and
how they’re related to modern Tibetans... we don’t know about that,” he adds.
Olsen says the team plans to address
this gap in the human fossil record; its
members will continue their work at
Nwya Devu and other sites on the pla-
teau this summer. One question Olsen
is especially interested in addressing is
where the toolmakers came from. “The
tools from Nwya Devu most closely
resemble contemporaneous artifacts
from Xinjiang (in northwest China),
Mongolia, and southern Siberia in Rus-
sia,” he writes to The Scientist. “Is this
pattern indicative of the directionality
of the initial settlement of the Tibetan
Plateau? We just don’t know the answer
to that question yet, and it will require
a much more robust sample size than
one site located in the middle of such a
large plateau.”
It’s also not clear whether early
humans on the plateau settled there, or vis-
ited intermittently. Mark Aldenderfer, an
archaeologist at the University of Califor-
nia, Merced, who was not involved in the
study but has collaborated with Olsen in
the past, says some archaeologists believe
the plateau could only have been perma-
nently occupied beginning around 5,200
years ago, once humans had agriculture
to help sustain them (Science, 347:248–
50, 2015). Aldenderfer has disputed this,
arguing that archaeological evidence,
and some currently available genetic evi-
dence, points to permanent occupation
of the plateau at sites more than 7,000
years old. For example, a 2013 analysis of
Y-chromosome and mitochondrial DNA
lineages in present-day Tibetans found
evidence for two waves of migration to the
area, with the first dated to about 30,000
years ago (Mol Biol Evol, 30:1761–78).
Humans would not have had much
success sustaining pregnancies and
establishing a long-term population atop
the plateau unless they had genes to help
them adapt—which is where Denisovans
may or may not come in. Nielsen says that
if Homo sapiens were braving the plateau
as early as the new study suggests, they
might even have interbred with Den-
isovans there, although he doesn’t con-
sider that the most likely scenario. That’s
because Denisovan alleles are also found
in some other East Asian populations,
suggesting they were acquired before the
plateau’s colonization.
The authors of the paper suggest a
different possibility, citing the similarity
of the Nwya Devu tools to others found
in Siberia, and the prevalence of Deniso-
van DNA in modern Melanesians: that
the Tibetan Plateau might have been one
area through which genetic traces of the
Denisovans made their way south across
the Homo sapiens population, confer-
ring tolerance to high altitude along the
w ay. Whoever the people at Nwya Devu
were, Zhang and Dennell write, their
discovery “provides a graphic example
of how successful our species has been
as a colonizing animal.”
—Shawna WilliamsTIBETAN TOOLS: Most of the 3,000 fragments
were from double-sided blades.The team calculated
the age of the tools at
between 30,000 and
40,000 years old.