ans cope with high-altitude conditions is
similar to an allele found in the Deniso-
van genome, and likely was acquired many
millennia ago through interbreeding
with the now-extinct species and spread
through the population thanks to natural
selection (Nature, 512:194–97, 2014).
Just when and where did the Deniso-
vans mate with Homo sapiens, and what
migration routes did their mixed offspring
follow? The remains in the Siberian cave
date to between 30,000 and 50,000 years
ago (Nature, 468:1053–60, 2010), and
a 2016 comparison of Denisovan with
modern human genomes estimated that
admixture occurred 44,000–54,000 years
ago (Curr Biol, 9:1241–47). But a study
published in November of last year could
provide a fresh clue—or a red herring.
In it, researchers with Beijing’s Institute
of Vertebrate Paleontology and Paleoan-
thropology and their colleagues excavated
an archaeological site 4,600 meters up
on the Tibetan plateau, unearthing morethan 3,000 stone tool fragments, most of
them from double-sided blades, scattered
through three layers of sediment. Using
a technique called optically stimulated
luminescence, which measures the pho-
tons emitted by minerals and can be used
to estimate the last time sunlight reached a
sample, the team calculated the age of the
tools at between 30,000 and 40,000 years
old. This suggested that the artifacts are
far more ancient than what had previously
been the oldest human settlement found
on the higher, central part of the plateau,
which was dated to around 7,400 years
old (Science, 362:1049–51, 2018; Science,
355:64–67, 2017).
“[W]e did not initially expect to find
archaeological evidence of humans in this
high and challenging environment any
earlier than the Last Glacial Maximum
[LGM] of roughly 18–22,000 years ago,”
notes John Olsen, an anthropologist at the
University of Arizona and a member of the
research team, in an email to The Scien-tist. “As the name implies, the LGM was a
period of relative cold and aridity within
the Pleistocene (Ice Age) and the com-
mon assumption was that initial human
occupation of the high plateau must have
occurred after the LGM... [but this]
seems not to have been the case.”
In an opinion article published
alongside the study, geochronologist
Jia-Fu Zhang of Peking University and
archaeologist Robin Dennell of the Uni-
versity of Exeter—neither of whom were
involved in the research—note that the
site, Nwya Devu, is near a ridge of black
slate that would have provided the raw
materials for the tools. “Because of the
proximity of the site to a large source of
flakable stone, the site is likely a work-
shop where tools were made that were
then used on hunting expeditions at
other locations,” Zhang and Dennell
argue. Furthermore, they write, although
no human remains were found at Nwya
Devu, 40,000-year-old Homo sapiensVIAFLO VOYAGER http://www.integra-biosciences.com
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