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January/February 2018^ DISCOVER^11
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It Takes Two
For years, paleogenetic studies
have been turning up hints
that our species interbred
with Neanderthals and
Denisovans between 40,
and 100,000 years ago. A
Nature Communications study
published in July, however,
found evidence the hook-ups
began much earlier: roughly
220,000 to 470,000 years ago.
Researchers extracted
maternally inherited
mitochondrial DNA (mtDNA)
from a 100,000-year-old
Neanderthal bone found in
a German cave in the 1930s.
The mtDNA is from a Homo
sapiens female who evolved
in Africa — our homeland —
and mated with a European-
evolved Neanderthal at least
220,000 years ago.
But the woman, who
passed her mtDNA down
through the Neanderthal
lineage, was not necessarily an
anatomically modern human,
notes paleogeneticist Johannes
Krause, a co-author of the
study. Although he agrees
recent evidence pushes back
the start date for our species,
Krause said the definition
of a modern Homo sapiens
remains subjective.
“The process of humans
evolving into anatomically
modern humans started
700,000 years ago,” says
Krause. That’s when genomic
models estimate the last
common ancestor of Homo
sapiens, Neanderthals and
Denisovans existed. “It’s a
gradual change. They didn’t
pop out of a box.”
Turning Up Down Under
The conventional timeline placed our species
in Australia at no earlier than about 47,
years ago, despite some archaeological and
genomic research hinting at a much earlier
arrival date. In July, however, a team reported
in Nature that thousands of artifacts from a
Northern Australia site were
about 65,000 years old.
And in August, also in
Nature, a separate team
reported that they believe
teeth found in an Indonesian
cave belonged to anatomically
modern humans who had
occupied the site 63,000 to
73,000 years ago.
That puts modern humans
far from home tens of
millennia before the now-
outdated human evolution
and migration timeline had
us even leaving Africa.
EASTERN MASH-UP
A pair of partial hominin skulls excavated in Xuchang,
China, are unlike any others.
Dated to more than 100,000 years old, the crania
have a unique blend of features: the internal ear
structure and back-of-skull depression seen only in
Neanderthals, which have never been found east of
Siberia; a low and broad shape consistent with earlier
East Asian hominins; and an enlarged braincase similar
to other late archaic and modern humans.
Trinkaus and colleagues, describing the partial
skulls in March in Science, won’t speculate on whether
they belonged to Homo sapiens transitioning from
archaic to modern, the elusive Denisovans or an
as-yet-unidentified hominin species.
“People have been thinking in terms of lineages
and discrete groups,” Trinkaus says, “These are not
separate entities. There’s a unity to humankind now,
and there was then.”
A top-down
view of a
partial skull
unearthed in
China. The
find is more
than 100,
years old and
shows a blend
of Neanderthal
and hominin
features.
A scan (bottom)
of a tooth (top)
that suggests
anatomically
modern
humans were
in Australia
many millennia
before we
TOP: XIUJIE WU. BOTTOM: TANYA SMITH AND ROKUS AWE DUE thought.