42 | New Scientist | 12 September 2020related to living orangutans – an idea that
matched expectations.
What made the result particularly
intriguing was that the Gigantopithecus
tooth the researchers sampled is 1.9 million
years old and came from a subtropical cave
in southern China. That is exactly the sort
of place in which H. erectus and enigmatic
species like H. naledi have lived over the
past 1.9 million years. The implication
is that the fossils they left behind might
contain enough protein to work out where
they fit in the hominin evolutionary tree.
“The Gigantopithecus study definitely
pushed the boundaries of what we know
about protein preservation,” says Jessica
Hendy at the University of York, UK.
By the time the Gigantopithecus paper came
out, the researchers had already moved on
from apes to hominins. A few months earlier,
Welker and his team had published work
describing the dentine proteome from a
160,000-year-old hominin jaw. The fossil,
they concluded, may have belonged to a
Denisovan. It was a conclusion with profound
implications, because the jawbone had been
found 3280 metres above sea level on the
Tibetan plain. Perhaps, they suggested,
Denisovans adapted to life at such altitudes.
Earlier this year, Welker and Cappellini
notched up another success. Their team
reconstructed an enamel proteome from
a tooth that was potentially 950,000 years
old and that belonged to another poorly
understood early human, Homo antecessor,
that once lived in Spain. The information
within the proteome firmed up the idea
that H. antecessor was closely related to
the common ancestor our species shared
with Neanderthals and Denisovans. It was
spectacular proof that ancient proteins
really can shine a light on the murkier early
chapters of our evolutionary history.
Now thoughts are turning to the
contentious hominins that walked Earth
more recently, particularly the Indonesian
“hobbit” (Homo floresiensis), discovered
in 2003, and H. naledi. Both were alive when
our species, Homo sapiens, evolved about
MA300,000 years ago, but both show a truly
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bizarre mix of features. H. floresiensis had a
chimpanzee-sized brain inside a miniature
H. erectus-like skull, while its shoulders,
wrists and feet are reminiscent of the ape-like
hominins, including the famous Lucy, that
lived in Africa more than 2 million years
ago. H. naledi, meanwhile, had a brain only
marginally larger than a chimpanzee’s,
hands that looked a little like Lucy’s and feet
very similar to those of living humans.
We still have no idea where either
H. floresiensis or H. naledi sits on the
human evolutionary tree. We don’t even
know whether they really are humans
that ultimately descended from a species
like H. erectus, or whether they group with
the ape-like hominins.Fresh clues
Both scenarios are plausible – and proteins
should help us figure out which is right,
says Welker. This is because the amino
acid sequences within proteins change
at a relatively constant rate, like a clock. It
isn’t a very accurate clock, he says, but by
comparing the ancient protein sequences
with similar sequences from living people,
it should be possible to determine whether
H. naledi and H. floresiensis branched off our
family tree a few hundred thousand years
ago – making them human – or more than
2 million years ago, when the Lucy-like
hominins had their heyday.
Collins says he is involved in ongoing
discussions about putting an H. naledi
specimen under the drill to extract proteins.
There is no official word on when – or if – the
work will go ahead. However, Lee Berger at
the University of the Witwatersrand, South
Africa, who leads the H. naledi research, says
he was due to take fossil samples to Europe
several months ago, only for the coronavirus
pandemic to thwart the plans.
Within a few years, then, proteins might
help some of our more inscrutable relatives
find a place in the human family tree.
Whether or not the scientists who study
hominin fossils will accept the evidence
from protein analysis is another matter.Clockwise from top left:
Homo neanderthalensis,
Homo antecessor, Homo
erectus and Homo sapiens“ We still have
no idea where
Homo naledi sits
on the human
evolutionary tree”