7 September 2019 | New Scientist | 15Physics Human origins
Leah Crane Michael Marshall
OUR X-ray vision has just got
sharper, thanks to a method of
imaging that uses radiation with
quantum properties.
One problem with X-ray images
is background radiation blurring
the picture. Conventionally, we
have avoided that by shielding the
area or using a huge dose of X-rays.
Now Sharon Shwartz at
Bar-Ilan University in Israel and
his colleagues have developed a
method that works by firing X-rays
into a diamond, which splits them
into two beams. Each photon in
one beam has a corresponding
photon in the other beam with
similar quantum properties.
One beam, called the idler, is
sent straight towards a detector.
The other, called the signal, is shone
through the object to be imaged
before hitting another detector.
Then, the readouts are compared.
Because each idler photon
corresponds to a particular signal
photon, it is easy to determine
which photons are from the
beam and which are just
background. “The photons are
created two by two, kind of like
Noah’s ark,” says Miles Padgett
at the University of Glasgow, UK.
This allowed Shwartz’s team
to make an extremely sharp image.
The picture had about a thousand
times less noise than images
taken with a single beam of X-rays
(Physical Review X, doi.org/c9zf).
The method is also more efficient
than using regular X-rays. “If you
have a better way to distinguish
which photons are coming from
the sample, you don’t have to use
as many of them,” says Shwartz.
“The hope in the long term is to
use this in medical imaging.” ❚
Quantum X-ray
machine takes
super-sharp snaps
FOR the first time, a partial skull
belonging to one of our most
important ancestral species has
been found. It sheds light on a
crucial stage of our evolution.
The skull was discovered in- Yohannes Haile-Selassie
from the Cleveland Museum
of Natural History in Ohio and
his colleagues were excavating
in the Woranso-Mille area of
Ethiopia. One day, a local man
named Ali Bereino approached
Haile-Selassie with an upper
jawbone. It appeared to come
from a human-like species.
Haile-Selassie accompanied
Bereino back to where he had
found it. “Three metres away
from the upper jaw was the
rest of the head,” he says.
The team sieved through the
surrounding sediment, much
of which was buried under
a pile of old goat faeces. This
unpleasant task yielded several
important pieces, including
some of the left cheekbone.
The skull seems to have
belonged to a male. Given
how badly worn his teeth
were, he was probably old
when he died. The ages of the
surrounding rocks suggest he
lived 3.8 million years ago.
“It’s a great find,” says Fred
Spoor at the Natural History
Museum in London.
The team has now identified
the bones as being from
Australopithecus anamensis
(Nature, doi.org/gf69hg;
doi.org/gf69hm).
Australopiths were the main
hominins living in Africa
between 2 and 4 million years
ago. This is several million
years after our ancestors split
from those of chimpanzees.
Australopiths walked upright
as we do, but their brains were
smaller than ours. We know
of several species, including
Australopithecus afarensis:
the species to which the famous
“Lucy” fossil belonged.
A. anamensis is crucial
because it is the oldest known
Australopith species. First
described in 1995, it lived about
4 million years ago. “We alreadyknew quite a lot about
anamensis,” says team
member Stephanie Melillo at
the Max Planck Institute for
Evolutionary Anthropology
in Leipzig, Germany. “But
we didn’t have a cranium.”
According to the team’s
analyses, our ideas about the
evolution of Australopithecus
now need a rethink.
Most anthropologists
agree that A. anamensis is the
ancestor species of A. afarensis,
which is widely thought to have
been our own ancestor. It is
both slightly older and slightly
more ape-like. However,
Melillo, Haile-Selassie and their
colleagues are now questioning
the standard story of how one
gave rise to the other.
Many believe this happened
by anagenesis. “That’s when one
species is evolving and gradually
wholesale turns into another
species,” says Melillo. The
transition from A. anamensis to
A. afarensis has been “one of the
strongest cases for anagenesis
in the fossil record”, she says.
But when the team compared
the new A. anamensis skull
with those from other
hominins, they concluded that
a previously unidentified bone
from 3.9 million years ago is
from A. afarensis. This is older
than the A. anamensis skull,
so the entire older species can’t
have gradually transformed
into the younger one.
Instead, they say, the
A. anamensis population must
have split in two, with one half
giving rise to A. afarensis and
the other hanging on as
A. anamensis for at least
100,000 years.
Spoor says this suggestion
is probably right, but that the
evidence against anagenesis
isn’t yet conclusive. ❚Skull from one of our early
ancestors found at last
We may
directly
descend
from
A. anamensisDALE OMORI, COURTESY OF THE CLEVELAND MUSEUM OF NATURAL HISTORYCMNH/MATTCROW1000
Number of times less background
radiation in new X-ray images
This skull came from
an Australopithecus
anamensis