20 February 2021 | New Scientist | 17MINIATURE brains grown in the
lab are helping to reveal how
modern humans survived when
other hominins died out.
Neanderthals and Denisovans
are some of our closest relatives.
They lived alongside us about
50,000 years ago when modern
humans migrated from Africa, but
they went extinct shortly after we
came into contact with them.
This might be because modern
humans outcompeted them, but
it may have just been bad luck.
Alysson Muotri at the
University of California, San
Diego, and his colleagues wanted
to know more about how our
brains differed from these other
hominins and whether this
could affect survival. His team
compared the genomes of
modern humans, Neanderthals
and Denisovans and found a
total of 61 genes that differed.
One gene, neuro-oncological
ventral antigen 1 (NOVA1),
particularly caught the group’s
eye. The gene is active during
brain development and influences
the developing nervous system.
The team found that the modern
human NOVA1 gene differed from
the Neanderthal and Denisovan
version by a single base pair.
To find out more, the team
used CRISPR genome editing
to change the modern NOVA
gene in human stem cells to
mimic the Neanderthal and
Denisovan version.
The team then prompted
the cells to develop into a brain
organoid – a small, simplified
version of the organ consisting
of clusters of brain cells in a dish.
The group also did the same
with standard human stem cells.
As they matured, the ancient
human organoids were smaller,
had a more wrinkled cell surface
and their cells multiplied more
slowly than the modern human
ones. “They are quite distinct from
modern humans, suggesting that
single base alteration can change
brain development,” says Muotri
(Science, doi.org/fvdh).This alteration also changed the
expression of 277 genes compared
with the modern organoids, and
caused 113 alternative splicing
events – a process that causes
one gene to code for multiple
proteins. Many of these proteins
were linked to brain development.
“The fact that virtually all
modern humans now carry
the modern version of the gene,strongly suggests that the
alteration is a benefit to our
species,” says Muotri. “If I
might speculate, it might suggest
that individuals carrying the
Neanderthal NOVA1^ alteration
have a potential different way to
process information,” he says, and
this may have affected survival.
Tony Capra at the University
of California, San Francisco, says
these new methods allow us to
directly test Neanderthal brains.
“We will be able to evaluate how
the Neanderthal genome worked
in more and more complex and
realistic models,” he says.
However, because Muotri and
his team used a modern human
genome with a single change,
Capra says this doesn’t truly
reflect the entire Neanderthal
or Denisovan genome. “It is
unlikely that a single ‘magic’
genetic change produced a
dramatic positive change in
these traits,” says Capra. He
says there are many parts of
our genome that contribute
to cognition and that evolution
may have acted on multiple
variants with smaller effects. ❚Ibrahim Sawal
C^ SANDI
EG
O^ HEALTHSCIENCE
SAnimal behaviour
Cockroaches munch
each other’s wings in
mutual cannibalism
THE key to a monogamous
relationship is cannibalism – at least
for wood-feeding cockroaches.
Most cases of sexual cannibalism
involve creatures like spiders eating
their suitors after mating. Males are
often the preyed upon. Eating them
could help females fatten up on
nutrients for use during pregnancy.
But males cannibalising females
is rare, and mutual cannibalism
is even rarer. The case of the
wood-eating cockroach may be one
of the only known examples of a
species that practises mutual sexual
cannibalism, says Haruka Osaki
at Kyushu University in Japan.
Osaki first noticed chewed wings
on wood-feeding cockroaches
(Salganea taiwanensis) that he
caught in forests in Okinawa.
To examine the phenomenon
more closely, he and his colleagues
collected wild cockroaches,
divided them into 24 pairs, and
videorecorded them for three days
in enclosures. They found that 12
of the pairs took turns consuming
each other’s wings after mating.The cannibalism was usually
preambled by foreplay in the form
of licking, and the recipients didn’t
appear to resist the love bites when
they came (Ethology, doi.org/fvcj).
The team also noted that the wings
lack flesh, so wouldn’t provide
much in the way of nutrition.
“This wood-feeding cockroach
must benefit somehow because
this behaviour has evolved and
been maintained,” says Osaki.Osaki and his team aren’t sure
why, but they have a few ideas.
These cockroaches usually mate
with one partner for life and stay
together to raise multiple broods
in galleries inside rotting wood.
Clipping each other’s wings may
encourage both partners to stick
around to help raise offspring,
especially as being wingless makes
them more vulnerable to predators
outside the log. Or, it could help
them move around in tight
passages. Removing body parts that
can attract mites or mould might
also help keep their brood cleaner. ❚
Joshua Rapp LearnAncient humans
The brains that time forgot
CRISPR gene editing helps create mini brains with Neanderthal characteristics
“Wood-feeding cockroaches
must benefit because this
behaviour has evolved
and been maintained”Ancient human brain
organoids created
by altering one gene61
Genes differing between
modern and ancient humans