by Dyani Lewis
CT scans revealing the different shapes
Neanderthal skull (left) and the skulls
modern humans at adult, juvenile and fetal stages.
suggests the effects
in modern skulls.
Researchers have gleaned insights into what makes human brains
bulbous from our closest evolutionary relative -
the Neanderthal - despite them
having died out millennia ago, according to an analysis (Neanderthal
Introgression sheds light on Modern Human Endocranial Globularity)
in the journal Current Biology.
Neanderthals and anatomically modern Homo sapiens coexisted in
Eurasia for several thousand years before the former vanished about
40,000 years ago.
But Neanderthals shared more than just their geography with our
They walked like us,
made jewellery and
bone tools like us, and they
bred with us.
In fact, the faint echoes
of those inter-species couplings can be seen in all modern humans
with non-African heritage, in the form of splashes of
Neanderthal DNA dotted throughout the H. sapien genome.
exactly look like us, though. They had shorter legs and
Their heads, too,
looked different. They had larger faces and, despite having
similar sized brains, the backs of their heads - and thus
the brains contained within - were more elongated.
A large international
team headed by Philipp Gunz from the
Max Planck Institute for Evolutionary
Anthropology in Germany has now taken a close look at
those brain shape differences and linked them to the smatterings of
Neanderthal genetic sequences within the genomes of modern
"It's a really novel
approach," says Darren Curnoe, a palaeo-anthropologist from
Australia's University of New South Wales, who was not involved
in the study.
To quantify the brain
shape differences between the species, Gunz and colleagues took
computed tomography (CT)
scans of seven Neanderthal and 19 modern European skulls to generate
virtual imprints of the interior braincase.
The team used the scans to calculate the average differences between
brain shapes of Neanderthals and humans, and came up with a measure
of "globularity" - how globular or elongate the brain is.
They then used this measure on magnetic resonance imaging (MRI)
scans of more than 4000 Europeans for whom genome data was also
available. Across the sample, some brains were more globular than
Next, they turned to the genome data of the cohort and looked at
more than 50,000 locations where Neanderthal DNA sequences can be
Non-Africans have an average 1-2% Neanderthal sequences in their
genome. But because one person's 1% isn't the same as the next
person's 1%, modern humans collectively contain roughly 40% of the
entire Neanderthal genome.
The team looked for instances where the presence of a Neanderthal
sequence was reflected in a less globular brain.
"When we look at
elongated versus round brains, we're looking at differences in
the speed and timing of brain growth," says Gunz.
Before birth, and for the
first two years of development, our skulls are soft and thin and
take on the globular shape of the expanding brain.
"If you grow really
quickly, early on, the thinner the bone and the wider the
sutures, the more round you become," says Gunz.
If brain growth is
slower, he says, the cranial bones are thicker and more resistant,
and the end result is more elongated.
Two Neanderthal genome sequences on chromosomes one and 18 popped
out of the analysis as being associated with less globular brain
shape. In both cases, the sequences aren't located within a gene, so
they don't affect the protein that is being built.
Instead, they lie in
adjacent sequences that can affect how a gene is regulated.
The two genes affected - known as
PHLPP1 - are linked to brain
development (neurogenesis) and the insulation of brain cells (myelination),
The Neanderthal variant of UBR4 dials down activity of the adjacent
In brains, UBR4 is active
in a region known as
the putamen, which is part of the
basal ganglia, an area important for fine motor control and
Mice that lack a functional UBR4 gene develop
microcephaly, a condition where the brain fails to reach its
"Fine motor control
is something needed for speech development," says Gunz, "so
these regions play important role in language acquisition and
"If we want to speculate about what might be the real life
impacts, maybe it takes you a little bit longer to acquire
The presence or absence
of Neanderthal variants at this spot in the genome could explain
some of the huge variation in how long it takes young children to
learn to speak.
"But it's much too
early to tell and it's not clear at all that the Neanderthal
variant is somehow worse than the modern human variant," says
"It might be better."
The Neanderthal variant
near PHLPP1 likely dampens white matter connectivity to the
cerebellum, a region that regulates motor movements.
differences are one of the key distinctions between ourselves
and Neanderthals, and very likely underpins some of the major
behavioral differences between our species," explains Curnoe.
But how much, if at all,
the Neanderthal variants identified in this study impact the
workings of modern brains is unclear.
"It's impossible to
predict what the cognitive correlates might be," says Gunz.
Any differences in modern
humans carrying these variants would be very subtle.
"I don't want to
sound like I'm promoting some new kind of phrenology," he says.
"We're not trying to argue that brain shape is under any direct
selection, and brain shape is directly related to behavior at
It does suggest that, at
least in terms of brain shape, some of those ghostly Neanderthal
sequences do still function in modern humans.
The study is far from the final word on genes controlling brain
"Endocranial shape is
a complex trait," says Gunz. "We expect that it is influenced by
genetic loci, each with only a
Gunz and his colleagues
are now embarking on a far larger study, taking in over 100,000
people whose combined genetic and MRI data will be stored in the
This, it is hoped, will be a large enough sample to shake out rarer
Neanderthal variants that are associated with differences in brain