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http://www.sciencedaily.com/releases/2010/11/
101108140421.htm
Brains of Neanderthals and Modern Humans Developed Differently
enlarge
The brains of Neanderthals and modern humans are very similar at the time of
birth. A reconstruction of a Neanderthal baby is compared to a modern human
newborn. While the face of the Neanderthal is already larger than in a modern
human at the time of birth, their brain shapes and volumes are very similar.
Internal casts of brain cavities of skulls (Neanderthal: red; modern humans:
blue) provide information about the relative size and form of the brain.
(Credit: Max Planck Institute for Evolutionary Anthropology)
ScienceDaily (Nov. 9, 2010) Researchers at the Max Planck Institute for
Evolutionary Anthropology in Leipzig, Germany have documented species
differences in the pattern of brain development after birth that are likely to
contribute to cognitive differences between modern humans and Neanderthals.
Whether cognitive differences exist between modern humans and Neanderthals is
the subject of contentious disputes in anthropology and archaeology. Because
the brain size range of modern humans and Neanderthals overlap, many
researchers previously assumed that the cognitive capabilities of these two
species were similar. Among humans, however, the internal organization of the
brain is more important for cognitive abilities than its absolute size is. The
brain's internal organization depends on the tempo and mode of brain
development.
Based on detailed measurements of internal shape changes of the braincase
during individual growth, a team of scientists from the MPI has shown that
these are differences in the patterns of brain development between humans and
Neanderthals during a critical phase for cognitive development.
Discussions about the cognitive abilities of fossil humans usually focus on
material culture (e.g. the complexity of the stone tool production process) and
endocranial volumes. "The interpretation of the archaeological evidence remains
controversial, and the brain-size ranges of Neanderthals and modern humans
overlap," says Jean-Jacques Hublin, director of the Department of Human
Evolution at the MPI-EVA in Leipzig where the research was conducted. Hublin
adds, "our findings show how biological differences between modern humans and
Neanderthals may be linked to behavioural differences inferred from the
archaeological record."
As the brain does not fossilize, for fossil skulls, only the imprints of the
brain and its surrounding structures in the bone (so called "endocasts") can be
studied. The researchers used state-of-the-art statistical methods to compare
shape changes of virtual endocasts extracted from computed-tomographic scans.
The distinct globular shape of the braincase of adult Homo sapiens is largely
the result of a brain development phase that is not present in Neanderthals.
One of the key pieces of evidence was the skull reconstruction of a Neanderthal
newborn. In 1914, a team of French archaeologists had excavated the skeleton of
a Neanderthal baby at the rock shelter of Le Moustier in the Dordogne. The
original bones of the skeleton had been lost to science for more than 90 years,
until they were rediscovered among museum collections by Bruno Maureille and
the museum staff. The restored original baby bones are now on permanent display
at the Musée National de Préhistoire in Les
Eyzies-de-Tayac-Sireuil. The museum's director Jean-Jacques Cleyet-Merle made
it possible to scan the delicate fragments using a high-resolution
computed-tomographic scanner (µCT). Using computers at the Max Planck
Institute's virtual reality lab in Leipzig, Philipp Gunz and Simon Neubauer
then reconstructed the Neanderthal baby from the digital pieces, like in a
three-dimensional jigsaw puzzle.
"When we compare the skulls of a Neanderthal and a modern human newborn, the
Neanderthal's face is already larger at the time of birth. However, most shape
differences of the internal braincase develop after birth," explains Gunz. Both
Neanderthals and modern human neonates have elongated braincases at the time of
birth, but only modern human endocasts change to a more globular shape in the
first year of life. Modern humans and Neanderthals therefore reach large adult
brain sizes via different developmental pathways.
In a related study, the same team of MPI researchers had previously shown that
the developmental patterns of the brain were remarkably similar between
chimpanzees and humans after the first year of life, but differed markedly
directly after birth. "We interpret those aspects of development that are
shared between modern humans, Neanderthals, and chimpanzees as conserved,"
explains Simon Neubauer. "This developmental pattern has probably not changed
since the last common ancestor of chimpanzees and humans several million years
ago." In the first year of life, modern humans, but not Neanderthals, depart
from this ancestral pattern of brain development.
Establishing when the species differences between Neanderthal and modern human
adults emerge during development was critical for understanding whether
differences in the pattern of brain development might underlie potential
cognitive differences. As the differences between modern humans and
Neanderthals are most prominent in the period directly after birth, they likely
have implications for the neuronal and synaptic organization of the developing
brain.
The development of cognitive abilities during individual growth is linked to
the maturation of the underlying wiring pattern of the brain; around the time
of birth, the neural circuitry is sparse in humans, and clinical studies have
linked even subtle alterations in early brain development to changes in the
neural wiring patterns that affect behaviour and cognition. The connections
between diverse brain regions that are established during this period in modern
humans are important for higher-order social, emotional, and communication
functions. It is therefore unlikely that Neanderthals saw the world as we do.
The new study shows that modern humans have a unique pattern of brain
development after birth, which separates us from our closest relatives, the
Neanderthals. This uniquely modern human pattern of early brain development is
particularly interesting in light of the recent breakthroughs in the
Neanderthal genome project. A comparison of Neanderthal and modern human
genomes revealed several regions with strong evidence for positive selection
within Homo sapiens, i.e. the selection occurred after the split between modern
humans and Neanderthals. Three among these are likely to be critical for brain
development, as they affect mental and cognitive development.
"Our findings have two important implications," says Philipp Gunz. "We have
discovered differences in the patterns of brain development that might
contribute to cognitive differences between modern humans and Neanderthals.
Maybe more importantly, however, this discovery will tell us more about our own
species than about Neanderthals; we hope that our findings will help to
identify the function of some genes that show evidence for recent selection in
modern humans."
Editor's Note: This article is not intended to provide medical advice,
diagnosis or treatment.
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Story Source:
The above story is reprinted (with editorial adaptations by ScienceDaily
staff) from materials provided by Max-Planck-Gesellschaft, via AlphaGalileo.
Journal Reference:
1. Philipp Gunz, Simon Neubauer, Bruno Maureille and Jean-Jacques Hublin.
Brain development after birth differs between Neanderthals and modern humans.
Current Biology, Volume 20, Issue 21, R921-R922, 9 November 2010 DOI:
10.1016/j.cub.2010.10.018
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Max-Planck-Gesellschaft (2010, November 9). Brains of Neanderthals and modern
humans developed differently. ScienceDaily. Retrieved November 10, 2010, from
http://www.sciencedaily.com /releases/2010/11/101108140421.htm
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