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Neanderthal genes influence brain development of modern humans


A characteristic feature of modern humans is the unusually round skull and brain, in contrast to the elongated shape seen in other human species. By studying Neanderthal DNA fragments found in the genomes of living Europeans, scientists have now discovered genes that influence this globular shape. An interdisciplinary research team, led by the Max Planck Institutes for Psycholinguistics and Evolutionary Anthropology, brought together fossil skull data, brain imaging and genomics, as reported in Current Biology.

Neanderthal genes influence brain development of modern humans
Computed tomographic scan of a Neanderthal fossil (La Ferrassie 1; left) and of a modern human (right). One of the
features that distinguishes modern humans from Neanderthals is a globular shape of the braincase. ​The cranium
was cut open virtually to reveal the inside of the braincase [Credit: © Philipp Gunz]
Modern human skulls have a unique 'globular' (round) shape. Our closest cousins, the long extinct Neanderthals, had the elongated skulls that are typical of most primates. This striking shape difference is suspected to reflect evolutionary changes in the relative sizes of structures of the human brain, perhaps even in the ways that key brain areas are connected to each other. However, brain tissue doesn't itself fossilize, so the underlying biological explanation has remained elusive.


An international research team, led by paleoanthropologist Philipp Gunz (MPI, Leipzig) and geneticists Simon Fisher and Amanda Tilot (MPI, Nijmegen), developed a new strategy to investigate this question. The team combined analysis of fossil skulls, ancient genome sequence data and brain imaging.

"Our aim was to identify potential candidate genes and biological pathways that are related to brain globularity," says Tilot. To focus their search, they took advantage of the fact that living humans with European ancestry carry rare fragments of Neanderthal DNA buried in their genomes, as a result of interbreeding between Neanderthals and the ancestors of modern Europeans. Different people carry different fragments, which are scattered through the genome.

Neanderthal genes influence brain development of modern humans
The authors combine paleoanthropology, archaic genomics, neuroimaging and gene expression to study biological
foundations of the characteristic modern human endocranial shape. Shown here are the coordinate measurements
used to capture endocranial shape from magnetic resonance images of several thousand modern humans
[Credit: © Philipp Gunz]
The researchers first used computed tomographic scans of fossil Neanderthal skulls and skulls of modern humans to make endocasts—virtual imprints of the interior of the braincase. They then developed a single measure of globularity, based on the differences in skull shape between humans and Neanderthals. Next, the scientists teamed up with colleagues at the Radboud University, the University of Greifswald and UC Irvine, to determine the degree of globularity of thousands of healthy present-day humans, using data from magnetic resonance imaging.


Although modern human brain and skull shapes are all clearly distinct from those of Neanderthals, the scientists still found considerable differences in globularity among the participants. Finally, the researchers studied the genomes of around 4,500 of the participants to identify the fragments of Neanderthal DNA that each person carried. Would any of these Neanderthal DNA fragments influence brain globularity in their living human sample?

The team found Neanderthal DNA fragments on chromosomes 1 and 18 that were associated with less globular (more elongated) brains. These fragments were associated with altered activity of two genes, UBR4 and PHLPP1, which are already known to play roles in important aspects of brain development (neurogenesis and myelination respectively). The strongest evidence for effects of these Neanderthal DNA fragments on gene activity were in the putamen (in the basal ganglia) and the cerebellum.

Neanderthal genes influence brain development of modern humans
Computed tomographicscan of the Neanderthal fossil from La Chapelle-aux-Saints (left) with a typical elongated
endocranial imprint (red) and of a modern human (right) showing the characteristic globular endocranial shape (blue).
 Arrows highlight the enlarged posterior cranial fossa (housing the cerebellum) as well as bulging of parietal bones
in modern humans compared to Neanderthals [Credit: © Philipp Gunz]
"The potential for links between evolutionary changes in brain globularity and mechanisms affecting the basal ganglia and cerebellum is intriguing," says Gunz. Both structures receive direct input from the motor cortex and are involved in the preparation, learning, and coordination of movements. The basal ganglia also contribute to cognitive functions such as memory, attention, planning, skill learning, and potentially speech and language evolution.


The authors stress that recent archaeological evidence has documented sophisticated symbolic behaviours in Neanderthals that had previously been attributed exclusively to modern humans, such as the enigmatic structure built deep inside Bruniquel cave, and Neanderthal cave-art from Iberia. As Gunz notes, "The focus of our study is on understanding the unusual brain shape of modern humans. These results cannot be used to make inferences about what Neanderthals could or could not do."

"The effects of carrying these rare Neanderthal DNA fragments are really subtle, but detectable due to the large sample size," explains Fisher, adding "This is only our first glimpse of the molecular underpinnings of globularity. Like other aspects of brain structure, globularity is a trait that is likely to be influenced by the combined effects of many different genetic variants."

This animation shows computed tomographic (CT) scans of a Neandertal cranium (left) 
and a recent modern human (right) [Credit: Philipp Gunz]

According to the research team, this discovery generates hypotheses that can be tested with new experiments, for example using human neuronal tissue that can be grown in the laboratory. Gunz and Fisher are now scaling-up the approach for investigations in larger samples such as the UK Biobank. They anticipate that future genome-wide screening studies will reveal additional genes associated with globularity, as well as indicate how this fascinating trait is linked to other aspects of human biology.

Source: Max Planck Society [December 13, 2018]

TANN

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3 comments :

  1. It'd be interesting to know whether brain functionality in the "Neanderthal noggin'" group of the present-day sample (those with more elongated skulls) differed significantly from those with more globular skulls.

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  2. Interesting article, but "This striking shape difference" (long low flat neandertal skull vs globular sapiens skull) "is suspected to reflect evolutionary changes in the relative sizes of structures of the human brain, perhaps even in the ways that key brain areas are connected to each other" is wrong, of course: this is 19th-century phrenology! Skull form has nothing to do with how the brain works, as we can see e.g. in artificial cranial deformation in some ancient societies.
    Comparative anatomy best explains why neandertal & sapiens skulls differed: elongated & flattened skulls are typically seen in swimming species (hydrodynamica). Early-Pleistocene archaic Homo dispersed intercontinentally, not running over open plains (physiologically & otherwise impossible), but simply following the African & southern Eurasian coasts (and from the coast inland along wetlands, lakes & rivers, or - in the other direction - to overseas islands), where brain-specific nutrients (DHA, iodine, taurine, oligo-elements etc.) were abundant. The Littoral Theory (bipedal wading & shallow diving for waterside & aquatic foods) also explains the pachy-osteo-sclerosis (dense & thick, heavy but brittle skeletons) in archaic Homo, as well as the innovations in lithic technology (cf stone tool use in sea- & other otters, marsh-mongoose etc to open shellfish). Google my Hum.Evol.paper "The Aquatic Ape evolves: Common Misconceptions and Unproven Assumptions about the so-called Aquatic Ape Hypothesis" Verhaegen 2013 Human Evolution 28: 237-266".

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  3. Since the Neanderthal brain was larger it seems just as logical to posit that the occipital lobe has shrunk.

    ReplyDelete


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