Neanderthal-Derived Genetic Variation Shapes Modern Human Cranium and Brain

The most recent evolutionary relative of Homo sapiens –– Homo neanderthalensis –– represents a lineage associated with archeological samples (e.g., tools, pigments) suggesting substantial cognitive achievements, and is typically contrasted with anatomically-modern humans by particular cranial features known from fossil remains. The initial DNA sequencing of the Neanderthal genome summarily unearthed an unprecedented ingress to Neanderthal biology, resulting not only in a catalog of shared ancestral alleles and divergent variation relative to H. sapiens but also evidence for gene flow from Neanderthals to modern humans, which continues to be increasingly supported by additional studies. Introduction of Neanderthal alleles was believed to have occurred in Eurasia, as modern humans ventured out of Africa, between 47,000 and 65,000 years ago and accounts for about 2% of the entire non-African human genome. The functional implications of this observation, however, are not fully understood. In fact, the recent GEITP email we shared (just earlier this week) suggested that the breeding of a female H. sapiens and male H. neaderthalensis resulted in subsequent Neanderthal generations having Homo sapiens mitochondria derived from that female.

If these DNA sequencing studies are biologically meaningful for their modern bearers, and, by extension, for their extinct originators, then individuals endowed with greater proportions of Neanderthal-derived sequence differences might be expected to harbor Neanderthal-like phenotypes. To test this hypothesis, rather than using an additive model in a genetic association analysis, authors [see attached] performed linear regressions of polygenic measures of Neanderthal-derived common variant data with magnetic resonance imaging (MRI) data. Previous reports have described methods for testing whether single-nucleotide polymorhpisms (SNPs) are derived from admixture of modern humans with Neanderthals.

Herein, using MRI in a large cohort of healthy individuals of European-descent, authors show the amount of Neanderthal-originating polymorphism carried in living humans is related to cranial and brain morphology. First, as a validation of their approach, authors demonstrate that a greater load of Neanderthal-derived genetic variants (higher “NeanderScore”) is associated with skull shapes resembling those of known Neanderthal cranial remains –– particularly in the occipital and parietal bones. Lastly, authors demonstrate convergent NeanderScore-related findings in the brain (measured by gray- vs white-matter volume, sulcal depth, and gyrification index) –– that localize to the visual cortex and intraparietal sulcus. These findings provide additinal insight into ancestral human neurobiology and suggest that Neanderthal-derived genetic variation is neurologically functional in our modern-day human population.

Sci Rep July 2o17; 7: 6308 doi:10.1038/s41598-017-06587-0

COMMENT: The story gets more complicated. We need more fossils to test.

COMMENT: It’s just like any field of science –– and not that different from peeling an onion.
“Peel away one layer (and you think you now have found all “the answers”), but then the next layer presents you with unanticipated complications –– which lead to new hypotheses, further testing of those hypotheses, and (usually) alterations/adjustments in our previous conclusions..!!”


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