Round skulls and brains are defining features of humans, but a new study has found that some individuals with specific Neanderthal DNA fragments have heads that are slightly less rounded. The research is giving scientists new insight into the evolution of modern brain shape and function.
Study co-lead author Philipp Gunz, who is a paleoanthropologist at the Max Planck Institute for Evolutionary Anthropology, explained: “We captured subtle variations in endocranial shape that likely reflect changes in the volume and connectivity of certain brain areas.”
According to co-lead author Amanda Tilot, the goal of the study was to identify “potential candidate genes and biological pathways that are related to brain globularity.”
The experts focused on the fact that living humans with European ancestry carry rare fragments of Neanderthal DNA in their genomes as a result of interbreeding between Neanderthals and the ancestors of modern Europeans.
The investigation was based on MRI brain scans and genetic information for about 4,500 people, including cranial shape and stretches of Neanderthal DNA. Ultimately, the researchers used the endocranial shape differences between Neanderthal fossils and modern human skulls to assess the shape of the participants’ brain images.
The Neanderthal DNA fragments identified in living humans contained two genes that have already been linked to brain development: UBR4 and PHLPP1.
“We know from other studies that completely disrupting UBR4 or PHLPP1 can have major consequences for brain development,” explained study senior author Simon Fisher.
“Here we found that, in carriers of the relevant Neandertal fragment, UBR4 is slightly down-regulated in the putamen. For carriers of the Neandertal PHLPP1 fragment, gene expression is slightly higher in the cerebellum, which would be predicted to have a dampening effect on cerebellar myelination.”
The study authors emphasized that the effects of carrying these rare Neanderthal fragments are subtle.
“The Neanderthal variants lead to small changes in gene activity and only push people slightly towards a less globular brain shape,” said Fisher. “This is just our first glimpse of the molecular underpinnings of this phenotype, which is likely to involve many other genes.”
The study is published in the journal Current Biology.
Image Credit: Philipp Gunz (CC BY-NC-ND 4.0)