Do You Carry Neanderthal DNA? The Shape Of Your Skull May Tell

January 15, 2021

The shape of your brain may say a lot about the Neanderthals in you. New research has found that modern humans, who carry certain genetic fragments from our closest extinct relatives, may have more rectangular brains and skulls than others.

Modern humans have unique, relatively spherical skulls and brains. In contrast, Neanderthals, the closest extinct relative of modern humans, had the elongated skulls and brains typical of most primates.

Previous research has suggested that these contrasting skull shapes may reflect differences in the size of various brain regions between modern humans and Neanderthals, and how these brain regions were connected.” However, brain tissue doesn’t fossilize, so the underlying biology has been elusive,” co-lead study author Philipp Gunz, a paleoanthropologist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, told Live Science.

To help solve this mystery, the scientists first performed CT (computed tomography) scans of seven fossil Neanderthal skulls and 19 modern human skulls. They developed impressions of the inside of the skulls’ thoracic cavities and measured their roundness.

Next, the researchers analyzed nearly 4,500 modern humans, for whom they had both genetic data and magnetic resonance imaging (MRI) scans of their brains.

“We reasoned that if we could identify specific Neanderthal DNA fragments in a sufficiently large sample of living people, we would be able to test whether any of these fragments drove a less spherical brain shape, allowing us to amplify genes that might be important for this feature,” senior study author Simon Fischer, a neurogeneticist at the Max Planck Institute for Psycholinguistics in Nijmegen, the Netherlands, told Live Science.

Previous work has found that modern humans and Neanderthals underwent multiple crossovers to introduce Neanderthal DNA into the modern human genome. In the new study, the scientists found that Neanderthal DNA fragments in modern humans’ chromosomes 1 and 18 are associated with less rounded brains.

“The implications of carrying these rare Neanderthal fragments are subtle,” said Fischer.” The effects of Neanderthal genetic variants are so small that when you meet someone, you don’t see them in their head shape.”

The Neanderthal DNA fragment contains two genes previously studied in connection with brain development. One is UBR4, which is associated with neurogenesis, and the other is PHLPP1, which is associated with the development of the fatty insulation around nerve cells.

The researchers found that this Neanderthal DNA had the strongest effect on brain structures known as the putamen and cerebellum – both of which are key to preparing, learning and coordinating movements. The putamen forms the outer part of the brain’s basal ganglia, which are associated with memory, attention, planning, learning of skills, and potentially speech and language.

Scientists note that if a person has more Neanderthal DNA than the average person, that doesn’t necessarily mean they have a more rectangular brain.” Two people with a very similar total amount of Neanderthal DNA – say, 1 percent of their genome – are likely to carry completely different fragments,” Fisher said.

The researchers also note that the differences in these skulls likely do not reflect any differences in the babies’ births. Gunz said modern humans and Neanderthals had similar brain and skull shapes at the time. He added that differences in brain development after birth likely led to significant differences in skull shape between the two lineages of adults.

Fisher said future research could look for more Neanderthal DNA associated with modern human brains and determine what specific effects these ancient genetic variations might have by growing brain tissue with Neanderthal DNA in the lab.