(CNN)Humans have unusually globular (or round) skulls and brains compared to our ancient ancestors -- including our closest extinct cousins the Neanderthals -- and a new study provides a possible explanation as to why.
Neanderthal genes could explain the shape of our skulls, study finds
For the first time, an interdisciplinary team of scientists have identified two genes that affect the shape of the modern human's skull -- and they originate from Neanderthals.
"Billions of people living today carry a small fraction of Neanderthal genes in their genome -- a distant echo of admixture when our ancestors left Africa and encountered Neanderthals," said study author Philipp Gunz, a paleoanthropologist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, via email.
These are typically humans with European ancestry stemming from interbreeding between Neanderthals and modern Europeans.
"By combining data from fossils, genetics and brain imaging we can learn something about evolutionary changes to brain development in our own species," said Gunz.
The team used MRI scans to analyze the cranial shape of about 4,500 peoples' brains before looking at their genomes to work out which fragments of Neanderthal DNA they carried.
They also studied fossil skulls and ancient genomes to compute the shapes of both Neanderthal and modern human skulls for comparison and then looked at whether any particular genes were linked to less globular brain shape in the people that carried them.
They found two genes variants that have a subtle effect on skull shape, on chromosomes one and 18, which when disrupted have major consequences for brain development, according to the research.
"It gives us our first glimpse of how genes might contribute to this particularly striking aspect of the anatomy of our species," said Simon Fisher, director of the Max Planck Institute for Psycholinguistics, which co-led the research.
The gene variants found on chromosomes one and 18 are linked to the expression of two nearby genes called UBR4 and PHLPP1 that affect the formation of new nerve cells and their insulation.
"We would like to understand more about globularity because it might relate to specific changes in the ways our brains are organized -- the relative sizes of different parts of the brain and how they are connected to each other, as compared to our ancestors."