There is a bizarre (but as far as we know, harmless) feature that some people may have inherited from Neanderthal ancestors – a flat(ter) head. This is according to a study recently published in the journal Current Biology.

The last common ancestor of modern humans and Neanderthals existed approximately 530,000 years ago yet most people of non-African descent have a little bit of Neanderthal DNA in them – the result of interbreeding between our forebearers and their hominin cousins. Collectively, scientists estimate 40 percent of the Neanderthal genome is represented in people alive today, possibly contributing to illnesses (like, depression) and even smoking habits.

Curiously, they could also affect the shape of our skull. Where humans tend to have a globular skull, other species of hominin (including Neanderthals) had a more elongated, more primate-like braincase.

To find out if the flatter head gene was inherited from our Neanderthal ancestors, scientists took computed tomography (CT) scans of 19 skulls of modern humans and seven skulls of Neanderthals, creating imprints of the skull's braincases to measure their roundness. They compared the results to genetic data and magnetic resonance imaging (MRI) scans of almost 4,500 people.

They found that there are two genes associated with a more Neanderthal shaped skull – PHLPP1 and UBR4. 

PHLPP1 controls myelin, a fatty substance, which covers neurons and is very important for long-range communication in the brain. According to the study, people who possess the Neanderthal version reveal an especially active expression of the gene in the cerebellum. In contrast, people who carry the Neanderthal version of UBR4 display a less active genome in a brain region called the putamen. The results suggest PHLPP1 evolved in modern humans to produce extra myelin and UBR4 evolved to make neurons grow faster in the putamen.

Why? The putamen and cerebellum are involved in attention, planning, memory, learning, and possibly language. Reflecting on the findings, senior study author Simon Fisher, a neurogeneticist at the Max Planck Institute for Psycholinguistics in Nijmegen, the Netherlands, told the New York Times these changes may have allowed modern humans to evolve a more sophisticated power of language and gave them a greater capacity to invent more efficient tools.

However, the effect of these Neanderthal genes on us today is small at most.

"The effects of carrying these rare Neanderthal fragments are subtle," Fisher told Live Science.

"The effects of the Neanderthal gene variants are small, you would not be able to see them in a person's head shape when you meet them."