Neanderthals died out around 40,000 years ago, but a new study reveals that their genetic legacy continues to influence our brains today.
Chiari malformation type 1 is a rare brain condition where the cerebellum, a brain area responsible for balance and posture, droops down slightly through a small hole in the skull called the foramen magnum.
New research provides evidence that the condition arises from lingering levels of Neanderthal DNA in our genomes, which may cause people with Chiari to have a more compact and flatter occipital bone — the part of the skull that cups the cerebellum.
Neanderthal Skulls and Chiari Research
Scientists first theorized that Neanderthal-like skulls might influence Chiari in 2013. Brazilian neurosurgeon Yvens Barbosa Fernandes published a paper after viewing ancient skull casts in a museum.
Early Homo sapiens could interbreed with other hominids, like the Neanderthals or Denisovans.
“The legacy of these interbreeding events can be identified in the genomes of many living humans,” wrote the authors of the new paper, including first author Kimberley Plomp of the University of the Philippines Diliman.
Fernandes suspected that one of these inherited traits might be the smaller crania seen in Chiari. His theory — the Archaic Homo Introgression Hypothesis — suggested that Chiari arose from skulls influenced by genes from three extinct Homo species: Homo erectus, Homo heidelbergensis, and Homo neanderthalensis. These skulls, paired with the human brain, could lead to “a mismatch between the size and shape of the brain and the size and shape of the cranium,” wrote the authors.
Read More: Brain Development Made Humans Distinct From Neanderthals 130,000 Years Ago
Mixed Results from Skull Modeling
In the latest work, Plomp constructed 3D models of eight fossil skulls and then compared them to the skulls of 46 individuals with Chiari malformation and 57 controls. The modeling showed that people with Chiari malformation do have skull shapes that are significantly different from those of unaffected controls. The comparison between modern and ancient skulls produced mixed results — the Chiari scans didn’t resemble Homo erectus or Homo heidelbergensis, but closely matched those of Neanderthals.
“Our results suggest the hypothesis should be narrowed to focus on introgressed genes from Neanderthals,” wrote the authors.
Chiari is usually diagnosed through MRI scans. The condition can cause headaches, as well as neck pain. The pain is often associated with laughing or coughing. The condition can also cause numbness or tingling, but cases can also be asymptomatic and lie dormant for years. While symptomatic Chiari is very rare, affecting only 1 in 1,000 people, ten times more people are thought to have the malformation without any symptoms.
Neanderthal brains were larger than those of modern-day humans, but their smaller occipital space left little room for the cerebellum. This difference has been linked to improved motor and social functioning among early humans, which may have helped them outcompete and ultimately replace Neanderthals.
Neanderthal genes are believed to have an impact on other regions of the modern human genome. A 2023 study found that this ancient DNA had an impact on the immune system and metabolism.
The Future of Chiari Research
The story of our skulls isn’t complete. The current research only shows an association between Chiari and Neanderthal skull shape, so Plomp’s team now plans genetic studies that will aim to track down any ancient DNA in people with Chiari that might be the root cause of their altered skull shape.
If causal genes are identified, it could lead to better diagnostics. Families at risk of the condition could receive early warning. Current treatment for the condition involves decompression surgery, which can involve removing pieces of the skull or the fusion of vertebrae.
Read More: Brutes and Brains: What We Know About Neanderthal Brain Size
Article Sources
Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:
PLOS One. Living on the edge: Was demographic weakness the cause of Neanderthal demise?
Evolution, Medicine, and Public Health. A test of the Archaic Homo Introgression Hypothesis for the Chiari malformation type I
PubMed. Prevalence and Impact of Underlying Diagnosis and Comorbidities on Chiari 1 Malformation
Medical Hypothesis. Evolutionary hypothesis for Chiari type I malformation
Scientific Reports. Reconstructing the Neanderthal brain using computational anatomy
Evolutionary Biology. The lingering effects of Neanderthal introgression on human complex traits
RJ Mackenzie is a freelance science reporter based in Glasgow, Scotland. He covers biological and biomedical science, with a focus on the complexities and curiosities of the brain. He has degrees in neuroscience from the University of Edinburgh and the University of Cambridge. He has written for National Geographic, Nature, and The Scientist, among other publications.
