According to new research from Simon Fraser University, a painful neurological disease affects up to 1% of people today, possibly due to ancient hybridization between humans and Neanderthals, tens of thousands of years ago.
This study links Chiari Deformity Type 1, a potentially fatal brain condition, to the genetic inheritance of our extinct cousins who walked the Earth with early modern humans.
The study, published in evolution, medicine and public health, uses advanced 3D skull analysis and statistical techniques to compare craniofacial shapes of living people with or without conditions, and can be performed on fossil specimens from multiple human species, including Neanderthals, homo erectus and homo heidelbergensis.
When the size of the skull does not match the size of the brain
Chiari Deformity Type 1 occurs when the posterior part of the skull is too small to accommodate the brain, forcing a part of the cerebellum to pass through the skull and encounter the opening of the spine. This can have a dangerous pinching effect, which can cause severe headaches, neck pain, dizziness, and death in extreme cases.
This affects 1 person with an estimated 1,000 people, although recent imaging studies have shown that the true prevalence is likely to be higher – possibly more than one in 100. Many cases are still undiagnosed because the symptoms may be subtle or attributed to other causes.
“In medicine, like other sciences, it’s important to clarify the causal chain,” Mark Collard, president of Canadian SFU research on human evolution, explained. “The more obvious the causal chain that may be the cause of the medical condition, the more likely people will be to manage or even resolve the situation.”
Fossil evidence points to the Neanderthal connection
The researchers analyzed CT scans from 103 living people (46 with Chiari deformities, 46 without 57 without humans), and eight of the model represent fossil skulls of different humans. Using 17 precisely mapped landmarks on each skull, they applied geometric analysis to compare craniofacial across groups.
The results show an amazing pattern: with larger skull-shaped features compared to Neanderthals compared to those who were unaffected. On the contrary, people without this condition showed greater similarity to other ancient human species.
Key research results:
- Affected individuals showed reduced cranial bank height and occipital development
- Brain hypnosis correlates with specific Neanderthal-like skull characteristics
- Modern humans retain 2-5% of Neanderthal DNA from ancient hybrids
- Skull shape differences mainly occur in the base area of the brain
- Geographic populations based on ancestors may face different levels of risk
Paleogenes in modern medicine
The study is based on established knowledge that the non-African population carries 2-5% of Neanderthal DNA from hybridization events that occurred tens of thousands of years ago. While most hereditary Neanderthal traits are harmless and even beneficial, some people may have problems when combined with modern human anatomy.
The team’s analysis showed that the skull height of Chiari deformed people has a flatter occipital bone and a different opening in the brain, which is closely consistent with the Neanderthal skull characteristics. This suggests that the genes that control skull development inherited from Neanderthals and may have caused a size mismatch with the larger, more spherical brains of modern humans.
“The hypothesis is that further testing is needed, but our research may mean that we will be one step closer to gaining a clear understanding of the causal chain that leads to Chiari deformity type 1,” Zarad pointed out.
Geographical significance for risk assessment
The results show that compared with African populations with the least Neanderthal DNA, people with higher levels of Neanderthal ancestry—especially those with European and Asian ancestry. However, the researchers stressed the need for other studies to confirm these geographic patterns.
The team initially tested a broader hypothesis that three extinct humans contributed the problematic genes, but their analysis narrowed down the possible sources of Neanderthals. Neither HOMO erectus nor Heidelbergensis exhibited similarity to the skull shape of affected modern humans.
This evolutionary medicine approach shows how studying ancient human relatives illuminate contemporary health challenges. The researchers used complex statistical shape analysis, far beyond traditional medical imaging, to reveal previously unknown skull features associated with the disease.
“It is not only interesting to study archaeology and human evolution. It also has the potential to help us understand and in some cases deal with the current problems,” he said. Zarad stressed. “In this case, we have used fossils to help us shed light on medical conditions, but there are many other contemporary issues archaeological and paleontological data that can help us better understand.”
Future studies will examine whether the prevalence of Chiari deformity will vary across the global population based on the level of Neanderthal ancestry, which may lead to screening and improvements in treatment strategies for this severe neurological condition.
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