Neanderthals (Homo neanderthalensis), the extinct group of archaic humans, inhabited Europe and Western and Central Asia during the Middle to Late Pleistocene, 0.2-0.3 million years ago. Homo sapiens or modern humans, too, emerged by that time as they are believed to have evolved in Africa around 300,000 years ago. Although Neanderthal extinction occurred roughly 40,000 years ago with the immigration of modern humans (Cro-Magnons), Neanderthals in Gibraltar may have persisted for thousands of years longer. Evidence from genetic studies and archaeology indicates that Neanderthals and Homo sapiens interbred, suggesting that these two separate species were capable of producing viable offspring. In fact, Homo sapiens interbred with multiple archaic human species, including Neanderthals and Denisovans. These interbreeding events took place at various times and locations after modern humans migrated out of Africa.

Scientists previously speculated that the ancient genes could be the source of a number of modern-day diseases. Recent research indicates that certain genes inherited from Neanderthals are linked to a brain disorder, called Chiari malformation type I (CMI), in modern humans! Researchers have come to this conclusion after examining ancient, as well as modern, skulls.

CMI is a condition where the cerebellar tonsils (the lower part of the cerebellum) descend through the foramen magnum (the opening at the base of the skull) into the spinal canal. This can cause a variety of symptoms, from headaches and neck pain to more serious neurological issues, or it may also be asymptomatic. In Chiari malformations, the skull is often smaller than usual or misshapen, causing a mismatch in size with the brain, specifically the cerebellum that then gets pushed down into the spinal canal. A smaller than normal occipital bone at the back of the skull is often associated with Chiari malformations, particularly Chiari type I. This condition occurs when the skull base is underdeveloped, leading to a reduced volume in the posterior fossa (the area at the back of the skull). It causes headaches, neck pain and other serious neurological problems. According to the National Institutes of Health (NIH), approximately one in 100 people meet the radiological criteria for CMI, while only about one in 1,000 experience symptomatic issues.

Several ancient human species, like Neanderthals and Homo erectus, possessed distinct skull shapes and features that differed from those of modern humans (Homo sapiens), reflecting their evolutionary adaptations to different environments and ways of life. A previous study proposed that Chiari malformation might be linked to genetic contributions from various ancient human species. This hypothesis, popularly known as the Archaic Homo Introgression Hypothesis, suggests that interbreeding between Homo sapiens and these ancient hominins could have resulted in the inheritance of genes, affecting skull development. Since then, ancient genes are passed down from one generation to the next and this process is known as heredity or inheritance. However, there was a lack of concrete evidence to support the claim or potential of this idea.

A team led by Osteoarchaeologist Dr Kimberly Plomp from the University of the Philippines has tested this hypothesis. They have mentioned: “The legacy of these interbreeding events can be identified in the genomes of many living humans.” Researchers have used 3D modelling and shape analysis techniques to compare 103 skulls of modern-day people with and without CMI, and eight fossil skulls from ancient species, including Homo erectus, Homo heidelbergensis and Homo neanderthalensis.

According to Dr Plomp, people with CMI have differences in skull shape. The analysis clearly shows the area where the brain connects to the spine. Interestingly, shapes of these skulls were not similar to all of the ancient hominins studied, only to Neanderthals. Interestingly, skulls from Homo erectus and Homo heidelbergensis were more similar to the skulls of modern humans without CMI. Hence, the researchers are of the opinion that the original hypothesis was too broad and should be adapted to look specifically at Neanderthal links. In the research paper, they have stated: “Rather than the genes being traceable to Homo erectus, Homo heidelbergensis and Homo neanderthalensis, our results are consistent with them being traceable just to Homo neanderthalensis.” Apart from proposing a Neanderthal Introgression Hypothesis to replace the previous study carried out in 2013, the latest study has stressed on how early Homo sapiens and Neanderthals mingled, interbred and exchanged genetic information.

Scientists have decided to continue working with the samples used in the recent study as both modern and ancient skulls, across ages, could provide them with more information about the relationship between CMI skull structures and skulls of the early peoples. It would also allow researchers to trace whether Neanderthals suffered from CMI and faced the same problems as people today. “The hypothesis also needs to be put to the test in groups of people from different parts of the world. We know that African populations have less Neanderthal DNA than populations in Europe and Asia, which should be reflected in cases of CMI,” stressed Dr Plomp.

Scientists believe that it would be easier to cure this disease in the future, if they could confirm the source. The information obtained from the study may help in the treatment of CMI. A section of researchers is optimistic that it would be possible to completely eradicate the disease. Meanwhile, the research is still in its early stages and it is not possible to say anything for sure right now. “The methods would seem to have the potential to help us develop a deeper understanding of the aetiology and pathogenesis of Chiari malformations, which could in turn strengthen diagnosis and treatment of the condition,” states the research paper.

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Published by Koushik Das

Koushik Das (born on May 16, 1976 in Kolkata) is a career journalist. Based in the Indian capital of New Delhi, Koushik writes mainly about foreign policies and current geopolitical issues, and rarely about other topics. His own political ideas are highly influenced by Antonio Gramsci, Louis Althusser, Michel Foucault, Michael Oakeshott and others. English philosopher and political theorist Oakeshott (Dec 11, 1901-Dec 19, 1990) says that “in political activity, men sail a boundless and bottomless sea. There is neither harbour for shelter nor floor for anchorage, neither starting-place, nor appointed destination. But we have to keep afloat”. (Rationalism in Politics, 1962) As a student of Political Science, Koushik loves to share his views on issues, which have great impacts on his thought process (and also on India, South Asia and of course on the global community), with his readers through his website – Boundless Ocean of Politics. By doing so, he tries to keep himself afloat. You will find some of his articles in https://inserbia.info/today/ (https://inserbia.info/today/author/kou_das13_i/), as he has been trying to assess the global geopolitics since 2003. You can also mail him at kousdas@gmail.com View all posts by Koushik Das