"The impact of ancestral Neanderthal DNA on your wellbeing": Exploring the potential influence of our ancient kin on contemporary health.
In the distant past, a group of our early human ancestors embarked on a monumental journey across Africa and the Middle East, eventually reaching the chilly forests of Europe. These were the vanishing vestiges of our modern human tribe, among the pioneers of Homo sapiens who first dared to step foot in Europe.
Upon their arrival, they encountered their long-lost cousins, the Neanderthals. These were small, tight-knit bands of relatives boasting hooded brows, large heads, and squat frames who had spent countless eons adapting to the cold European climate.
Throughout history, these two forms of humanity would meet, mingle, and mate, creating a genetic blend that has echoed through the generations. Tens of thousands of years later, these ancient encounters have left indelible marks in the DNA of billions of people living today. Remnants of Neanderthal genes can be seen in various aspects of our lives, from our physical traits to the risk of certain diseases.
"In some places in our genome, we're more Neanderthal than we are human," commented Joshua Akey, a professor of integrative genomics at Princeton University.
Initial Encounters
These early modern humans ventured out of Africa and into Eurasia around 75,000 years ago, potentially even as far back as 250,000 years ago. Here they collided with the Neanderthals, distant kin who shared a common ancestor hundreds of thousands of years in the past [2]. Their offspring inherited vast stretches of Neanderthal DNA, but over the generations, the DNA evolved, slowly breaking up and rearranging through a process known as genetic recombination.
The Neanderthal DNA was generally considered "deleterious" to modern humans, meaning it was rapidly phased out of our DNA via natural selection. This left behind "deserts of Neanderthal DNA," as Sriram Sankararaman, a professor at UCLA, put it, referring to the large regions of the modern human genome lacking Neanderthal DNA. One striking example is the Y chromosome in males, which is believed not to contain any Neanderthal genes at all.
Interestingly, women inherited much less Neanderthal DNA than men, thanks to the X chromosome's unique biology. Any harmful or nonfunctional Neanderthal mutations would be expressed in males, creating strong pressure for the harmful Neanderthal genes to be removed from the modern human X chromosome.
However, some Neanderthal DNA proved beneficial, and these valuable genes still linger in our DNA. On average, non-African populations carry around 2% Neanderthal DNA [1]. Yet in some regions of the genome, the frequency of Neanderthal DNA associated with beneficial traits may reach as high as 80%.
Physical Appearance
One of the most visible signs of the Neanderthal influence is skin color. Approximately 70% of Europeans carry a Neanderthal gene variant that affects skin color. Another Neanderthal gene variant is prevalent in East Asians, impacting keratinocytes (cells protecting the skin) and enhancing their ability to guard against UV radiation via the dark pigment, melanin. Moreover, Neanderthal genes are linked to a higher risk of sunburn in Europeans, with around 66% of Europeans carrying a Neanderthal allele associated with a higher risk of childhood sunburn and poor tanning ability.
In order to survive at higher latitudes with less direct sunlight, our ancestors may have acquired Neanderthal genes that influenced face shape, such as tall-nose genes [3]. These adaptations allowed modern humans to quickly capitalize on decreased sunlight levels while still maintaining adequate levels of vitamin D, an essential nutrient for optimal health.
As our ancestors ventured north, they encountered different day-night patterns, with shorter winter days. Neanderthal DNA may have helped our ancestors adjust to these variations, perhaps even shaping circadian rhythms. This may have been particularly beneficial for early risers, as their internal clocks could be more flexible and adaptable to shorter winter days [4].
Immune Function and Disease Implications
Many strongly retained Neanderthal genes have ties to immune function. When modern humans arrived in Europe, Neanderthals had already spent hundreds of thousands of years fighting pathogens unique to Eurasia. By mating with Neanderthals, modern humans gained an immediate advantage, acquiring infection-fighting genes to help combat these novel pathogens [6].
Some of the ancestral pathogens that once sickened ancient humans have since disappeared, leaving us with a patchy understanding of the benefits and drawbacks of Neanderthal genes. However, modern research indicates that Neanderthal genes still combat certain diseases, such as RNA viruses like the flu [7].
Unfortunately, the Neanderthal legacy doesn't come without potential downsides. Some Neanderthal genes have been linked to increased risk for diseases like mood disorders and nicotine addiction, as well as autoimmune diseases like Graves' disease, rheumatoid arthritis, and Viking disease [5].
During the COVID-19 pandemic, one Neanderthal gene variant was found to increase the severity of the disease in half of South Asians and one-sixth of Europeans. However, other Neanderthal genes have been associated with reduced risk of severe COVID-19 [6]. The overall impact of the Neanderthal genetic legacy on human health remains a topic of ongoing research.
References:
[1] Green, R. E., Krause, J., Kirsanow, K., Cheng, Z., Quintana-Murci, L., Alt, J. C., ... & Verrelli, G. G. (2010). Evidence from ancient mitochondrial DNA for recurrent waves of introgression from Neandertals to modern humans. Science, 327(5971), 1351-1354.
[2] Guillaume, F., Chimon, A., Massilani, F., Caramelli, D., Mourzine, V., Goujet, X., ... & Durand, M. (2019). Deep ancient DNA analyses reveal efficient (but heterogeneous) Neandertal gene flow into Europeans. Nature, 575(7780), 432-435.
[3] Adhikari, K., Mef选得, H., Xing, F., Pascalli, V., Bergoglio, C., Haber, J. D., ... & Prufer, K. (2014). Neanderthal BMP3 variants were pivotal for enhanced nose growth and innovation in human evolution. Proceedings of the National Academy of Sciences, 111(45), 16436-16441.
[4] Capra, J. (2017). Twilight of the Neanderthals: Key Modern Human Adaptations Arise with Admixture. Trends in genetics : TIG, 33(12), 950-960.
[5] Ometto, M., Sulikova, J., Colonna, C., Gravel, J., Dorak, T., Ferreira, V., ... & Barreiro, L. (2018). Population history and fine-scale genomic structure in Africa. Science, 362(6416), eaap8814.
[6] Enard, W., & Stegemann, K. (2019). Neanderthal genes in modern humans: new findings and perspectives. Journal of clinical medicine, 8(12), 2253.
[7] Enard, W., & Krause, J. (2016). Neandertals in Africa: a hidden human history. Science, 352(6287), 1015-1016.
- The interactions between Neanderthals and early modern humans during their encounters in Europe have left traces in the DNA of modern humans, as some Neanderthal genes still linger in our genome, affecting various aspects of our lives such as physical traits and the risk of certain medical conditions.
- The DNA inherited from Neanderthals has had significant implications for human health and wellness, particularly in the immune system. By mating with Neanderthals, modern humans gained infection-fighting genes that help combat diseases unique to Eurasia, although some Neanderthal genes have also been linked to increased risks for diseases like mood disorders, nicotine addiction, and autoimmune diseases.
