"Exploring the Impact of Neanderthal Genes on Modern Human Health: The Legacy of our Prehistoric Relatives"
In ancient times, intrepid human beings voyaged for miles upon miles, crossing continents until they found themselves in Europe's chilly forests. These pioneers were long-lost members of our modern human family, and among the first Homo sapiens to step foot on European soil.
Here, these explorers would’ve encountered distant cousins—Neanderthals. These small groups of cousins had telltale features like heavy brows, large skulls, and squat bodies, as they had spent eons adapting to Europe's frigid climate. Multiple encounters over the millennia occurred between these two forms of humanity, and theymate each other on several occasions.
Tens of thousands of years later, these ancient meet-ups have left traces in the genetic code of billions of people alive today. These lingering genes impact us in myriad ways, from our appearance to our risk of certain diseases.
"In some places in our genome, we're more Neanderthal than we are human," Joshua Akey, a professor of integrative genomics at Princeton University, shared with Live Science.
These were our closest human relatives, and this is their legacy.
Meeting Faces
By around 75,000 years ago, the ancestors of most modern Eurasians ventured out of Africa and into Eurasia. It was here, in this region, that they came face-to-face with Neanderthals, who had last shared a common ancestor with modern humans hundreds of thousands of years ago. Modern humans interbred with Neanderthals on multiple occasions over the course of time.
Initially, modern humans inherited large chunks of Neanderthal DNA, known as whole chromosomes. However, this DNA got broken up and rearranged through a process called genetic recombination, gradually eliminating the telltale Neanderthal traces over time. Neanderthal DNA was generally disadvantageous to modern humans, as it was weeded out through evolution. This process created vast expanses devoid of Neanderthal DNA, particularly in the human Y chromosome.
Some Neanderthal DNA offered advantages to modern humans, helping them survive and reproduce. On average, Neanderthal DNA occupies 2% of the genomes of people outside Africa. However, the frequency of Neanderthal DNA that codes for beneficial traits may be as high as 80% in some regions of the genome, Akey noted.
Physical Appearance
The legacy of Neanderthals is often apparent in a person's skin color. A Neanderthal gene variant on chromosome 9 that influences skin color is carried by 70% of Europeans today. Another Neanderthal gene variant found in most East Asians regulates keratinocytes, which protect the skin against harmful UV radiation via a dark pigment known as melanin.
Neanderthal gene variants are also associated with a greater risk of sunburn in modern humans and, according to some research, a heightened risk of childhood sunburn and poor tanning ability in around 66% of Europeans.
The Ticking Clock
Neanderthal DNA may have helped H. sapiens adapt to the larger differences in day and night length at northern latitudes. Lingering Neanderthal genes affect our circadian clock, which regulates key internal processes like body temperature and metabolism. In fact, some early risers can thank Neanderthals for their circadian clock genes, as discovered by John Capra and his colleagues.
Internal Defenses
Many beneficial Neanderthal genes deal with immune function. By mating with Neanderthals, modern humans received an instant injection of those infection-fighting genes, which had already been adapted to fight pathogens that had been prevalent among Neanderthals for hundreds of thousands of years[1]. While many of the ancestral pathogens that sickened ancient humans are long lost to time, some of the Neanderthal genes still work against modern pathogens, such as the flu, HIV, and hepatitis C.
However, some Neanderthal genes that once helped our ancestors may pose risks in today's world. They have been linked to mood disorders such as depression and brain signaling pathways that increase the likelihood of nicotine addiction.
And even the immune advantages that come from Neanderthals may have drawbacks. For instance, researchers discovered in 2016 that Neanderthal genes that prime the immune system to fight pathogens could also predispose people to allergic diseases [2]. In addition, Neanderthal genes have been associated with a higher risk of developing autoimmune diseases like Graves' disease, rheumatoid arthritis, and what has been dubbed "Viking disease," in which fingers become flexed or immobilized.
One Neanderthal gene variant has been linked to severe cases of COVID-19. This variant, found on chromosome 3, is present in half of South Asians and one-sixth of Europeans. However, the story is complicated, as other Neanderthal genes, carried by up to half of people in Eurasia and the Americas, are associated with a reduced risk of severe COVID-19.
Overall, it's tricky to blame any one Neanderthal gene for a particular disease or condition, says Capra. This is especially true for major health issues like heart disease and cancer, where dozens or hundreds of genes, along with myriad environmental factors, come into play.
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"Technology and science have helped uncover the influence of Neanderthals on modern humans, with medical-health research shedding light on the impact of Neanderthal DNA on our health-and-wellness, particularly in our appearance, internal defenses, and risk of certain medical-conditions. For instance, Neanderthal DNA is linked to skin color, immune function, and even the risk of developing autoimmune diseases or severe cases of COVID-19."
"In the realm of space-and-astronomy, the discovery of Neanderthal DNA has added a new layer to our understanding of human history, tracing our ancestral connections beyond Europe's chilly forests to the vast expanses of our cosmic family tree."
