The Echo of the Neanderthals: How Our Ancient Cousins Still Shape Modern Humans
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For millennia, the genetic legacy of Neanderthals has subtly influenced the evolution and health of Homo sapiens, impacting everything from our immune systems to our susceptibility to certain diseases. Tens of thousands of years after interbreeding with our ancestors, traces of Neanderthal DNA persist in the genomes of billions of people alive today, revealing a complex and ongoing story of adaptation and survival.
“In some places in our genome, we’re more Neanderthal than we are human,” explained Joshua Akey, a professor of integrative genomics at Princeton University, highlighting the surprising extent of this ancient genetic inheritance. These weren’t simply encounters between distinct species, but a merging of lineages that continues to resonate within us.
The First Encounter and Interbreeding
Approximately 75,000 to 250,000 years ago, the ancestors of modern Eurasians embarked on a journey out of Africa and into Eurasia, where they first encountered Neanderthals. These hominins, distinct from Homo sapiens with their hooded brows, large heads, and stocky builds, had already spent centuries adapting to the colder climates of Europe. Over millennia, these groups met, mingled, and crucially, mated.
Initially, modern humans inherited entire chromosomes from Neanderthals, according to Sriram Sankararaman, a professor at UCLA specializing in computer science, human genetics, and computational medicine. However, through the process of genetic recombination, these large segments of DNA were gradually broken down and reshuffled across generations.
The Genetic Legacy: A Mixed Blessing
While much of the Neanderthal DNA inherited by early Homo sapiens proved “deleterious” and was subsequently removed through natural selection, resulting in “deserts of Neanderthal DNA” across the genome, some fragments proved beneficial and persisted.Notably, the Y chromosome in males appears to be largely devoid of Neanderthal genes, possibly due to incompatibility with human genes or random genetic drift. Similarly,the X chromosome carries significantly less Neanderthal ancestry,likely because harmful mutations on this chromosome are more readily expressed in males.
Today, Neanderthal DNA comprises, on average, 2% of the genomes of people outside of Africa. This small percentage belies a notable impact, especially on immune function.HLA genes are linked to immune function. By the time Homo sapiens arrived in Europe, Neanderthals had already evolved defenses against Eurasian pathogens. Interbreeding provided modern humans with an immediate boost to their immune systems. David Enard, an assistant professor at the University of Arizona, explained that these Neanderthal-derived immune genes were quickly favored by natural selection. A 2018 study demonstrated that Neanderthal DNA helped modern humans combat RNA viruses, including influenza, HIV, and hepatitis C.
The Darker Side of Inheritance
Though, the Neanderthal legacy isn’t entirely positive. While largely absent in the brain, suggesting strong selection against its expression, Neanderthal genes have been linked to mood disorders like depression and nicotine addiction. Moreover, the immune benefits can come with a cost. Scientists have discovered links between Neanderthal genes and an increased risk of allergic diseases, autoimmune conditions like Graves’ disease and rheumatoid arthritis, and even “Viking disease,” characterized by bent or frozen fingers.
Notably, a Neanderthal gene variant on chromosome 3 has been associated with a higher risk of severe COVID-19 in South Asian and European populations. Despite these associations, Capra cautioned against simplistic blame, emphasizing that most diseases are influenced by a complex interplay of genes and environmental factors.
What Lies Ahead?
the traces of Neanderthals will likely persist in our genomes for hundreds of thousands of years, with some fragments gradually disappearing while others become firmly embedded.Akey believes that leveraging new genomic technologies like CRISPR and gene editing will be crucial for understanding the precise biological mechanisms by which Neanderthal sequences influence human traits and diseases.
moreover, scientists are investigating how modern human DNA may have impacted Neanderthals, utilizing artificial intelligence to reconstruct a more detailed picture of our long-lost cousins. ultimately, deciphering the role of Neanderthal DNA in our genomes provides valuable insights into what makes us uniquely human, as Sankararaman stated, revealing the functionally significant regions of our genome that were critical during a pivotal period in our evolutionary history.
