Have you ever complained about having a "bad immune system?" Your Neanderthal ancestors could be to blame.
Neanderthal DNA constitutes up to 4 percent of the modern human genome, but the exact impacts of this DNA have remained largely unknown—until now.
A team of researchers from across the United States came together to assess how these ancient genes affect modern humans, compiling their results in a paper published in the journal eLife in March. Specifically, they were able to pinpoint the involvement of Neanderthal DNA in human development, metabolism and the immune system.
"The overall effect of Neanderthal alleles on metabolism/immune system is complex," Sriram Sankararaman, a co-author on the study and Professor of Computer Science, Genetics and Computational Medicine at the University of California, Los Angeles, told Newsweek.
"In our study, we were able to pinpoint the impact of specific introgressed Neanderthal [gene variants]. For example, we were able to find instances of introgressed [gene variants] that impact the function of genes known to be important for immune function."
One of the most significant examples of this was a genetic variant that affects the structure of an important receptor on the surface of white blood cells. This receptor is involved in the process of phagocytosis—when white blood cells engulf bacteria, parasites and infected cells. The Neanderthal variant of this gene would therefore likely disrupt our cells' ability to clear infections, making us more prone to getting sick.
A different Neanderthal variant was found to disrupt a key component of cellular energy production. This builds on previous studies reporting that Neanderthal DNA may be an important contributor to COVID-19 susceptibility. Having Neanderthal DNA isn't necessarily bad, though.
"A number of studies have shown that Neanderthal DNA can have a beneficial impact," Sankararaman said. "The most striking example is a region in a gene BNC2 associated with skin and hair color, where more than half of present-day Europeans carry Neanderthal DNA likely due to the adaptive benefit conferred by this introgressed DNA.
"There are several other regions in the genome where we see this pattern, including regions that are known to be important for immune function. However, the bulk of introgressed Neanderthal DNA appears to have been deleterious."
As a result, Neanderthal DNA has largely been selected against in the evolution of our species. "Across the traits that we examined there is a consistent pattern of Neanderthal DNA contributing less to these traits than expected, which is the pattern that we would expect if this DNA is deleterious and is being gradually removed from the modern human population," Sankararaman said.
Modern humans and Neanderthals are thought to have existed side by side for thousands of years, roughly 40,000 years ago. During this time, they bred together, which is thought to have helped early humans adapt to their new environment. However, their selective advantage appears to have largely dwindled since then.
"Our species evolved as it moved into new environments by acquiring DNA through interbreeding," Sankarararaman said. "This DNA, in turn, has shared the set of traits that we see today.
"The increasing availability of large datasets that link genetics to health and disease outcomes combined with ancient genomes will allow us to get new insights into how our species evolved. This is an exciting time to be studying these questions."
Uncommon Knowledge
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Newsweek is committed to challenging conventional wisdom and finding connections in the search for common ground.
About the writer
Pandora Dewan is a Senior Science Reporter at Newsweek based in London, UK. Her focus is reporting on science, health ... Read more
