The Grapevine

Our Immune System Genes Tell An Ancient Human/Neanderthal Love Story

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The story of mankind is more complicated than you might think. Graeme Churchard CC BY 2.0

You can thank your ancient Neanderthal ancestors for your strong immune system — or at least that's the consensus of two independent studies recently added to the American Journal of Human Genetics.

Although Neanderthals are largely regarded as a lesser species that died out after being overcome by superior homo sapiens, scientists now believe Neanderthals did not become extinct, but instead were bred into the human species. According to National Geographic, a new theory of human evolution posits the two species made love, not war. In fact, scientists speculate that when ancient Homo Sapiens first left Africa and encountered Neanderthals in Asia and Europe, they interbred so much that today nearly every human (except for those whose ancestors never ventured out of Southern Africa) have a tiny bit of Neanderthal DNA preserved in their genes.

But, the studies suggest these remnants of Neanderthal genes do more than serve as a living record of a prehistoric love affair.

Survival

Both papers focus on a group of genes known as Toll-like receptor (TLR) genes. Expressed on the cell surface, these genes detect and respond to components of bacteria, fungi, and parasites. They play an essential role in eliciting inflammatory and antimicrobial responses, as well as activating our immune response.

In one of the studies, a team of scientists from various institutions explored the evolution of the human immune system by looking at the genetics of present-day people available on the 1000 Genome Project. They discovered the TLR 1-6-10, a specific type of TLR gene, was among the genes that presented the highest Neanderthal ancestry in both Europeans and Asians.

In the other study, a team of researchers from the Max Planck Institute for Evolutionary Anthropology in Germany set out to find evidence of non-human genes in the present day human genome. In doing so, they stumbled upon the same association between the immune system promoting TLR genes and ancient Neanderthals.

"What has emerged from our study as well as from other work on introgression is that interbreeding with archaic humans does indeed have functional implications for modern humans, and that the most obvious consequences have been in shaping our adaptation to our environment," study author Dr. Janet Kelso explained in a recent statement. "Improving how we resist pathogens and metabolize novel foods."

While breeding with another species, especially one as unattractive as the Neanderthal, may sound unappealing, in reality this match-up was actually very advantageous.

"Neanderthals, for example, had lived in Europe and Western Asia for around 200,000 years before the arrival of modern humans," said Kelso. "They were likely well adapted to the local climate, foods, and pathogens." She explained that by breeding with this well-adapted species, ancient humans guaranteed their offspring would inherit these local adaptations, ensuring the survival of our species. A beautiful end, to a beautiful love story.

Source: Dannemann M, Andres AM, Kelso J. Introgression of Neanderthal- and Denisovan-like Haplotypes Contributes to Adaptive Variation in Human Toll-like Receptors. The American Journal of Human Genetics . 2016.

Deschamps M, Laval G, Fagny M, et al. Genomic Signatures of Selective Pressures and Introgression from Archaic Hominins at Human Innate Immunity Genes. The American Journal of Human Genetics. 2016.

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