DNA from Extinct Human Relative May Have Shaped Modern Papuans’ Immune System

DNA from Extinct Human Relative May Have Shaped Modern Papuans’ Immune System

DNA from Denisovans, an extinct human species, that was found in the genomes of Indigenous Papuans may mold their immune system

Children playing near Kimbe, the capital of Papua New Guinea’s West New Britain Province. New research suggests that DNA from an extinct human race, Denisovans (in the genomes of modern Papuans), may have helped to shape their immune system. Credit: Marc Dozier/Hemis/Alamy Stock Photo

A new study suggests that DNA from extinct human species may have influenced the immune systems of New Guineans.

Thousands of years ago, the ancestors of modern humans met and mated with Neandertals–and also with their close cousins and contemporaries, Denisovans. Though both Neandertals and Denisovans later went extinct (with Denisovans possibly sticking around until as recently as 15,000 years ago), billions of people around the world still carry the proof of these interactions in their DNA.

It’s not clear why these genetic fragments derived from extinct human beings have remained. But the new study, published on Thursday in PLOS Genetics, finds disease resistance might have been involved. The research–conducted by Irene Gallego Romero, a human evolutionary geneticist at the University of Melbourne in Australia, and her colleagues–suggests that certain mutations from long-gone Denisovans may help today’s Papuans fend off viral infections.

This latest study is the first to examine the role Denisovan genetics plays in today’s humans, according to Joshua Akey, a Princeton University population geneticist who was not involved with the research.

The idea that extinct species of human beings continue to influence human biology today is not new. In the past decade, researchers have linked Neandertal DNA in modern humans to things ranging from smoking habits to celiac disease. Scientists have also suggested that Denisovan DNA may have contributed to high-altitude adaptation in Tibetans.

However, studies linking Denisovan mutations with modern human biology have been rare. Akey says that most of the research has been done on Europeans. The average Neandertal DNA content of humans outside Africa is 2 percent. Denisovan DNA is found in only a small percentage of people from Asia and the Pacific.

Scientists who are interested in the biological roots of Denisovan genetic DNA must look beyond the large European genomic data bank. New Guinean and Australian Indigenous peoples have the highest concentrations, on average, of Denisovan DNA. So Gallego Romero and her colleagues decided to sort through the genomes of 56 Papuans to examine what parts of their genetic sequences retained Denisovan DNA.

The team discovered an unusually high number of Denisovan mutations within gene sequences that control the immune system. The mutations were not found in genes, as was the case with other studies. They were instead found in parts of the genome that control when, where, and how much a gene can be expressed. The Denisovan mutations were found in genes that regulate the response to viral infection.

But just because mutations were found in these areas doesn’t mean they had an active impact on how cells behave. The researchers created cells containing some Denisovan mutations to test this. The researchers then compared the expression of genes in these cells with those containing non-Denisovan variants. Two of the mutations affected the expression of immune genes. This suggests that such mutations can have an impact on many Papuans’ immune responses.

Why do Papuans still have these mutations? Gallego Romero believes that adapting to new environments was a key factor. “When you think of humans walking around this part of the world 60,000 years ago, one of the biggest challenges is encountering new pathogens that could wipe you out,” she says. The New Guinean Denisovans may have needed to adapt to local diseases for tens of thousands more years before modern humans arrived. The descendants of Denisovans may have had mutations that helped them overcome the worst cases of these diseases.

This research shows that studying different groups can help reveal how people adapt to new environments. Lluis Quintana–Murci, a population geneist at France’s Pasteur Institute, said that such research can help “highlight how humanity diversity is important for adaptation.” He says, “There are so many populations that are still understudied.” Researchers are now focusing their attention on new populations. “I am certain that we will learn new information.”

ABOUT THE AUTHOR(S)

    Freda Kreier is a freelance journalist who likes writing about the natural world, DNA and the distant past. You can find more of her work at www.fredakreier.com.

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