Pacific islanders got a double whammy of Stone Age DNA
Melanesians only people known to inherit substantial DNA from both Neandertals, Denisovans
Modern-day Melanesians carry a two-pronged genetic legacy of ancient interbreeding that still affects their health and well-being, researchers say.
Unlike people elsewhere in the world, these Pacific islanders possess nuclear DNA that they inherited from two Stone Age hominid populations, say population geneticist Benjamin Vernot, formerly of the University of Washington in Seattle, and his colleagues. At least some of that ancient DNA contains genes involved in important biological functions, the researchers find. Nuclear DNA is passed from both parents to their children.
The finding means that ancestors of people now living in the Bismarck Archipelago, a group of islands off Papua New Guinea’s northeastern coast, mated with Neandertals as well as with mysterious Neandertal relatives called Denisovans, the scientists conclude online March 17 in Science.
In support of previous research, the researchers find that non-Africans — including Melanesians — have inherited an average of between 1.5 and 4 percent of their DNA from Neandertals. But only Melanesians display substantial Denisovan ancestry, which makes up 1.9 to 3.4 percent of their DNA, the researchers say. (Present-day African populations possess little to no Neandertal or Denisovan DNA.)
The bits of Neandertal and Denisovan DNA carried by Melanesians encompass genes involved in metabolism and immunity, indicating that interbreeding influenced the evolutionary success of ancient humans, Vernot’s group reports.
The new study reconstructs the microscopic landscape of Neandertals’ and Denisovans’ contributions to Melanesians’ DNA “in impressive detail,” says Harvard University paleogeneticist Pontus Skoglund.
Vernot’s team studied DNA from 35 Melanesians at 11 locations in the Bismarck Archipelago. Analyses concentrated on DNA from 27 unrelated individuals. The researchers also looked for evidence of ancient interbreeding in previously acquired genomes of close to 1,500 modern-day individuals from different parts of the world. Denisovan DNA for comparisons came from fragmentary fossils found in a Siberian cave; comparative Neandertal DNA came from a genome previously extracted from a 50,000-year-old woman’s toe bone.
Among Melanesians, DNA sequences attributed to Neandertals and Denisovans encompassed several metabolism genes. One of those genes influences a hormone that increases blood glucose levels. Another affects the chemical breakdown of lipids. Other Melanesian genetic sequences acquired through ancient interbreeding either include or adjoin genes that help to marshal the body’s defenses against illness.
These findings follow evidence suggesting that once-useful genes that ancient humans inherited from Neandertals now raise the risk of contracting certain diseases (SN: 3/5/16, p. 18). Vernot’s group reaches no conclusions about good or bad effects of ancient hybrid genes in Melanesians.
No sign of Neandertal or Denisovan DNA appears in areas of Melanesians’ genomes involved in brain development, the scientists say. So brain genetics, for better or worse, apparently evolved along a purely human path.
Denisovans’ evolutionary history remains poorly understood. Previous DNA comparisons suggest that Denisovans must have reached Southeast Asia. Skoglund suspects that’s where the ancestors of Melanesians bred with Denisovans.
Substantial interbreeding of humans with Denisovans probably occurred only once, Vernot and his colleagues suspect. Genetic exchanges of humans with Neandertals took place at least three times, they add. These estimates are derived from comparisons of shared Denisovan and Neandertal DNA sequences among individuals in different parts of the world.
Story today on a news website in India:
New York: An international team of scientists has discovered that residents of the remote equatorial islands of Melanesia share fragments of genetic code with two extinct human species.
The researchers compared the DNA sequences of 35 modern people living on islands off the coast of New Guinea with DNA drawn from two early human species: Denisovans, whose remains were found in Siberia, and Neanderthals, first discovered in Germany.
“Substantial amounts of Neanderthal and Denisovan DNA can now be robustly identified in the genomes of present-day Melanesians, allowing new insights into human evolutionary history,” the study said.
“As genome-scale data from worldwide populations continues to accumulate, a nearly complete catalog of surviving archaic lineages may soon be within reach,” the study noted.
The findings were published in the journal Science.
Th researchers collected the modern-day blood samples used in the study about 15 years ago in Melanesia. This is the first time full genomes from those samples have been sequenced.
“I’m surprised that these Neanderthal and Denisovan genomes made it out to this remote place,” said one of the researchers Andrew Merriwether, molecular anthropologist at Binghamton University in New York.
“We know people have been there for at least 48,000 years because we find human remains that go back that far, but no one has ever been able to connect them to any other place. When you compare most of their genome sequences, they don’t cluster with any other group. They’ve been there and been isolated for a very, very long time,” Merriwether noted.
Studies like this one may enable scientists to answer big questions about human migrations and evolution thousands of years ago.
How did ancient humans travel — and cross the ocean — to get to Melanesia, and when and where did the Denisovan DNA enter our gene pool?
The researchers believe that sequencing of additional DNA samples found in Asia may one day help to answer those questions.
First Published: Friday, March 18, 2016 – 17:41