Residents of the remote equatorial islands of Melanesia share fragments of genetic code with two extinct human species. That’s the key finding of a new study published March 17 in the journal Science.
An international team contributed to the research, which 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 Neandertals, first discovered in Germany.
“Substantial amounts of Neandertal and Denisovan DNA can now be robustly identified in the genomes of present-day Melanesians, allowing new insights into human evolutionary history,” they wrote. “As genome-scale data from worldwide populations continues to accumulate, a nearly complete catalog of surviving archaic lineages may soon be within reach.”
D. Andrew Merriwether, a molecular anthropologist at Binghamton University, 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 Neandertal and Denisovan genomes made it out to this remote place,” he said. “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.”
Earlier studies have revealed some genetic overlap (about 2 percent) between Neandertals and non-African populations and little or no Neandertal and Denisovan ancestry among Africans. This new research suggests Neandertals and modern human ancestors intersected at least three times. It also found an overlap of between 1.9 and 3.4 percent in the genetic codes of Denisovans and modern-day Melanesians.
Skepticism about the new findings is entirely appropriate, said Merriwether, who specializes in reconstructing the past using samples from contemporary populations and ancient DNA from the archaeological record.