DNA data point to unknown hominid: Melanesians carry clues to ancestor not revealed by fossils.
People from Melanesia, a South Pacific region encompassing Papua New Guinea and surrounding islands, may carry genetic evidence of a previously unknown extinct hominid, Ryan Bohlender reported October 20. That species is probably not Neandertal or Denisovan, but a different, related hominid group, said Bohlender, a statistical geneticist at the University of Texas MD Anderson Cancer Center in Houston. "We're missing a population or we're misunderstanding something about the relationships."
This mysterious relative was probably from a third branch of the hominid family tree that produced Neandertals and Denisovans, a distant cousin of Neandertals. While many Neandertal fossils have been found in Europe and Asia, Denisovans are known only from DNA from a finger bone and teeth found in a Siberian cave (SN: 12/12/15, p. 14).
Bohlender isn't the first to suggest that remnants of archaic human relatives may have been preserved in human DNA even though no fossil remains have been found. In 2012, another group suggested some people in Africa carry DNA heirlooms from an unknown extinct hominid species (SN: 9/8/12, p. 9).
Less than a decade ago, scientists discovered that human ancestors mixed with Neandertals. People of non-African descent still carry a small amount of Neandertal DNA: Bohlender's team calculates that European and Chinese people carry about 2.8 percent. Europeans have no hint of Denisovan ancestry, and people in China have a tiny amount--0.1 percent, according to Bohlender. But 2.74 percent of the DNA in people in Papua New Guinea comes from Neandertals. And Melanesians have about 1.11 percent Denisovan DNA, Bohlender estimates, not the 3 to 6 percent estimated by other researchers. While investigating the Denisovan discrepancy, Bohlender and colleagues came to the conclusion that a third group of hominids may have bred with the ancestors of Melanesians.
Another group of researchers, led by Eske Willerslev, an evolutionary geneticist at the Natural History Museum of Denmark in Copenhagen, recently came to a similar conclusion. The group examined DNA from 83 aboriginal Australians and 25 people from native populations in the Papua New Guinea highlands (SN: 10/15/16, p. 6). Denisovan-like DNA was found in the study volunteers, the researchers reported in the Oct. 13 Nature. But the DNA is distinct from Denisovans and may be from another extinct hominid. That hominid could be Homo erectus or the extinct hominids found in Indonesia known as hobbits (SN: 4/30/16, p. 7), Willerslev speculates.
But researchers don't know how genetically diverse Denisovans were, says Mattias Jakobsson, an evolutionary geneticist at Uppsala University in Sweden. A different branch of Denisovans could be the group that mated with ancestors of Australians and Papuans.
Statistical geneticist Elizabeth Blue of the University of Washington in Seattle agrees that so little is known about the genetic makeup of extinct groups that it's hard to say whether the extinct hominid DNA actually came from an undiscovered species. DNA has been examined from few Neandertal fossils, and Denisovan remains have been found only in that single cave in Siberia. Denisovans may have been widespread and genetically diverse. If so, Blue says, the Papuans' DNA could have come from a Denisovan population that had been separated from the Siberian Denisovans for long enough that they looked like distinct groups, much as Europeans and Asians today are genetically different from each other.
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|Title Annotation:||GENES & CELLS|
|Author:||Saey, Tina Hesman|
|Date:||Nov 12, 2016|
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