People from Melanesia, a region in the South Pacific, carry genes of a yet-to-be-identified extinct human species, suggest findings of a new study presented at the American Society of Human Genetics meeting in Canada on Oct. 20.

University of Texas MD Anderson Cancer Center statistical geneticist Ryan Bohlender said that the hominid species is not likely Neanderthal or Denisovan but one that belongs to a third but related branch of family tree that produced the Neanderthals and the Denisovans, an extinct distant relative of Neanderthals known only from DNA collected from a finger bone and teeth that were discovered in a Siberian cave.

"We're missing a population or we're misunderstanding something about the relationships," Bohlender said.

An earlier study, which was published in the journal Science in March this year, provided evidence that prehistoric human ancestors interbred with Neanderthals and Denisovans hundreds of thousands of years earlier. It found that the genes of the Denisovans and Neanderthals that interbred with the prehistoric human ancestors exist among modern-day Asians, Europeans and Melanesians.

Research suggests that the interbreeding is possibly behind some characteristics of modern-day humans, which include skin color, rate of metabolism and even risks for smoking addiction and depression. Allergies may also be blamed on the presence of Neanderthal DNA.

For the new study, Bohlender's team wanted to know the amount the amount of Denisovan and Neanderthal DNA that humans carry up to this day. Using a computer model for their analysis, they found that Chinese and Europeans carry about 2.8 percent of Neanderthal DNA.

The researchers likewise found that the modern settlers in the South Pacific regions have 2.74 percent of their DNA coming from Neanderthals.

The researchers estimate that the Denisovan DNA present in these people is as low as around 1.11 percent, which is lower compared with estimates of other researchers that range between 3 and 6 percent.

The findings led Bohlender and his colleagues to conclude that a third group of hominids has possibly bred with the ancestors of the Melanesians.

The Neanderthals and Denisovans are hominid species that migrated out of Africa about 300,000 years ago and settled in Europe and some parts of Western Asia.

"One important insight stems from the observation that modern non-Africans and archaic populations share more derived alleles than they should if there was no admixture between them," Bohlender said, citing that sequencing of complete Neanderthal and Denisovan genomes offers insights into human history.

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