People from Papua New Guinea and north-east Australia carry small amounts of DNA of an unidentified, extinct human species, a new research analysis has suggested.
The analysis suggests the DNA is unlikely to come from Neanderthals or Denisovans, but from a third extinct hominid, previously unknown to archaeologists. Statistical geneticist Ryan Bohlender and his team investigated the percentages of extinct hominid DNA in modern humans.
They found discrepancies in previous analyses and found that interbreeding between Neanderthals and Denisovans was not the whole story to our ancestors' genetic makeup.
Mr Bohlender presented his analysis to the American Society of Human Genetics in Canada, saying that scientists were either "missing a population" or "misunderstanding something about the relationships".
Mr Bohlender and his colleague used a computer model to figure out the amount of Neanderthal and Denisovan DNA carried by modern humans. They found Europeans and Chinese people carry about 2.8 per cent of Neanderthal DNA. But Europeans have no Denisovan ancestry, and Chinese people only have 0.1 per cent.
Modern populations from South Pacific regions including Vanuatu, the Solomon Islands, Fiji, Papua New Guinea, New Caledonia, West Papua, and the Maluku Islands have 2.74 per cent of their DNA as coming from Neanderthals. Mr Bohlender estimates the amount of Denisovan DNA in these people is as low as about 1.11 per cent, not the 3 to 6 per cent estimated by other researchers.
Therefore, Mr Bohlender and his colleagues came to the conclusion that a third group of hominids may have bred with the ancestors of Melanesians. "The sequencing of complete Neanderthal and Denisovan genomes has provided several insights into human history," Mr Bohlender said. "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. "We now know that the ancestors of modern non-Africans met, and introgressed with, Neanderthals and Denisovans."
Neanderthals and Denisovans are two hominid species that migrated out of Africa. According to theory, Neanderthals left Africa about 300,000 years ago, settling in Europe and parts of western Asia.
The Denisovan species was only discovered in 2008 when paleoanthropologists discovered a 40,0000-year-old tooth and pinkie bone from a young girl in a Siberian cave. Scientists examined the DNA from the bone and found that, although the girl was closely related to Neanderthals, it was distinct enough to merit classification as a new species.
There was a genetic overlap between the Denisovan genome and that of some present-day east Asians, and a group of Pacific Islanders living in Papua New Guinea.
This is why the discovery of a possible third hominid species is a remarkable discovery, especially considering the discovery was made from DNA of modern people.
Mr Bohlender's findings are supported by an earlier study from the University of Cambridge which sequenced the genome of 83 Aboriginal Australians from the Pama-Nyungan-speaking language group, which covers 90 per cent of the continent, and 25 Highland Papuans. It revealed Papuan and Aboriginal ancestors left Africa around 72,000 years ago and then split from the main group around 58,000 years ago.
They reached the supercontinent of 'Sahul' that originally united Tasmania, mainland Australia and New Guinea around 50,000 years ago, picking up the DNA of Neanderthals, Denisovans and another extinct hominin along the way.
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