New genetic modeling hasn’t linked the species to either Neanderthal or Denisovan, two ancient species represented in the fossil record. The species has actually been related to a third, unknown human relative that has long puzzled archaeologists.
According to Ryan Bohlender, a statistical geneticist from the University of Texas, “We’re missing a population, or we’re misunderstanding something about the relationships.”
After examining the percentages of extinct hominid DNA modern humans still carry today, Bohlender and his team have discovered inconsistencies in previous analyses suggesting that there’s more to it than our relations to Neanderthals and Denisovans.
The researchers believe that our early ancestors traveled out of Africa between 100,000 and 60,000 years ago, and first encountered other hominid species on the Eurasian landmass. This contact marked our species in a way that Europeans and Asians still carry distinct genetic variants of Neanderthal DNA in their own genomes.
But, this is not all we’ve got from them.
In a separate study earlier this year, certain genetic variants inherited by Europeans from Neanderthals were linked to several health problems such as a slightly higher risk of depression, heart attack, and a few skin disorders.
Evidence showing that modern genital warts, commonly known as the human papillomavirus (HPV), were sexually transmitted to Homo sapiens after our ancestors slept with Neanderthals and Denisovans once they left Africa were found in another study published earlier this month. Although the Homo sapiens relation to the Neanderthals has been studied extensively, little is known of our relation with the Denisovans – the distant cousins of Neanderthals.
The reason for this is that plenty remains of Neanderthals have been uncovered throughout Europe and Asia, while all archaeologists have been able to find from the Denisovans is a lone finger bone and a couple of teeth found in a Siberian cave in 2008.
New computer model has helped Bohlender and his team to determine the amount of Neanderthal and Denisovan DNA carried by modern humans. The researchers found about 2.8% of Neanderthal DNA in both Europeans and the Chinese, an amount that coincides with previous findings.
However, the research didn’t run as smoothly when the team started investigating Denisovan DNA, particularly in relation to modern populations inhabiting Melanesia, a region of the South Pacific including Vanuatu, the Solomon Islands, Fiji, Papua New Guinea, New Caledonia, West Papua, and the Maluku Islands.
In the words of Hesman Saey for Science News:
“Europeans have no hint of Denisovan ancestry, and people in China have a tiny amount – 0.1 percent, according to Bohlender’s calculations. But 2.74 percent of the DNA in people in Papua New Guinea comes from Neanderthals.
And Bohlender estimates the amount of Denisovan DNA in Melanesians is about 1.11 percent, 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.”
“Human history is a lot more complicated than we thought it was,” he added.
The results of this study match the findings of a separate study carried out by researchers from the Natural History Museum of Denmark, who investigated DNA from 83 Aboriginal Australians and 25 natives from the Papua New Guinea highlands – the most inclusive genetic study of Indigenous Australians ever. The study also found that Indigenous Australians date back more than 50,000 years ago, which defines them as the oldest continuous civilization on Earth.
The study also found that these peoples carry DNA resembling that of the Denisovans, but different enough to be recognized as coming from a third, unidentified hominid.
According to lead researcher Eske Willerslev “Who this group is we don’t know.”
However, more specific evidence, preferably in the form of fossils, is needed to confirm the theory of a third human species. Prior to this, we can only hypothesize about the findings.
This could also indicate that our identification of Denisovan DNA is more unclear than we think, assuming that the only specimen of this species is a finger bone and a couple of teeth.
Also, it could point toward more complex interactions of the Homo sapiens with ancient humans.
With any luck, more scientific evidence of the genetic make-up of our oldest ancestors will shed new light on the complex history our species shared with them.
The findings of Bohlender’s study were presented at the 2016 American Society of Human Genetics meeting in Canada last week.