Researchers found what is believed to be the highest degree of archaic human ancestry ever documented. The latest study from the University of Washington revealed that Melanesians retain both Neanderthal and Denisovan ancestry in their genes, shedding new light on early human evolution and gene flow.
Denisovans are related to, but distinct from, Neanderthals. However, both Neanderthals and Denisovans went extinct several thousand years ago. It follows then, the family roots of Melanesians - people native to Vanuatu, the Solomon Islands, Fiji, Papua New Guinea, New Caledonia, West Papua and the Maluku Islands - go incredibly deep.
"I think that people (and Neanderthals and Denisovans) liked to wander," said lead author Benjamin Vernot, a University of Washington postdoctoral student in genomic sciences. "And yes, studies like this can help us track where they wandered."
Researchers analyzed the genomes of 1,523 individuals from around the world, including 35 Melanesians. They confirmed that all non-African people surveyed inherited roughly 1.5 to 4 percent of their genomes from Neanderthals. Melanesians, however, were the only population that also had significant Denisovan ancestry, representing between 1.9 and 3.4 percent of their genome.
Prior to this study, substantial amounts of Denisovan DNA had been detected in the genomes of only few present-day human populations living in Oceania.
"Denisovans are the only species of archaic humans about whom we know less from fossil evidence and more from where their genes show up in modern humans," added Joshua Akey, senior author of the study from the University of Washington's Department of Genome Science.
Understanding when and where archaic hominins and our modern ancestors co-existed and interbred has been the focus of many recent studies.
"Different populations of people have slightly different levels of Neanderthal ancestry, which likely means that humans repeatedly ran into Neanderthals as they spread across Europe," Vernot explained.
Previously, researchers had located large regions of the genome where no humans carried any Neanderthal sequences. Building on past work, the recent study confirmed that some of those regions are also devoid of Denisovan sequences.
Researchers explained that those regions of the modern human genome that appear particularly depleted of archaic sequences are those that play a role in speech and language development, suggesting that these skills could have set modern humans apart from Neanderthals and Denisovans.
"These are big, truly interesting regions," Akey added. "It will be a long, hard slog to fully understand the genetic differences between humans, Denisovans and Neanderthals in these regions and the traits they influence."
On the other hand, researchers noted that those that contain more archaic DNA may represent regions were archaic adaptations, such as immunity to unfamiliar pathogens, were advantageous.
Vernot concluded that their study "demonstrates how we can learn about human history, and our archaic relatives, by studying ancient and modern DNA."
Their findings were recently published in the journal Science.
