More evidence reveal that our prehistoric human ancestors had interbred with Neanderthals and another archaic line of ancient humans called Denisovans hundreds of thousands of years ago.
A previous study conducted by scientists from the Max Planck Institute for Evolutionary Anthropology says that Neanderthals and Denisovans may have only split 430,000 years ago. If the findings of this study are correct, it would mean that the species Homo antecessor could be the common ancestor of modern humans, Neanderthals and Denisovans, scientists said.
Now, a new study found that the genes of the Denisovans and Neanderthals who had interbred with our prehistoric ancestors actually live on today among modern Asians, Europeans, and in the Melanesians of Papua New Guinea.
Led by scientist Svante Paabo who is also from the Max Planck Institute, the international team of researchers focused on the genetic code of Melanesians in particular, comparing the DNA sequences of 35 modern humans on islands off the New Guinea coast with DNA from Neanderthals and Denisovans.
Their findings confirm theories that our human ancestors did not interbreed with other hominin species until after they left Africa. Even today, there is barely a trace of Neanderthal DNA in modern Africans.
When our ancient human ancestors started traveling across Eurasia, they lived side-by-side and had a few run-ins with other species. Paabo said diverse populations of modern humans have various levels of Neanderthal DNA, and this means that ancient humans often ran into Neanderthals as they moved across Europe.
"Substantial amounts of Neanderthal and Denisovan DNA can now be robustly identified in the genomes of present-day Melanesians," the researchers say.
Molecular anthropologist Andrew Merriwether of Binghamton University said this is the first time that full genomes from blood samples collected 15 years ago in Melanesia have been sequenced.
He said he was surprised that Denisovan and Neanderthal DNA even made it out as far as Papua New Guinea. They know that people have been on the island at least 48,000 years, especially because they have found human remains whose age go back that far.
However, no one has ever been able to connect the remains to any other place, he said.
"When you compare most of their genome sequences, they don't cluster with any other group," said Merriwether. "They've been there and been isolated for a very, very long time."
In fact, researchers found that the genetic connection between ancient hominins and modern Melanesians were between 1.9 to 3.4 percent. This meant that modern human ancestors and early humans have interbred on at least three separate occasions.
Benjamin Vernot of the University of Washington, who is also part of the study, said he believes that Denisovans and Neanderthals liked to wander.
"And yes, studies like this can help us track where they wandered," added Vernot.
The question now is this: how did the Denosivans make their way to the island of Melanesia?
"Most people know back a few generations, maybe five generations, but where did we come from before that? That's what we want to find out," added Merriwether.
The findings of the study are featured in the journal Science. The authors were from the Max Planck Institute, Binghamton University, Italy's University of Ferrara, the University of Washington, Temple University, the Coriell Institute for Medical Research, the University of Cincinnati, and the Institute for Medical Research in Papua New Guinea.