Modern human DNA is actually a cocktail. While we call ourselves Homo sapiens, we're actually a mixture of other species like Neanderthal and Denisovan, early human ancestors. This latter group's DNA, recently discovered in 2010, is particularly common in East and Southeast Asia populations, but a new in Cell provides evidence that another ancestor, one that branched off from Denisovans long ago, lived in Papau New Guinea and also mated with modern humans as soon as 15,000 to 30,000 thousand years ago.
This would make them the youngest archaic relative in our human lineage.
Genetic differences among this newfound lineage led scientists to conclude that these early humans were their own distinct group separate from both Neanderthals and Denisovans, from which they separated some 283,000 years ago. They were found to have been "three very different groups, with more diversity among them than seen today in modern humans," Murray Cox, a population geneticist, told .
The new species is partly Denisovan, likely born from two of the three species' divergences. According to Cox, the newly discovered branch of Denisovans "is about as different from the Denisovan individual found in Denisova Cave as it is from Neanderthals," says Murray Cox, a population scientist from Massey University in New Zealand, who was involved with the study. "This means that if we're going to call Neanderthals and Denisovans by special names, this new group probably needs a new name, too," said Cox.
When the two Denisovan lineages split some 283,000 years ago, one—closely related to the Denisovans found in the Siberian cave—was mainly found in East Asia while the newly discovered lineage could be found in Papua New Guinea and South Asia. The latter was not as closely related to the Siberian Denisovan lineage.
A human genome analysis showed inconsistencies in pieces of DNA from populations in Southeast Asia and New Guinea indicating that modern humans bred with more than one lineage of Denisovan.
According to the study, the DNA of modern Papuans contained "hundreds of gene variants from two deeply divergent Denisovan lineages." One lineage had previously been seen in modern Papuan and South Asian DNA, but the other lineage had never been seen before.
Scientists would like to use this study to better understand how inherited genetic variants caused by interbreeding with ancient hominins affects human health today, particularly the underserved populations living on the islands of southeast Asia.
Many things are unknown about this human relative, but with more research, scientists will hopefully uncover more about this chapter in ancient human history.