Scientists have long understood that when early human ancestors migrated from Africa to the Asia-Pacific region, they bred with two other hominins upon their arrival; the Neanderthals and the Denisovians. But a new genomic analysis has uncovered that in South and Southeast Asia, early humans arriving from Africa bred with a mysterious separate, unknown, now-extinct third hominin.
The new study was conducted by Jaume Bertranpetit at Pompeu Fabra University in Spain, who along with colleagues mapped the genomes of 10 Andamanese individuals--that is, aboriginal people of India's Andaman Islands in the Bay of Bengal--and compared their DNA to that of 60 ethnically diverse individuals from mainland Indian populations.
Through this DNA analysis, the researchers found that yes, as expected, there was ancestry from African migration 60,000 years ago, from Neanderthals and from Denisovians--but the Andameanese individuals also shared a small segment of DNA that does not match any known hominin. And this DNA has not been found in any living Europeans or East Asian individuals.
There is however one strong contender when it comes to the source of this mystery DNA: Homo erectus. There's only one problem, as Bertranpetit told New Scientist:
We do not have any direct evidence.
Which is the general thorn in the side of the study of human ancestry and the history of H. erectus; there's absolutely no preserved genetic material in any fossils that have so far been discovered. So all the evidence is pretty much circumstantial. Yes, H. erectus was the first to leave Africa, yes it was the first hominin to share traits with modern humans, and yes H. erectus lived in Asia between 1.8 million and 33,000 years, so had an ovelap with modern humans. But did they breed with humans? We simply can't prove it.
There is also a possibility that this mystery DNA segment comes from multiple different unknown hominins, which could make identification of our unidentified human ancestor(s) even more complicated or arguably impossible.
As Alan Cooper of the University of Adelaide, Australia told New Scientist, when modern humans migrated in--what this and other recent studies show to be--a single out-of-Africa movement:
Europeans headed west, and everybody else headed east. And then within Asia, it became horribly complicated in terms of the movement, because there were several hominins floating around in that space – Denisovans, Neanderthals and now this third group.
Lead image, Andaman Islands, via Wikimedia Commons