Ancestors of Modern East Asians had Sexual Encounters with both Southern and Northern Denisovan Populations During Migrations into Eurasia 60,000 years ago
Sex always sells in the media; perhaps then it should come as no surprise that the detection of yet another instance of ‘interspecies sex’ has made international headlines this week. Even though the couples involved in this sex have long since decomposed to dust, it has done little to lower public interest in the story.
Just a few years ago scientists investigating bone fragments at the Denisova Cave site in Siberia revealed a new human species to the world, the Denisovans. Since then we have learned that Denisovans were an ancient race, separated from our direct ancestors by over 700,000 years of evolution and that at some stage they were present in large numbers across the Asian region. Thanks to the recovery of ancient DNA and mapping of the full Denisovan genome the world also learned that Denisovans had sexual encounters with modern humans perhaps 45,000 to 50,000 years ago.
Denisovan genes are not found in all living humans today, in fact, there are two main population clusters. The East Asian genome holds 0.2% Denisovan genes while some of the indigenous people of Australasia, especially those of Papua, have a huge 5%. The discovery that Papuans carry this high level of this archaic human genetics has led a growing number of scientists to suspect the Denisovans were encountered very close to Papua, perhaps on a neighbouring island.
The newly published paper Analysis of Human Sequence Data Reveals Two Pulses of Archaic Denisovan Admixture composed by Browning et al. for the journal Cell, offers an additional and somewhat revolutionary discovery. Scientists associated with the University of Washington contrasted the genome extrapolated from the samples of Siberian Denisovan DNA against samples of DNA from numerous modern populations. The result of this exhaustive process was that the team discovered a complex relationship between the Siberian samples and Denisovan genes inherited by modern humans in Asia.
East Asians, particularly Chinese and Japanese people, carry genes that are closely related to the Siberian Denisovans and others from a more distantly related group, these others seem to be the same population responsible for the interbreeding signature detected among modern Papuans. That the ancestors of East Asians have this unique signature for two interbreeding events has caused considerable confusion as to how this came about and why no other populations evidence this interaction.
The logical deduction from this new finding is that some of the modern humans from Australasia moved up into Southeast and East Asia carrying Denisovan genes with them. Members of this group then encountered a second population of Denisovans which was closely related to the individuals uncovered at the Denisova Cave site (not necessarily living physically near to them). Interbreeding must have been on a limited scale – as evidenced by the low proportion of genes still carried today.
It may have been that the modern human group far outnumbered the Denisovans or that only a few respective individuals successfully mated as the groups passed each other on the road. Samples of DNA from the Denisova Cave site also revealed that one of the Denisovans, a young girl, carried genes from modern humans closely related to modern Papuan people confirming that the genetic traffic went both ways.
These migrants from Australasia did rather well in Asia because today they have several million descendants. They also seem to have absorbed other human sub-species in the region, as East Asians carry the highest proportion of Neanderthal genetics of any modern population group. Indeed, modern Eat Asians have around 30% higher Neanderthal genetics than observed in the European genome. Around one-quarter of the ancient DNA that Browning found didn’t match either Neanderthal or Denisovan DNA. It could be that various so-called ‘ghost populations’ mated with early modern humans in Asia and leaving just their genes but no fossils.
How does this fit with Out of Africa?
The trouble with all this information is that it does not fit at all well with the migration model most scientists support, the Recent Out of Africa Hypothesis. Geneticists calculate that the populating of Eurasia happened between 60,000 to 45,000 years ago, with Europe reached last. Researchers often assume that modern humans encountered Neanderthals in the Middle East and then met Denisovans somewhere in Central Asia. These acquired genes should then have been common among early Asians, some of whom would also go on to be the ancestors of Europeans and the ancestors of Australasian Aboriginal populations. Bizarrely we see that after some East Asians doubled back on themselves and moved westwards towards Africa, assumedly passing through Denisovan and Neanderthal territories, they lost all of their Denisovan genes and much of their acquired Neanderthal DNA.
The story of the European ancestors with their loss of archaic genes and choice of a peculiar elongated migration route (having already passed Europe on route to Asia) is strange enough, but when we consider the Australasians things begin to decide seriously whacky. Even though genetic models keep on confirming that ancestral Eurasians separated from their assumed African source population sometime after 60,000 years ago, gradually expanding eastwards, archaeology places modern humans in Australasia no less than 65,000 years ago. Australia is almost right at the end of the migration routes from Africa; only America is positioned further to the east.
To incorporate the latest discoveries into the consensus models, we are asked to believe that ancestral Australian Aboriginals arrived on their continent before their ancestors even left Africa. The ancestors of Aboriginals are shared with modern East Asians, yet the two populations carry wildly different levels of archaic genes. Further to this, the only way to make sense of East Asians having genes from the Southern Denisovans seems to require Aboriginals sailing down through Indonesia to acquire them. After several generations of mixing with Denisovans, some of the descendants then made the extremely difficult voyage back to mainland Asia and mixed extensively with other modern humans living there.
Occam’s Razor – Simple is Superior
There is a common principle in modern science which tends to guide the methodology in research, Occam’s Razor, attributed to the 14th-century logician and Franciscan friar William of Ockham. Occam’s principle states that “entities should not be multiplied unnecessarily.”
Today scientists have rephrased the wording of Occam’s principle, “when you have two competing theories that make exactly the same predictions, the simpler one is the better.”
Out of Australia vs Out of Africa
Unknown to many readers there is indeed a competing theory on the matter of the populating of Eurasia. This second model explains all aspects of the populating of Eurasia, that is to say, that it fits every last piece of evidence we have available, and it is also far simpler than the Out of Africa Theory.
Knowing that we have modern humans living in Australia earlier than 60,000 years ago, we can start the migrations into Eurasia from that continent without any need for new archaeological discoveries; foundational migrations occurred between 60,000 to 45,000 years ago. We can imagine that as one wave of migrants moved out of Australia, they encountered Southern Denisovans living in the north or perhaps on a neighbouring island. These explorers then headed north towards East Asia were they gradually expanded their range. The modern humans absorbed local remnant populations of Neanderthals, Denisovans and other hominins. The descendants of this group make up the greater part of today’s Asian populations.
We can then imagine a separate wave of migrants left Australia from the North Coast, island hopping their way towards Southeast Asia without passing through Denisovan territories situated on the islands to their east or on Papua (which was then part of continental Australia). Once these wanderers reached mainland Asia, they moved west through coastal South Asia and then gradually made their way towards the Middle East. Around 45,000 years ago descendants of this group moved through Western Asia and then entered Europe and North Africa.
The above is a very simplified summary of a fully formed scientific theory which has been in print since April 2017. The model is not only simple and elegant, but it is a far superior to the existing hypothesis as it matches the physical archaeology and the extensive body of genetic research.
The only problem with the Out of Australia and Into Africa Theory is that it requires an uncomfortable paradigm displacement. There are now a great many leading scientists aware of this superior scientific model. Sadly, scientists are proving heavily resistant to debating this competing model in public. It is for that reason you do not hear about it from prominent academics and that the mainstream media is completely unaware of its existence.