Not everyone is convinced by the late dates Cox proposes. “There are definitely multiple Denisovan populations, but the claim that they interbred 15,000 to 30,000 years ago is extraordinary,” population geneticist Benjamin Vernot of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, told Science.
“I’m skeptical,” added Cosimo Posth of the Max Planck Institute for the Science of Human History in Jena, Germany. He suggests the hints of a late mating could reflect an encounter of previously isolated modern populations rather than of moderns and Denisovans. In this scenario, modern humans mated with Denisovans, then the modern populations diverged, with each branch retaining a different set of Denisovan genes. The moderns then reconnected, mixing the two sets of Denisovan DNA together again."The above is a quote from an article about a purported introgression of Denisovan DNA into a modern human population in Papua only 15-30K ago. Posth proposes an alternative explanation. That is that this wasn't a true admixture of modern humans and Denisovans in the relatively recent past, but rather two groups of modern humans- each with their own genes from a much earlier admixture event, produced this effect. It doesn't mean he is right. There were some odd hominins walking around apparently even in the fairly recent past over in Asia. But it does mean that there is starting to be a little push-back and a pro is appealing to the same sort of alternative explanations I have.
This is very similar to what I proposed in my article explaining why I believe that Eurasians don't have 1.5% of their genes from Neanderthals. I think the actual amount directly obtained from Neanderthals is zero. Rather than take a super-broad view of the word "human" I take a narrow one. Human's aren't anything that walks upright with a big brain and makes tools. We have other traits, like recursive thought and speech, we make art for its own sake, and have true empathy along with a desire to connect to something bigger than ourselves- culminating in religion. If the other hominins didn't have that then we would not have much to say to each other, even if they could talk.
So I propose that around 50K ago a special group of hominins came to be. I think created by a Divine Act, but we can argue about that later. I call them "Adamics" since the word "human" has been mis-appropriated to mean any hominin. They entered a world with a "zoo" of creatures which looked a lot like us on the outside but not the inside. Some of these would be classified as "Archaic Homo Sapiens" but they were not our ancestors. Perhaps early on our ancestors had limited inbreeding with them, but not directly with Neanderthals and Denisovans. If these Archaic Homo Sapiens had ancestors which interbred with Neanderthals and Denisovans then our ancestors could have picked up some segments indirectly from limited interbreeding with them. This is much like the way Posth is describing the supposed recent introgression of Denisovan genes.
Most of the genes from this admixture won't stick out, and many more have been lost. But a few do stick out, and we interpret that as stretches where we interbred with Neanderthals or Denisovans. What may have happened instead was that Adamics did a limited amount of interbreeding with "other" Homo Sapiens that were either more like these creatures genetically to start, or had interbred with them and had stretches of their DNA which they passed to some of our ancestors.
IOW words I am offering an explanation (and this is an alternative explanation, not my current actual view which aligns more with Dr. Amos referenced below) very much like the one Cosimo Posth gives for the supposed signal of "recent Denisovan admixture" and applying it to all instances of supposed admixture. The "limited admixture" scientists are detecting would then be with things that would be classified as "Archaic Homo Sapiens" or perhaps even modern humans, but they lacked those traits I mentioned earlier. Still, it wasn't as big a jump as they think, and once the Adamics got their feet under them even that introgression completely or almost completely ended.
That's why there is no sign of any admixture between living Europeans and Neanderthals once we got to Europe despite the thousands of years they supposedly lived side-by-side. The party line requires introgression with them 50K ago that was so significant that it is still easily detectable in all Eurasians today. Yet somehow there is no genetic trace in living Europeans of any more such intermixing from 40K ago or 30K ago. My explanation for the disparity is simple. The Adamics didn't mix with Neanderthals 55K ago either, but did to a very limited extent with lines of Archaic Homo Sapiens in the Near East who had some genes that were much closer to Neanderthals. The reason we can't detect any introgression from later in Europe in living Europeans is because there were few to no "other" H. Sapiens to be had there- just Neanderthals. Adamics had no interest in Neanderthals. They may have viewed them like trolls.
So then why are Eurasians less diverse than Africans except for Neanderthal/Denisovan genes? The same thing happened in Africa, but the "others" the Adamics in Africa intermixed with were not in the same environment with Neanderthals and Denisovans so their genetic input didn't look like what the Eurasian Adamics got. It could be part of the explanation for increased African diversity however. IOW some of the Eurasian diversity looks like the genes of other hominins we know about, so we call it such. The African diversity may be the result of something that we don't know about, so we think they have been around for 200K years diversifying.
We don't have hominin suspects for the increased African diversity, so we just say they were more diverse before any introgression. But maybe that's not so. Fact is, sub-Saharan Africans get most of their greater diversity from a few small populations, like Pygmies and San. Take away the few hot spots of extra diversity and Sub-Saharan Africans aren't so much more diverse than the rest of us. Maybe there was one recent (50-70Kyears ago) population of H. Sapiens that had the traits I described above that made them "Adamics". They started in NE Africa and the Mid-east. From there one group went south and another east and another north. Each of them had some limited admixture with the "other" Homo Sapiens who were already in decline. The reason that the most human genetic diversity is at the edge of the range- south Africa, far west Africa, and in far east Asia with Denisovan-like genes, is that the genetic signature of the "others" has not yet been so swamped at the extreme ends of our range as it was in the middle.
Others, albeit not under their real name, have advanced an idea like I am suggesting. See this article and plug in "Adamics" for what he calls "Afrasians" and the "other Homo Sapiens" for what he calls "Paleoafricans" and its pretty much the same idea. See also here. The only difference is he thinks the "Afrasians" who went to Eurasia had limited mixing with the more distant Neanderthals and Denisovans while the outlier Afrasian group in Africa had limited mixing with "other" H. Sapiens which he calls "Paleoafricans". I am suggesting that both groups of Afrasians/Adamics had limited mixing with "other" H. Sapiens. The ones that lived in Eurasia just looked genetically a whole lot more like the other hominins there.
All that is if any explanation is necessary. A Cambridge professor has a lot of documentation showing the signal of introgression is an illusion. So far, I still think he has made the best case.
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The article really has very little to do with my book on the work of Christ in Early Genesis, but here it is....
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