Is the Evidence for Neanderthal-Sapiens Admixture Exaggerated and Over-Stated?

Cambridge Zoology Professor William Amos thinks so.  He has an alternative explanation for the data which suggests interbreeding occurred. He says that most of the signal can be explained by a lower mutation rate in the group of humans leaving Africa due to the fact that they had little diversity in their genes to start with. It is worth reading the abstract on the above link. That does not even consider the possibility that at least some of the gene similarities are due to viral infections, not interbreeding. That is, Eurasians and Neanderthals share some genetic material because they were infected by the same strains of virus and viruses can insert material into the genome. Eurasians picked up strains that Africans lacked because they lived in the same area as Neanderthals, not because of interbreeding.

To be fair, even Dr. Amos thinks that "some" inbreeding "probably" occurred, but this is yet another example of how the science media takes a "finding" in an area we are just beginning to really understand and repeats it until it becomes part of the narrative even when a lot of questions remain.

It now appears that some of those genes which the OOA humans got from (presumably) Neanderthals was actually the ancestral condition of the gene in both species which had been lost in modern humans. IOW, the Neanderthals did not give the Out-of-Africa Humans strictly neanderthal genes, some if not most of the genetic material scientists are ascribing to hybridization with Neanderthals could simply be the genes our species once had in common with them but lost being returned to us through mating with "somebody". That "somebody" may have been Neanderthals, or it may have been from a group of humans which left Africa earlier than the main OOA group (actually I don't think all of humanity began in Africa, I think almost all of the genes of humanity that survived were from Africa. In this view the OOA humans simply met the few survivors of humanity that had been outside of Africa from the beginning and absorbed or eliminated them so that little genetic trace remains except in a few backwaters as noted in the link above).

So even a large proportion of the "Neanderthal" genes we wind up keeping may not really have been exclusively "theirs" anyway. Thus, whatever the true figure of percentage of neanderthal genome possessed by the average Eurasian, it is liable to be lower than the oft-cited 1.5%. Maybe I'm not "1.5% Neanderthal" as my genetic testing (and that of many of European ancestry) claimed. Maybe its half that, maybe a tenth of that. It could even be none.

The only reason why people cite admix is because some genes in Neanderthals are highly similar in modern humans. These are all "adaptive genes" and cis-regulatory areas. The stretches of the genome which really count (genes coding for structural elements like bone formation and particularly brain function) are different - these are called "Neanderthal deserts" and puzzle researchers.

There is a lab at Stanford University that is working on adaptive evolution......about 30% of mutations in the human proteome are driven by viruses alone. It is high time that people started ignoring D stats and started questioning whether, faced with identical viruses in identical areas, all hominin species (including modern humans) would not anyway identically adapt - ie identical mutations happen in both species because they are driven by the identical viruses. The same would be true in Africa, where parasites not present in the Northern Hemisphere are rife, driving adaptive mutations in the opposite direction. Adaptive mutations in two similar species does not mean admix. In Africa, both chimpanzees and modern humans have adapted to malaria by way of a mutation that causes sickle cell anaemia. No-one cites admix in this instance - it's parallel adaptation.

Let's keep testing.....