Hypothesis: A modern human range expansion ∼300,000 years ago had a critical role in Neandertal origins

[Micael]

This is a preprint paper that is currently generating a lot of discussion. The suggested range expansion of a modern human population into Europe 200,000-300,000 years ago clashes a bit with many previous calculations, pushing that date back by a lot, and opens up questions as to whether the ”out of Africa” model as it has been presented needs to be modified. I’m personally starting to lean towards the modern human lineage more likely having actually developed around the eastern Mediterranean, and at least not exclusively in Africa. (But I don’t consider this settled by any means.)

Abstract

This paper proposes that a critical event in Neandertal evolution was a range expansion of early modern humans into Europe 300 thousand years ago (ka). As bands of early modern humans spread, they incorporated resident archaic people leading ultimately to so much admixture that the resulting population carried ∼3-7% modern ancestry. I identify multiple ways in which this would lead to a high probability of these direct ancestors of Neandertals retaining early modern human lineages at both mitochondrial DNA and Y chromosomes while clustering with Denisovans genome-wide. A previous explanation for these patterns without the unique population dynamics associated with a range expansion has less than a 3% chance of matching the data. In Africa, the hypothesis also has explanatory power: if the expanding population also mixed African archaic humans, it could account for the evidence that all humans living today are admixed between lineages that separated more than a million years ago and remixed ∼300 ka. This hypothesis of a bicontinental range expansion correlates with shared archaeological traits between West Eurasia and Africa that were far less present in East Asia, including Levallois point stone tools, improved hafting, use of fire and ochre, and larger and more organized campsites. Motivated by the evidence that an early modern human expansion had a role in Neandertal and modern human evolution, I identify 66 loci spanning <0.1% of the genome where people today share ancestry with Neandertals more recently than separation from Denisovans. This includes a haplotype at FADS1/FADS2 that codes for an enzyme modifying polyunsaturated plant-derived fatty acids and may reflect adaptation to a more diversified diet, and an amino acid substitution at ARHGAP32 modulating neural connections that may be important in modern human cognitive evolution.

Full preprint available here:
https://www.biorxiv.org/content/10.6489 ... 1.711219v2

[MFOM]

Interesting, i cannot begin to imagine the politics in challenging the out of Africa theory

[Pdf27]

Interesting, i cannot begin to imagine the politics in challenging the out of Africa theory

Depends which bit of the theory - prior to Homo Erectus it seems pretty bomb-proof that all our ancestors lived in Africa. After that things get very messy and we're working with probabilities that DNA is changing the underlying data for on a regular basis. This particular study is talking about some DNA moving the other way, and it's kinda hard to see that not happening at some point so this isn't hugely surprising.

[Micael]

Recently the ”linear” out of Africa theory has usually been presented as archaic humans migrating from Africa in waves, and then modern humans emerged in Africa (fairly far south) and wandered out of there 50,000 years ago. The author of this paper believes that his findings support this instead:

IMG_5383.jpeg

That is to say that modern humans evolved in an area encompassing northern Africa and part of the Middle East. Then injected some genetic material into the European archaic population, and a lot more into the African archaic population, and then eventually the population of modern humans started expanding elsewhere in earnest.

It will be seen as controversial by some, even if it can be described as a mere modification of the out of Africa theory, because there’s a whole lot of people who have lashed their careers and reputations to the mast of the theory of a sub-saharan origin of modern humans. Also, because it has taken on a strong political dimension in the sense that the out of Africa theory has been used as a vehicle for boosting up sub-saharan Africans ”we are all Africans” etc. In a sense that is probably still true, ie pre-Homo Erectus as mentioned above, but the notion that the modern human breed originated a bit further to the north can be a touchy subject.

Partially separate from this I am also going to venture a guess that we’re eventually going to wind up at the conclusion that the much earlier origins of predecessor archaic humans were in northern Africa rather than in the middle to southern parts frequently suggested.