African diversity is very likely the outcome of admixture with archaic hominids in Africa and not the result of Homo sapiens having originated in Africa.
In my post "Into Africa: sub-Saharan genetic diversity is due to introgression with archaics", I shared some papers "on the subject of the admixture of Homo sapiens and archaic hominins in Africa, which may be the cause of the "genetic diversity" which is the main evidence supporting an African origin of modern humans".
Today I read a very interesting paper: Recovering signals of ghost archaic admixture in the genomes of present-day Africans by Arun Durvasula and Sriram Sankararaman, doi: https://doi.org/10.1101/285734, which deals with an archaic admixture into the West African Yoruba people.
The paper states: "Our results suggest that Yoruban individuals trace about 7.9% of their genomes to an as yet unidentified archaic population. This is in agreement with some results from previous papers in other African populations such as the Biaka and the Baka, suggesting that there was a rich diversity of hominin species within Africa and that introgression was commonplace".
The authors discard a Neanderthal origin for this archaic DNA: ". It is plausible that this archaic ancestry is, at least partly, the result of Neanderthal introgression into the Yoruba mediated by more recent west Eurasian gene flow into Yoruba [10]. However, the proportion of Neanderthal ancestry in Yoruba is very small (about 2 × 10−4) so that we would not expect this small proportion to explain our signal".
Furthermore, they report that ", it is unclear whether the archaic signatures found here are from the same as those found in other African populations" which means that we could expect many admixture events in Africa between H. sapiens and archaics.
These introgression events are, in my opinion, the source of the great genetic diversity found in Africa. Diversity which is used to support an African origin of modern humans. The logic is the following: out of the great genetic diversity in Africa only part of it went into the rest of the world due to the small size of migrating populations, then bottlenecks reduced this diversity even more. Conclusion the higher African genetic diversity is proof of their ancestral position to all other humans.
But what if... H. sapiens originated in Asia (from H. erectus stock) and re-entered Africa, mixing there in the ancestral homeland with achaic hominids? The outcome would be an input of archaic genes into African H. sapiens causing them to have a greater genetic diversity. But in this case the cradle of mankind would be Asia and not Africa.
And that is what I posted here: "This leads me to ask, what if African heterozygosity was enriched by recent admixture with other hominins in Africa? an inflow of different relic alleles elevated African diversity above that of non-Africans. Could current lower Amerindian heterozygosity reflect an ancient population just like that of Denisovans or Neanderthals?".
Surely more papers will explore this "ghost" signal among Africans and clarify the matter.
Patagonian Monsters - Cryptozoology, Myths & legends in Patagonia Copyright 2009-2018 by Austin Whittall ©
No comments:
Post a Comment