A pair of papers behind paywalls deal with the issue of Neanderthal and Human admixture. I will share both abstracts:
1Complex History of Admixture between Modern Humans and Neandertals, Benjamin Vernot and Joshua M. Akey DOI: http://dx.doi.org/10.1016/j.ajhg.2015.01.006:
Recent analyses have found that a substantial amount of the Neandertal genome persists in the genomes of contemporary non-African individuals. East Asians have, on average, higher levels of Neandertal ancestry than do Europeans, which might be due to differences in the efficiency of purifying selection, an additional pulse of introgression into East Asians, or other unexplored scenarios. To better define the scope of plausible models of archaic admixture between Neandertals and anatomically modern humans, we analyzed patterns of introgressed sequence in whole-genome data of 379 Europeans and 286 East Asians. We found that inferences of demographic history restricted to neutrally evolving genomic regions allowed a simple one-pulse model to be robustly rejected, suggesting that differences in selection cannot explain the differences in Neandertal ancestry. We show that two additional demographic models, involving either a second pulse of Neandertal gene flow into the ancestors of East Asians or a dilution of Neandertal lineages in Europeans by admixture with an unknown ancestral population, are consistent with the data. Thus, the history of admixture between modern humans and Neandertals is most likely more complex than previously thought.
In other words Europeans and East Asians carry Neanderthal genes but this cannot be explained by a reduction of Neanderthal genes in Europeans due to the forces of Natural selection. Instead it may be due to either of the following: (i) a second admixture with East Asians and ⁄ or (ii) European admixture with another "ancient" population which watered down the Neanderthal component.
Either option is interesting, there have been hints at an archaic admixture event with a yet to be defined ancestral group (H. erectus? Denisovans?). Additionally Neanderthal presence is strong among East Asians and, may I point out: Amerindians. And this is surely due to a "deeper" admixtwure event.
2.Benjamin Vernot, Joshua M. Akey, Complex History of Admixture between Modern Humans and Neandertals The American Journal of Human Genetics, Available online 12 February 2015.
It has been hypothesized that the greater proportion of Neandertal ancestry in East Asians than in Europeans is due to the fact that purifying selection is less effective at removing weakly deleterious Neandertal alleles from East Asian populations. Using simulations of a broad range of models of selection and demography, we have shown that this hypothesis cannot account for the higher proportion of Neandertal ancestry in East Asians than in Europeans. Instead, more complex demographic scenarios, most likely involving multiple pulses of Neandertal admixture, are required to explain the data.
More evidence to the multiple admixture event in East Asia.
These papers make me wonder about the geographic range of Neanderthals.They have been found in Altai, but surely they expanded well East, into East Asia, Beringia and, why not? America.
Did they admix in the New World and back migrations returned their DNA to East Asia? Are the current time frames correct? When did these multiple admixtures take place? Are we to believe that they took place in the 60 -30 ky window between the purported Out of Africa event and the demise of the Neanderthals?
Additional studies will surely settle these issues.
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