Genetic study Recurrent gene flow between Neanderthals and modern humans over the past 200,000 years

[Tautalus]

Editor’s summary

Our understanding of admixture between humans and Neanderthals has changed dramatically over the past decade and a half. Once thought not to have occurred at all, there is now ample evidence for gene flow from Neanderthals to humans and vice versa. Li et al. used a new framework to model the increasingly complex dynamics of introgression between humans and Neanderthals and the ramifications for both populations. They identified regions of human ancestry in Neanderthals, estimated population sizes for Neanderthals were about 20% lower than previously thought, and proposed the possibility of two pulses of gene flow from humans to Neanderthals. This study comprehensively synthesizes our current knowledge of hominin admixture.
​

https://www.science.org/doi/10.1126/science.adi1768

 

[Tautalus]

Interesting. Neanderthals ended up disappearing because their population was so small that they were absorbed by modern humans.

"More broadly, the quantitative patterns of recurrent gene flow between modern humans and Neanderthals that we describe over the course of ~200 ka offer a perspective on factors possibly related to the disappearance of Neanderthals. Specifically, we show that the magnitude of H→N gene flow decreased through time, from 5 to 10% at 250 to 200 ka, to 0.5% at 120 to 100 ka, to 0% for late Neanderthals who lived between 47 and 39 ka. Conversely, as H→N gene flow ceased, numerous examples of N→H admixture began to appear. These include N→H gene flow ~60 to 50 ka with an initial Neanderthal admixture proportion as high as 10%, possible additional waves of N→H admixture in specific modern human populations such as East Asians, and ancient DNA from several early modern humans who lived ~39 to 45 ka that show evidence of more-recent N→H gene flow. This asymmetric admixture pattern, where gene flow is primarily detected in one direction, initially from H→N but then from N→H, suggests a Neanderthal population that was decreasing in size over time, eventually reaching a point where it was not large enough to absorb modern humans into their gene pool. At this time, gene flow reverses direction, and the one-way flow of Neanderthal genes into modern humans may have contributed to the extinction of Neanderthals. Specifically, the assimilation of Neanderthals into modern human populations as they spread throughout Eurasia would have effectively increased the size of modern human populations while simultaneously decreasing the size of an already at-risk Neanderthal population. Our finding that the effective population size of Neanderthals was likely even smaller than previously estimated would only hasten the assimilation process, and the replacement of the Y chromosome and mitochondrial DNA in late Neanderthals by modern humans may have marked an irrevocable path toward the disappearance of one of the few remaining hominin lineages that coexisted with modern humans."​

 

[bicicleur 2]

just now, a 200 ka Denisovan from the Denisova cave has been sequenced

https://www.science.org/content/article/most-ancient-human-genome-yet-has-been-sequenced-and-it-s-denisovan?fbclid=IwZXh0bgNhZW0CMTEAAR1tHYVfxUJ8-7EIpMoV5aPbvTBNFPKJXKWh6LcXKCgnOij_pHp3UcmU0NE_aem_by80Ed3LRZ26nVG2yQC1QA

it has some admixture from an unkown branch of early Neanderthals