Angela
Elite member
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- Ethnic group
- Italian
See:
Martin Petr, Svante Pääbo, Janet Kelso*, Benjamin Vernot*
"The limits of long-term selection against Neandertal introgression"
https://www.biorxiv.org/content/biorxiv/early/2018/07/04/362566.full.pdf
"Several studies have suggested that introgressed Neandertal DNA was subjected tonegative selection in modern humans due to deleterious alleles that had accumulated inthe Neandertals after they split from the modern human lineage. A striking observation insupport of this is an apparent monotonic decline in Neandertal ancestry observed inmodern humans in Europe over the past 45 thousand years. Here we show that thisapparent decline is an artifact caused by gene flow between West Eurasians andAfricans, which is not taken into account by statistics previously used to estimateNeandertal ancestry. When applying a more robust statistic that takes advantage of twohigh-coverage Neandertal genomes, we find no evidence for a change in Neandertalancestry in Western Europe over the past 45 thousand years. We use whole-genomesimulations of selection and introgression to investigate a wide range of modelparameters, and find that negative selection is not expected to cause a significant longtermdecline in genome-wide Neandertal ancestry. Nevertheless, these modelsrecapitulate previously observed signals of selection against Neandertal alleles, inparticular a depletion of Neandertal ancestry in conserved genomic regions that are likelyto be of functional importance. Thus, we find that negative selection against Neandertalancestry has not played as strong a role in recent human evolution as had previouslybeen assumed."
The functionally important deleterious genes were wiped out pretty quickly it seems, and it appears that very little continuing selection has gone on.
Interesting that according to the authors it's gene flow from West Eurasians into Africans which complicated the mathematics, not the reverse.
Also, Basal Eurasians, contrary to assertions by other scholars previously, have, according to them, the same amount of Neanderthal ancestry as any other Eurasians, i.e. about 2.5%
So, the initial admixture with Neanderthals could indeed have taken place in the Middle East, and the location of the Basal Eurasians wouldn't be a problem. They could have been located there as well.
LeBrok was always skeptical that selection against such "weak" deleterious genes continued past the first stage of admixture. If other papers don't suggest this is an incorrect analysis, it seems he was right.
Didn't Dienekes at one point say something like this, i.e. that gene flow between Africa and Eurasia might lead to misconceptions or problems with the analysis?
Martin Petr, Svante Pääbo, Janet Kelso*, Benjamin Vernot*
"The limits of long-term selection against Neandertal introgression"
https://www.biorxiv.org/content/biorxiv/early/2018/07/04/362566.full.pdf
"Several studies have suggested that introgressed Neandertal DNA was subjected tonegative selection in modern humans due to deleterious alleles that had accumulated inthe Neandertals after they split from the modern human lineage. A striking observation insupport of this is an apparent monotonic decline in Neandertal ancestry observed inmodern humans in Europe over the past 45 thousand years. Here we show that thisapparent decline is an artifact caused by gene flow between West Eurasians andAfricans, which is not taken into account by statistics previously used to estimateNeandertal ancestry. When applying a more robust statistic that takes advantage of twohigh-coverage Neandertal genomes, we find no evidence for a change in Neandertalancestry in Western Europe over the past 45 thousand years. We use whole-genomesimulations of selection and introgression to investigate a wide range of modelparameters, and find that negative selection is not expected to cause a significant longtermdecline in genome-wide Neandertal ancestry. Nevertheless, these modelsrecapitulate previously observed signals of selection against Neandertal alleles, inparticular a depletion of Neandertal ancestry in conserved genomic regions that are likelyto be of functional importance. Thus, we find that negative selection against Neandertalancestry has not played as strong a role in recent human evolution as had previouslybeen assumed."
The functionally important deleterious genes were wiped out pretty quickly it seems, and it appears that very little continuing selection has gone on.
Interesting that according to the authors it's gene flow from West Eurasians into Africans which complicated the mathematics, not the reverse.
Also, Basal Eurasians, contrary to assertions by other scholars previously, have, according to them, the same amount of Neanderthal ancestry as any other Eurasians, i.e. about 2.5%
So, the initial admixture with Neanderthals could indeed have taken place in the Middle East, and the location of the Basal Eurasians wouldn't be a problem. They could have been located there as well.
LeBrok was always skeptical that selection against such "weak" deleterious genes continued past the first stage of admixture. If other papers don't suggest this is an incorrect analysis, it seems he was right.
Didn't Dienekes at one point say something like this, i.e. that gene flow between Africa and Eurasia might lead to misconceptions or problems with the analysis?
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