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Thread: Natural Selection in Britain During the Last 2,000 Years

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    Natural Selection in Britain During the Last 2,000 Years

    Detection of human adaptation during the past 2,000 years


    Abstract
    Detection of recent natural selection is a challenging problem in population genetics, as standard methods generally integrate over long timescales. Here we introduce the Singleton Density Score (SDS), a powerful measure to infer very recent changes in allele frequencies from contemporary genome sequences. When applied to data from the UK10K Project, SDS reflects allele frequency changes in the ancestors of modern Britons during the past 2,000 years.
    We see strong signals of selection at lactase and HLA, and in favor of blond hair and blue eyes. Turning to signals of polygenic adaptation we find, remarkably, that recent selection for increased height has driven allele frequency shifts across most of the genome. Moreover, we report suggestive new evidence for polygenic shifts affecting many other complex traits. Our results suggest that polygenic adaptation has played a pervasive role in shaping genotypic and phenotypic variation in modern humans.

    [...]

    While the major determinants of human skin color are near fixation and thus not testable by SDS, there is a strong overall enrichment of selection in favor of derived variants associated with lighter pigmentation, especially of hair and eye color (p=3x10-9 for mean SDS>0).
    The strongest signal is for selection in favor of a blond hair variant at the KITLG locus, currently at 12% frequency (p=2x10-6 ), and a weaker signal in favor of blond hair at SLC24A4 (p=8x10-3).
    We also replicate a known signal for blue eyes at the HERC2/OCA2 locus (p=2x10-5 ). We speculate that recent selection in favor of blond hair and blue eyes may reflect sexual selection for these phenotypes in the ancestors of the British, as opposed to the longer-term trend toward lighter skin pigmentation in non-Africans, generally thought to have been driven by the need for Vitamin D production .

    [...]

    We have shown that selection on milk digestion, and on physical attributes including blond hair and blue eyes continued well into historical times. Our results also suggest that polygenic selection played an important role in the evolution of many complex traits.

    Selection on height alone has affected allele frequencies at most SNPs genome-wide, and we anticipate that competing effects of linked SNPs on different traits may be an important feature of short-term adaptation. It is important to note that the measured traits are, themselves, not necessarily direct targets of selection; it is likely that each of these traits shares variants with other correlated phenotypes as well.
    Nonetheless, our results suggest that selection on complex traits has been an important force in shaping both genotypic and phenotypic variation within historical times.
    Source

    Fascinating, an obvious proof, that evolution is still going on even now and even more, that it can happen within a relatively short time span.
    Yet another powerful argument against claims, that the divergence time between human populations wasn't long enough to produce significant differences.
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    Ancient DNA: List of All Studies analyzing DNA of Ancient Tribes and Ethnicities(post-2010)


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    I agree that sexual selection is more important in explaining depigmentation than is anything like Vitamin D. Also the timescale is of interest becayse around the time of the Roman withdrawl a plague wiped out urban Britain as Angles, Jutes and Saxons arrived. Is it impossible that Germanic immigration caused the depigmentation? The population was not static and the Brythonic Welsh can be dark.

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    Quote Originally Posted by Catterick View Post
    Is it impossible that Germanic immigration caused the depigmentation? The population was not static and the Brythonic Welsh can be dark.
    No, that's certainly possible and I also already thought about it. It's somewhat puzzling, that the effect of Germanic immigration isn't adressed in the paper.

    It's certainly the case, that Anglosaxon settlement brought more light(and tall) genes with it and this could partly explain the depigmentation.
    Likewise, they would have brought a somewhat different physical ideal with them and via sexual selection, it would have depigmented the gene pool even more.

    See also, from the Genomic Signals of Migration and Continuity in Britain Before the Anglo-Saxons study I posted before:
    In particular, we inferred genotypes at SNP positions to predict eye and hair pigmentation29. The most common predicted phenotype in the Roman burial samples is brown eyes and black/brown hair. However, one sample, 6DRIF-18, was estimated to have had a distinctive appearance with blue eyes and blonde hair, as did the single Anglo-Saxon individual.
    We also inferred that blood group O is the most common in the Roman samples (Supplementary Table 17). The Iron-Age sample is also estimated as blood type O and the Anglo-Saxon is likely to have been type B or possibly type A.
    Five samples returned imputed lactase persistence genotypes: two Roman burials and the Iron-Age individual were likely to have been lactase persistent, while two Romans, 6DRIF-22 and the suspected migrant 3DRIF-26 were homozygous for the ancestral non-persistence variant.
    And the day they sold us out, Our hearts grew cold
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    Ancient DNA: List of All Studies analyzing DNA of Ancient Tribes and Ethnicities(post-2010)


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