Post by Admin on Oct 10, 2023 20:46:58 GMT
Fig 4. Adaptation to high-latitude environments.
(A) Plot of similarity between Mesolithic allele frequency and FIN allele frequency in contrast to difference to TSI allele frequency using the statistic Dsel. The figure shows all positive Z scores representing the number of standard deviations each SNP deviates from the mean. The green-highlighted SNPs are all located in the TMEM131 gene. The plot was made with qqman [49]. (B) Derived allele frequencies for three pigmentation-associated SNPs (SLC24A5, SLC45A2, which are associated with skin pigmentation, and OCA2/HERC2, which is associated with eye pigmentation). The dashed line connecting EHG and WHG represents potential allele frequencies if SHG were a linear combination of admixture between EHG and WHG. The solid horizontal line represents the derived allele frequency in SHG. The blue symbols representing SHGs were set on the average genome-wide WHG and EHG mixture proportion (on x-axis) across all SHGs, and the thick black line represents the minimum and maximum admixture proportions across all SHGs. Dashed horizontal lines represent modern European populations (CEU). The p-values were estimated from simulations of SHG allele frequencies based on their genome-wide ancestry proportions (S9 Text). Data shown in this figure can be found in S1 Data. CEU, Utah residents with Central European ancestry; EHG, eastern hunter-gatherer; FIN, modern-day Finnish individual; SHG, Scandinavian hunter-gatherer; TSI, modern-day Tuscan individual; WHG, western hunter-gatherer.
doi.org/10.1371/journal.pbio.2003703.g004
In addition to performing this genome-wide scan, we studied the allele frequencies in three pigmentation genes (SLC24A5, SLC45A2, which have a strong effect on skin pigmentation, and OCA2/HERC2, which has a strong effect on eye pigmentation) in which the derived alleles are virtually fixed in northern Europeans today. The differences in allele frequencies of those three loci are among the highest between human populations, suggesting that selection was driving the differences in eye color, skin, and hair pigmentation as part of the adaptation to different environments [50–53]. All of the depigmentation variants at these three genes are in high frequency in SHGs in contrast to both WHGs and EHGs (Fig 4B). We conduct neutral simulations of the allele frequencies in an admixed SHG population to estimate p-values for observing these allele frequencies without selection (S9 Text). The p-values for all three SNPs are lower than 0.2; the combined p-value [54] for all three pigmentation SNPs is 0.028. Therefore, the unique configuration of the SHGs is not fully explained by the fact that SHGs are a mixture of EHGs and WHGs, but could rather be explained by a continued increase of the allele frequencies after the admixture event, likely caused by adaptation to high-latitude environments [50,52].
Conclusion
By combining information from climate modeling, archaeology, and Mesolithic human genomes, we were able to reveal the complexity of the early migration patterns into Scandinavia and human adaptation to high-latitude environments. We disentangled two migration routes and linked them to particular archaeological patterns. We also demonstrated greater genetic diversity in Mesolithic northern Europe compared to southern and central Europe—in contrast to modern-day patterns—and showed that many genetic variants that were common during the Mesolithic period have been lost today. These findings reiterate the importance of human migration for dispersal of novel technology in human prehistory [14–20,27,40,55–58].