Post by Admin on Jan 10, 2023 17:59:58 GMT
Figure 2. Genotypes from ancient Scandinavians projected onto the first two principal components of modern West Eurasians
(A) The mean and 95% confidence interval for each ancient group for PC1 and PC2.
(B) All ancient individuals from the five different periods.
See also Figure S1 and Table S3.
Interestingly, the mean projected PC1 and PC2 coordinates of ancient Scandinavians change over time (Figures 2A and S1A–S1P). First, the Pre-Viking individuals are significantly different from modern Scandinavians for both PC1 and PC2 (Wilcoxon test p values 1.107e−11 and 0.0057, respectively; Figure 2A; Table S4). They are consistently shifted toward the positive values for PC1 in the direction of Neolithic and Mesolithic Scandinavian hunter-gatherers, with some individuals falling outside the range of all modern Europeans (Figure S1Q). The Viking and Late Viking groups are also significantly different from modern Scandinavians on PC1, but in the opposite (negative) direction (Wilcoxon test p values are 0.0199 and 0.0084, respectively). In contrast, the more recent Medieval and Post-Medieval Scandinavians are not significantly differentiated from their modern counterparts on PC1 (Wilcoxon test p values are 0.1299 and 0.2509, respectively). However, for PC2, Post-Medieval Scandinavians are significantly different from their modern counterparts (Wilcoxon test p value 1.142e−6) (Table S4).
Figure S1. Ancient Scandinavians projected onto the first two or three principal components of modern West Eurasians, related to Figure 2
(A–R) Ancient Scandinavians projected onto the first two principal components.
(S and T) Ancient Scandinavians projected onto the first and the third principal components.
Our results indicate a surge of gene flow from the British-Irish Isles into Scandinavia during the Viking period, with additional gene flow from the east in the Late Viking period, consistent with results reported in a previous study.8 We formally tested for the impact of gene flow into Scandinavia from different sources across time using f4-statistics of the form f4(Mbuti, ancient group; Danish, modern population). Here, the Mbuti represents an outgroup, the modern population is a proxy for a potential ancient non-Scandinavian source population and individuals from Denmark represent the southernmost Scandinavian population. To detect gene flow from the west, south, and east of Europe into the different temporal groups of Scandinavia, we selected three modern populations as proxies for different European regions: Irish for west (British-Irish), Sardinian for south (south Europe), and Lithuanian for east (Baltic). To better understand the timing and geographical extent of gene flow from east, west, and south Europe into Scandinavia, we split the ancient individuals from Norway and Sweden by sub-regions: north, central, and south, with the Swedish island of Gotland as a separate region (Figure 1).
We find that affinity to the three non-Scandinavian source populations is low in the Pre-Viking period but higher in nearly all other subsequent periods of ancient Scandinavians, consistent with gene flow from these regions into Scandinavia during the Viking period (Figures 3A–3C).