Tautalus
Regular Member
- Messages
- 575
- Reaction score
- 1,463
- Points
- 93
- Ethnic group
- Portuguese
- Y-DNA haplogroup
- I2-M223 / I-FTB15368
- mtDNA haplogroup
- H6a1b2y
This preprint investigates whether the second plague pandemic (the Black Death and subsequent outbreaks from the 14th to the early 19th century) left detectable signatures of natural selection in the human genome and how it affected population movement in northern Europe. Using whole-genome sequences from 529 ancient individuals from Lund (Sweden), Trondheim (Norway), and Vilnius (Lithuania), the authors compare people who lived before and after the arrival of the Black Death. The study is substantially larger than previous ancient DNA analyses and is designed to test both evolutionary and demographic consequences of the pandemic.
The central finding is that the researchers found no convincing evidence that the Black Death caused strong positive selection on specific human genetic variants. Genome-wide analyses failed to replicate previously proposed targets of plague driven selection, including genes such as ERAP2, TICAM2, NFATC1, CTLA4, or RIPK2, and no new robust genome wide significant signals were identified. Although this does not exclude weaker or highly polygenic selection, the data strongly argue against large shifts in allele frequencies caused by plague mortality. The authors also show that their study had sufficient statistical power to detect changes of the magnitude reported in earlier studies, making the failure to replicate previous claims particularly notable.
In contrast, the study uncovers clear demographic effects. Before the Black Death, all three cities contained people with a much broader range of ancestries than afterward. Pre-plague populations included numerous migrants from across northern and western Europe, while post-plague populations became genetically more similar to present day local populations. This pattern reflects a marked decline in long distance immigration following the pandemic. In Lund, for example, more than half of pre-plague individuals had ancestry originating outside Scandinavia, whereas after the plague only about 9% did. Similar, though less dramatic, patterns were observed in Trondheim and Vilnius.
Using identity-by-descent analyses and comparisons with modern reference populations, the researchers identified the likely origins of many migrants. Pre-plague Lund contained individuals with ancestry linked to Germany, the Low Countries, France, Britain, Ireland, eastern Europe, Finland, and even one person with Ashkenazi Jewish related ancestry. Trondheim included several individuals with strong Icelandic ancestry, consistent with the close medieval ties between Iceland and Norway. Vilnius showed migrants primarily associated with East Slavic populations, alongside a few more distant ancestry outliers. Migration within Scandinavia continued after the plague, but long distance immigration declined substantially.
The authors argue that this reduction in genetic diversity cannot be attributed solely to plague mortality. Instead, it likely reflects the combined effects of several major historical processes occurring around the same time: the end of the Viking Age, the spread and consolidation of Christianity, the onset of the Little Ice Age, and the severe social and economic disruption caused by repeated plague outbreaks. Medieval cities such as Lund and Trondheim had been highly cosmopolitan centers that attracted missionaries, merchants, craftsmen, and travelers from across Europe; after the Black Death these international networks weakened, leading to more locally rooted populations.
Overall, the paper challenges one of the most influential hypotheses in ancient human genomics, that the Black Death produced strong natural selection on immune genes that remains detectable today. Instead, it concludes that the pandemic's most visible genetic legacy was demographic rather than adaptive: it reshaped patterns of migration and reduced long range mobility across northern Europe, while leaving little evidence for large evolutionary changes in specific genes. Detecting subtler adaptive effects, if they exist, will require substantially larger ancient DNA datasets than are currently available.
AbstractThe central finding is that the researchers found no convincing evidence that the Black Death caused strong positive selection on specific human genetic variants. Genome-wide analyses failed to replicate previously proposed targets of plague driven selection, including genes such as ERAP2, TICAM2, NFATC1, CTLA4, or RIPK2, and no new robust genome wide significant signals were identified. Although this does not exclude weaker or highly polygenic selection, the data strongly argue against large shifts in allele frequencies caused by plague mortality. The authors also show that their study had sufficient statistical power to detect changes of the magnitude reported in earlier studies, making the failure to replicate previous claims particularly notable.
In contrast, the study uncovers clear demographic effects. Before the Black Death, all three cities contained people with a much broader range of ancestries than afterward. Pre-plague populations included numerous migrants from across northern and western Europe, while post-plague populations became genetically more similar to present day local populations. This pattern reflects a marked decline in long distance immigration following the pandemic. In Lund, for example, more than half of pre-plague individuals had ancestry originating outside Scandinavia, whereas after the plague only about 9% did. Similar, though less dramatic, patterns were observed in Trondheim and Vilnius.
Using identity-by-descent analyses and comparisons with modern reference populations, the researchers identified the likely origins of many migrants. Pre-plague Lund contained individuals with ancestry linked to Germany, the Low Countries, France, Britain, Ireland, eastern Europe, Finland, and even one person with Ashkenazi Jewish related ancestry. Trondheim included several individuals with strong Icelandic ancestry, consistent with the close medieval ties between Iceland and Norway. Vilnius showed migrants primarily associated with East Slavic populations, alongside a few more distant ancestry outliers. Migration within Scandinavia continued after the plague, but long distance immigration declined substantially.
The authors argue that this reduction in genetic diversity cannot be attributed solely to plague mortality. Instead, it likely reflects the combined effects of several major historical processes occurring around the same time: the end of the Viking Age, the spread and consolidation of Christianity, the onset of the Little Ice Age, and the severe social and economic disruption caused by repeated plague outbreaks. Medieval cities such as Lund and Trondheim had been highly cosmopolitan centers that attracted missionaries, merchants, craftsmen, and travelers from across Europe; after the Black Death these international networks weakened, leading to more locally rooted populations.
Overall, the paper challenges one of the most influential hypotheses in ancient human genomics, that the Black Death produced strong natural selection on immune genes that remains detectable today. Instead, it concludes that the pandemic's most visible genetic legacy was demographic rather than adaptive: it reshaped patterns of migration and reduced long range mobility across northern Europe, while leaving little evidence for large evolutionary changes in specific genes. Detecting subtler adaptive effects, if they exist, will require substantially larger ancient DNA datasets than are currently available.
The second plague pandemic (early 14th-early 19th centuries), which was caused by Yersinia pestis, had a profound demographic, socio-economic and cultural impact across Eurasia and North Africa. Many regions in Europe and the Middle East are estimated to have lost 40-60% of their human populations, with some areas suffering even higher mortality. Whether exposure to Y. pestis drove strong positive selection on protective genetic variants in the human genome, and how it shaped migration patterns, remains debated, despite several recent studies based on ancient DNA. Here, we analyse a markedly larger, higher coverage, and geographically diverse dataset based on shotgun sequencing of genomes from 529 ancient individuals to a mean depth 8.8x dating to either before or after the arrival of the pandemic at three sites in northern Europe: Trondheim (Norway), Lund (Sweden) and Vilnius (Lithuania). Genome-wide scans for signatures of selection provide no evidence for strong positive selection acting on specific genetic variants driven by Y. pestis exposure: we neither replicate selection signatures reported by previous studies nor identify new genome-wide significant candidates. However, for all three sites, we observe evidence for a reduction in long-range immigration, indicated by a drop in the diversity of ancestry that followed the arrival of Y. pestis and broadly coincided with the end of the Viking Age, Christianisation and the onset of the Little Ice Age. Our results shed important light on the demographic impact of major sociohistorical changes that occurred during the late Medieval period in Scandinavia and the Baltic region and link Christianisation to increased diversity in ancestry before the pandemic.
A) Map showing the three sites: Lund, Trondheim, and Vilnius, and the number of ancient individuals from each site by period that passed quality control.
B) Projections of all ancient individuals onto a PCA of present-day West Eurasian populations with PC1 broadly representing north-south differentiation and PC2 eastwest differentiation.
The level of Gaelic ancestry is surprisingly high. This may be explained by the fact that before the Black Death, Scandinavian cities such as Lund and Trondheim were highly cosmopolitan, with migrants arriving through Viking era connections, trade, slavery, and Christian networks. Individuals with high Gaelic ancestry likely represent recent immigrants or their descendants, while lower levels reflect older admixture. After the Black Death, long distance migration declined sharply, making the populations more locally Scandinavian and reducing the proportion of Gaelic ancestry.
Supervised ADMIXTURE analysis using present-day reference populations representative of Gaelic and Norse ancestry. ADMIXTURE proportions are shown for individuals from (A) Trondheim and (B) Lund using Gaelic and Norse as potential source populations (Supp. Table 5). Individuals are ordered by their inferred Gaelic ancestry proportion within each site.
Last edited: