Post by Admin on Jul 1, 2022 18:24:57 GMT
Discussion
The power of ancient metagenomics lies in its potential to provide direct evidence for testing long-standing historical hypotheses and reveal phylogeographical patterns of microbial diversity through time41. One such debate concerns the events that triggered the second plague pandemic, as well as the time and place of its emergence. Recently, an analysis of historical, genetic and ecological data led to the suggestion that the emergence of Y. pestis branches 1–4 occurred more than a century before the beginning of the Black Death. According to the proposed model, this initial diversification was mediated by people and was linked with territorial expansions of the Mongol Empire across Eurasia during the early thirteenth century22,26,42. By contrast, we present ancient Y. pestis data from central Eurasia that support a fourteenth-century emergence; therefore, earlier outbreak attributions remain to be explored. At present, the narrow-focused sampling chosen for this study does not allow for an assessment of the spread of the BSK001/003 strain. Previous studies have shown that Y. pestis can disseminate rapidly without accumulation of genetic diversity17,21, thus potentiating a contemporaneous presence of the same strain across a large geographical range. Nevertheless, the known range of extant plague foci associated with lineages ancestral to BSK001/003 provide support for its emergence in central Eurasia and possibly in the extended Tian Shan region. Although the dynamics that triggered the bacterium’s emergence in this region are unknown, previous studies showed that environmental factors, such as natural disasters and sudden changes in temperature and precipitation can have an impact on Y. pestis host ecologies and, as a result, can trigger outbreaks in human populations43,44,45,46. Although we have no evidence to infer such connections with the Kara-Djigach epidemic, we envision that our precise 1338–1339 date will serve as a reference point for future environmental, archaeological and historical research focusing on the events that caused a Y. pestis introduction into human populations and precipitated the second plague pandemic.
The onset of the Black Death has been conventionally associated with outbreaks that occurred around the Black Sea region in 1346 (refs. 1,47), eight years after the Kara-Djigach epidemic. At present, the exact means through which Y. pestis reached western Eurasia are unknown, primarily due to large pre-existing uncertainties around the historical and ecological contexts of this process. Previous research suggested that both warfare and/or trade networks were some of the main contributors in the spread of Y. pestis21,22,26,47,48. Yet, related studies have so far either focused on military expeditions that were arguably unrelated to initial outbreaks47 or others that occurred long before the mid-fourteenth century22,26. Moreover, even though preliminary analyses exist to support an involvement of Eurasian-wide trade routes in the spread of the disease48, their systematic exploration has so far been conducted only for restricted areas of western Eurasia21,47. The placement of the Kara-Djigach settlement in proximity to trans-Asian networks9,49, as well as the diverse toponymic evidence and artefacts identified at the site (Supplementary Information 2) lend support to scenarios implicating trade in Y. pestis dissemination. Therefore, an investigation of early-to-mid-fourteenth-century connections across Asia, interpreted alongside genomic evidence, will be important for disentangling the bacterium’s westward dispersals.
Past and present experiences have demonstrated that reconciling the source of a pandemic is a complex task that cannot be accomplished by a single research discipline. Although the ancient Y. pestis genomes reported in this Article offer biological evidence to settle an old debate, it is the unique historical and archaeological contexts that define our study’s scope and importance. As such, we envision that future synergies will continue to reveal important insights for a detailed reconstruction of the processes that triggered the second plague pandemic.
The power of ancient metagenomics lies in its potential to provide direct evidence for testing long-standing historical hypotheses and reveal phylogeographical patterns of microbial diversity through time41. One such debate concerns the events that triggered the second plague pandemic, as well as the time and place of its emergence. Recently, an analysis of historical, genetic and ecological data led to the suggestion that the emergence of Y. pestis branches 1–4 occurred more than a century before the beginning of the Black Death. According to the proposed model, this initial diversification was mediated by people and was linked with territorial expansions of the Mongol Empire across Eurasia during the early thirteenth century22,26,42. By contrast, we present ancient Y. pestis data from central Eurasia that support a fourteenth-century emergence; therefore, earlier outbreak attributions remain to be explored. At present, the narrow-focused sampling chosen for this study does not allow for an assessment of the spread of the BSK001/003 strain. Previous studies have shown that Y. pestis can disseminate rapidly without accumulation of genetic diversity17,21, thus potentiating a contemporaneous presence of the same strain across a large geographical range. Nevertheless, the known range of extant plague foci associated with lineages ancestral to BSK001/003 provide support for its emergence in central Eurasia and possibly in the extended Tian Shan region. Although the dynamics that triggered the bacterium’s emergence in this region are unknown, previous studies showed that environmental factors, such as natural disasters and sudden changes in temperature and precipitation can have an impact on Y. pestis host ecologies and, as a result, can trigger outbreaks in human populations43,44,45,46. Although we have no evidence to infer such connections with the Kara-Djigach epidemic, we envision that our precise 1338–1339 date will serve as a reference point for future environmental, archaeological and historical research focusing on the events that caused a Y. pestis introduction into human populations and precipitated the second plague pandemic.
The onset of the Black Death has been conventionally associated with outbreaks that occurred around the Black Sea region in 1346 (refs. 1,47), eight years after the Kara-Djigach epidemic. At present, the exact means through which Y. pestis reached western Eurasia are unknown, primarily due to large pre-existing uncertainties around the historical and ecological contexts of this process. Previous research suggested that both warfare and/or trade networks were some of the main contributors in the spread of Y. pestis21,22,26,47,48. Yet, related studies have so far either focused on military expeditions that were arguably unrelated to initial outbreaks47 or others that occurred long before the mid-fourteenth century22,26. Moreover, even though preliminary analyses exist to support an involvement of Eurasian-wide trade routes in the spread of the disease48, their systematic exploration has so far been conducted only for restricted areas of western Eurasia21,47. The placement of the Kara-Djigach settlement in proximity to trans-Asian networks9,49, as well as the diverse toponymic evidence and artefacts identified at the site (Supplementary Information 2) lend support to scenarios implicating trade in Y. pestis dissemination. Therefore, an investigation of early-to-mid-fourteenth-century connections across Asia, interpreted alongside genomic evidence, will be important for disentangling the bacterium’s westward dispersals.
Past and present experiences have demonstrated that reconciling the source of a pandemic is a complex task that cannot be accomplished by a single research discipline. Although the ancient Y. pestis genomes reported in this Article offer biological evidence to settle an old debate, it is the unique historical and archaeological contexts that define our study’s scope and importance. As such, we envision that future synergies will continue to reveal important insights for a detailed reconstruction of the processes that triggered the second plague pandemic.