Changes in human effective population size overlap the beginning and end of a critical time in European medieval history, also characterized by the Black Death epidemic

Abstract

The intersection of historiography and archaeology has long pondered over the impact of known historical events on census size. In recent times, genetic methods have successfully traced changes over time in the genetic size of a given population. Moreover, the correlation between genetic and census sizes of a population is contingent on several demographic assumptions that are relatively simple for our species. Our research endeavours to examine the changes in effective population size (Ne) in all human populations in the 1000 Genomes Project over the past two millennia. We compared our findings with estimates from historical censuses where available. Our investigation confirms what was already observed in France and reveals a common pattern found in most European populations, which manifests as a drastic population decrease beginning around the year 1300 and growth after the year 1600. This profile aligns well with known wars, famines, and epidemics that characterized these trying times in Europe. The most notable among them being the second plague epidemic, caused by Y. pestis, which in Europe commenced in 1347/8 and is also known as the "Black Death". Our findings demonstrate that changes in genetic population size through time can serve as a dependable proxy for census size, which is independent of potential biases in the written historical record. Consequently, we provide a robust estimate of the impact caused by the population crisis that followed the year 1300 on the European genomic landscape in light of previous results. Our study offers a new paradigm for interpreting the past and underscores the potential of genetic methods in reconstructing historical events.