NEW YORK — Migration from continental northern Europe shaped the genetic makeup of early England, a new study drawing on ancient DNA and archaeological data has found.
Following the decline of the Roman Empire, the British Isles underwent a period of cultural change and a shift in language. But as researchers from the Max Planck Institute for Evolutionary Anthropology and elsewhere noted, the extent to which these changes were due to the influx of migrants from Europe has been unclear.
Using genome-wide analysis of DNA from more than 270 individuals from ancient England and about 200 from other regions of northwest Europe, the researchers pieced together details of a large-scale migration from Denmark, Germany, and the Netherlands into eastern and southern England during the post-Roman period and how these newcomers intermixed with the local population.
"[We have] now gained really fascinating insights into population-scale and individual histories during post-Roman times," said Max Planck's Joscha Gretzinger, the first author of the study, published in Nature this week, in a statement. "Not only do we now have an idea of the scale of migration, but also how it played out in communities and families."
The researchers collected samples from nearly 500 skeletal remains from 37 different sites in England, Ireland, Denmark, Germany, and the Netherlands. These samples all dated back to between the years 200 and 1300 CE. They extracted DNA from these and performed targeted or whole-genome sequencing. After filtering, they generated a dataset of 278 ancient individuals from England and 182 from Ireland or continental Europe, which they further combined with previously published data on 1,089 post-Neolithic northwest Europeans and more than 10,000 present-day Europeans.
The researchers then superimposed their ancient dataset onto a principal component analysis (PCA) of present-day northwest Europeans. Bronze Age individuals from Britain and Ireland largely clustered with modern western British and Irish individuals, while medieval English individuals mostly clustered with present-day and ancient continental northern Europeans. The researchers noted, though, that medieval English individuals had varying degrees of continental northern European ancestry.
That portion of continental northern European ancestry also changed over time and varied by location. Samples from England dating back to the Early Middle Ages or the Iron Age had very low continental northern European ancestry, about 1 percent, which increased to about 15 percent during the Roman period. But most early medieval individuals had a much higher portion of continental northern European ancestry — an average of 76 percent. Continental northern European ancestry was particularly high in eastern England, as compared to southwestern England.
The researchers were also able to glimpse the local effect of this influx of migrants. At one burial site near Dover, they uncovered evidence of integration within a family, as a woman with unadmixed continental northern European ancestry and her then admixed daughters were buried alongside their unadmixed western British ancestry relatives. But at a different burial site, Apple Down, they noted that individuals with different ancestries were buried separately, suggesting social separation.
"We see considerable variation in how this migration affected communities," said co-author Duncan Sayer, an archaeologist from the University of Central Lancashire.
The researchers further traced the source of this continental northern European ancestry, homing in on a region spanning the northern Netherlands to very southern Sweden, but centered on Lower Saxony in Germany.
While these ancient populations can be modeled as a two-way mix of western British and continental northern European ancestry, modern-day English populations cannot; only about 40 percent of the ancestry of modern English populations is derived from continental northern European ancestry. Instead, a three-way model that also incorporates French Iron Age ancestry is a better fit.
"It remains unclear whether this additional ancestry related to Iron Age France is connected to a few punctuated migration events, such as the Norman conquest, or whether it was the result of centuries-long mobility across the English Channel," senior author Stephan Schiffels from Max Planck added. "Future work, specifically targeting the medieval period and later, will reveal the nature of this additional genetic signal."