Prehistoric diseases shed light on human migration
New techniques in gene analysis are enabling a more detailed look at the impact of disease on migratory patterns in eastern and central Europe over a period of around 3 000 years, in the late Stone Age and early Bronze Age. Changes haves been variously attributed to searching for new food sources, changing climates and economies, massive population growth, social transformations and new infectious diseases. “Disease has been underestimated as a potential factor in people moving around during those transformative periods,” explains project coordinator Wolfgang Haak, Department of Archaeogenetics, Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany. He notes the recent COVID-19 pandemic has highlighted how much disruption epidemics or pandemics can cause. The 5-year PALEoRIDER project, funded by the European Research Council, documented the genetic profiles of over 1 000 ancient human remains from key regions in Europe that experienced transformative changes, and their exposure to pathogens. This data was combined with archaeological and historical analysis. “By studying the teeth, we had access to potential pathogens. We can look at the diseases those people might have contracted,” says Haak. This is similar to work on ancient pathogen genomics under the APGREID project.
Collecting genomic data using DNA capture techniques
A large database was established of comparable enriched genomic data of both humans and pathogens from key archaeological sites. New DNA capture techniques were central to analysing archaeological remains. “The human DNA has decayed and fragmented and is overlaid with other environmental DNA, such as from soil, fungi and other microbes, so the fraction of actual human DNA is really low – often only about 1 %,” adds Haak. “Capture assays fish out the human-specific DNA, and specifically, the variants across the human genome globally that we know are there,” explains Haak. “With capture assays you generate targeted high-quality data, so the 1 % to 10 % of human DNA in an ancient sample can be brought to above 50 %.” The amount of pathogen DNA in a tooth is even lower, so capture techniques are particularly useful for reconstructing a genome sequence. Researchers can then assess whether a pathogen trace is modern or has DNA damage indicating it is ancient, while controlling for background genetic ancestry in humans, to avoid false positives.
Early evidence of diseases
“We were able to corroborate previous evidence of a number of pathogens, in particular, early forms of Yersinia pestis (Y. pestis) or the plague during the early Bronze Age,” he notes, as well as Salmonella enterica, and prehistoric viruses such as Hepatitis B. The unexpectedly large number of pathogens detected through time suggests infectious diseases, such as Y. pestis appeared more than 3 000 years before the earliest outbreaks attested by written sources, providing an alternative explanation for large-scale population replacements.
More interaction than previously believed
“Around 5 000 years ago we see a genetic shift across most of western Eurasia, with the expansion of pastoralist societies from the Eastern steppes. At that time, we also see the first appearance of an early form of Y. pestis and many cases of individuals who were positive, not in mass graves but in regular burials.” “There’s not just one strain emerging, but many. There is a lot of contact, mobility, exchange and knowledge transfer in this ‘globalised’ Bronze Age world, reflected in the history of human-pathogen interactions,” Haak adds. “The big questions, still unresolved, are the origins and the mode of transmission – whether they spread with the early pastoralists, or can be ascribed generally to the new pastoral lifestyle which brought closer interaction with animals, contracting diseases that are jumping from one species to the next.”
Keywords
PALEoRIDER, Bronze Age, Stone Age, genetics, DNA, DNA capture, pandemics, genomics, archaeological, prehistoric diseases, human migration, teeth, plague, Yersinia pestis, Salmonella enterica, Hepatitis B
