Close cohabitation between our ancient ancestors and the animals they began to domesticate thousands of years ago played a crucial role in the spread of disease, according to new research published today in the journal Nature.
The study, a collaboration between researchers at the University of Cambridge and the University of Copenhagen, examined DNA from more than 1,300 ancient humans, the oldest of which date back as far as 37,000 years.
The research, led by Professor Eske Willerslev, represents the largest study of its kind ever undertaken and suggests that periods of large-scale human migration played a key role in the introduction of potentially harmful pathogens.
Ancient Bacteria and Other Pathogens
The study examined ancient DNA obtained from 214 known human pathogens carried by prehistoric humans in Eurasia. Beginning around 6,500 years ago, zoonotic diseases began to emerge through the likely transmission from animals to humans, with their prevalence beginning around 1500 years later.
A key finding from the study involved the earliest known tracing of bacteria like Yersinia pestis, which is associated with pneumonic, septicemic, and bubonic varieties of plague.
Additional early traces associated with the bacterium responsible for diseases like diphtheria were discovered at even earlier dates, with the origins of Corynebacterium diphtheriae dating back as far as 11,100 years ago.
Similarly, evidence of the Hepatitis B virus was found 9,800 years ago, and malaria (Plasmodium vivax) by around 4,200 years ago. Leprosy was also discovered emerging around 1,400 years ago.
37,000 Years of Infectious Disease
The exhaustive study collected more than 1,300 samples, which included DNA extracted from ancient bones and teeth, providing unique insights into the presence of bacteria, viruses, and parasitic organisms that impacted ancient humans.
“We’ve long suspected that the transition to farming and animal husbandry opened the door to a new era of disease,” Willerslev said in a statement, adding that “now DNA shows us that it happened at least 6,500 years ago.”
Willerslev notes that these infections weren’t just responsible for the onset of illness, however, noting that it is possible “they may have contributed to population collapse, migration, and genetic adaptation.”
Approximately 5,000 years ago, a sudden rise in zoonotic pathogens appears to directly coincide with the migrations of Yamnaya herders to north-western Europe from the Pontic Steppe. Today, the genetic lineages of those ancient migrations are still found in the residents of modern northwestern Europe.
Ancient Pathogens, Modern Cures
Fundamentally, Willerslev and his colleagues believe that the research could help to bolster future efforts to develop vaccines, in addition to helping researchers understand how diseases emerge and what drives their mutations.
Martin Sikora, an Associate Professor at the University of Copenhagen and first author of the new study, said that understanding how these occurrences happened in the ancient world “can help us prepare for the future.”
“Many of the newly emerging infectious diseases are predicted to originate from animals,” Sikora said in a statement. Willerslev added that some of the most successful pathogenic mutations in the past are also likely to reemerge, making it all the more important that researchers understand them today.
“This knowledge is important for future vaccines, as it allows us to test whether current vaccines provide sufficient coverage or whether new ones need to be developed due to mutations,” Willersley said.
The team’s study, “The spatiotemporal distribution of human pathogens in ancient Eurasia,” appeared in Nature on July 9, 2025.
Micah Hanks is the Editor-in-Chief and Co-Founder of The Debrief. He can be reached by email at micah@thedebrief.org. Follow his work at micahhanks.com and on X: @MicahHanks.