The Black Death: What New Evidence Says About Its Origin and Toll

The Black Death is the textbook example of a historical catastrophe. A plague swept across Asia, Africa and Europe in the late 1340s, killed enormous numbers of people, and in many accounts remade medieval society. All of that is broadly true. But over the past few years, new kinds of evidence have sharpened some parts of the story and complicated others.

Even the dates depend on who is counting. A 2022 study in Nature dates the pandemic to 1346 through 1353. A study published the same year in Nature Ecology and Evolution uses 1347 through 1352. Both are defensible, since they define the start and end differently.

This guide covers the cause, origin, route into Europe, death toll and long-term effects, and where specialists still disagree. It is history, not medical guidance.

The cause: Yersinia pestis

Plague is caused by the bacterium Yersinia pestis. The US Centers for Disease Control and Prevention (CDC) explains that people usually catch it from the bite of an infected rodent flea or, less often, by handling an infected animal. Plague still occurs in rural parts of the western United States and in parts of Africa and Asia, and antibiotics can cure it if given quickly.

For the medieval pandemic, the debate over the cause is largely settled. The 2022 Nature Ecology and Evolution paper, led by A. Izdebski, says ancient DNA research has "conclusively identified" Y. pestis as the cause. Researchers now treat the Black Death as the first wave of what they call the second plague pandemic, a long series of recurring outbreaks. Even here the framing differs. The 2022 Nature study led by Maria Spyrou calls it "nearly 500-year-long," while a 2025 Scientific Reports paper on medieval Cambridge describes a 300-year period of outbreaks every 10 to 20 years.

Where it began

Where the pandemic started has been argued over for a long time. Spyrou and colleagues note that earlier proposals ranged from western Eurasia to eastern Asia. Their study focused on two cemeteries, Kara-Djigach and Burana, near Lake Issyk-Kul in what is now Kyrgyzstan. The cemeteries were excavated between 1885 and 1892, and their tombstones show an unusually large number of burials in 1338 and 1339, some of them giving "pestilence" as the cause of death.

The team recovered ancient DNA from seven people buried there. Two reconstructed Y. pestis genomes turned out to be a single strain sitting right at the point where the bacterium split into the major lineages linked to the pandemic. Comparing it with modern plague reservoirs in the Tian Shan region, the authors concluded that the evidence supports an early 14th-century source in central Eurasia.

How it reached Europe

The usual account has the plague arriving through the Black Sea region, and a 2025 paper in Communications Earth and Environment by Martin Bauch and Ulf Büntgen accepts that route. It notes, though, that the reasons for the pandemic's timing, spread and virulence "are still debated." The authors argue that a cooler climate after volcanic eruptions led to famine around the Mediterranean from 1345 to 1347. That pushed Venice, Genoa and Pisa to import grain in 1347 from the Mongols of the Golden Horde around the Sea of Azov, which brought the bacterium into Mediterranean ports.

Treat this as a well-argued hypothesis that connects climate, trade and disease, not a settled fact. The paper itself says "we argue."

How many died

You will often read that the Black Death killed a third or half of Europe. The published figures vary:

• Spyrou and colleagues (Nature, 2022) say it is estimated to have killed up to 60 percent of the western Eurasian population.
• A 2022 Nature study led by Jennifer Klunk says it killed up to 30 to 50 percent of the population of Afro-Eurasia.
• Izdebski and colleagues note that many people believe it killed half of Europe's population.
• The 2025 Cambridge study, led by John Robb, says England's population fell from around 5 million to about half that and took two to three centuries to recover.

Izdebski's team tested the "half of Europe" idea with pollen. They gathered pollen records from 261 radiocarbon-dated lakes and wetlands in 19 countries, looking for farmland reverting to wild vegetation, a sign that too few people were left to work it. They found the Black Death was devastating in some regions but had "negligible or no impact in others." Their point is that mortality varied a lot by place, shaped by local culture, ecology, economy, society and climate. A single continental percentage hides that variation. Not everyone reads the pollen the same way. In a published comment the same year, Daniel Curtis argued that a drop in grain pollen indicates population decline but not necessarily Black Death mortality. The authors replied that his concerns were about interpretation, not their data.

What it changed, and what it didn't

The Cambridge paper summarizes the well-documented effects in England. Settlements were abandoned, fields became pasture (which helped the wool trade), wages rose as workers became scarce, and laborers became less tied to estates. Contemporaries complained that harvest workers now expected meat with their meals.

The same paper also describes how historians have moved away from the older, more dramatic view. A traditional narrative, it says, held that the plague launched a "Golden Age of the English Labourer" and a shift toward the modern world. Most historians, the authors write, now take a more nuanced view, with arguably more continuity than change. Political stability held, no social ranks disappeared, and religious change was gradual. Many historians see the plague as speeding up changes already under way, such as the move from serf labor to free labor. The authors also point to a crisis that came first: the Great Famine of 1315 to 1320, which they say killed 10 to 15 percent of England's population.

The Cambridge team's own evidence fits that view. They studied 18 skeletal and molecular indicators in 336 adults buried in Cambridge between 940 and 1561. They found no dramatic changes in health or lifestyle that could be directly blamed on the epidemic. Some trends, such as a decline in average height, had started before it.

A mark left in human genes?

Klunk's team analyzed 206 ancient DNA samples from London and Denmark, taken from before, during and after the Black Death. They report signs of natural selection at immune-related genes, with a variant near the gene ERAP2 as the strongest candidate. They also found that some of the protective variants overlap with ones linked today to a higher risk of autoimmune disease. This finding is disputed. In 2025 Nature published a critique by Alison Barton and colleagues, who argued that the evidence for selection does not hold up, including at ERAP2. The original team corrected an error in how it estimated allele frequencies and replied that its combined evidence still supports selection on ERAP2. Genetics has opened a new line of evidence, but its results here remain unsettled.

Key takeaways

• Ancient DNA has confirmed Yersinia pestis as the cause of the Black Death, and a 2022 study points to an origin in central Eurasia in the early 14th century.
• How it reached Europe is still being worked out. One recent hypothesis links Italian grain imports in 1347 to a climate-driven famine.
• Death-toll estimates range from about 30 to 60 percent, and a pollen study argues that mortality varied greatly from region to region, though its reading has been challenged.
• Many historians now see the plague as speeding up changes already under way rather than single-handedly transforming society.
• A claimed genetic legacy in immune genes remains disputed.
• Dates, totals and even the length of the "second pandemic" differ between studies, so check how each source defines them.

Sources

• Spyrou, M. A., et al., The source of the Black Death in fourteenth-century central Eurasia, Nature (June 2022)
• Izdebski, A., et al., Palaeoecological data indicates land-use changes across Europe linked to spatial heterogeneity in mortality during the Black Death pandemic, Nature Ecology and Evolution (February 2022)
• Curtis, D. R., Reduction in grain pollen indicates population decline, but not necessarily Black Death mortality, Nature Ecology and Evolution (September 2022)
• Izdebski, A., et al., Reply to Curtis, Nature Ecology and Evolution (September 2022)
• Klunk, J., et al., Evolution of immune genes is associated with the Black Death, Nature (October 2022)
• Klunk, J., et al., Author Correction: Evolution of immune genes is associated with the Black Death, Nature (January 2025)
• Barton, A. R., et al., Insufficient evidence for natural selection associated with the Black Death, Nature (February 2025)
• Vilgalys, T. P., et al., Reply to: Insufficient evidence for natural selection associated with the Black Death, Nature (February 2025)
• Bauch, M., and Büntgen, U., Climate-driven changes in Mediterranean grain trade mitigated famine but introduced the Black Death to medieval Europe, Communications Earth and Environment (December 2025)
• Robb, J., et al., More continuity than change following the Black Death epidemic in medieval Cambridge, Scientific Reports (September 2025)
• Centers for Disease Control and Prevention, About Plague (updated August 24, 2026)