New DNA study: Ancient plague wiped out Europe’s first farmers

Around 3000 BCE, a way of life in Europe appears to falter abruptly: megalithic tombs are left unfinished, building projects slow, and early farming communities thin out. New evidence now suggests that an early form of plague may have been one of the forces behind this disruption.

For decades, archaeologists have debated why the first farmers in northern Europe declined so sharply during the Late Neolithic. A large-scale genetic study of ancient skeletons from Sweden and Denmark paints a troubling picture: plague seems to have circulated thousands of years before the famous medieval pandemic-and it may have returned repeatedly within the same family networks.

A sudden break in the Late Neolithic: the “neolithic decline”

Across many parts of Europe, the archaeological record changes markedly around 3000 BCE. Monumental megalithic tombs are constructed less often, settlements become harder to trace, and the footprint of early agricultural societies becomes noticeably fainter. Specialists refer to this shift as the neolithic decline.

For a long time, the leading explanations centred on crop failures, exhausted soils, or climatic instability. A study led by researchers at the Universities of Copenhagen and Gothenburg, published in Nature, argues that an infectious disease could also have been pivotal: plague, caused by the bacterium Yersinia pestis.

Genetic analyses indicate that, as early as 5,000 years ago, Scandinavia experienced recurring plague outbreaks-reappearing within the same families over multiple generations.

From ancient DNA to family histories: how the evidence was built

The research team examined remains from 108 people recovered from nine Stone Age burial sites in Sweden and Denmark. These included several monumental megalithic tombs in Falbygden (western Sweden), a coastal site near Gothenburg, and one burial complex in Denmark.

In total, the scientists sequenced 174 teeth and bone samples. They used Shotgun-Deep-Sequencing, a method that reads as much DNA as possible from a sample rather than targeting only selected genes. This approach is particularly valuable for highly degraded material, allowing tiny fragments to be identified-including genetic traces left by pathogens.

Alongside this, the team combined isotopic analyses with full-genome data to reconstruct kinship ties and infer aspects of social organisation. The result is an unusually detailed view of how early farming households lived-and how they died.

One additional strength of this approach is that it can connect biology to burial practice. Where multiple related individuals were interred in the same megalithic tombs, the genetic data makes it possible to ask whether disease clustered within households, whether certain lineages were hit repeatedly, and how mortality might have reshaped community leadership and labour.

Plague in one in six individuals

Even experienced researchers were taken aback by the results. Clear genetic evidence of Yersinia pestis appeared in samples from roughly 17% of the individuals tested. Crucially, these signals recur across generations and, in some cases, within the same family burial contexts.

• 108 individuals examined from nine burial grounds
  
• 174 teeth and bone samples genetically sequenced
  
• Around 17% showed detectable plague infection
  
• Three distinct ancient plague strains identified
  
• Repeated outbreaks traced across at least six generations in one family

In one especially well-documented family, the data suggests at least three separate plague episodes spanning six generations. In other words, the pathogen did not simply pass through once; it appears to have returned-echoing the later pattern of epidemic waves seen in medieval Europe.

Not the medieval plague: what the ancient strains could (and could not) do

The bacterial strains identified differ markedly from the agent responsible for the major European outbreaks in the 14th century. The ancient variants lacked a key piece of genetic machinery: the ymt gene. In medieval plague, this gene helps the bacterium survive inside a flea’s gut, enabling efficient spread via flea bites.

Without the ymt gene, the classic “rat–flea–human” transmission chain is unlikely to have operated in the same way. Researchers therefore propose that Stone Age plague may have spread largely directly between people-for example through bodily fluids, respiratory droplets, or close contact within crowded living spaces.

Early plague was probably less dependent on fleas and more driven by direct contact-an acute risk in densely settled farming communities with poor hygiene.

This interpretation aligns with the burial-site pattern: multiple infected individuals appear within the same burial complexes, often with demonstrable family relationships. That distribution looks more like within-household or within-village spread than repeated, random introductions from outside.

How plague may have reshaped early farming societies

When a pathogen repeatedly strikes a community, the consequences extend far beyond immediate deaths. Family groups can fragment, agricultural know-how is lost, herds and fields go unattended, and children may be left without parents and grandparents-the very people who carried essential skills in early farming economies.

The study suggests plague could have contributed on several fronts:

• Population loss: concentrated mortality over short periods, especially in dense settlements
  
• Social instability: disrupted inheritance, deaths among leaders, and weakening of established hierarchies
  
• Cultural breaks: fewer people to sustain traditions, including the construction of monumental graves such as megalithic tombs
  
• Space for newcomers: depopulated areas becoming easier for later groups to enter and settle

Archaeologists particularly highlight the final point. After the neolithic decline, many regions of Europe show the arrival of new groups with origins in the Pontic–Caspian steppes. Some scholars argue that epidemics may have lowered demographic and social barriers, helping to open routes for these migrations.

A closely related factor is mobility itself. As communities reorganised-whether due to labour shortages, abandoned land, or the pull of safer areas-movements of people may also have accelerated the movement of pathogens, creating feedback loops between settlement change and disease spread.

How firm are these conclusions?

The findings are striking, but they are not without limits. Most of the individuals studied came from monumental tombs, which were typically used by socially privileged groups. People of lower status may have been buried differently-or may be underrepresented archaeologically.

That means the reconstructed impact of plague could disproportionately reflect an elite segment of society. How severely the disease affected ordinary farmers or neighbouring communities remains harder to judge from this dataset alone.

What the study shows	What remains uncertain
Frequent plague infections within certain families across generations	Exact death rates across the wider population
Three clearly distinguishable ancient plague strains	Origins and spread routes beyond Scandinavia
A chronological overlap with the neolithic decline	The precise share of plague versus climate or harvest crises

For that reason, some specialists urge caution: plague may be a crucial piece of the puzzle, but not necessarily the only driver of population decline. Poor sanitation, less productive farming systems, and regional climate events could all have increased vulnerability and amplified the effects of outbreaks.

What this changes in our understanding of epidemics

These results underline how strongly infectious diseases may have shaped human history long before written records. Many abrupt shifts seen in archaeology-rapid cultural change, abandoned settlements, conspicuous gaps in habitation-are difficult to explain through climate or technology alone.

Ancient DNA analysis gives researchers a way to test whether pathogens contributed to those turning points. In decayed fragments of bone and teeth, there is effectively an archive of past epidemics-one that can reveal patterns with relevance well beyond prehistory.

For epidemiologists, the study is also a case study in evolution. Over millennia, Yersinia pestis appears to have shifted from a form that was likely passed mainly between humans to one highly adapted to fleas and rodents, capable of sweeping across continents in the Middle Ages. Genetic changes that look minor on paper can fundamentally alter transmission routes-and therefore the scale of risk.

Why a 5,000-year-old plague still matters

The Covid-19 pandemic reminded many people how profoundly a novel disease can disrupt society. The Stone Age plague shows that this is not a modern phenomenon: even small, tightly packed communities with limited medical options could be pushed rapidly to their limits when a new pathogen took hold.

It also reinforces another lesson: diseases rarely act in isolation. They collide with already-stressed systems-after poor harvests, during conflict, or amid economic strain. That interplay was true for early farmers and remains true today. The neolithic decline illustrates that an epidemic is never purely a medical event; it is also social and economic.

Thinking about future pandemics, there is more to learn from prehistory than it might first appear. Pathogens adapt quickly, their spread is tightly bound to human behaviour, and they can reshape migration, power structures, and cultural trajectories. Those dynamics are already visible in the remains of farming families buried in Scandinavian megalithic tombs some 5,000 years ago.