Have you ever imagined that diseases we know today—like malaria, hepatitis, or even the plague—have been haunting humans for thousands of years? It turns out that the history of disease didn’t begin in modern times. In fact, it has been intertwined with human life since the days of hunting and gathering—and only got worse when humans began domesticating animals.
A major study recently published in Nature reveals an epic story of the relationship between humans and pathogens over the past 37,000 years.
Scientists from various countries—including Denmark, Sweden, and Australia—analyzed DNA from 1,313 ancient human skeletons found across Europe, Central Asia, Northern Asia, and Southeast Asia. They searched for traces of bacteria, viruses, and parasites that once lived inside our ancestors. The results? Surprising, and full of new insights.
When Teeth and Bones Speak
This was no ordinary study. Instead of focusing on ancient artifacts or tools, the research team extracted information directly from ancient human teeth and bones.
From these remains, they were able to retrieve ancient microbial DNA—a kind of biological archive of the diseases that once infected humans. In total, they identified 5,486 DNA sequences belonging to various bacteria, viruses, and parasites.
Some of the pathogens identified include Streptococcus and Actinomyces bacteria, which are actually quite common in the mouths of modern humans. However, since many samples were taken from teeth, it’s possible that their presence was slightly “overrepresented” in the data.
Still, the data remains incredibly valuable. The team successfully identified 214 distinct pathogens from the samples.
Among the most astonishing discoveries were the oldest known traces of the diphtheria-causing bacterium (Corynebacterium diphtheriae), dating back 11,100 years. They also found DNA from malaria parasites that are around 4,200 years old, hepatitis B virus from 9,800 years ago, and the leprosy-causing bacterium from about 1,400 years ago.
The Rise of Zoonosis: When Animals Become the Culprit
One of the most important findings from this study is related to zoonosis, diseases transmitted from animals to humans. You’re probably familiar with the term, especially after the COVID-19 pandemic, which also originated from animals. But when exactly did diseases start jumping from animals to humans?
The answer: around 6,500 years ago. That’s when the earliest signs of zoonotic transmission began to clearly appear in the data.
The trend peaked about 5,000 years ago, coinciding with the widespread domestication of livestock. In other words, as humans began living in closer proximity to cows, goats, and other animals, they also unknowingly opened the door to new pathogens.
According to researchers, the drastic lifestyle changes during the Holocene era—when societies shifted from hunting and gathering to farming and herding—triggered a major epidemiological transition. This led to a surge in diseases transmitted from animals to humans, the effects of which are still felt today.
Outbreaks, Migration, and Evolution
What makes this study even more fascinating is the way these diseases didn’t just make people sick, they may have actually shaped human history and genetics.
For example, the team found evidence of plague outbreaks dating back 5,500 years, long before the infamous Black Death of the Middle Ages. In some sites, they discovered clusters of individuals buried together, all infected with the same pathogen. This suggests the occurrence of local epidemics that may have wiped out entire communities.
Researchers believe that as herding communities began migrating with carts and pack animals like oxen and horses, they weren’t just spreading goods and culture—they were also spreading disease. These diseases then reached new populations with little or no immunity.
Over time, the pressure from such pathogens likely drove genetic adaptation in humans. Some groups may have developed resistance to specific diseases, while others remained vulnerable and were eventually marginalized, or even wiped out.
Scientific Challenges and the Future of Vaccines
As groundbreaking as this study is, it also comes with certain limitations. For example, researchers did not find any traces of Mycobacterium tuberculosis—the bacterium that causes tuberculosis (TB).
This is surprising, considering TB is known to be an ancient disease. However, scientists believe this may be because tuberculosis often doesn’t leave much detectable DNA in bones or teeth, or because the bacterial load was too low to be identified using the methods applied in the study.
Another key limitation is that the research focused on DNA-based pathogens, not RNA viruses. Many important viruses—such as influenza—have RNA genomes, which are more fragile and degrade more easily over time, making them much harder to preserve in ancient remains.
This means that there are likely many ancient diseases we still cannot trace, simply due to the current technological limitations.
