Paleogenomics: How teeth told the history of epidemics!

The coronavirus pandemic is changing lives and the global economy, historians tell us, but this is not the first time this has happened in the history of humanity. The earliest written evidence of tiny infectious organisms destroying human society dates back to 541, when the Justinian plague killed 50 million people. Even earlier, in 165 AD, the Antonine plague claimed the lives of 5 million people - for the II century this is a very significant figure.

Until now, it was believed that there were no major pandemics before. However, paleogenomics - a nascent branch of science that studies the DNA of ancient tooth remains - has shown that people were introduced to the concept of "plague" thousands of years earlier than anticipated. There is more and more evidence that the first epidemics changed humanity and predetermined its further development.

“In the case of Covid-19, we see similar processes, but we see them unfolding in real-time,” said Ann Stone, Professor-Director of the School of Human Evolution and Social Change in Arizona.

Palaeogenomics, which uses high-quality medical instruments like those currently used to track the coronavirus, has revolutionized medical history, according to Maria Spieru, a Microbiologist at the Max Planck Institute in Germany. Where historical evidence is lacking, ancient DNA samples provide an opportunity to fill in the gaps, sometimes in the most surprising ways. One of these discoveries was the plague. Until 2015, we thought the plague was a 3000-year-old disease.

Scientists and archaeologists now believe, however, that the plague bacteria that led to the medieval Black Death, killed up to half of Europe's population, led to massive contamination some 5,000 years ago, back in the Stone Age. The bacteria, after entering the bloodstream and likely killing the host, circulated in the pulp chamber of the teeth, which protected DNA from millennia of environmental wear and tear. In the past decade, scientists have been able to extract and analyze this DNA.

Stone Age Plague: How did it differ?

The Stone Age Plague had a slightly different genetic identity. Tracking the evolution of these differences helps infectious disease biologists better understand what causes disease and how to prepare for current outbreaks. For example, the plague bacteria in the Stone Age lacked the genes needed to move from fleas to humans, which likely contributed greatly to the widespread of the Black Death. Without the flea gene, the disease likely used another transmitter animal that came into contact with humans. In 2018, a team from the University of Copenhagen published the first evidence that ancient plague bacteria found in a Swedish settlement had the ability to kill and could be life-threatening in the era of "mega-settlements."

“This was probably the first pandemic,” said Simon Rasmussen, a university geneticist and lead researcher in the study of plague. During the Stone Age, also called the Neolithic period, people began to congregate in large settlements, where up to 10,000 people live in close quarters with animals and have little or no sanitation. “This is a great place for a new pathogen to emerge,” he added.

Paleogenomics has also enabled archaeologists to fill one of the biggest gaps in archeology. Pathogens rarely leave marks on bones, and entire populations can die out without leaving a hint of a cause. Thanks to the ability to read traces of DNA stored in teeth, historians learn about diseases in ancient people.

Christian Christiansen, an archaeologist at the University of Copenhagen, believes his group's research sheds light on the reasons for the demographic transformation of the Stone Age, called the Neolithic decline, which archaeologists have long studied.

Settlements at that time were disappearing faster than they appeared, and within several hundred years, most of the population was replaced by migrants from the Eurasian steppe. Researchers have previously hypothesized that disease played a key role in the destruction of the indigenous population. But now they have proof.