Five and a half thousand years ago, dozens of fishermen died near Lake Baikal. Their teeth retained the DNA of the bacteria that caused the plague. Science journalist and author of the Telegram channel”Flour for life» Ilya Kabanov explains how the study of ancient burials has almost become a detective story and why this discovery changes our understanding of the history of epidemics.
An archaeological detective story: How researchers discovered two hunters mysteriously dead in the Baikal region – and traced the plague
About five and a half thousand years ago, small groups of hunter-gatherers appeared I wandered around Along the Angara River in the Baikal region – through an area rich in deer, elk, fish and badgers. They did not build cities, did not farm, and did not keep pets except dogs. Meanwhile, scientists know a lot about their lifestyle thanks to research. For example, the ancient inhabitants of Siberia. I enjoyed it Bow and arrows. In addition, they knew how to burn pottery.
The burial places were in a barn far from each other, sometimes at a distance of up to 340 kilometers. But the people buried in it are still related to recent common ancestors. Traveling along the river or by water may have helped them maintain contact. Meanwhile, there is almost none in the genomes. In other words, these people usually find partners outside their close family circle. Their burial practices differed: in one burial, bodies were usually placed parallel to the river, in others – perpendicular.
For archaeologists, in particular, specialists from Irkutsk State University and the Institute of Ethnology and Anthropology of the Russian Academy of Sciences, burial grounds are one of the main sources of information about the life of hunter-gatherers on Baikal. Using bones, cadavers, grave goods, and ancient DNA, it is possible to reconstruct not only diet and family ties, but sometimes also the circumstances of death. In a recent article in the journal Nature, an international group of researchers (including specialists from Russia) led by Eski Willerslev lesson The remains of 46 people from four burials: Ust-Ida 1, Shumilika, Bratsk Stone and Serovo.
As often happens with Willerslev’s research, which Medusa wrote about in an article about the causes of mammoth extinction, the new work resembles the plot of a Trucrime podcast. There is a crime scene with remains of dead people. Many of them died in a short period of time. Among the victims were an unusually large number of children and teenagers. Relatives are buried in some graves. However, no traces of violence were found on the bones.
To investigate this mystery, archaeologists sought help from geneticists who were interested in the teeth of ancient people. If the infection enters the bloodstream shortly before death, traces may remain in dental tissue. The researchers tested ancient DNA for traces of pathogens, and found it in 18 of the 46 people Yersinia pestis – Bacteria that cause plague. In Ost-Ida, the largest cemetery studied, traces of plague were found in a third (11 of 31) of those buried. Another well-preserved plague genome was obtained from Shumilkha, and several less complete genomes were obtained from Bratsk Stone and Serovo.
The mere presence of DNA from the cause of the plague in the body does not prove that this particular cause led to death. It is possible for a person to become infected with the disease but die from another disease. However, in this particular case, several signs coincided: close burial dates, common graves for the afflicted, family ties between the deceased, an unusually high infant mortality rate, and the absence of another obvious cause of death. The authors of the article came to the conclusion that they did not encounter isolated random infections, but with outbreaks in small communities of fishermen.
The researchers point out that in the event of an outbreak, people could die within a few decades, and perhaps much faster. Their pathogenic genomes were very similar. This likely indicates one phase of the outbreak.
The archaeological context coincides with the genetic context. There is an unusually large number of mass graves at Ust-Ida, and no evidence has been found that the burials were later opened and new dead added. This means that the deaths may have occurred almost simultaneously.
Another detail – Age of the deceased. In Ust-Ida and Bratsky Kamin, child mortality was particularly high, peaking at approximately 7.5 to 11 years of age. For other Baikal tombs of that time, this image is unusual.
For example, in the grave in Bratsky Kamen lie three girls aged from four to nine years. Two of them were probably relatives, perhaps cousins; The third could belong to the same maternal line. DNA was found on all three Yersinia pestis. The authors of the article consider this a sign of infection within the family.
A similar picture exists on Ust-Ida-1. In one of the graves lie an aunt and nephew. Both were diagnosed with plague. In other cases studied by Willerslev’s team, siblings and other relatives were buried nearby or in adjacent graves. Not all of them had a positive identification of bacteria, but this is to be expected for ancient DNA: a negative result does not always mean there is no infection.
The authors found no other clear causes of death. There were no signs of trauma to the bones that could explain such deaths. In one case, traces were found, but the authors consider this infection not to be fatal. Taken together, the evidence makes a very strong case.
Eski Willerslev explained in a press conference the importance of this discovery: “We have discovered the oldest evidence of mass deaths caused by the plague.” Plague is an important part of human history and has been with our species for a long time. By studying its origins and development, we can better understand our history.
The difference in “diagnosis”: Why the Baikal plague is not the same disease that killed millions in medieval Europe
The breed found in the Baikal region lacks the gene ymtwhich helps the bacteria to remain in the flea’s digestive tract and allows for effective transmission through flea bites. This option appeared later. This means that five and a half thousand years ago, the infection spread differently on Lake Baikal.
Where did it come from? The main “suspects” are badgers. Recent natural outbreaks of plague in Central and Northeast Asia are often associated with marmots and other rodents. Infection can occur after hunting, slaughtering, and eating raw or undercooked meat from these animals. For hunter-gatherers in the Baikal region, contact with wild animals was a normal part of life, so animal-to-human transmission of bacteria seems plausible.
However, the exact route of transmission is unknown. After the first infection, the disease can spread between people through airborne droplets. This again points to family ties between the dead and the mass graves.
Scientists do not yet know why children are particularly at risk. Perhaps it has to do with the characteristics of the immune response. Or adults have encountered a similar infection before and had partial protection. Or maybe they were. But there is no direct confirmation of these versions.
Historical significance: How the discovery of plague among ancient hunter-gatherers challenges theories about the origins of human infection
The new research is important to the debate about the origins of epidemics. It is often explained by the transition to agriculture and livestock breeding: people began to live more densely, acquired domestic animals, and established permanent settlements. All this opened the way for the spread of infection. But Baikal’s discovery shows that such a hypothesis does not explain everything.
People from Ust-Ida, Shumilika, Bratsk Kamen and Serovo were not farmers. Local groups remained dependent on hunting and gathering. They had vessels, bows, stone tools, and complex funerary traditions, but no domesticated plants or animals. However, the plague was already nearby. For outbreaks, contact with wild animals and small related populations was sufficient.
Although hunter-gatherer societies are generally considered environmentally poor, these people are mobile, live in small groups, and are not dependent on a single resource. The most important is the discovery near Lake Baikal.
Speaking to reporters, Eski Willerslev recalled that as a child he dreamed of becoming a hunter-gatherer and imagined such a life to be very romantic. He added that after studying, he no longer wanted to do so. There is a rationale for this joke: the lives of hunter-gatherers were more complex and dangerous than usually imagined.