Scientists announced a big discovery on Oct. 22: The plague — a deadly disease caused by the bacteria Yersinia pestis — is likely much, much older than we originally thought.
This news came after researchers found plague DNA in ancient Asian and European teeth. The evidence suggests that the plague bacteria emerged and started infecting humans as early as 5,000 years ago — nearly three times earlier than we previously had evidence for.
While exciting on its own, this new evidence also sheds light on another enigmatic and unexplained facet of human history: previously mysterious epidemics and the shifting migration patterns of ancient humans.
“This study changes our view of when and how plague influenced human populations and opens new avenues for studying the evolution of diseases,” study author Eske Willerslev, of the University of Copenhagen, said in a press release.
The symptoms of the disease as we know it today are particularly nasty and can manifest in different ways, depending upon how someone was exposed to the bacteria.
The most common form, bubonic plague, is generally transmitted from the bite of an infected flea and can cause a sudden fever, headache, chills, weakness, and large, swollen, and painful lymph nodes. If not treated quickly with antibiotics, the infection can spread to the rest of the body and become fatal within days.
Before this announcement, we knew that plague bacteria Yersinia pestis was the well-understood culprit behind three massive pandemics in ancient history — and their resulting changes to the course of human civilizations.
The earliest pandemic we know for sure was caused by this bacteria was the Plague of Justinian in about 550 AD, which spread across Asia, North Africa, Arabia, and Europe and killed an estimated 30 to 50 million people.
Next came the Black Death about 800 years later, which wiped out about half of the European population during the mid-1300s. And later a third pandemic emerged in China in the 1850s, killing tens of thousands of people.
Now that we have evidence suggesting that the black plague bacteria Y. pestis is so much older, researchers are considering the possibility that it could have played a role in the demise of other human civilizations.
“Earlier putative plagues, such as the Plague of Athens nearly 2,500 years ago and the second century’s Antonine Plague, have been linked to the decline of Classical Greece and the undermining of the Roman army,” according to a press release.
Researchers have never been sure what caused the Plague of Athens — and now, with the results of this and a previous study, they’re now considering the Y. pestis bacteria as one possible cause.
In June of 2015, the team of researchers and their collaborators performed a behemoth DNA analysis of ancient European skeletons from the Bronze Age. They found that the population’s genetic profile surprisingly shifted abruptly and dynamically during that 2,000-year period.
“About 4,500 years ago, for example, the DNA of Europe’s inhabitants suddenly took on a strong resemblance to that of the Yamnaya, a nomadic people from western Russia,” journalist Carl Zimmer wrote for the New York Times. Which means that these nomads seems to have moved into the area.
The reason for the migration was unclear, according to a press release, but now, this new evidence provides a potential explanation. These large scale migrations of western Russia nomads into the genetically distinct region of European hunter-gatherers could have been influenced by the plague. If one population is wiped out by a noxious disease or sent scrambling to find a new place to live, the authors suggest, another population may have moved in to replace them.
While it’s hard to know exactly what the disease was like back then, given that this early form of the bacteria lacked the genes necessary to survive in fleas — the main vector of transmission to humans — it did contain the genes necessary to kill humans.
And those deaths may have shaped the course of human history in ways we never could have imagined, opening potentially exciting new avenues of research.
“Our findings reveal that one can find ancient pathogenic microbes in ancient human material showing no obvious morphological signs of disease,” Willerslev said in a press release. “So plague is just one disease to look at, and one could explore all kinds of diseases like this in the future.”
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