The Formidably Lethal Black Death

"What we found in the Swedish grave site is not only the oldest sample of the Y.pestis genome, but also the oldest version of the genome. Think of it as the root of the tree."
"We were thinking, 'Where have we seen this drop [historical population drop] before?' and that got us thinking about the Black Plague."
"If you die from it [the pathogen] and it's in your blood, then we can find it [DNA traces]."
Simon Rasmussen, metagenomics researcher, Technical University of Denmark

The remains of a 20-year-old woman from around 4900 BP that was killed by the first plague pandemic. Credit, Karl-Goran Sjogren, University of Gothenburg

At the dawn of the Bronze Age, -- around 4,500 years ago -- the Black Plague was known to have existed; however no evidence exists of an earlier appearance. Now, an ancient grave in Sweden has yielded new evidence to scientists who have discovered the oldest known strain of a deadly bacteria responsible for the deaths of millions of people worldwide over thousands of years, called Yersinia pestis.

Its other identification through more basic nomenclature? The plague. This microscopic bacteria has been responsible for destroying huge swaths of the human population for over five thousand years, in the process destroying entire empires, inciting political uprisings; in its wake a permanent regional gene pool identity. Most people are vaguely familiar with the world's most notorious pandemic known as the Great Plague, or the Black Death.

In 1334 that dread pandemic began in China, spreading along trade routes to Constantinople [Turkey], finally reaching Europe in the 1340s. An estimated 24 million people died around the globe. Half the population of Europe was wiped out, according to researchers at the Centers for Disease Control and Prevention.

Originally spread by rats, Plague can still erupt in populations of ground squirrels and other small mammals in the Americas, Africa and Asia, though it is considered to be under control in most urban areas across the world. The relationship between humans and plague goes back even further than scientists had realized, however, revealed in a new study published in the journal Cell.

The scientists that unearthed the deadly bacteria in that Swedish grave have connected it to a previously unknown plague outbreak that struck Europe roughly 5,700 years ago. Known to the researchers was that the European population had plummeted some five to six thousand years ago. A phenomenon known as the Neolithic decline. Which led Dr. Rasmussen and his colleagues to think in terms of a plague pandemic.

The group of researchers used databases of DNA extracted from ancient human remains; teeth -- to determine if the plague was present in Europe at the end of the Neolithic period. Blood circulates through the centre of our teeth, making it possible to detect the DNA of pathogens that were present at time of death in a person's bloodstream through examination of a tooth sample, Dr. Rasmussen explained.

The researchers found a match through scanning for genetic sequences, resembling modern-day Y.pestis. in DNA extracted from the tooth of a 20-year-old woman who had died between 5,040 and 4,867 years ago. There were areas in Europe where the disease could have flourished in the Neolithic era, the researchers concluded, even though the  young woman hadn't lived in prime plague territory.

In the meta-settlements of the Trypillia Culture, built between 6,100 and 5,400 years ago, located in present-day Ukraine, Romania and Moldova, the largest of which was home to as many as 20,000 people, archaeologists have shown that such settlements were abandoned and burned about once every 150 years. Culture, religious ritual, or efforts to cleanse the areas of deadly bacterial outbreaks?

According to the proposal launched by the researchers, the plague first evolved in these mega-settlements, transforming from a somewhat benign stomach bug to a deadly microscopic killer some 5,700 years ago, just about the time the Swedish strain diverted from all others in existence at the time which might explain the periodic burning of buildings; possibly set aflame to eradicate disease.

It makes sense that the plague would have made inroads from these urban settlements to the small Swedish farming village, resulting from a vast trade network newly inaugurated by the exploitation of wagons pulled by animals. And as the disease spread along trade routes throughout the continent, the Neolithic decline took place.

The bacteria Yersinia pestis, which causes plague, has been killing people for at least 5000 years.

SCIENCE ARTWORK/Science Source