Plague: Why Europe’s late stone age population crashed

Excavated dwellings at Skara Brae (Orkney, Scotland), Europe’s most complete Neolithic village. (Wikipedia)

How was the study carried out?

The researchers involved in the study analysed DNA obtained from human bones, and teeth excavated from ancient burial tombs in Scandinavia — seven from an area in Sweden called Falbygden, one from coastal Sweden close to Gothenburg and one from Denmark.

The remains of 108 people — 62 males, 45 females, and one undetermined — were studied. Eighteen of them — 17% — were infected with plague at the time of death.

The researchers were able to chart the family tree of 38 people from Falbygden across six generations, spanning about 120 years. Twelve of them — 32% — were infected with plague. Genomic findings indicated that their community had experienced three distinct waves of an early form of plague.

What were the findings?

The researchers reconstructed full genomes of the different strains of the plague-causing bacterium Yersinia pestis responsible for these waves. They determined that the last one may have been more virulent than the others, and identified traits indicating the disease could have spread from person to person to cause an epidemic.

“We learned that the Neolithic plague is an ancestor to all later plague forms,” said Frederik Seersholm, geneticist at University of Copenhagen, and the study’s lead author.

A later form of this same pathogen caused the Justinian Plague of the 6th century AD and the 14th century Black Death that ravaged Europe, North Africa, and the Middle East. Because the strains circulating during the Neolithic decline were much earlier versions, the plague may have produced different symptoms than witnessed in the epidemics millennia later.

The study demonstrated that the plague was abundant and widespread in the area examined. “This high prevalence of plague indicates that plague epidemics played a substantial role in the Neolithic decline in this region,” said Martin Sikora, geneticist at University of Copenhagen and co-author of the study.

The Neolithic, or New Stone Age, saw humans switch to settled farming and animal domestication, from a roving hunter-gatherer lifestyle. The Neolithic population crash in Northern Europe occurred from about 3300 BCE to 2900 BCE. By that time, cities and sophisticated civilisations had already arisen in places like Egypt and Mesopotamia.

The populations of Scandinavia and Northwestern Europe disappeared entirely, only to be later replaced by the Yamnaya people who migrated from a steppe region of present-day Ukraine. They are the ancestors of modern Northern Europeans.