Evrim Yazgin
Cosmos science journalist
DNA from 108 individuals from Scandinavia who lived during the Late Stone Age suggests that repeated plague outbreaks contributed to falling populations.
The DNA analysis is presented in a Nature paper published today.
“In the period between 5,300 and 4,900 years before present, populations across large parts of Europe underwent a period of demographic decline,” the authors write. “However, the cause of this so-called Neolithic decline is still debated.”
Competing theories, they say, include an agricultural crisis and outbreaks of an early form of plague.
An international team of researchers analysed the DNA from individuals spanning 6 generations in the Scandinavian Neolithic (about 6,000–4,000 years ago). The ancient people’s remains were found at 8 megalithic grave sites in Sweden and a stone cist (a small, coffin-like stone box) in Denmark.
Of the bodies uncovered, 17% showed signs of the plague-carrying bacterium Yersinia pestis. Analysis reveals the plague took hold in at least 3 distinct waves over about 120 years. These early strains also showed signs of virulence factors – molecules which assist bacteria as they colonise the host’s cells – never before seen in Y. pestis. These may have been lethal.
The first 2 waves were small and contained. The third, however, was more widespread.
“Because plague was infecting a significant proportion of the population, excess mortality associated with the disease could have undermined the long-term viability of society, leading to the eventual collapse of this form of Neolithic society,” the authors write in their conclusion.
In addition, the DNA analysis also reveals intimate details about the family and social structure of these Neolithic communities.
The bulk of these details come from the 7 megaliths (large stones used to construct structures or monuments such as tombs) from Falbygden in southwestern Sweden.
Multiple reproductive partners were identified for 4 males, while no instances were found of females with multiple reproductive partners. This suggests a patrilineal social structure.
One female was found buried in a different tomb to her 2 brothers. This, the authors say, suggests that female individuals might have moved to neighbouring groups to establish families.
“Taken together, the data presented here provide a highly detailed and intimate snapshot of what life was like in Neolithic Falbygden, Sweden,” the authors write.
