The trajectory of human population growth has not been uniformly consistent but has rather been characterized by notable and sometimes peculiar fluctuations. At several junctures throughout our recorded history, communities have experienced abrupt and substantial contractions.
One such era of significant demographic reduction occurred during the Neolithic period, approximately five millennia ago, when numerous communities across various parts of Europe experienced widespread collapse.
The underlying causes, or perhaps a confluence of reasons, for this extensive phenomenon have long eluded definitive explanation, though a number of hypotheses have been put forth by scientists to account for what is termed the ‘Neolithic decline‘.
Now, through the meticulous examination of ancient DNA recovered from 132 individuals interred within a burial site in what is presently France, a research contingent spearheaded by scholars from the University of Copenhagen is commencing the process of reconstructing the events of that epoch.
“A distinct genetic discontinuity is evident between the two phases of interment. The individuals interred within the tomb prior to the collapse and those buried subsequent to it appear to represent entirely separate ancestral groups,” states geneticist Frederik Seersholm, affiliated with the University of Copenhagen and the primary author of the published study.
“This observation strongly indicates that a profound event transpired, such as a considerable disruption that precipitated the decline of one population segment and the ingress of another.”
The Neolithic decline is estimated to have taken place around 3000 BCE. In the preceding centuries, populations had expanded, reliance on hunting and gathering diminished, technological advancements proliferated, and agrarian societies flourished.
However, a catalyst appears to have triggered a dramatic alteration in population demographics. In numerous regions, including Scandinavia, indigenous farming populations vanished and were supplanted by groups originating from the Eurasian steppe.
At a location designated as Bury, situated approximately 50 kilometers north of Paris in France, a substantial megalithic structure, recognized as a gallery grave or allée sépulcrale, was utilized for communal burials around the epoch of this significant societal upheaval.
While the precise impact of this decline in this specific area is not as thoroughly understood as in other locales, the research team hypothesized that the skeletal remains discovered there might also bear evidence of the mortality event.
The tomb contained the skeletal remains of hundreds of individuals, which prior analyses had indicated were interred during two distinct periods, separated by an interval of several centuries during which no burials took place. This temporal gap aligns with the timeframe of the Neolithic decline.
The researchers successfully extracted and sequenced 132 genomes from individuals across both burial phases, revealing a pattern consistent with findings elsewhere in Europe. The population present before the Neolithic decline was genetically distinct from the population that succeeded it.
Furthermore, the initial burial phase, dating from approximately 3200 to 3100 BCE, exhibited an unexpectedly high proportion of individuals who had perished at a relatively young age.
“This particular mortality profile deviates from what one would anticipate in a stable, healthy population,” observes archaeologist Laure Salanova, associated with the French National Center for Scientific Research.
“It suggests the occurrence of a catastrophic event, potentially attributable to disease, widespread famine, or inter-group conflict.”
Subsequent analysis of the second burial phase revealed strong genetic affiliations with populations from southern France and the Iberian Peninsula, implying migration and subsequent resettlement from these regions into the Paris Basin following the Neolithic decline.
The precise trigger for this disruption remains elusive, but the accumulated evidence, including the newly obtained genetic insights, points towards a synergistic effect of multiple pressures rather than a singular catastrophic occurrence.
The research team identified DNA from several pathogenic bacteria within the skeletal remains, particularly in individuals from the earlier burial phase. These included Yersinia pestis, the microorganism responsible for the Black Death centuries later, and Borrelia recurrentis, the causative agent of louse-borne relapsing fever.
The presence of Y. pestis has been documented in other European skeletal remains from the Neolithic decline period, although its precise role in contributing to the population collapse is currently a subject of ongoing scientific discussion.
“The detection of pathogenic DNA confirms that infectious diseases were impacting human communities during this era,” explains genomicist Martin Sikora of the University of Copenhagen.
“While there is no definitive evidence to assert that plague alone precipitated the population collapse, the cumulative burden of disease could have been one of several contributing elements.”
Concurrently, environmental data from the region indicates a period of forest regrowth, with vegetation reclaiming agricultural lands – a phenomenon typically associated with a reduction in human agricultural activity.
The kinship analyses among the deceased also provided significant insights. Prior to the demographic decline, the interred individuals were all closely related, suggesting a tightly knit community comprised of familial units.
Following the decline, the observed familial relationships were less cohesive and exhibited greater temporal spacing. This shift, according to the researchers, may signify a more dispersed and less densely populated society.
Collectively, these findings strongly suggest a population subjected to multifaceted pressures, followed by a significant demographic transition once these stressors abated.
Although the precise correlation between this localized pattern and the broader Neolithic decline remains to be fully elucidated, it undeniably provides a compelling depiction of a disruptive period that had a continent-wide impact across Europe.
“The continued pursuit of nuanced understandings of these localized historical dynamics, rather than overlooking them in favor of overarching narratives of change, is poised to yield novel, compelling, and authentic accounts of Late Neolithic Europe,” writes archaeologist Tom Booth of University College London in a companion editorial piece.
