Humans
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The construction of complex megalithic tombs was a hallmark of the Neolithic period in Europe, yet this practice seems to have ceased rather abruptly at the end of the fourth millennium BCE. Numerous hypotheses have been proposed to explain this sudden shift, and a new study suggests that the cause may be linked to a massive population crash known as the “Neolithic decline”.
The rest of this article is behind a paywall. Please sign in or subscribe to access the full content.Previous genetic analyses in Scandinavia have indicated that the cessation of megalithic tomb building coincided with a rapid turnover in the population, as Neolithic farmers were replaced by a wave of immigrants from the Eurasian Steppe. To test whether a similar phenomenon occurred elsewhere in Europe, the study authors examined the DNA of 132 individuals buried at the Neolithic tomb of allée sépulcrale at Bury, near Paris.
Their results reveal that the tomb was used in two separate phases, the first of which lasted from roughly 3200 to 3100 BCE and is characterized by individuals with local ancestry. The second phase, however, is made up of corpses displaying Iberian and southern French heritage, hinting at a population turnover that began around 2900 BC.
"We can see a clear genetic break between the two burial phases. The people who used the tomb before and after the collapse appear to be two completely different populations," said study author Frederik Seersholm in a statement. "This tells us that something significant happened, like a major disruption that led to the decline of one population and the arrival of another."
According to the researchers, these results match those from other Neolithic tombs in Germany, Denmark, and Sweden, which also show evidence of population turnovers at the beginning of the third millennium BCE. Collectively, these findings hint at a widespread Neolithic decline, as megalithic tomb-building societies died out and were later replaced by immigrants from southern Europe or the Eurasian Steppe.
In addition to carrying foreign DNA, these later arrivals also display cultural differences when compared with the original builders of these tombs, particularly in relation to funerary practices. At Bury, for instance, burials from the first phase were typically aligned with the main axis of the tomb and placed in an extended body position. Second-phase burials, on the other hand, show no such alignment and are characterized by flexed body positions.
The big question, therefore, concerns the cause of this continent-wide Neolithic decline. Searching for clues, the study authors note that the first phase of internment at Bury contains an exceptionally high number of infant and child skeletons. This, they write, is “suggestive of excess mortality, particularly affecting juvenile individuals, perhaps indicating a catastrophic event, such as war, famine or a disease outbreak.”
The study authors also found high rates of DNA from deadly pathogens such as Yersinia pestis – which causes the plague – in skeletons from the first phase at Bury. This raises the possibility that the Neolithic decline was caused by a disease outbreak, a prospect that has been suggested before, although it remains a somewhat speculative and contentious hypothesis at this stage.
"While there is no strong case to say that plague alone caused the population collapse, the total disease load could have been one of several contributing factors," explained study author Martin Sikora.
Despite these lingering uncertainties, the results of this new study appear to confirm the widespread nature of the Neolithic decline, indicating that the cessation of megalithic tomb construction was indeed linked to a mass die-off across Europe. After a hiatus, the communal tombs built by these Neolithic communities were then re-used by separate cultures who spread into the newly vacated territories created by this population crash.
“We may thus consider the possibility that both the Iberian northward migration and the expansion from the steppe were related responses to the Neolithic decline, as widespread demographic contraction would have created a vacuum that neighbouring groups could expand into,” conclude the researchers.
The study has been published in the journal Nature Ecology and Evolution.
