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Neolithic decline
Neolithic decline
Neolithic decline
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The Neolithic
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Longshan culture
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Shijiahe culture
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Neolithic Tibet
South Asia
Lahuradewa
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Marine archaeology
 in the Gulf of Cambay
Bhirrana
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Jhukar
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Khiamian culture
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Neolithic topics
↓ Chalcolithic

The Neolithic decline was a rapid collapse in populations between about 3450 and 3000 BCE[1][2] during the Neolithic period in western Eurasia. The specific causes of that broad population decline are still debated.[2] While heavily populated settlements were regularly created, abandoned, and resettled during the Neolithic, after around 5400 years ago, a great number of those settlements were permanently abandoned.[2] The population decline is associated with worsening agricultural conditions and a decrease in cereal production.[3] Other suggested causes include the emergence of communicable diseases spread from animals living in close quarters with humans.[2]

The population increase between 5950 and 5550 BP (4000 to 3600 BC) that preceded the decline was catalysed by the introduction of agriculture,[4][3] along with the spread of technologies such as pottery, the wheel, and animal husbandry.[2] After the Neolithic decline, there were massive human migrations from the Pontic–Caspian steppe into eastern and central Europe, beginning approximately 4800 BP (2850 BC).[2]

Plague

[edit]

An ancient version of the Yersinia pestis has come up from multiple skeletal studies throughout Eurasia, skeletons which have dated back to around the estimated periods of the Neolithic Decline.[2][3][5][4][6] Additionally, genomes of the plague have been found as far back as 5,000 BP in areas such as Latvia and Sweden.

Discoveries in Europe

[edit]

One 5,000-year old individual buried in Riņņukalns, Latvia, was infected with an early Yersinia pestis strain, shortly after it split from its antecessor Y. pseudotuberculosis c. 7,000 years ago.[7]

A tomb in modern-day Frälsegården in Gökhem parish, Falbygden, Sweden, contained 79 corpses buried within a short time of one another about 4,900 years ago.[2] This discovery uncovered fragments of a unique strain of the plague pathogen Yersinia pestis found in two individual's teeth.[2][3][4] The strain contained the "plasminogen activator gene that is sufficient to cause pneumonic plague", an extremely deadly form of the plague which is airborne and directly communicable between humans.[4] This strain of plague, researchers claim, alongside high demands of resources whilst living in close proximity to each other, would have allowed a pneumonic plague to quickly spread amongst inhabitants and wipe them out.[2]

In the gallery graves of the Neolithic Wartberg Culture, dozens or up to hundreds of individuals are preserved. A recent study by researchers from Kiel University (Collaborative Research Centre 1266) have found that only two of 133 examined individuals were infected.[8] As most were not, they conclude that no massive plague outbreak occurred. Moreover, they found the bacterium in bones of a dog. It is possible that dogs played a role in infections, but more research is required on this topic.[9][8]

Neolithic-era human teeth from Eurasia have also shown evidence of some of the oldest strains of Yersinia pestis.[6] The ages of the skeletons identified between 2,800 and 5,000 years old, with seven of the one hundred and one individuals carrying similar sequences of the bacterium.[6] Additionally, studies of the ancient strains discovered show these ancient strains lack the Yersinia murine toxin (ymt), which would have prevented the strains from using fleas as a vector.[6]

Discoveries in Asia

[edit]

A similar site was found in China in 2011; the site Hamin Mangha in northeast China dates back to approximately 5000 years ago and features a small structure filled with almost 100 bodies.[10] Whilst there are several theories as what the reasons are for so many bodies in one location, such as a geological disaster or a ritual sacrifice, a plague is also considered as a hypothesis.[10] In the case of the plague, despite being the weakest of the hypotheses, the placement of the bodies suggesting others carrying them in, alongside being intact before being burned, and the lack of artifacts alongside the bodies.[10] Two other sites like these have been found in Northeast China: Miaozigou and Laijia,[5][10] but archaeologists did not speculate as to the causal agent.[11]

Counterarguments

[edit]

Some studies, as those from the researchers from the Kiel University, have contested the hypothesis that the plague was responsible for the Neolithic decline. Analysis of the plague bacteria that infected a hunter-gatherer in Latvia during this period indicates that, unlike modern plague strains, the strain which afflicted this man was incapable of causing flea-spread bubonic plague and could only cause septicemic plague via a rodent bite or a largely non-contagious case of pneumonic plague, implying that the disease would have had difficulty spreading across vast distances in a short amount of time.[12] The man identified in this particular case, after being studied, does not have a clear indicator of how much he was actually affected by the bacteria.[12] Importantly, and supported by the results from the gallery graves of the Wartberg Culture, they do not see indications for a mass-outbreak.[7][12][9]

Epidemiology

[edit]

Gene studies of ancient Yersinia pestis

[edit]

Studies of the ancient variations of the bacteria have tried to show connections to the specific strain they studied and the more modern strands, such as ones during the Black Death.[2][6] Studies in Sweden, on the Gok2 Neolithic Yersinia pestis strain, discovered it to be the basal to all known Y. pestis strains with the use of genome reconstruction, as well as containing plasminogen activators genes that would have allowed it to start a pneumonic plague.[2] Other cases revealed a lack of ability to be able to use fleas as a vector of transmission; the case in Sweden contained Yersinia murine toxin which prevented the use of fleas, alongside a separate case studying late bronze-age bodies revealing the use of fleas in transmission would have occurred around the time after the collapse, being a few hundred years off.[2][6]

References

[edit]

Sources

[edit]
  • Colledge, Sue; Connolly, James; Crema, Enrico; Shennan, Stephen (23 August 2019). "Neolithic population crash in northwest Europe associated with agricultural crisis". Quaternary Research. 92 (3): 686. Bibcode:2019QuRes..92..686C. doi:10.1017/qua.2019.42. S2CID 202186375. Retrieved 13 November 2019.
  • Rasmussen, Simon; Allentoft, Morten Erik; Nielsen, Kasper; Orlando, Ludovic; Sikora, Martin; Sjögren, Karl-Göran; Pedersen, Anders Gorm; Schubert, Mikkel; Van Dam, Alex; Kapel, Christian Moliin Outzen; Nielsen, Henrik Bjørn; Brunak, Søren; Avetisyan, Pavel; Epimakhov, Andrey; Khalyapin, Mikhail Viktorovich (2015-10-22). "Early divergent strains of Yersinia pestis in Eurasia 5,000 years ago". Cell. 163 (3): 571–582.
  • Rascovan, Nicolas; Sjögren, Karl-Göran; Kristiansen, Kristian; Nielsen, Rasmus; Willerslev, Eske; Desnues, Cristelle; Rasmussen, Simon (10 January 2019). "Emergence and Spread of Basal Lineages of Yersinia pestis during the Neolithic Decline". Cell. 176 (2): 295–305. doi:10.1016/j.cell.2018.11.005. PMID 30528431. S2CID 54447284.
  • Susat, Julian; Lübke, Harald; Immel, Alexander; Brinker, Ute; Macāne, Aija; Meadows, John; Steer, Britta; Tholey, Andreas; Zagorska, Ilga; Gerhards, Guntis; Schmölcke, Ulrich; Kalniņš, Mārcis; Franke, Andre; Pētersone-Gordina, Elīna; Teßman, Barbara (2021-06-29). "A 5,000-year-old hunter-gatherer already plagued by Yersinia pestis". Cell Reports. 35 (13). doi:10.1016/j.celrep.2021.109278. ISSN 2211–1247. PMID 34192537.
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Neolithic decline

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The Neolithic decline refers to a widespread population collapse and cultural disruption that occurred across parts of during the period, approximately 5,500 to 4,900 calibrated years (cal ), marking the end of large-scale farming communities and the transition to the . This event is characterized by sharp reductions in human activity, evidenced by fewer archaeological sites and radiocarbon dates, with declines ranging from 20% to 60% in some regions over mere centuries. Primarily affecting northern and , including and the , the decline coincided with the cessation of monumental constructions like megalithic tombs and the . Several interconnected factors contributed to this decline, with recent genetic evidence pointing to recurrent outbreaks of plague caused by an ancestral strain of Yersinia pestis. Analysis of ancient DNA from 108 individuals across nine Scandinavian sites revealed infection rates as high as 17%, with three distinct plague strains circulating over about 120 years, potentially leading to excess mortality in affected communities. In parallel, agricultural crises exacerbated the situation, as archaeobotanical records show a marked decrease in cereal production and weed taxa frequencies, linked to climatic deterioration and a shift toward cultivation on less fertile soils during the period from roughly 5,550 to 4,950 cal BP. Archaeological and statistical analyses further indicate that European Neolithic societies exhibited early warning signals of prior to the , such as increasing variance and in population proxies derived from summed probability distributions of 2,378 radiocarbon dates across nine regions. These signals suggest a loss of resilience in social-ecological systems, transitioning from phases of growth (around 5,950–5,550 cal ) to rapid , influenced by environmental pressures and possibly social factors like migration or conflict. The decline's impacts were profound, leading to regional abandonments, reduced settlement density, and the eventual emergence of more mobile, pastoralist-oriented societies.

Background

Neolithic context

The marked the profound transition from nomadic societies to sedentary communities reliant on , beginning around 10,000 BCE in the of Southwest Asia. This shift involved the deliberate cultivation of wild and the herding of animals, enabling permanent settlements and laying the foundation for complex societies. By approximately 7000 BCE, these practices had spread westward into southeastern via migration and , introducing farming to the continent. Central to this revolution were key innovations in , including crops such as wheat and in the , which provided reliable food sources. Animal followed, with like , sheep, , and pigs bred for labor, , and , enhancing dietary diversity and resource availability. These developments allowed for the production of food surpluses beyond immediate needs, supporting population expansion and freeing individuals for non-subsistence activities. In , the Early Neolithic phase spanned roughly 7000–5000 BCE, characterized by the (LBK), which featured settlements and the adoption of Southwest Asian domesticates across central regions. This was followed by the Middle Neolithic expansion from 5000–3500 BCE, during which farming communities proliferated northward and westward, adapting crops and livestock to diverse environments like the soils of the basin. These agricultural foundations fostered initial societal transformations, including the growth of clustered villages that housed hundreds of inhabitants and served as centers for communal life. Monumental megalithic structures, such as passage tombs and stone circles, emerged in , reflecting organized labor and possible ritual practices. Trade networks also developed, facilitating the exchange of materials like and flint over hundreds of kilometers, which strengthened inter-community ties. This era of expansion culminated in a subsequent around 3000 BCE.

Population dynamics prior to decline

During the early period in , around 6500 BCE, the is estimated to have been approximately 1 million inhabitants, primarily concentrated in the initial farming communities spreading from the southeast. By 4000 BCE, this had expanded to between 2.5 and 12 million people, reflecting sustained growth at rates of 0.08–0.12% per year. These figures are reconstructed using summed probability distributions of radiocarbon dates from thousands of archaeological sites, which serve as proxies for settlement density and demographic trends across the continent. The primary driver of this expansion was the Neolithic demographic transition, triggered by agricultural surplus that enhanced and supported larger family sizes. Farming practices allowed for higher birth rates, as indicated by elevated juvenility indices in data—measuring the proportion of subadults under 15—which rose significantly post-agriculture adoption, alongside initial declines in due to more stable . This shift from to cultivation enabled communities to sustain growth for several before external pressures emerged. Regional variations in population distribution were pronounced, with denser settlements in fertile river valleys like the , where local densities reached 8.5 persons per km² in core settlement zones during the Linearbandkeramik culture. In contrast, northern Europe exhibited sparser populations, with overall densities around 0.6 persons per km² and more dispersed sites reflecting to less productive landscapes. These patterns, inferred from site distributions and radiocarbon analyses, highlight how environmental suitability influenced demographic hotspots. By the late Middle Neolithic, around 4500–4000 BCE, early signs of strain appeared in the form of localized resource , as proxies showed increasing variance and slower recovery from perturbations in multiple regions. This trend abruptly reversed around 3000 BCE, marking the onset of broader decline.

Evidence of Decline

Archaeological indicators

Archaeological excavations across reveal evidence of widespread settlement abandonment during the late , particularly evident in the sudden cessation of occupation at settlements associated with late cultures. Similar patterns appear in (TRB) settlements in and , where village clusters like those near the peninsula were vacated by circa 3000 BCE, leaving behind clusters of post-built longhouses and storage pits without subsequent layers of occupation. These abandonments correlate with estimated drops of 20–60% in regional site densities over short periods. A notable reduction in monumental further underscores the decline, with fewer megalithic tombs and henges constructed in Britain and after approximately 3500 BCE. In Britain, the construction of passage graves and long barrows, such as those at West Kennet and , tapered off, replaced by sparser, smaller-scale earthworks, reflecting diminished communal labor investment. Scandinavian examples, including dolmens and gallery graves in southern and linked to the , show a peak in building activity from 3500–3300 BCE followed by a sharp decrease, with only isolated monuments erected thereafter. This shift is evident in the through the absence of new megalithic alignments and a reliance on earlier structures for reuse. Changes in artifact assemblages also signal reduced craftsmanship and societal complexity during this period. Polished stone tools, ceramics, and adornments from earlier Neolithic phases in exhibit high standardization and fine finishing, but late assemblages from sites like those of the in the region display cruder, less varied implements, with fewer specialized tools and a decline in decorative motifs on . This transition indicates a contraction in production scales and skill transmission, as seen in the reduced volume and quality of lithic . These indicators are most pronounced in Central and , encompassing cultures like the Funnelbeaker and Globular Amphora, where settlement networks fragmented and material culture simplified between 3500 and 3000 BCE. In contrast, Mediterranean regions, such as and the , exhibit continuity in village occupation and artifact production with minimal disruption during the same timeframe. Recent studies, including analyses of site distributions in , corroborate these patterns with evidence of rapid abandonment aligning with dated infection events around 5200 years ago.

Demographic reconstructions

Demographic reconstructions of the decline rely primarily on statistical analyses of radiocarbon data to infer trends, as direct records are unavailable. A key technique involves constructing summed probability distributions (SPDs) of calibrated radiocarbon dates from archaeological sites, which serve as proxies for relative sizes under the assumption that more dates reflect higher activity and thus larger s. These SPDs are often refined using Bayesian modeling to account for chronological uncertainties, sampling biases, and taphonomic effects, enabling more robust estimates of fluctuations. Such methods have revealed a ~30–50% drop in Northwest between 3500 and 2500 BCE, marking a sharp transition from peaks to lower levels. Seminal studies underscore the scale and timing of this decline. For instance, an analysis of 7,944 radiocarbon dates from over 100 sites across 12 regions in identified population peaks around 4000 BCE, followed by abrupt crashes to baselines by 2500 BCE, with the most pronounced declines in the mid-4th millennium BCE. Another study examining 13,658 dates from 2,378 sites in nine regions applied Bayesian frameworks to detect early warning signals, such as rising variance in date distributions, preceding collapses estimated at 20–60% within a century. These reconstructions align with patterns of site abandonments observed archaeologically, providing corroborative evidence for widespread depopulation. The strongest demographic evidence emerges from Britain, , and , with the decline centered around 3000 BCE. In Britain, particularly in areas like , SPDs indicate a rapid contraction after initial expansion, reducing regional populations to a fraction of their former size. Similar boom-bust cycles appear in Scandinavian regions such as and , and Central European loess plains, where Bayesian models confirm synchronous drops post-3500 BCE.

Environmental and Agricultural Factors

Climatic fluctuations

Paleoclimate reconstructions indicate that the Sub-Boreal phase, spanning approximately 3000–2000 BCE, marked a transition to cooler and wetter conditions in compared to the preceding Atlantic phase, stressing agricultural systems. records from lake sediments across the continent reveal shifts in vegetation, with increased representation of moisture-loving taxa such as (Betula) and (Alnus), signaling higher humidity and reduced summer warmth during this interval. These environmental shifts coincided with the decline, as cooler temperatures and elevated precipitation disrupted established farming practices. Proxy data from multiple sources, including tree-ring chronologies and lacustrine sediments, further substantiate regional cooling trends during the Sub-Boreal transition, with variable temperature reductions across . Dendrochronological analyses of subfossil pines from northern regions show narrower ring widths, indicative of shorter growing seasons due to delayed springs and earlier frosts. Such changes likely constrained crop maturation periods, contributing to diminished yields of staple grains like emmer wheat and . These climatic stressors were part of a broader transition from the warmer Atlantic phase, with the Sub-Boreal representing a pivotal shift toward more variable conditions, exacerbating vulnerabilities from ~5500 cal onward. The impacts of the Sub-Boreal cooling were regionally variable, with northern Europe, particularly Scandinavia, experiencing more pronounced effects than southern areas. In Scandinavia, pollen profiles from peat bogs and lakes document glacier activity and mire expansion during the broader Sub-Boreal transition (~5000–4000 BP), reflecting cooler summers and increased winter precipitation that severely limited arable land. Southern Europe, by contrast, saw milder disruptions, with pollen assemblages indicating sustained Mediterranean vegetation resilience amid less extreme temperature drops. This north-south gradient aligns temporally with archaeological evidence of population contractions in northern Neolithic settlements, where environmental pressures exacerbated resource scarcity. Prior to the Sub-Boreal escalation, the Middle (ca. 5000–3500 BCE) featured relatively stable but punctuated climatic fluctuations, including minor dry episodes inferred from lake-level records in . These earlier dry phases, around 5300 cal yr (ca. 3300 BCE), involved brief reductions in that temporarily affected water availability but did not trigger widespread decline. However, post-3500 BCE, conditions intensified into the cooler and wetter regime of the Sub-Boreal, amplifying vulnerabilities in Neolithic communities across .

Soil and crop challenges

In , slash-and-burn agriculture, a common practice among early farming communities, initially enriched soils through the addition of ash-derived nutrients but led to rapid exhaustion over time. Long-term experimental reconstructions in temperate regions, such as those conducted at Forchtenberg since 1998, demonstrate that while first-year yields under this system could reach 1.8–5 tons per —comparable to modern non-fertilized farming—repeated burning and cultivation without sufficient periods caused significant nutrient depletion. After 2–3 years of continuous use, breakdown accelerated, reducing and necessitating short cultivation cycles followed by periods of 10–20 years to maintain ; failure to do so resulted in yields dropping below 10% of initial levels under alone. Archaeobotanical evidence from late Neolithic sites across northwest and further indicates declining crop yields, particularly for dominant cereals like wheat (Triticum dicoccum). and charred plant remains show a marked reduction in cereal production coinciding with the mid-Neolithic population crash around 5450–4950 cal yr BP, linked to shifts toward less fertile, acidic soils and increased presence of weeds tolerant of nutrient-poor conditions. This decline is evidenced by lower densities of remains and a proportional increase in hardier but lower-yielding crops like , reflecting overall agricultural stress rather than isolated failures. Rising population densities during the exacerbated these issues by intensifying land use, leading to widespread and in . analyses from regional lake and mire sediments reveal a progressive decline in oak (Quercus) and hazel (Corylus avellana) starting around 6000 , with forest cover dropping from mid-Holocene maxima above 80% to more open landscapes by the . This clearance for arable fields and pastures, driven by demographic expansion, promoted on slopes and further degraded soil structure, as indicated by increased open-land indicators like grasses and in the records. Adaptation to these challenges proved limited, as Neolithic farmers maintained heavy reliance on a narrow range of staple crops, primarily and , with minimal diversification into or other resilient species. Archaeobotanical assemblages from sites and confirm emmer's dominance throughout the period (ca. 4000–2500 cal BC), comprising over 70% of remains in many contexts, which heightened vulnerability to yield fluctuations from soil degradation. This lack of broader or varietal innovation, possibly constrained by insufficient manuring on extensive plots, contributed to systemic agricultural instability without effective long-term solutions.

Role of Infectious Diseases

Emergence of plague

The bacterium , the causative agent of plague, evolved from the enteric pathogen through a series of genetic changes that enhanced its and transmissibility in human populations. Genomic analyses indicate that this occurred approximately 5,700 to 6,000 years ago, marking the emergence of basal Y. pestis lineages capable of systemic infections but lacking key adaptations for flea-mediated transmission. These early strains did not possess the ymt , which encodes a essential for survival in the gut and enabling the bubonic form of plague; as a result, Neolithic Y. pestis variants were primarily adapted for human-to-human spread—likely via pneumonic transmission through respiratory droplets or possibly lice vectors—rather than zoonotic cycles involving vectors. In the context of Neolithic farming communities, the transmission of these basal Y. pestis strains likely occurred through , where the pathogen spreads via respiratory droplets from infected individuals, facilitating rapid outbreaks in densely settled agricultural villages. This mode of dissemination was particularly suited to the social and environmental conditions of early farming societies in , where increased population densities and close proximity in households amplified interpersonal contact and aerosol transmission. The earliest direct evidence of Y. pestis infection in dates to around 2900 BCE (4900 cal BP), identified through extracted from the teeth of a Neolithic individual in , aligning with the period of widespread agricultural expansion across the continent. This discovery suggests that plague emerged contemporaneously with the intensification of farming practices, potentially contributing to localized population disruptions during the . Recent 2024 genomic studies have further confirmed the endemic presence of pre-Black Death Y. pestis strains in , revealing repeated infection events across multiple generations within single communities, such as those in and , where the pathogen persisted and cycled for over a century. These findings underscore the bacterium's role as a recurring threat in early agrarian societies, with basal lineages diversifying and spreading independently across long before the more virulent medieval pandemics.

Regional discoveries

Archaeological evidence for infections during the period has primarily emerged from sites across , where analysis has revealed the pathogen's presence in remains dating to around 5000–2900 BCE. In , key discoveries include the Ajvide site on , dated to approximately 3300–2900 BCE, where Y. pestis DNA was identified in a from cultural layers and in a from a , suggesting possible zoonotic transmission within a settlement; detections at Ajvide represent isolated cases rather than high prevalence in the group. Further Swedish evidence comes from the Falbygden region, including sites like Frälsegården, where repeated infections spanned multiple generations, with overall detection rates of 17% (18 of 108 individuals) across analyzed tombs dated 3100–2900 BCE. In and the , graves from the have yielded sporadic Y. pestis DNA detections, highlighting endemic circulation at low levels. Notable finds include the (5300–4900 cal ), where two out of 133 individuals tested positive, indicating isolated infections among Funnel Beaker culture populations. Baltic evidence is exemplified by the Riņņukalns site in (5300–5050 cal ), where Y. pestis was detected in a single male's remains, marking one of the earliest confirmed cases in the region. Limited archaeological evidence for Neolithic Y. pestis has been reported from , particularly the Eurasian steppes around 3000 BCE, where strains were identified in human remains from sites in , likely maintained in reservoirs without signs of large-scale human outbreaks. These Asian finds suggest early divergence of the but no confirmed major Neolithic epidemics in the area. The timeline of these discoveries began with the initial identification of ancient Y. pestis strains in 2015 from Eurasian sites, including and , predating later pandemics. Subsequent studies expanded this in 2021 with the Latvian find, and by 2024, analyses confirmed multi-generational outbreaks in , underscoring the 's role in regional . Methodologically, these detections rely on dental pulp analysis from skeletal remains, which preserves DNA effectively due to its vascular , allowing targeted sequencing to confirm Y. pestis presence without contamination from modern sources.

Genetic and Epidemiological Insights

Ancient pathogen studies

Genomic analyses of () from skeletal remains have revealed the presence of , the bacterium responsible for plague, across during the period approximately 3000–500 BCE. A landmark 2024 study sequenced 18 Y. pestis genomes from 108 individuals buried in southern , dating to around 5300–4850 calibrated years before present (cal ), equivalent to the . These findings indicate that plague was widespread, affecting at least 17% of the sampled population and spanning large geographical distances in the region. Cumulatively, by 2024, over 30 Y. pestis strains from contexts in had been sequenced, providing a broader phylogenetic framework for understanding the pathogen's early evolution. In a specific community at the Frälsegården site in , the study identified three distinct infection waves caused by related but divergent Y. pestis strains over a span of about 120 years, affecting six consecutive generations of farmers. This repeated exposure suggests recurrent outbreaks within the same population, potentially contributing to demographic instability. Prevalence estimates from these Swedish Neolithic farmers indicate active infections in up to 28% of individuals at death at the Frälsegården site, higher than prior assessments and underscoring plague's role as a significant selective pressure during this era. Analysis of these ancient genomes highlights key virulence factors that shaped Neolithic plague dynamics. Notably, the strains lacked the ymt gene, which encodes a essential for vector competence and bubonic transmission, implying alternative pathways such as direct human-to-human spread via respiratory droplets. Conversely, the presence of the pla gene, encoding , enabled efficient capability, facilitating rapid dissemination in dense farming communities. These genetic traits distinguish early Y. pestis from later medieval variants and align with archaeological evidence of non-flea-mediated epidemics. Advancements in aDNA methodologies post-2018 have been crucial for these discoveries, overcoming longstanding challenges in extracting and authenticating low-yield pathogen DNA from degraded remains. Innovations include optimized dental pulp extraction protocols, double-stranded library preparation, and targeted capture enrichment, which enhance endogenous DNA recovery while minimizing modern contamination through techniques like UV irradiation and sodium hypochlorite treatment. These improvements enabled the successful reconstruction of high-coverage Y. pestis genomes from Neolithic teeth and bones, previously inaccessible due to poor preservation and inhibitor issues. A 2025 study further extends these insights by recovering a Y. pestis genome from a 3rd-millennium BCE domesticated sheep on the Eurasian Steppe, suggesting early zoonotic potential and animal reservoirs during the transition to the Bronze Age.

Infection patterns and spread

In Neolithic communities, characterized by dense village settlements, the early strains of Yersinia pestis primarily spread through human-to-human contact, likely via respiratory droplets in the pneumonic form or human-louse transmission, as these basal lineages lacked the ymt gene essential for efficient flea vectoring. Genomic clustering from ancient DNA reveals tight familial transmission patterns, indicating household-level outbreaks in close-knit farming groups where poor sanitation and shared living spaces amplified contagion. The basic reproduction number (R0) for pneumonic plague, inferred from such clustering and modern epidemiological analogs, is estimated at 2.8–3.5, reflecting moderate but sustained transmissibility in pre-antibiotic populations without herd immunity. Evidence from southern Scandinavia demonstrates the multi-generational persistence of plague, with genomic studies identifying repeated infections across six generations in a single family pedigree spanning approximately 120 years around 5,200 years ago. In this group, 28% of individuals carried Y. pestis, linked to three distinct outbreak events involving different strains (A, B, and C), while broader sampling detected the in 17% of 108 farmers, suggesting underestimation of true prevalence due to DNA preservation biases. These recurrent epidemics likely imposed 30–50% mortality on affected households, as inferred from extinctions and demographic modeling, eroding over time. Plague dispersal was enhanced by human mobility, including seasonal migrations and trade networks that connected settlements across . In the , exchange along amber trade routes facilitated pathogen movement between coastal and inland communities, as evidenced by strain distributions linking Swedish and Danish sites to broader Pontic-Caspian origins. Genomic strains confirm successive waves, with ancestral lineages propagating via these pathways during intensified and wheeled transport around 5,000 years .

Debates and Alternative Explanations

Criticisms of disease-centric models

Critics of disease-centric models for the Neolithic decline argue that the evidence for plague as a primary driver is hampered by significant sampling biases in studies. The vast majority of Y. pestis detections come from Northern European sites, particularly in , , , and , where cold climates favor DNA preservation. In contrast, there is scant evidence of early plague strains from Southern or , regions that also experienced population declines, suggesting the phenomenon may not have been universal across the continent. Furthermore, the correlation between plague presence and population declines may reflect coincidence rather than causation, as Y. pestis has been identified in only 10–20% of sampled sites overall, often appearing as isolated or opportunistic infections rather than widespread epidemics. For instance, a analysis of 133 individuals from megalithic graves in detected the bacterium in just two unrelated cases, indicating sporadic occurrences insufficient to explain mass mortality. This low prevalence rate, combined with the bacterium's early suggesting limited for human-to-human transmission, undermines claims of plague as the dominant factor. Temporal discrepancies further challenge the model, with archaeological records showing that population declines in Central and Northwest began centuries before the earliest confirmed Y. pestis strains around 5300 cal BP. In northwest Europe, for example, a crash associated with agricultural shifts occurred between approximately 5550 and 4950 cal yr BP, predating known plague infections. Methodological concerns in ancient DNA research also contribute to skepticism, particularly the risk of false positives due to DNA degradation and damage patterns like cytosine deamination, which can mimic pathogen sequences in pre-2024 studies. Such issues highlight the need for cautious interpretation of sparse genomic data when attributing large-scale societal changes to infectious diseases.

Social and integrated theories

Social theories of the decline emphasize the role of internal societal dynamics, such as , resource exhaustion, and institutional collapse, in precipitating widespread disruptions across around 3000 BCE. Centralized Neolithic settlements, including mega-sites like those of the Tripolye culture in (encompassing 100–400 hectares and supporting 5,000–15,000 inhabitants), succumbed to ecological and economic pressures that undermined their hierarchical structures. These societies, reliant on intensive and large-scale communal organization, experienced demographic declines linked to soil degradation and unsustainable population densities, as evidenced by archaeological records of abandoned tells and reduced settlement sizes. In response, social reorganization favored decentralized, kin-based units, fostering the emergence of warrior aristocracies and individualized burial practices that marked a shift toward social formations. Integrated theories incorporate social factors with environmental and epidemiological elements to explain the decline as a multifaceted rather than a singular catastrophe. Similarly, in Central and , increased mobility—evidenced by strontium isotope analysis showing nonlocal individuals in burials—facilitated the spread of Yamnaya steppe ancestry into Corded Ware cultures, blending social and patrilocality with incoming technologies like . These migrations, peaking around 2900 BCE, intertwined with low-level plague () transmission, which may have weakened but not solely caused community fission, alongside conflicts indicated by skeletal trauma and defensive enclosures. Such models highlight a translocal social fluidity, where short-lived settlements (lasting 1–2 decades) and fluid community networks enabled resilience, contrasting with rigid hierarchies. The adoption of long-distance in metals (e.g., from the , tin from distant sources) further restructured economies, empowering emergent elites and accelerating the decline of agrarian collectivism. Overall, these integrated perspectives portray the decline as a transformative phase driven by synergistic pressures, culminating in diversified social identities and institutions that laid the groundwork for complexity.

References

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