Archaeological evidence suggests that the demographics of Mid-Holocene (Late Mesolithic to Initial Bronze Age, ca. 7000-3000 BCE) Europe are characterized by recurrent booms and busts of regional settlement and occupation density with an overall tendency towards a gradual population increase. Here, using a spatially-explicit agent-based model, we investigate the impact of climatic forcing and violent conflict to account for the observed population patterns. We demonstrate that climate variation during the European Mid-Holocene is unable to explain these cycles. In contrast, density-dependent conflict can produce cyclic demographic patterns with time scales and amplitudes similar to those established from population proxies (radiocarbon dates) in our focus period. These results suggest that inter-group conflict played a crucial role in the demographics of this period.

Soil fertility is an important constraint on farmers and thus its depletion presents a possible negative feedback mechanism that could have impacted early adopters of agriculture. In this paper, we present a formal mathematical analysis of the question whether such a negative feedback can lead to population cycles in the context of early agriculturalists, such as those of Neolithic Europe where the presence of booms and busts patterns is suggested by an increasing amount of evidence. We do this by considering candidates of second-order analytic models that capture dynamical interaction among farmers and soil fertility. Using general mathematical arguments, we show that under plausible conditions, the feedback between population growth and soil resource depletion is unlikely to lead to population cycles. This result is the consequence of two factors. First, there is an important mathematical difference between biotic (i.e. logistic) and abiotic resource replenishment; soil nutrients are better modeled by the abiotic case which leads to more stable dynamics. Second, under realistic conditions, the resource replenishment process has fast time-scales compared to attainable population growth rates, reinforcing the tendency of stable dynamics. Both of these factors play a role when considering early agricultural societies, and imply that nutrient depletion is not a credible mechanism for patterns of boom and bust cycles observed in the archaeological record.

Archaeological evidence suggests that the population dynamics of Mid-Holocene (Late Mesolithic to Initial Bronze Age, ca. 7000–3000 BCE) Europe are characterized by recurrent booms and busts of regional settlement and occupation density. These boom-bust patterns are documented in the temporal distribution of 14C dates and in archaeological settlement data from regional studies. We test two competing hypotheses attempting to explain these dynamics: climate forcing and social dynamics leading to inter-group conflict. Using the framework of spatially-explicit agent-based models, we translated these hypotheses into a suite of explicit computational models, derived quantitative predictions for population fluctuations, and compared these predictions to data. We demonstrate that climate variation during the European Mid-Holocene is unable to explain the quantitative features (average periodicities and amplitudes) of observed boom-bust dynamics. In contrast, scenarios with social dynamics encompassing density-dependent conflict produce population patterns with time scales and amplitudes similar to those observed in the data. These results suggest that social processes, including violent conflict, played a crucial role in the shaping of population dynamics of European Mid-Holocene societies.

The impact of inter-group conflict (warfare) on large-scale population declines has long been debated, especially for prehistoric or non-state societies. In this work, we consider that beyond direct battle casualties, which are typically limited, conflicts can also create a “landscape of fear” in which many non-combatants near theaters of conflict abandon their homes and migrate away. This migration has two impacts: It causes population decline in the abandoned regions and increased population density in better protected areas that are targeted by refugees. This higher density, in turn, can place additional stress on local supplies, potentially leading to reduced fertility and increased mortality due to malnutrition and disease. Using both an analytic and agent-based model we investigate the impact of these interactions on population dynamics of small-scale societies. We demonstrate that these indirect effects of conflict are sufficient, even in the absence of combatant casualties, to produce substantial, long-term population boom-and-bust patterns. In particular, our agent-based model is able to account for the large-scale spatial and temporal boom-and-bust patterns observed in radiocarbon data from mid-Holocene Europe. We also demonstrate that greater availability of defensible locations, by acting to protect and maintain the supply of combatants, increases the permanence of the landscape of fear and likelihood of endemic warfare.

No abstract