European Neolithic societies showed early warning signals of population collapse

Abstract

archaeological data (14–16) are narrowing the gap between theory and data. This study presents what we believe to be the first statistical evidence for EWSs of regime shifts in human population dynamics. Our case studies include 2,378 archaeological sites from nine regions of Neolithic Europe, ca. 8–4 kya. Previous research has observed evidence of major demographic regime shifts in the form of large-scale boom-bust dynamics among many of these Neolithic cases (17). Estimated population declines range from 20% to 60% in as little as a century. The population proxies that revealed these boom-bust dynamics are based on the temporal frequencies of radiocarbon-dated archaeological sites, which are represented as summed probability densities (SPDs). This site-based population proxy assumes that the temporal frequencies of occupied human settlements in a given region index relative human population size. Use of SPD-based approaches to inferring population change has been debated in the literature (18–26). Critics have raised concerns about confounding factors including atmospheric effects, sampling biases, taphonomic processes, or calibration error; however, the methods used here and elsewhere (20) attempt to control for these sources of error by (i) correcting systematic biases in the data and (ii) comparing the corrected empirical patterns to null SPD models that simulate exogenous processes. Thus, current SPD methods reflect a significantly more conservative version of the approach that Rick (27) originally proposed. We analyze archaeological SPDs for two classes of EWSs: critical slowing down (CSD) and flickering. CSD describes a general increase in the time it takes a system to recover from external