Holocene fluctuations in human population demonstrate repeated links to food production and climate

Abstract

We consider the long-term relationship between human demography, food production, and Holocene climate via an archaeological radiocarbon date series of unprecedented sampling density and detail. There is striking consistency in the inferred human population dynamics across different regions of Britain and Ireland during the middle and later Holocene. Major cross-regional population downturns in population coincide with episodes of more abrupt change in North Atlantic climate and witness societal responses in food procurement as visible in directly dated plants and animals, often with moves toward hardier cereals, increased pastoralism, and/or gathered resources. For the Neolithic, this evidence questions existing models of wholly endogenous demographic boom-bust. For the wider Holocene, it demonstrates that climate-related disruptions have been quasi-periodic drivers of societal and subsistence change.

Keywords: Britain; Ireland; agriculture; archaeology; radiocarbon.

Fig. 1.

(A) The kernel-smoothed intensity of archaeological radiocarbon dates from Britain and Ireland showing uneven spatial sampling (the subregions used in Fig. 2 are marked with white borders). (B) The proportion of dated samples with genus- or species-level identifications. (C) A summed probability distribution of all dates compared with a 95% Monte-Carlo envelope of equivalent random samples drawn from a fitted logistic model of population growth and plateau.

Fig. 2.

Regional summed probability distributions for (A) south/east England, (B) North/west England and Wales, (C) Scotland, and (D) Ireland compared with a 95% Monte Carlo envelope produced by permutation of each date’s regional membership.

Fig. 3.

Radiocarbon-inferred population and North Atlantic climate proxies. (A) Aggregate anthropogenic radiocarbon dates from Britain and Ireland (as Fig. 1C, the y axis is linear). (B) Total solar irradiance (12). (C) GISP2 potassium ion density (note descending axis) (17). (D) North Atlantic ice-rafted debris (note descending axis) (19). Shaded blue zones indicate suggested onset and duration of cold/wet episodes with the first one, the well-known “8.2 ky” event before the Neolithic and not addressed directly here.

Fig. 4.

The changing relative importance of major food sources across Britain and Ireland as visible in food samples directly dated for radiocarbon. (A) Hazelnuts. (B) Wheat (undifferentiated by species). (C) Barley, oats, and legumes. (D) Animals regularly used food sources. The colored lines are calculated as the proportions (calculated only from ∼4250 BCE onwards due to small sample sizes before that time). Ordinary summed probability distributions are shown in gray (y axes are all rescaled 0–1 for easier comparison). Accompanying permutation tests are provided in Figs. S6 and S7.