Agriculture, population growth, and statistical analysis of the radiocarbon record

Abstract

The human population has grown significantly since the onset of the Holocene about 12,000 y ago. Despite decades of research, the factors determining prehistoric population growth remain uncertain. Here, we examine measurements of the rate of growth of the prehistoric human population based on statistical analysis of the radiocarbon record. We find that, during most of the Holocene, human populations worldwide grew at a long-term annual rate of 0.04%. Statistical analysis of the radiocarbon record shows that transitioning farming societies experienced the same rate of growth as contemporaneous foraging societies. The same rate of growth measured for populations dwelling in a range of environments and practicing a variety of subsistence strategies suggests that the global climate and/or endogenous biological factors, not adaptability to local environment or subsistence practices, regulated the long-term growth of the human population during most of the Holocene. Our results demonstrate that statistical analyses of large ensembles of radiocarbon dates are robust and valuable for quantitatively investigating the demography of prehistoric human populations worldwide.

Keywords: agriculture; archeology; hunter-gatherers; paleodemography; radiocarbon dating.

Fig. 1.

The SPD for Wyoming and Colorado for the last 15,000 y plotted on a log-linear scale. The SPD is corrected for taphonomic loss (Materials and Methods). On this scale, the SPD 6,000–13,000 calibrated years before present (cal BP) appears to increase linearly. This scaling is a signature of exponential growth. The dotted lines delineate the time interval (6,000–13,000 cal BP) where the population is clearly undergoing long-term exponential growth. The solid gray lines are meant as a guide.

Fig. 2.

(A) The SPD and best-fit exponential model are plotted in red and blue, respectively. The gray and black areas denote the 68% and 95% confidence intervals of the exponential model fit determined from bootstrapping (Materials and Methods). (B) The deviation of the data relative to the model ($\mathrm{\Delta }=$ SPD/model) plotted on a logarithmic scale. Factors of 1.25 and 1.5 correspond to 0.10 and 0.18 dex, respectively.

Fig. 3.

The growth rate we measure (“This Work”) and those found in the literature. Peros (26), Johnson (27), and Shennan (28) are measured from a SPD. Goldewijk (32) is calculated from population estimates found in the literature, which are not derived from the radiocarbon record. Goldewijk et al. (32) also examine population growth on each continent independently. They report continental growth rates of 0.03–0.05% for 2,000–12,000 cal BP (table 3 of ref. 32). The width of each box represents the 1σ error, and each box extends over the period in which the growth rate was measured. Johnson et al. did not provide an estimate of the error, and therefore their measurement is plotted as a line.