Sahul-wide human population growth

Sahul-wide human population growth estimates from temporal distribution of archaeological dates between 40 ka and 5 ka

This R code recalculates Sahul-wide human population growth using a resampling approach (values originally presented in Williams, A.N., 2013. A new population curve for prehistoric Australia. Proc. R. Soc. Lond. B 280, 20130486).

This code accompanies the main analysis from this repository

General approach

1. calibrate raw radiocarbon dates to calendar year using the rcarbon package (using the shcal20 calibration curve for non-marine dates, and the marine20 calibration curve for marine dates (e.g., marine shells)
2. bin calibrated dates into 200-year interval bins (iteratively, sampling from calibrated range per date)
3. apply smoothing spline (df = 25) to number of dates per bin (iteratively)
4. apply taphonomic correction (i.e., number of dates necessarily declines with age because of taphonomic loss - mean correction data from: Williams, A.N., 2012. The use of summed radiocarbon probability distributions in archaeology: a review of methods. J. Archaeol. Sci. 39, 578-589)
5. calculate Williams' (2013) mean annual population growth (GRann) and instantaneous rate of exponential growth (r) for each resampled, corrected series:

GRann = 0.5(n_i-1-n_i)/n_i

r = log(n_i/n_i-1)

where n_i = number of dates in the older bin, n_i-1 = number of dates in the younger bin

6. correlate GRann & r for each iteration
7. calculate 95% confidence interval of correlation
8. plot reconstructed population growth curves per temporal bin (± 95% confidence limits)
9. plot taphonomically corrected number of dates per temporal bin ((± 95% confidence limits)

Required R packages

• ggplot2
• stratigraphr
• DescTools
• rcarbon
• stringr