Fig. 4
Left: Conceptual model of human paleodemography. Subsistence success/failure and (partially dependent) mortality determine the relative growth rate (RGR) of human populations. Subsistence, in turn, is influenced by climate stability and the latter probably also by solar activity. During a boom, climate stability favors subsistence success enabling positive and high RGR (orange states). During a bust (blue colors), variations in climatic conditions induce subsistence failures, which in turn, enhance mortality through, e.g., malnutrition. Mortality also increases under elevated population density as a delayed consequence of a boom. Our logit model uses three configurations of input variables: ‘1V’ describes an endogenous control by past population growth and resulting low or high population density. The ‘2V’ variant reflects exogenous control incorporating solar activity and climate stability. The combination of the exogenous the endogenous configurations makes the ‘3V’ variant. Right: Idealized growth cycles. Human RGR (black line) alternating between boom (orange shading) and bust phases (light blue) with corresponding population density (brown line).
