Low Total Fertility in Simple Economic Systems

Low total fertility rates throughout the world have lead to concerns about economic growth, military security, international political power, environment impacts, and quality of life. Overall total fertility rates of today's societies are complex emergent functions of culture, biology, and economic policies that are notoriously difficult to forecast. In order to study the dynamic, stochastic nature of total fertility rates, population and wealth trajectories as functions of infertility and birth cost are generated from a minimal, endogenous, agent-based model of a simple foraging economy. A harvesting model from mathematical ecology is added to reflect death by "natural causes". With these added limits of finite lifespans, decreasing total fertility rates are shown to lead to population levels consistently below the actual carry capacity of the landscape. These below carry-capacity population levels generate higher total and per capita wealth. The stochastic population trajectories generated demonstrate instabilities that significantly increase the likelihood of extinction within reasonable time frames. Society may possibly be encouraged by this increasing wealth (and perhaps reduced environmental degradation) to continue decreasing total fertility rates, further increasing the extinction risk. Conversely, the additional wealth might increase total fertility rates through relatively lower birth costs. Tax-funded subsidies are added to the model to determine if directly reducing birth costs can significantly increase total fertility rates to escape these stochastic instabilities. This research demonstrates that understanding attempts to mitigate the consequences of declining total fertility rates must include modeling of the dynamic and stochastic nature of these population trajectories.