Low Total Fertility in Simple Economic Systems

TL;DR

This paper uses an agent-based model to explore how economic, biological, and cultural factors influence fertility rates, population stability, and wealth, revealing complex dynamics and potential risks of extinction in simple economic systems.

Contribution

It introduces a minimal, stochastic, agent-based model incorporating ecological harvesting and lifespan limits to analyze fertility and population dynamics.

Findings

Lower fertility leads to populations below carrying capacity.

Decreased fertility can increase wealth but also raises extinction risk.

Tax subsidies may help stabilize fertility rates.

Abstract

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.