On Math and Menopause: Refining Agent-Based Modeling Approaches to Life History Evolution

Abstract

The evolution of menopause remains an enduring puzzle of human life history: why do females stop reproducing decades before the end of their lives? This thesis investigates the emergence of menopause using an agent-based modeling framework based on Kim et al. (2019). While the original model presupposes a constant mortality hazard, this work develops biologically grounded functions of childhood mortality implied by the Grandmother Hypothesis and Embodied Capital Hypothesis. We further test a formulation of grandmaternal care based on X-chromosome relatedness between grandmothers and grandoffspring. We run four sets of simulations: a replication of the original model, two models incorporating our alternative childhood mortality structures, and a model in which grandmaternal care is distributed according to genetic relatedness. Our results demonstrate that menopause evolves robustly across models that include grandmothering, but population survival is highly sensitive to the structure of childhood mortality. Mortality hazards consistent with the Grandmother Hypothesis frequently lead to extinction before menopause can evolve, while Embodied Capital mortality structures support both survival and the emergence of post-reproductive life. In contrast, X-linked care allocation leads to widespread population collapse and fails to produce menopause. Across all experiments, we observe a strong positive relationship between lifespan and interbirth interval, indicating that the model primarily selects for longevity rather than isolating the effects of grandmothering. We find that this is due to the encoded relationships between grandmaternal care, mortality, and longevity. This coupling of life history features limits the model’s ability to directly test evolutionary hypotheses. We conclude with recommendations to decouple these relationships and to refine agent-based model structures to better investigate dispersal, grandmothering, and menopause.