Why studying females reveals more about aging: The reproductive resilience hypothesis for the evolution of sex-specific aging

Abstract

Classical evolutionary theories of aging, including antagonistic pleiotropy (AP) and the disposable soma theory (DST), explain why aging exists but are often applied without considering how sex-specific reproductive strategies shape the forces of natural selection on survival. They do not explain why females consistently outlive males across taxa, despite their greater reproductive investment, or why in some contexts, such as eusocial queens, extraordinary fecundity is coupled with exceptional longevity. To explain these patterns, we propose the reproductive resilience hypothesis (RRH), which posits that when reproductive success depends on prolonged survival and caregiving, natural selection favors coupling reproduction with enhanced somatic maintenance rather than trading it off. We suggest that reproductive events, including age at sexual maturity, pregnancy, lactation, and menopause, are pivotal life-history transitions and must be explicitly integrated into studies of sex differences that drive aging and susceptibility to age-related diseases. We further propose that loss of reproductive resilience is a sex-specific hallmark of aging that coordinates the emergence of multiple downstream hallmarks, helping explain the acceleration of systemic aging and age-related disease following reproductive decline. We propose that, for these reasons, studying females should be prioritized, as it has unique implications for discovering pathways to slow aging and prevent age-related diseases, ultimately benefiting both women and men.