Biological Foundations of Universal Sexual Transition

The prevailing framework describes “menopause” in women and “andropause” in men as sex-specific declines in reproductive hormones that mark the end of fertility. This framing emphasizes deficit and loss. In this paper, I propose a corrective reinterpretation: menopause and its male analogues are not failures of the body but part of a universal, late-life sexual transition. Across sexes, aging brings systematic changes in hormone levels, secondary sex characteristics, psychological profiles, and social roles. These changes are not pathological but developmental. Late life is a transition from procreative sexual dimorphism to a convergent phenotype blending traits of both sexes. I trace the history of the menopause concept, present biological and sociological evidence for sex convergence with age, and compare these natural processes with gender-affirming hormone therapies to highlight mechanistic parallels. I then define metrics—the Transition Index (TI) and Sex-Characteristic Convergence Score (SCC)—to quantify transition trajectories. Candidate datasets and statistical models are described to make the hypothesis falsifiable. The implications are wide-ranging: new biomarkers for longevity research, new approaches to clinical care, challenges to rigid gender binaries, and recognition of elders as stabilizers in social systems. The central claim is radical but testable: there is no menopause or andropause. There is only universal sexual transition.