Do women age like whales? Integrating diverse perspectives on human menopause and postreproductive life spans

Abstract

For women, menopause at around age 51 years is the ultimate step in a gradual, decades-long period of fertility loss. In ‘proximate’, physiological terms, it is a result of a finite declining pool of ovarian follicles and the accompanying decay of functional feedback pathways in the hypothalamic–pituitary–ovarian axis. In women and other female mammals, the length of the fertile life span is constrained developmentally by basic mechanisms of mammalian oocyte formation, selection, and eventual exhaustion. Reproductive aging in both women and men can be viewed as canonical aging syndromes correlated with the increasing prevalence of other aging-related diseases and disabilities. Human life expectancy rarely exceeded 25–30 years until the 1800s, and average life expectancy at birth has risen by almost 40 years since 1990, thereby also increasing the average length of women's postreproductive life span (PRLS) by 30 years or more in industrialized cultures. While there has been little rigorous comparative analysis or attempt to integrate clinical and physiological perspectives with those of comparative zoologists, many researchers have argued that midlife menopause with a long PRLS is an exceptional pattern of aging among vertebrates and an adaptation that promotes the reproductive success of older women's close genetic relatives. This review samples a range of perspectives on the origins of human menopause and PRLS and discusses strengths and pitfalls of different standpoints. It argues for a more holistic, interdisciplinary synthesis of perspectives on female reproductive aging combining physiological and epidemiological viewpoints with those from comparative physiology and evolutionary medicine.