Document Type



A mathematical model based on bioassay is applied to 3 reproductive events in women: menarche, cumulative fertility, and menopause. By a maximum likelihood method, probits are regressed on the logarithm of age from conception (x') for these 3 events in the Dobe !Kung of western Botswana, the Micronesians of Yap, and the population of the United States. In these populations, parallelism of the lines for menarche and menopause indicate graded developmental responses in a single tissue: the uterine endometrium. In each population, its cumulative fertility line shows a standard deviation in x' units which is a simple multiple of the common standard deviation of menarche and menopause. On this basis, a world model, symmetrical on the x' axis, is proposed from an extensive search of the literature. For any specific population, this model yields percentiles for the timing and variability of menarche, cumulative fertility and menopause by comparison with the world standard.