I will highlight two predictions of the model that we are testing using the endocrine observations. First, the model predicts that the increased variability in ovarian cycles at later reproductive ages results from a third phase of the menstrual cycle that we have named the inactive phase. This phase is a period of ovarian quiescence resulting from a stochastic absence of growing ovarian follicles. The timing and length of inactive phases reflect the age-specific size of the ovarian follicle pool. Preliminary results have supported the idea of the three-phase menstrual cycle (Holman et al. in press, O'Connor et al. 1998; O'Connor et al. 2001), and I have begun extensive analyses of the endocrine data. The second prediction is that post-menopausal women should occasionally experience follicular development, which can be detected hormonally but may not result in menses. We have recently presented empirical support for this idea (Holman et al. 2002).

The larger significance of the fecundability, pregnancy loss and ovarian aging work is that it provides a framework for understanding reproductive aging and the end of the reproductive life span. I recently present a paper at the Gerontological Society of America (Holman et al. 2001), where I argued that there is an important distinction between reproductive aging, which is dominated by a gradual age-related increase in risk of pregnancy loss, and ovarian aging, which plays an important role in the maintenance of regular menstrual cycles across the reproductive years but does not appear to play a role in reproductive aging per se. Within anthropology, these findings provide fruitful insights into the on-going debate over an evolutionary role for menopause. My colleagues and I have begun to explore these implications (Wood et al. 2001, in press) and I expand on the issues in my book (Holman, forthcoming).

References cited

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