The Female Cycle
Monthly bleeding may have been commonplace among nuns, spinsters, and the infertile centuries ago, but it could hardly have been common among the women to whose uteri we all owe our existence. When they were not pregnant, their breast feeding encouraged lactation, which suppressed ovarian cycling. Short (1976) estimates that it may have been uncommon to experience three consecutive menstrual cycles in a lifetime under these conditions. Accordingly, the human female endocrine system’s menstrual cycle has not been subjected to selection pressure for its clock-like attributes. In fact, there are diverse clues that some fraction of women are reflex ovulators, not spontaneous cyclers at all (Clark and Zarrow, 1971).1 In a reflex ovulator, mature follicles await rupture by a surge of hormone that is elicited only by sexual stimulation. The ovum then starts its journey down the fallopian tube, and pregnancy (or, less likely, recycling) ensues.
KeywordsLuteinizing Hormone Corpus Luteum Successive Interval Sexual Stimulation Flow Onset
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- 1.Rats too (Taleisnik et al., 1966; Moss et al., 1977).Google Scholar
- 2.Note that real discontinuities in the rephasing response do not necessarily reveal discontinuities in the oscillator mechanism. If they did, one might have to look askance on Bogumil’s simulation because its discontinuities correspond to no conspicuous physiological event For example, a smooth kinetic scheme whose attracting cycle is knotted has a phaseless set of peculiar topology in the pertinent state space. This results in surprising discontinuities of new phase over a whole range of (old phase, stimulus magnitude) combinations.Google Scholar