Culture and menstruation the ideal of synchronised tidal, lunar, menstrual and seasonal periodicities whose overall harmony (it is believed) confers spiritual power and fertility. To many, such cultural associations appear persuasive in view of the fact that in humans, the menstrual cycle quite closely approximates the moon's 29.5-day synodic cycle, unlike in chimpanzees (~36 days) or bonobos (~40 days). Statistical information from hunter gatherers is lacking, but where large-scale western studies focus on women's peak reproductive years—removing outlier values—the cycle length gravitates around 29.1–29.5 days, while the figure for women in their thirties shortens toward 28 days. In no extant human population has
Human sexual response cycle Human sexual response cycle The human sexual response cycle is a four-stage model of physiological responses to sexual stimulation, which, in order of their occurrence, are the excitement phase, plateau phase, orgasmic phase and resolution phase. This physiological response model was first formulated by William H. Masters and Virginia E. Johnson, in their 1966 book "Human Sexual Response". Since then, other human sexual response models have been formulated. The excitement phase (also known as the arousal phase or initial excitement phase) is the first stage of the human sexual response cycle, which occurs as a result of physical or mental