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
Menstrual synchrony with lunar phases. However, neither of them agree on what phase of the lunar cycle menstrual cycles synchronize with. Cutler hypothesizes the synchronization with the full moon and Law with the new moon. Neither offer hypotheses regarding how lunar phases cause menstrual synchrony and neither are consistent with previous studies that found no relationship between menstrual cycles and lunar cycles. More recently, Strassmann investigated menstrual synchrony among Dogon village women. The women were outdoors most nights and did not have electrical lighting. She hypothesized that Dogon women would be ideal for detecting a lunar influence on menstrual cycles, but she