Menstrual synchrony by chance when there is menstrual cycle variability. Yang and Schank argued that when there is cycle variability (i.e., either women have irregular cycles, have cycles of different frequencies, or both), most women will have the opportunity to experience synchrony even though it is a result of cycle variability and not a result of a mechanism such as the exchange of pheromones. For example, consider two women A and B. Suppose A has menstrual cycles that are 28 days long and B has cycles that are 30 days long. Suppose further that when A and B become close friends, B
Menstrual cycle than the developed world. The average age of menarche is approximately 12.5 years in the United States, 12.7 in Canada, 12.9 in the UK and 13.1 years in Iceland. Factors such as genetics, diet and overall health can affect timing. The cessation of menstrual cycles at the end of a woman's reproductive period is termed menopause. The average age of menopause in women is 52 years, with anywhere between 45 and 55 being common. Menopause before age 45 is considered "premature" in industrialised countries. Like the age of menarche, the age of menopause is largely a result of cultural and