Menstrual cycle The first period usually begins between twelve and fifteen years of age, a point in time known as menarche. They may occasionally start as early as eight, and this onset may still be normal. The average age of the first period is generally later in the developing world and earlier in developed world. The typical length of time between the first day of one period and the first day of the next is 21 to 45 days in young women and 21 to 35 days in adults (an average of 28 days). Menstruation stops occurring after menopause which usually occurs
Menstrual cycle of the menstrual cycle, regardless of fertility. Behavior towards potential mating partners changes during different phases of the menstrual cycle. Near ovulation, women may have increased physical attraction and interest in attending social gatherings with men. During the fertile phase of the cycle, women appear to prefer males who are more masculine. The intensity of mate guarding differs across the phases of the cycle, with increased mate guarding occurring when woman are fertile. During the fertile phase, many women experience more attraction, fantasies and sexual interest for extra pair men but not for the primary partner. They also engage in