Menstruation (mammal)
Most female mammals have an estrous cycle, yet only ten primates species, four bats species, the elephant shrew, and the spiny mouse have a menstrual cycle. The relatedness of these groups suggests that four distinct evolutionary events have caused menstruation to arise.
Yanomami women
Up until the time of menstruation, girls are treated as children, and are only responsible for assisting their mothers in household work. When they approach the age of menstruation, they are sought out by males as potential wives. Puberty is not seen as a significant time period with male Yanomami children, but it is considered very important for females. After menstruating for the first time, the girls are expected to leave childhood and enter adulthood, and take on the responsibilities of a grown Yanomami woman. After a young girl gets her period, she is forbidden from showing her genitalia and must keep herself covered with a loincloth.