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
The start of "menstruation" symbolizes the beginning of womanhood. Girls typically start menstruation around the age of 12-15. Girls are often betrothed before menarche and the marriage may only be consummated once the girl starts menstruating, though the taboo is often violated and many girls become sexually active before then. The Yanomami word for menstruation ("roo") translates literally as "squatting" in English, as they use no pads or cloths to absorb the blood. Due to the belief that menstrual blood is poisonous and dangerous, girls are kept hidden away in a small tent-like structure constructed of a screen of leaves. A deep hole is built in the structure over which girls squat, to "rid themselves" of their blood. These structures are regarded as isolation screens.