Menstruation (mammal)
Menstruation in mammals is the shedding of the uterine lining (endometrium). It occurs on a regular basis in uninseminated sexually reproductive-age females of certain mammal species.
Culture and menstruation
Menstruation in synchrony with the moon is widely assumed in myths and traditions as a ritual ideal. The idea that menstruation is—or ideally ought to be—in harmony with wider cosmic rhythms is one of the most tenacious ideas central to the myths and rituals of traditional communities across the world. One of the most thoroughgoing analyses of primitive mythology ever undertaken was that of the French anthropologist Claude Lévi-Strauss, who concluded that, taken together, the indigenous myths of North and South America expressed men's worry that, unless women's periods were carefully monitored and synchronised, the universe might descend into chaos.