Mr. Tea
Let's Talk About Ceps
I think all the menstrual cycle stuff has pretty much been put down to pheremones (synching with other women) and natural light (phases of the moon), but happy to be shown otherwise.
Yeah, it must be pheremones when you have women living together - I guess the moonlight thing is only ever found in societies where people still spend a lot of time outside at night without bright (i.e. electric) artificial lighting all over the place.