RE: Menstrual Cramp, Dysmenorrhea, and Everything In Between

In 1993, Margie Profet wrote in the journal published on The University of Chicago Press that menstruation serves as cleansing/defence against pathogen transmitted by sperm. Personally, I do not agree with this, as even ladies who haven't had any penetrations, do menstruate.

Well adaptations happen to what has commonly been the environment in the past, not necessarily to what is actually the environment right now. If most women were expected to be having sex by a given age, then menstruation could evolve for the reason Profet stated, thought admittedly it does sound a bit far fetched, and at any rate would only be part of the answer.