Do all female mammals menstruate?
Menstruation (mammal)
Menstruation in mammals is the shedding of the uterine lining (endometrium). It occurs on a regular basis in uninseminated[1] sexually reproductive-age females of certain mammal species.
Endometriosis
Retrograde menstruation alone is not able to explain all instances of endometriosis, and additional factors such as genetic or immune differences need to be invoked to account for the fact that many women with retrograde menstruation do not have endometriosis. In addition, endometriosis has shown up in people who have never experienced menstruation including men,[41] fetuses,[42] and prepubescent girls.[43][44] Further detracting from the retrograde menstruation theory are cases of endometriosis showing up in the brain[45] and lungs.[46] This theory has numerous other associated issues.[47]