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.
Menstruation
Beginning in 1971, some research suggested that menstrual cycles of cohabiting human females became synchronized (menstrual synchrony). However, there is currently significant dispute as to whether menstrual synchrony exists. A 2013 review concluded that menstrual synchrony likely does not exist.