Menstruation
Most female mammals have an estrous cycle, yet only ten primates species, four bats species, the elephant shrew, and the spiny mouse have a menstrual cycle. The relatedness of these groups suggests that four distinct evolutionary events have caused menstruation to arise.
Hoover-Drickamer effect
A similar phenomenon of menstrual synchrony has been investigated multiple times to determine whether or not it even exists, and if it is adaptive in nature. The same cannot be said of variations in duration of estrus. The rationale behind investigations into menstrual synchrony could also be applied to duration of estrus, including male monopolization of fertile females. While one argument against menstrual synchrony is to reduce interfemale competition, particular differences between species in terms of mating period and length may influence how useful the ability to mediate and change estrus is in the first place. Given that mice can breed year round, it may be adaptive for females to be able to influence each other's frequency of sexual receptivity in order to increase the likelihood of overall species survival.