Most mammals go through some sort of estrous, but only a few menstruate. The main difference is that humans and some other primates have the capability to mate

Most mammals go through some sort of estrous, but only a few menstruate. The main difference is that humans and some other primates have the capability to mate and rear young pretty much at any time of the year, which is why the women are generally always capable of becoming fertilized. There are other, more advanced social theories that go into the role menstruation plays in society, but historically, menstruating monthly has been an advantage, not a disadvantage.