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.
Estrous cycle
Humans have menstrual cycles rather than estrous cycles. They, unlike most other species, have concealed ovulation, a lack of obvious external signs to signal estral receptivity at ovulation (i.e., the ability to become pregnant). There are, however, subtle signs to which human males may favorably respond, including changes in a woman's scent and facial appearance. Some research also suggests that women tend to have more sexual thoughts and are more prone to sexual activity right before ovulation. Animals with estrous cycles often have unmistakable outward displays of receptivity, ranging from engorged and colorful genitals to behavioral changes like mating calls.