Female humans, unlike most other mammals, have a nearly constant “sexual receptivity.” This means their sexual interest is not limited to their ovulation period and that ovulation is concealed, unlike other female mammals.
Some evolutionary anthropologists would say this state of extended receptivity is really just a way for a particular woman to ensure she can keep a particular man satisfied so he’ll stick around to help with sustaining and protecting the family.
Her sexual receptivity is a mechanism to limit his number of current sexual partners. But couldn’t it also just be because sex is fun and women enjoy it as much, if not more, than men?
Women have the capacity to experience multiple orgasms within a single session of sexual activity, unlike men, who require a recovery period after having sex. Their bodies don’t respond to sexual stimulation and ejaculation is impossible.
At ejaculation, a man’s body throws a massive, systemic ‘shut off’ switch, which effectively puts his sexuality in ‘park,’ leans back the seat, and turns lulling music on the radio.
The hypothesized reason for this phenomenon is that it gives a man’s body an opportunity to begin replenishing the sperm stores spent in ejaculation.
Since women don’t ejaculate, no recovery period is needed. It’s likely the reason why multiple and extended orgasms are easier for women than for men.
As women age, they tend to move toward their sexual prime, not away from it, as is the case with men.
All this suggests that women have a sexuality that outstrips men. If anything, their number or sexual partners should be equal to or greater than a man’s, perhaps far greater.
There’s no perceptible change in a human female (a change in appearance or scent) when she is “in heat” and near ovulation.
Some examples of such changes are swelling and redness of the genitalia in baboons and bonobos Pan paniscus, and pheromone release in the feline family.
In contrast, the females of humans and a few other species have few external signs of fecundity, making it difficult to for the male to consciously work out by means of external signs only if a female is near ovulation.
While women can be taught to recognize their own level of fertility but whether men can detect fertility in women is highly debated.
Several small studies have found that fertile women (compared to women in infertile portions of the menstrual cycle, or using hormonal contraception) appear more attractive to men.
It has also been suggested that a woman’s voice may become more attractive to men during this time. Two small studies of monogamous human couples found that women initiated sex significantly more frequently when fertile.
But male-initiated sex occurred at a constant rate, without regard to the woman’s phase of menstrual cycle.
It may be that a woman’s awareness of men’s courtship signals increases during her highly fertile phase due to an enhanced olfactory awareness of chemicals specifically found in men’s body odor.
One theory suggests that ovulation became hidden after monogamous relationships became the norm in Homo erectus.
Concealed ovulation allowed the woman to mate secretly at times with a genetically superior man, gaining the benefit of his genes for her offspring, while still retaining the benefits of the pair bond with her usual sexual partner.
Her usual sexual partner would have little reason to doubt her fidelity, because of the concealed ovulation, and would have high, albeit unfounded, paternity confidence in her offspring.
His confidence would encourage him to invest his time and energy in assisting her to care for the child, even though it was not his own.