The female orgasm, especially vaginal, may play a role in evolution. This could explain its elusiveness because its purpose is to allow the woman to distinguish (unconsciously, of course) the right partner from the wrong one. This explains why orgasms occur more frequently when a woman feels relaxed and is with an attentive sexual partner with whom there is emotional harmony, ideal for long-term commitment.
But there is another perspective: the orgasm could be one of the weapons that the female body uses to select, without realising it, the father of her children. During orgasm the size of the vagina reduces by 30%. The contractions of the uterus during orgasm may in fact facilitate fertilisation favouring the ascent of a greater number of sperm cells along the tubes, while the orgasm itself can affect the force with which the sperm cells travel. The body therefore guides the predisposition to have an orgasm according to the "suitability" of the current partner or the circumstances of the moment. In other words, behind the apparent unpredictability of the female orgasm, could be a specific reproductive strategy, which even the woman herself is not aware of.
Perhaps there is even a third possibility: that the orgasm is still something for women to really conquer. The advantages described above may have helped ensure greater ease in achieving orgasm, but she may still find herself "half-way" in the evolutionary journey towards full orgasmic control, the prerogative of the male. In other words, evolution can benefit from the fact that the woman is able to experience an orgasm, but has not yet had time to allow this to really take root. Maybe our evolutionary direction could thus be leading to a female orgasm with greater ease, because taking pleasure in the sexual act helps to keep a couple together.
But just how long should sex last for a woman to achieve pleasure? While for a man (not affected by PE) only 2 minutes may be enough, a woman reaches orgasm on average 10-20 minutes after sex begins. That's why it’s so important that the male is able to concentrate on the act of intercourse in all its phases, starting with foreplay, and not only on achieving orgasm, and control his excitement for the time necessary for the woman to achieve pleasure. According to a study conducted in the U.S. and Canada, satisfactory sexual intercourse lasts between 3 and 13 minutes. But it’s the quality of sexual relations and not the speed, that represents the only indisputable value in a couple’s relationship.
References
1
Carrada G, Jannini EA. La scienza dell'amore tutto quello che è stato scoperto sulla sessualità e che nessuno aveva mai sospettato prima. EditoreBaldini e Castoldi, 1999.
2
Weiten W, Dunn DS, Hammer EY. Psychology Applied to Modern Life: Adjustment in the 21st Century. Cengage Learning 2011.
3
Corty EW, Guardiani JM. J Sex Med 2008;5:1251–1256.