Orgasm is a primitive and fundamental response of the human body because male orgasm triggers ejaculation, which is vital for reproduction. Male orgasm involves the brain (which responds to erotic stimuli by increasing blood flow to the genitals) and the penis. The penis and the clitoris develop from the genital tubercle in the foetus. They are equivalent organs. Women are only capable of orgasm because they have the remnants of a phallus.
The ducts that form the vagina in a female foetus waste away in the male. If the vagina was a sex organ, women would have needed to evolve a completely different mechanism (separately from the male) for responding erotically. It is highly unlikely that the vagina could ever have evolved as a sex organ in women alone. The implication is that women evolved a responsiveness that has no reproductive function and no useful purpose of any kind. We only evolve functionality for reproductive or survival reasons.
It is assumed that a woman can orgasm one time from vaginal stimulation and another from clitoral stimulation. Alternatively, it is assumed that some women need clitoral stimulation while others need vaginal stimulation. Either way, the implication is that women have evolved two quite different routes for achieving orgasm. No one ever provides a rational explanation for how a physiological mechanism can vary between women and from one occasion to the next. Nor do they explain how such a mechanism could have evolved. One of the problems is that no one explains the exact mechanism by which even male orgasm is achieved. So, in our ignorance, we are easily persuaded by all kinds of non-scientific assumptions that do not make any logical sense. Orgasm occurs as a result of specific physiological responses.
We have sensitivity in external anatomy that helps protect our bodies from injury. The vagina evolved from primitive egg ducts and (like all organs that are internal to the body) has little sensitivity. Research indicates that only the outermost portion (entrance) of the vagina and rectum have any sensitivity. The vagina is part of the birth canal. The intense climaxes women report during childbirth come from peaks of sensation as the baby’s head stretches the vaginal entrance (often tearing the skin). This sensation can be replicated by the hand (called vaginal fisting) but not by the penis (regardless of size).
Anatomy such as the vagina, which is essentially a cavity, could never be a sex organ. A cavity can always be penetrated. Once orgasm is reached a person desists from further stimulation. But there is no point at which the vagina can no longer be penetrated. This is the clearest anatomical evidence that the vagina is not a sex organ. A cavity is made to hold something. In the case of the rectum, it is faeces. In the case of the vagina, it’s semen. Neither of these organs is erectile. Mental arousal causes blood to flow into the penis and clitoral organ (the corpora cavernosa), which makes orgasm possible.
Intercourse involves the penis (a phallus) entering the vagina (a cavity). There is limited opportunity for the penis to stimulate the vagina in any way because it is relatively long and thin, while the vagina is like the inside of a balloon. The only possibility is that the penis jabs or pokes at the walls of the vagina. This is not the kind of stimulation that causes orgasm. Stimulation (aimed at orgasm) needs to massage the blood-flow within the erectile organ.
There is no requirement for someone who is the receiver of an erect penis to be aroused. The receiver offers a body orifice for a penetrating male to ejaculate into. The mouth is the most sensitive of all body orifices but men appreciate that giving oral sex cannot not cause orgasm. They probably also know that being a receiver of anal intercourse does not cause orgasm. It is only female anatomy that is ascribed an imaginary sensitivity. Unresponsive women have no incentive to question these emotional beliefs. Women who never orgasm cannot easily refute men’s fantasies about their responsiveness.
Women never contest these myths because of their general embarrassment over sex, their uncertainty over their own arousal and their desire to please men sexually. Most women are unresponsive and so they don’t appreciate that orgasm is achieved by stimulating specific anatomy. To a responsive woman (once she has been given names for her internal anatomy), it is just as obvious that the clitoris is the source of her orgasm as it is to a man that the penis is the source of his. Mental arousal that arises from focusing on specific erotic concepts, indicates to us the anatomy that needs to be stimulated. Anyone who has ever been aroused can identify their sex organ.
The hymen is a small flap of skin that covers the entrance to the vagina (in most but not all women). When the hymen is broken there may be a little blood and some discomfort. Before the days of tampons, women’s hymens were broken the first time they engaged in intercourse. This is clear evidence that women did not masturbate by inserting objects into the vagina. In modern times when women use tampons to absorb their menstrual blood, they do not obtain any sexual pleasure from inserting tampons into their vaginas. If women had orgasms from inserting objects (such as an erect penis) into the vagina they would seek this kind of stimulation themselves. Yet research has indicated that women who masturbate stimulate the clitoris and the labia majora. Specifically, the only women who engage in vaginal stimulation are those who are told by men that they should orgasm by stimulating the vagina. Clearly, they have never had an orgasm in their lives.
There is, however, no evidence that the vagina is ever the sole source of arousal, or even the primary source of erotic arousal in any female. (Alfred Kinsey)
Excerpt from Learn About Sexuality (ISBN 978-0956-894748)