The publisher's final edited version of this article is available at Horm Behav See other articles in PMC that cite the published article. Abstract In men and women sexual arousal culminates in orgasm, with female orgasm solely from sexual intercourse often regarded as a unique feature of human sexuality.
However, orgasm from sexual intercourse occurs more reliably in men than in women likely reflecting the different types of physical stimulation men and women require for orgasm.
In men, orgasms are under strong selective pressure as orgasms are coupled with ejaculation and thus contribute to male reproductive success. By contrast, women's orgasms in intercourse are highly variable and are under little selective pressure as they are not a reproductive necessity.. The proximal mechanisms producing variability in women's orgasms are little understood. In Marie Bonaparte proposed that a shorter distance between a woman's clitoris and her urethral meatus CUMD increased her likelihood of experiencing orgasm in intercourse.
She based this on her published data which were never statistically analyzed. In Landis and colleagues published similar data suggesting the same relationship, but these data too were never fully analyzed. We analyzed raw data from these two studies and found that both demonstrate a strong inverse relationship between CUMD and orgasm during intercourse. Unresolved is whether this increased likelihood of orgasm with shorter CUMD reflects increased penile-clitoral contact during sexual intercourse or increased penile stimulation of internal aspects of the clitoris.
CUMD likely reflects prenatal androgen exposure, with higher androgen levels producing larger distances. Thus these results suggest that women exposed to lower levels of prenatal androgens are more likely to experience orgasm during sexual intercourse. This gender disparity in the reliability of reaching orgasm during sexual intercourse has been thought to reflect evolutionary Lloyd, or social Hite, processes.
An anatomical explanation for this disparity has also been proposed such that variation in the distance between a woman's clitoral glans and her vagina predicts the likelihood that she will experience orgasm in intercourse Narjani, Specifically it was proposed that if this distance is less than 2.
This relationship has not been statistically evaluated, but two historical studies provide data supporting such a relationship Narjani, ; Landis, Landis, and Bowles, We use an unconventional approach to investigate the proposed relationship between variation in women's genitals and orgasm during intercourse. We first explore the history of this idea in the scientific and popular literature and then present statistical analysis of the two available historical datasets with data relevant to the proposed relationship Narjani, ; Landis, Landis, and Bowles, While there are challenges to the validity of these data, we find them sufficiently supportive of a relationship between women's genital anatomy and the occurrence of orgasm in intercourse to feel that they can serve as the basis for developing modern well-controlled studies of the relationship between women's genital anatomy and the occurrence of orgasm in intercourse.
Orgasm is the culmination of sexual arousal, and the promise of orgasm may provide primary motivation for individuals to engage in sexual intercourse. However, sexual arousal itself is rewarding and likely common to the sexuality of all mammals. Studies of animals have shown that sexual arousal is rewarding even when sexual intercourse doesn't occur Meisel, Camp and Robinson, Certainly humans, at least men, sometimes seek out activities, such as strip clubs, where sexual arousal without orgasm is the primary goal and where sexual intercourse is unlikely to occur.
In male mammals, sufficient sexual arousal leads to ejaculation and orgasm. Thus it is possible that orgasm occurs in all male mammals.
The case in females is less clear. While there is evidence that female sexual arousal is rewarding Meisel, Camp and Robinson, , it is unclear whether humans, or possibly primates, Goldfoot, et al. Even in primates female orgasm is not universal, with little evidence of its occurrence outside of humans. To further complicate matters, there remains a lack of complete agreement on what constitutes female orgasm Meston, et al.
Although sexual arousal precedes orgasm in women, the specific sexual stimulation that triggers orgasm varies greatly among women. Women reach orgasm from direct clitoral stimulation, indirect clitoral stimulation, vaginal stimulation or stimulation of internal areas surrounding the vagina.
Some women experience orgasm solely from sexual intercourse, whereas other women require concurrent stimulation of the external parts of the clitoris in order to reach orgasm during sexual intercourse, and some women never experience orgasm in intercourse under any conditions.
A period of increasing sexual arousal precedes orgasm, typically from genital stimulation, in those women who experience orgasm.
Given the differences in male and female genitals it is likely that the nature and extent of genital stimulation necessary for orgasm differs between men and women. This appears to certainly be the case for orgasms which occur solely from sexual intercourse.
A striking sex difference in the onset of the occurrence of orgasm has been known for more than 50 years Figure 1. Post-pubertal males routinely, and apparently easily, experience orgasm, as indicated by their reliable ejaculatory reflex, but female orgasm appears to develop more slowly and is less predictable than male orgasm.
While there are women who reach orgasm as easily and routinely as do men, and some women who experience orgasm more easily and multiple times during a single session of sexual intercourse, this is not women's typical experience with orgasm. This sex difference in the onset of orgasm is illustrated by when the maximum number of men or women have experienced orgasm.
Figure 1 illustrates the cumulative incidence, across time, of males ejaculating Kinsey, Pomeroy and Martin, in comparison to the cumulative occurrence of orgasm in women Kinsey, Pomeroy, Martin, and Gebhard, Taken together these data suggest that orgasm is a different phenomenon in women than in men, occurring under different developmental influences and likely reflecting genital differences between men and women.