, Research Paper
The function of the female orgasm.
This is something I wrote while I was at college about a year ago and it details some new research that has been published about the possible purpose of the female orgasm, which I think is pretty interesting… It’s pretty dry and academic in tone and contains some fairly specialist language, but most of it should be pretty clear to most people. If anyone has a question or wants some more information on this kind of thing, mail me: [email protected] Does the female orgasm have a function and, if so, what is it? The female orgasm, and indeed female sexuality in general, has been one of the most consistently debated areas in human behavioural ecology. For many years the field was characterised by a paucity of any real experimental evidence; largely because of the ethical and practical difficulties encountered in researching this area. However in recent years a number of studies have been published which go some way towards shedding some light on the possible adaptive significance of the female orgasm. In the history of the field there have generally been two diametrically opposed positions taken up by researchers. The first position holds that orgasm in females is of little or no adaptive significance and that it is merely a phylogenetic holdover from normal development of the male. This idea springs from the fundamental observation that while male orgasm is essential for conception to take place, female orgasm is not, and indeed does not always (or even often) occur during copulation. This view is represented by writers such as Donald Symons (1979): ?the potential for female orgasm can be understood as a by-product of selection for male orgasm? in much the same way as the existence of nipples on males can be accounted for by the selection for lactation in females. Symons cites the fundamental neuro-muscular similarity of male and female orgasms as support for this position, citing Masters and Johnson?s demonstration that the contractions reliably occur at exactly the same time interval (0.8 seconds) in both sexes. One of Symons central arguments is that the female orgasm is highly individually variable and unpredictable. Symons proposes this to mean that the mechanism is revealed not to be an adaptation purely by virtue of its seeming inefficiency and unreliability. This point is also made by Hrdy (1981) who comments: ?a physiological mechanism….that is important to fitness (or reproductive success) and properly adapted to its task should work better than that.? Symons calls on a variety of other evidence to back up his position; primarily ethnographic studies (including, unfortunately, the now badly discredited work of Margaret Mead on the people of Samoa) but the absence of any real empirical data is highly conspicuous, mainly because very little real experimentation had been done at this time. The other position taken by researchers in this field is that female orgasm is indeed adaptive and serves a clearly defined, and beneficial, purpose. One of the first writers to put this idea onto any firm footing was Desmond Morris in ?The Naked Ape? (1967). Morris espoused two possible functions for the female orgasm; firstly that mutual enjoyment of the act of copulation facilitates the formation of a strong pair bond between males and females and secondly, that the female orgasm promotes contentment and drowsiness leading to sleep. This second point (rather ungraciously termed the ?poleaxe hypothesis? by Baker and Bellis ) is judged to be of importance because of the bipedal gait of humans. If a human female stands up after copulation gravity may have some effect on the number of sperm retained, therefore the adoption of a supine posture after copulation may be adaptive for conception. However, these arguments are again devalued by a lack of hard evidence to support them. In the last few years several extremely significant studies have been performed which have gone some way towards solving this problem. The study performed by Baker and Bellis directly tested two hypotheses; the ?poleaxe? hypothesis of Morris (1967) and an alternative theory first espoused by Fox et al (1970) termed the ?upsuck? hypothesis. This argument contends that female orgasm actively facilitates conception by the sucking of the contents of the vagina into the uterus. Baker and Bellis collected samples of semen from the male participants of their study in order to estimate the amount that would normally be ejaculated. They then also collected samples of ?flowbacks? (the mixture of semen and vaginal mucous that is ejected by the female after copulation) from the couples participating in their study. This, together with analysis of the ?flowbacks? and a nationwide survey of female sexual behaviour, enabled Baker and Bellis to come to some definite conclusions about the merits of the two hypotheses. After analysis it was found that the data did not support Morris?s (1967) ?poleaxe hypothesis?, but that the ?upsuck? hypothesis of Fox et al (1970) was amply supported. It seems that sperm retention is at its best when the female has a copulatory orgasm any time between one minute before the male ejaculates and forty-five minutes after. Female orgasms occurring more than one minute before the male?s ejaculation had no significant effect on sperm retention by the female. This suggests that ?the upsuck mechanism continues to function for at least 1 min after the female subjectively first experiences the climax.? An even more intriguing finding of this study was the effects that inter-copulatory orgasms, either spontaneous (nocturnal) or masturbatory, could have on sperm retention. It was found that orgasms occurring between copulations had a significant effect on the sperm retention of the next copulation, effectively reducing it. Baker and Bellis theorise that inter-copulatory orgasms lower the pH of the cervical mucous by sucking up the more acidic vaginal mucous. As the functioning of sperm is severely compromised in acidic environments this makes it harder for any sperm to penetrate the cervix on subsequent copulations. As a passing note they also make the observation that since most vaginal infections prefer an alkaline environment then intercopulatory orgasms may be serving an antibiotic purpose by lowering the pH of the female tract. This idea, though intriguing, needs further investigation in a medical context before any definitive statements can be made. This data then suggests the idea that female humans have a set of behaviours for profoundly (though unconsciously) affecting the likelihood of insemination. Baker and Bellis (1993) make the point that the factors that have been ignored in previous discussions of female orgasm (i.e. non-copulatory orgasm, copulation without orgasm and female orgasm before male orgasm ) may actually have significant effects on the likelihood of insemination and ?The whole pattern hints strongly at a female strategy to influence sperm retention differently at different copulations.? Precisely when and how these strategies are applied is another question entirely; and one that a study by Randy Thornhill et al attempted to address. Thornhill et al?s study went some way to untangling the factors that influenced the likelihood of female orgasm. The study involved 86 heterosexual, sexually active couples at the University of New Mexico. Each participant filled in an extensive questionnaire which detailed personal information, (i.e. age, height, weight, ethnicity, socio-economic class etc.) estimated future earning potential of each partner, a measure of investment and level of affection in the relationship and various questions concerning sexual attitudes and behaviour; most importantly a female orgasm questionnaire. The participants were also measured for fluctuating asymmetry; the hypothesis being that the level of fluctuating asymmetry (FA) of the male is an indication of male genetic quality and that therefore male FA would have a significant effect on the frequency of female orgasms. After a laborious and complex statistical procedure which attempted to control for a large number of confounding variables, Thornhill et al arrived at the conclusion that females with low FA partners do indeed exhibit more copulatory orgasms than females with high FA partners. Their results also suggest that male body weight and physical attractiveness also have an effect on the frequency of female orgasms; though more work needs to be done in order to clarify the possible interactions of these factors. These results also tie in nicely with the data from extra-pair copulations (EPC?s) in Baker and Bellis?s (1993) survey in which it was found that polyandrous females retained significantly less sperm during in-pair copulations than during EPC?s. This is probably because the EPC?s were conducted with males of lower FA (i.e. higher genetic quality) than their regular partners. They also examined the hypothesis that ?female orgasm promotes preferential bonding with males who are capable or willing to invest? but found no indication that female orgasm is dependent upon male love or investment in the relationship. They also draw attention to the positive correlation between each partners report of female orgasm frequency and timing and suggest that there may well be selection pressure on males to be able to detect female orgasm; presumably as a cue to greater likelihood of paternity. Subsequently Hrdy (1996) came up with some important criticisms of Thornhill et al?s (1996) reasoning. She turns Thornhill?s ideas around and argues that females were first selected to solicit multiple partners and that orgasm as a possible selective sperm retention mechanism evolved from that behaviour. She also accuses Thornhill et al of being un-parsimonious in supposing that orgasm developed to selectively retain sperm: ?why solve a (presumably relatively simple?) cell transport problem through the evolution of a complex psychophysiological phenomenon?. Her argument is that selective sperm retention evolved after (and as a modification of) orgasmic response. There are other important criticisms of Thornhill et al?s study, not least of which are the inherent problems involved in drawing meaningful conclusions from a retrospective questionnaire, and the large number of confounding variables that they attempted to conbtrol. However, Thornhill et al?s data does show a high degree of internal consistency, which suggests reasonably accurate results. A curious aspect of the study was the measurements of FA; facial characteristics were not measured for FA even though this is presumably a much more potent factor in attractiveness than hand span or ankle width. Although it has been found that facial attractiveness is correlated with body symmetry in other studies, this was not the case in Thornhill et al?s sample. Possibly a replication with a larger sample size and more ongoing (rather than retrospective) recording of sexual behaviour would be beneficial in clearing up these issues. In conclusion then, the data from recent studies do seem to refute the older ideas of Symons (1979), Morris (1967) and others, and do seem to point to a significant function for the female orgasm i.e. selective sperm retention; possibly of low FA males. The ongoing debate concerning the conditions under which it may have evolved can be partially resolved by realising that it may have originally evolved as an adaptation for males, but the physiological potential has been exploited by females for a different purpose. Because of the inherent methodological and practical difficulties associated with research in this field however, a substantial amount of further research is required before we can unequivocally determine this question, the exact factors that influence orgasm, and even the extent of it?s influence on the likelihood of conception. References. R. Baker and R. Bellis (1993) Human sperm competition: ejaculate manipulation by females and a function for the female orgasm. Animal Behaviour 46: 887-909. S. Hrdy (1981) The woman that never evolved. Harvard University Press. S. Hrdy (1996) The evolution of female orgasms: logic please but no atavism. Animal Behaviour 52: 851-852. D. Morris (1967) The Naked Ape. Cape. D. Symons (1979) The Evolution of Human Sexuality. Oxford University Press. R. Thornhill et al (1995) Human female orgasm and mate fluctuating asymmetry. Animal Behaviour 50: 1601-1615. R. Thornhill and S. Gangestad (1996a) The evolution of human sexuality. Trends in Ecology and Evolution 11: 98-102. R. Thornhill and S. Gangestad (1996b) Human female copulatory orgasm: a human adaptation or phylogenetic holdover. Animal Behaviour 52: 853-855.