Editing Orgasm (section)

== Theoretical biological and evolutionary functions in females ==
{{anchor|Theoretical_biological_and_evolutionary_functions}}

=== Shifts in research ===

The function or functions of the human female orgasm have been debated among researchers.<ref>{{cite book |last1 = Wheatley |first1 = John R |last2 = Puts |first2 = David A |editor1-last = Shackelford |editor1-first = Todd K |editor2-last = Hansen |editor2-first = Ranald D |title = The Evolution of Sexuality |date = 2015 |publisher = Springer International Publishing |chapter = Evolutionary Science of Female Orgasm }}</ref> Researchers have several hypotheses about the role if any, of the female orgasm in the reproductive and therefore evolutionary process.<ref name="Geoffrey Miller" /><ref name="Wallen K, Lloyd EA" /><ref name="Lloyd" /><ref name="Gould" /> The literature started with the argument that female orgasm is a byproduct of shared early male [[ontogeny]], where male orgasm is an [[adaptation]].<ref>Symons, D. (1979). The evolution of human sexuality. Oxford: Oxford Univ. Press.</ref> Research has shifted to investigate and also support the sire-choice hypothesis, which proposes that female orgasm has been shaped by [[natural selection]] to function in the selection of high-quality sires (male parents) for offspring. Therefore, orgasm increases the chances of conceiving with males of high genetic quality.<ref>{{cite journal |last1 = Puts |first1 = D. A. |last2 = Dawood |first2 = K. |last3 = Welling |first3 = L. L. |date = 2012 |title = Why women have orgasms: An evolutionary analysis |journal = Archives of Sexual Behavior |volume = 41 |issue = 5 |pages = 1127–1143 |doi = 10.1007/s10508-012-9967-x |pmid = 22733154 |s2cid = 13125596 }}</ref><ref>{{cite journal |last1 = Ellsworth |first1 = Ryan M. |last2 = Bailey |first2 = Drew H. |title = Human Female Orgasm as Evolved Signal: A Test of Two Hypotheses |journal = Archives of Sexual Behavior |date = July 12, 2013 |volume = 42 |issue = 8 |pages = 1545–1554 |doi = 10.1007/s10508-013-0152-7 |pmid = 23857519 |s2cid = 42000263 }}</ref> Research by [[Randy Thornhill]] et al. (1995) suggests that female orgasm is more frequent during intercourse with a male partner with low [[fluctuating asymmetry]].<ref>{{Cite journal |title = Human female orgasm and mate fluctuating asymmetry |journal = Animal Behaviour |date = January 1, 1995 |pages = 1601–1615 |volume = 50 |issue = 6 |doi = 10.1016/0003-3472(95)80014-X |first1 = Randy |last1 = Thornhill |first2 = Steven W. |last2 = Gangestad |first3 = Randall |last3 = Comer |s2cid = 44103857 }}</ref>

=== Selective pressure and mating ===

Wallen K and Lloyd EA state, "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."<ref name="Wallen K, Lloyd EA" />

[[Desmond Morris]] suggests in his 1967 popular science book ''[[The Naked Ape]]'' that the female orgasm evolved to encourage physical intimacy with a male partner and help reinforce the [[pair bond]]. Morris suggested that the relative difficulty in achieving female orgasm, in comparison to the male's, might be favorable in [[Darwinism|Darwinian]] evolution by leading the female to select [[Mating|mates]] who bear qualities like patience, care, imagination, and intelligence, as opposed to qualities like size and aggression, which pertain to mate selection in other primates. Such advantageous qualities thereby become accentuated within the species, driven by the differences between male and female orgasms. If males were motivated by and taken to the point of, orgasm in the same way as females, those advantageous qualities would not be needed, since self-interest would be enough.

=== Fertility ===

There are theories that the female orgasm might increase fertility.<ref name="Geoffrey Miller" /><ref name="Lloyd" /><ref name="Gould" /> For example, it has been suggested that the 30 percent reduction in the size of the vagina could help clench the penis (much like, or perhaps caused by, the [[pubococcygeus muscle]]s), which would make it more stimulating for the male (thus ensuring faster or more voluminous ejaculation). The British biologists Baker and Bellis have suggested that the female orgasm may have a [[peristalsis]] or "upsuck" action (similar to the [[esophagus]]' ability to swallow when upside down), resulting in the retaining of favorable sperm and making conception more likely.<ref>{{cite journal |doi = 10.1006/anbe.1993.1272 |last1 = Baker |first1 = R. R. |last2 = Bellis |first2 = M. A. |date = 1993 |title = Human sperm competition: Ejaculate manipulation by females and a function for the female orgasm |journal = Animal Behaviour |volume = 46 |issue = 5 |pages = 887–909 |s2cid = 53165064 }}</ref> They posited a role of female orgasm in [[Human sperm competition|sperm competition]].

The observation that women tend to reach orgasm more easily when they are ovulating also has led to the suggestion that it is tied to increasing fertility.<ref>{{cite news |first = David |last = Adam |url = https://www.theguardian.com/science/2005/jun/08/genetics.research |department = Science |date = June 8, 2005 |title = Female orgasm all in the genes |newspaper = [[The Guardian]] |url-status = live |archive-url = https://web.archive.org/web/20170302095146/https://www.theguardian.com/science/2005/jun/08/genetics.research |archive-date = March 2, 2017 }}</ref> Evolutionary biologist Robin Baker argues in ''[[Sperm Wars]]'' that occurrence and timing of orgasms are all a part of the female body's unconscious strategy to collect and retain sperm from more evolutionary fit men.<ref>{{Cite book |last = Baker |first = Robin |title = Sperm Wars: Infidelity, Sexual Conflict, and Other Bedroom Battles |publisher = Basic Books |date = 2006 |isbn = 1-56025-848-9 }}</ref> This theory suggests that an orgasm during intercourse functions as a bypass button to a woman's natural cervical filter against sperm and pathogens, and that an orgasm before functions to strengthen the filter.

Desmond Morris proposed that orgasm might facilitate conception by exhausting the female and keeping her horizontal, thus preventing the sperm from leaking out. This possibility sometimes called the "Poleaxe Hypothesis" or the "Knockout Hypothesis",  is now considered unlikely. A 1994 [[TLC (TV channel)|Learning Channel]] documentary on sex had fiber optic cameras inside the vagina of a woman while she had sexual intercourse. During her orgasm, her pelvic muscles contracted and her [[Vaginal portion of cervix|cervix]] repeatedly dipped into a pool of semen in the [[vaginal fornix]], which might ensure that sperm would proceed by the [[external orifice of the uterus]], making conception more likely.<ref>{{cite video |people = [[Desmond Morris]] (host) |date = 1994 |title = [[The Human Animal (TV series)|The Human Animal]] |medium = TV |publisher = The Learning Channel }}</ref>

Evolutionary psychologists Christopher Ryan and Cacilda Jethá, in their discussion of the female orgasm, address how long it takes for females to achieve orgasm compared to males, and females' ability to have multiple orgasms, hypothesizing how especially well suited to multiple partners and [[insemination]] this is. They quote [[primate sexuality]] specialist Alan Dixson in saying that the monogamy-maintenance explanation for female orgasm "seems far-fetched" because "females of other primate species, and particularly those with multimale-multifemale [promiscuous] mating systems such as macaques and chimpanzees, exhibit orgasmic responses in the absence of such bonding or the formation of stable family units." On the other hand, Dixson states that "Gibbons, which are primarily monogamous, do not exhibit obvious signs of female orgasm."<ref name="Ryan">{{cite book |title = Sex at Dawn |isbn = 978-0-06-220794-4 |publisher = HarperCollins |date = 2012 |page = 263 |last1 = Ryan |first1 = Christopher |first2 = Cacilda |last2 = Jethá }}</ref>

The [[female promiscuity]] explanation of female sexuality was echoed at least 12 years earlier by other evolutionary biologists, and there is increasing scientific awareness of the female [[proceptive phase]].<ref>{{cite news |last = Browne |first = Anthony |url = https://www.theguardian.com/uk/2000/sep/03/anthonybrowne.theobserver |title = Women are promiscuous, naturally |department = UK News |date = September 2, 2000 |newspaper = [[The Guardian]] |url-status = live |archive-url = https://web.archive.org/web/20160304225027/http://www.theguardian.com/uk/2000/sep/03/anthonybrowne.theobserver |archive-date = March 4, 2016 }}</ref> Though Dixson classifies humans as mildly polygynous in his survey of primate sexuality, he appears to have doubts, when he writes, "One might argue that ... the female's orgasm is rewarding, increases her willingness to copulate with a variety of males rather than one partner, and thus promotes sperm competition." Ryan and Jethá use this as evidence for their theory that [[partible paternity]] and promiscuity was common for early modern humans.<ref name="Ryan" />

=== Adaptive or vestigial ===

The clitoris is [[homology (biology)|homologous]] to the penis; that is, they both develop from the same embryonic structure.<ref name="Schünke" /><ref name="Francoeur" /> While researchers such as [[Geoffrey Miller (psychologist)|Geoffrey Miller]], [[Helen Fisher (anthropologist)|Helen Fisher]], [[Meredith Small]] and [[Sarah Blaffer Hrdy]] "have viewed the clitoral orgasm as a legitimate adaptation in its own right, with major implications for female sexual behavior and sexual evolution,"<ref name="Geoffrey Miller" /> others, such as [[Donald Symons]] and [[Stephen Jay Gould]], have asserted that the clitoris is [[vestigiality|vestigial]] or nonadaptive and that the female orgasm serves no particular evolutionary function.<ref name="Geoffrey Miller" /><ref name="Gould" /> Gould acknowledged that "most female orgasms emanate from a clitoral, rather than vaginal (or some other), site" and stated that his nonadaptive belief "has been widely misunderstood as a denial of either the adaptive value of female orgasm in general or even as a claim that female orgasms lack significance in some broader sense". He explained that although he accepts that "clitoral orgasm plays a pleasurable and central role in female sexuality and its joys," "[a]ll these favorable attributes, however, emerge just as clearly and just as easily, whether the clitoral site of orgasm arose as a [[Spandrel (biology)|spandrel]] or an adaptation". He said that the "male biologists who fretted over [the adaptionist questions] simply assumed that a deeply vaginal site, nearer the region of fertilization, would offer greater selective benefit" due to their Darwinian, ''[[summum bonum]]'' beliefs about enhanced reproductive success.<ref name="Gould" />

Proponents of the nonadaptive hypothesis, such as Elisabeth Lloyd, refer to the relative difficulty of achieving female orgasm through vaginal sex, the limited evidence for increased fertility after orgasm, and the lack of statistical correlation between the capacity of a woman to orgasm and the likelihood that she will engage in intercourse.<ref name="Lloyd" /><ref name="Chivers">{{cite journal |first1 = Meredith L. |last1 = Chivers |first2 = Michael W. |last2 = Wiedermana |title = A Narrow (But Thorough) Examination of the Evolutionary Significance of Female Orgasm |journal = [[Journal of Sex Research]] |volume = 44 |issue = 1 |pages = 104–105 |date = 2007 |doi = 10.1080/00224490709336797 |df = mdy-all }}</ref> "Lloyd is by no means against evolutionary psychology. Quite the opposite; in her methods and in her writing, she advocates and demonstrates a commitment to the careful application of evolutionary theory to the study of human behavior," stated [[Meredith Chivers|Meredith L. Chivers]]. She added that Lloyd "meticulously considers the theoretical and empirical bases for each account and ultimately concludes that there is little evidence to support an adaptionist account of female orgasm" and that Lloyd instead "views female orgasm as an ontogenetic leftover; women have orgasms because the urogenital neurophysiology for orgasm is so strongly selected for in males that this developmental blueprint gets expressed in females without affecting fitness, just as males have nipples that serve no fitness-related function".<ref name="Chivers" />

A 2005 [[twin study]] found that one in three women reported never or seldom achieving orgasm during sexual intercourse, and only one in ten always orgasmed. This variation in the ability to orgasm, generally thought to be psychosocial, was found to be 34 percent to 45 percent genetic. The study, examining 4000 women, was published in ''[[Biology Letters]]'', a [[Royal Society]] journal.<ref>{{cite news |url=http://news.bbc.co.uk/2/hi/health/4616899.stm |title=Female orgasm is 'down to genes{{'-}} |work=[[BBC]] |date=June 7, 2005 |access-date=May 28, 2006 |url-status=live |archive-url=https://web.archive.org/web/20161021184246/http://news.bbc.co.uk/2/hi/health/4616899.stm |archive-date=October 21, 2016  }}</ref><ref>{{cite journal |last1 = Dunn |first1 = Kate M |last2 = Cherkas |first2 = Lynn F |last3 = Spector |first3 = Tim D |title = Genetic influences on variation in female orgasmic function: a twin study |journal = Biology Letters |type = Abstract |date = September 22, 2005 |volume = 1 |issue = 3 |pages = 260–263 |doi = 10.1098/rsbl.2005.0308 |pmc = 1617159 |pmid = 17148182 }}</ref> Elisabeth Lloyd has cited this as evidence for the notion that female orgasm is not adaptive.<ref name="Lloyd" /><ref name="Lloyd2">{{cite web |url = http://mypage.iu.edu/%7Eealloyd/Reviews.html#IsntItObviousThat |title = Reviews |publisher = Mypage.iu.edu |access-date = October 15, 2010 |archive-date = April 1, 2020 |archive-url = https://web.archive.org/web/20200401223451/http://mypage.iu.edu/~ealloyd/Reviews.html#IsntItObviousThat |url-status = dead }}</ref>

Miller, Hrdy, Helen O'Connell, and [[Natalie Angier]] have criticized the "female orgasm is vestigial" hypothesis as understating and devaluing the psychosocial value of the female orgasm.<ref name="Geoffrey Miller" /> Hrdy stated that the hypothesis smacks of [[sexism]].<ref>{{cite news |author = Christopher Shea |title = Orgasmic science |work = The Boston Globe |date = April 24, 2005 }}</ref> O'Connell said, "It boils down to rivalry between the sexes: the idea that one sex is sexual and the other reproductive. The truth is that both are sexual and both are reproductive."<ref name="O'Connell" /> O'Connell used [[Magnetic resonance imaging|MRI]] technology to define the true size and shape of the clitoris, suggesting that it extends into the anterior wall of the vagina ([[#Females|see above]]).

O'Connell describes typical textbook descriptions of the clitoris as lacking detail and including inaccuracies, saying that the work of [[Georg Ludwig Kobelt]] in the early 19th century provides a most comprehensive and accurate description of clitoral anatomy. She argues that the bulbs appear to be part of the clitoris and that the distal urethra and vagina are intimately related structures, although they are not erectile in character, forming a tissue cluster with the clitoris that appears to be the center of female sexual function and orgasm.<ref name="O'Connell" /> By contrast, Nancy Tuana, at the 2002 conference for ''Canadian Society of Women in Philosophy'', argues that the clitoris is unnecessary in reproduction, but that this is why it has been "historically ignored", mainly because of "a fear of pleasure. It is pleasure separated from reproduction. That's the fear". She reasoned that this fear is the cause of the ignorance that veils female sexuality.<ref name="Cairney">{{cite web |last = Cairney |first = Richard |title = Exploring female sexuality |publisher = ExpressNews |date = October 21, 2002 |access-date = December 21, 2011 |url = http://www.expressnews.ualberta.ca/article.cfm?id=3201 |archive-date = December 21, 2011 |archive-url = https://web.archive.org/web/20111221175533/http://www.archives.expressnews.ualberta.ca/article/2002/10/3201.html }}</ref>

=== Induced Ovulations ===
{{Main article|Induced ovulation (animals)}}

Some spontaneously ovulating species can occasionally undergo mating-induced preovulatory LH surges. These species require mating to stimulate the vagina and cervix, resulting in ovulation in the females. Research suggests that the female orgasm evolved from copulation-induced ovulation.
<ref>{{cite journal |doi = 10.1073/pnas.1910295116 |title = An experimental test of the ovulatory homolog model of female orgasm |date = 2019 |journal = Proceedings of the National Academy of Sciences |volume = 116 |issue = 41 |pages = 20267–20273 |pmid = 31570579 |bibcode = 2019PNAS..11620267P | vauthors = Pavlicev M, Zupan AM, Barry A, Walters S, Milano KM, Kliman HJ, Wagner GP |doi-access = free |pmc = 6789565 }}</ref>

=== Fringe theories ===

Brody Costa et al. suggest that women's vaginal orgasm consistency is associated with being told in childhood or adolescence that the vagina is the important zone for inducing female orgasms. Other proposed factors include how well women focus mentally on vaginal sensations during penile-vaginal intercourse, the greater duration of intercourse, and their preference for above-average penis length.<ref name="Brody, Weiss">{{cite journal |title = Vaginal orgasm is associated with vaginal (not clitoral) sex education, focusing mental attention on vaginal sensations, intercourse duration, and a preference for a longer penis |journal = [[The Journal of Sexual Medicine]] |pages = 2774–81 |date = August 2010 |pmid = 19732304 |doi = 10.1111/j.1743-6109.2009.01469.x |volume = 7 |issue = 8 |vauthors = Brody S, Weiss P }}</ref> Costa theorizes that vaginal orgasm is more prevalent among women with a prominent [[tubercle of the upper lip]].<ref name="Brody, Costa">{{cite journal |title = Vaginal orgasm is more prevalent among women with a prominent tubercle of the upper lip |journal = [[The Journal of Sexual Medicine]] |date = June 2011 |pmid = 21676178 |doi = 10.1111/j.1743-6109.2011.02331.x |volume = 8 |issue = 10 |pages = 2793–9 |vauthors = Brody S, Costa RM }}</ref> His research indicates that "[a] prominent and sharply raised lip tubercle has been associated with greater odds ([[odds ratio]] = 12.3) of ever having a vaginal orgasm, and also with greater past month vaginal orgasm consistency (an effect driven by the women who never had a vaginal orgasm), than less prominent lip tubercle categories." Lip tubercle was not associated with social desirability responding, or with orgasm triggered by masturbation during penile-vaginal sex, solitary or partner clitoral or vaginal masturbation, vibrator, or cunnilingus.<ref name="Brody, Costa" />

An empirical study carried out in 2008 provides evidence for Freud's implied link between the inability to have a vaginal orgasm and psychosexual [[Defence mechanisms|immaturity]]. In the study, women reported their past month's frequency of different sexual behaviors and corresponding orgasm rates and completed the Defense Style Questionnaire (DSQ-40), which is associated with various [[Psychopathology|psychopathologies]]. The study concluded that a "vaginal orgasm was associated with less somatization, dissociation, displacement, autistic fantasy, devaluation, and isolation of affect." Moreover, "vaginally anorgasmic women had immature defenses scores comparable to those of established (depression, social anxiety disorder, panic disorder, and obsessive–compulsive disorder) outpatient psychiatric groups." In the study, a vaginal orgasm (as opposed to a clitoral orgasm) was defined as being triggered solely by penile–vaginal intercourse.<ref>{{cite journal |title = Vaginal orgasm is associated with less use of immature psychological defense mechanisms |journal = [[The Journal of Sexual Medicine]] |pages = 1167–1176 |date = May 2008 |doi = 10.1111/j.1743-6109.2008.00786.x |pmid = 18331263 |author1 = Brody S |author2 = Costa R.M. |volume = 5 |issue = 5 }}</ref> According to [[Wilhelm Reich]], the lack of women's capacity to have a vaginal orgasm is due to a lack of [[orgastic potency]], which he believed to be the result of culture's suppression of genital sexuality.<ref>Reich, Wilhelm (1984) Children of the Future: On the Prevention of Sexual Pathology. New York: Farrar Straus and Giroux, footnote on p. 142: "1949: The statement that the girl's clitoral masturbation is normal is also due to the then prevalent psychoanalytic concept that the little girl had no vaginal genatility. The lack of vaginal genatility was later shown by sex-economy to be an artifact of our culture, which suppresses genitality completely and instills castration anxiety not only in the boy but also in the girl. This creates a true secondary drive in the form of penis envy and predominance of clitoral genitality. Psychoanalytic theory mistook these artificial secondary drives for primary, natural functions."</ref>