Why women have orgasms: an evolutionary analysis

The complexity of female orgasm and ejaculation

The anatomy and physiology of the female orgasm are often neglected. The female orgasm is a normal psychophysiological function to all women, and some even can achieve ejaculation as part of the normal physiological response at the height of sexual arousal. The complexity of female sexuality requires a deep understanding of genital anatomy. The clitoris is the principal organ for female pleasure. The vaginal stimulation of the anterior vaginal wall led women to orgasm due to the stimulation of the clitourethrovaginal complex and not due to stimulation of a particular organ called the G spot in the anterior distal vaginal wall. Female ejaculation follows orgasm. It consists of the orgasmic expulsion of a smaller quantity of whitish fluid produced by the female prostate. Squirting can be differentiated from female ejaculation because it is the orgasmic transurethral expulsion of a substantial amount of diluted urine during sexual activity, and it is not considered pathological. The female orgasm is influenced by many aspects such as communication, emotional intimacy, long-standing relationship, adequate body image and self-esteem, proper touching and knowledge of the female body, regular masturbation, male sexual performance, male and female fertility, chronic pain, and capacity to engage in new sexual acts. Stronger orgasms could be achieved when clitoral stimulation, anterior vaginal wall stimulation, and oral sex is involved in the same sexual act.

Evolution and Morphology of Genitalia in Female Amniotes

Despite their evolutionary and biomedical importance, studies of the morphology and function of female genitalia have continued to lag behind those of male genitalia. While studying female genitalia can be difficult because of their soft, deformable and internal nature, recent advances in imaging, geometric analyses of shape and mechanical testing have been made, allowing for a much greater understanding of the incredible diversity of form and function of female genitalia. Here we summarize some of these methods, as well as discuss some big questions in the field that are beginning to be examined now, and will continue to benefit from further work, especially a comparative approach. Topics of further research include examination of the morphology of female genitalia in situ, in-depth anatomical work in many more species, studies of the interplay between natural and sexual selection in influencing features of vaginal morphology, how these diverse functions influence the mechanical properties of tissues, and studies of clitoris morphology and function across amniotes. Many other research topics related to female genitalia remain largely unexplored, and we hope that the papers in this issue will continue to inspire further research on female genitalia.

The Effect of Female Orgasm Frequency on Female Mate Selection: A Test of Two Hypotheses

Female orgasm has been a mystery that psychologists have been attempting to understand for decades. Many have contended that female orgasm is a functionless by-product of male orgasm, while others have argued that female orgasm may be an adaptation in its own right, offering several adaptationist accounts of female orgasm. In the current research, we tested predictions derived from two hypotheses regarding adaptive functions of female orgasm: female orgasm indicates partner mate value or female orgasm promotes long-term, pair bonding. 199 female undergraduates participated in an experiment where they imagined themselves as a member of a romantic relationship provided in a scenario. Within these scenarios, the relationships varied between either short- or long-term and the frequency that the female experienced orgasm during intercourse varied between never, occasionally, and almost always. Participants answered questions regarding relationship satisfaction and perceptions of the fictional relationship. A series of analysis of variance (ANOVAs) indicated that females assigned to conditions of experiencing more frequent orgasms reported greater relationship satisfaction, across both short- and long-term relationships. The relationship between female orgasm frequency and relationship satisfaction was fully mediated by the female's perceived love for her hypothetical partner but not by perceptions of her hypothetical partner's commitment. Taken together, this study provides preliminary support for the hypothesis that female orgasm evolved as a mate-selection tool for females and promotes long-term, pair bonding but does not provide support for the hypothesis that female orgasm evolved as an indicator of male value.

Differences in Orgasm Frequency Among Gay, Lesbian, Bisexual, and Heterosexual Men and Women in a U.S. National Sample

There is a notable gap between heterosexual men and women in frequency of orgasm during sex. Little is known, however, about sexual orientation differences in orgasm frequency. We examined how over 30 different traits or behaviors were associated with frequency of orgasm when sexually intimate during the past month. We analyzed a large US sample of adults (N = 52,588) who identified as heterosexual men (n = 26,032), gay men (n = 452), bisexual men (n = 550), lesbian women (n = 340), bisexual women (n = 1112), and heterosexual women (n = 24,102). Heterosexual men were most likely to say they usually-always orgasmed when sexually intimate (95%), followed by gay men (89%), bisexual men (88%), lesbian women (86%), bisexual women (66%), and heterosexual women (65%). Compared to women who orgasmed less frequently, women who orgasmed more frequently were more likely to: receive more oral sex, have longer duration of last sex, be more satisfied with their relationship, ask for what they want in bed, praise their partner for something they did in bed, call/email to tease about doing something sexual, wear sexy lingerie, try new sexual positions, anal stimulation, act out fantasies, incorporate sexy talk, and express love during sex. Women were more likely to orgasm if their last sexual encounter included deep kissing, manual genital stimulation, and/or oral sex in addition to vaginal intercourse. We consider sociocultural and evolutionary explanations for these orgasm gaps. The results suggest a variety of behaviors couples can try to increase orgasm frequency.

Endocrinology of human female sexuality, mating, and reproductive behavior

Hormones orchestrate and coordinate human female sexual development, sexuality, and reproduction in relation to three types of phenotypic changes: life history transitions such as puberty and childbirth, responses to contextual factors such as caloric intake and stress, and cyclical patterns such as the ovulatory cycle. Here, we review the endocrinology underlying women's reproductive phenotypes, including sexual orientation and gender identity, mate preferences, competition for mates, sex drive, and maternal behavior. We highlight distinctive aspects of women's sexuality such as the possession of sexual ornaments, relatively cryptic fertile windows, extended sexual behavior across the ovulatory cycle, and a period of midlife reproductive senescence-and we focus on how hormonal mechanisms were shaped by selection to produce adaptive outcomes. We conclude with suggestions for future research to elucidate how hormonal mechanisms subserve women's reproductive phenotypes.

Testing the mate-choice hypothesis of the female orgasm: disentangling traits and behaviours

BACKGROUND

The evolution of the female orgasm in humans and its role in romantic relationships is poorly understood. Whereas the male orgasm is inherently linked to reproduction, the female orgasm is not linked to obvious reproductive or survival benefits. It also occurs less consistently during penetrative sex than does the male orgasm. Mate-choice hypotheses posit that the wide variation in female orgasm frequency reflects a discriminatory mechanism designed to select high-quality mates.

OBJECTIVE

We aimed to determine (1) whether women report that their orgasm frequency varies between partners, (2) whether this variation reflects mates' personal characteristics, and (3) whether this variation reflects own and partner sexual behaviour during intercourse.

DESIGN

We collected survey data from 103 women who rated (1) the extent to which their orgasm frequency varied between partners, (2) the characteristics of previous sexual partners who induced high-orgasm frequency and those who induced low-orgasm frequency, and (3) the specific behaviours during sex with those partners. This is the first study to test within-woman variation in orgasm and partner traits.

RESULTS

Overall, women reported variation in their orgasm rates with different partners. Partners who induced high-orgasm rates were rated as more humorous, creative, warm, faithful, and better smelling than partners who induced low-orgasm rates, and also engaged in greater efforts to induce partner orgasm.

CONCLUSIONS

Some assumptions and predictions of mate-choice hypotheses of female orgasm were supported, while other aspects of our findings provide reasons to remain sceptical.

The whole versus the sum of some of the parts: toward resolving the apparent controversy of clitoral versus vaginal orgasms

BACKGROUND

The nature of a woman's orgasm has been a source of scientific, political, and cultural debate for over a century. Since the Victorian era, the pendulum has swung from the vagina to the clitoris, and to some extent back again, with the current debate stuck over whether internal sensory structures exist in the vagina that could account for orgasms based largely on their stimulation, or whether stimulation of the external glans clitoris is always necessary for orgasm.

METHOD

We review the history of the clitoral versus vaginal orgasm debate as it has evolved with conflicting ideas and data from psychiatry and psychoanalysis, epidemiology, evolutionary theory, feminist political theory, physiology, and finally neuroscience.

RESULTS

A new synthesis is presented that acknowledges the enormous potential women have to experience orgasms from one or more sources of sensory input, including the external clitoral glans, internal region around the "G-spot" that corresponds to the internal clitoral bulbs, the cervix, as well as sensory stimulation of non-genital areas such as the nipples.

CONCLUSIONS

With experience, stimulation of one or all of these triggering zones are integrated into a "whole" set of sensory inputs, movements, body positions, autonomic arousal, and partner- and contextual-related cues, that reliably induces pleasure and orgasm during masturbation and copulation. The process of integration is iterative and can change across the lifespan with new experiences of orgasm.

What is orgasm? A model of sexual trance and climax via rhythmic entrainment

Orgasm is one of the most intense pleasures attainable to an organism, yet its underlying mechanisms remain poorly understood. On the basis of existing literatures, this article introduces a novel mechanistic model of sexual stimulation and orgasm. In doing so, it characterizes the neurophenomenology of sexual trance and climax, describes parallels in dynamics between orgasms and seizures, speculates on possible evolutionary origins of sex differences in orgasmic responding, and proposes avenues for future experimentation. Here, a model is introduced wherein sexual stimulation induces entrainment of coupling mechanical and neuronal oscillatory systems, thus creating synchronized functional networks within which multiple positive feedback processes intersect synergistically to contribute to sexual experience. These processes generate states of deepening sensory absorption and trance, potentially culminating in climax if critical thresholds are surpassed. The centrality of rhythmic stimulation (and its modulation by salience) for surpassing these thresholds suggests ways in which differential orgasmic responding between individuals-or with different partners-may serve as a mechanism for ensuring adaptive mate choice. Because the production of rhythmic stimulation combines honest indicators of fitness with cues relating to potential for investment, differential orgasmic response may serve to influence the probability of continued sexual encounters with specific mates.

Measuring sperm backflow following female orgasm: a new method

BACKGROUND

Human female orgasm is a vexed question in the field while there is credible evidence of cryptic female choice that has many hallmarks of orgasm in other species. Our initial goal was to produce a proof of concept for allowing females to study an aspect of infertility in a home setting, specifically by aligning the study of human infertility and increased fertility with the study of other mammalian fertility. In the latter case - the realm of oxytocin-mediated sperm retention mechanisms seems to be at work in terms of ultimate function (differential sperm retention) while the proximate function (rapid transport or cervical tenting) remains unresolved.

METHOD

A repeated measures design using an easily taught technique in a natural setting was used. Participants were a small (n=6), non-representative sample of females. The introduction of a sperm-simulant combined with an orgasm-producing technique using a vibrator/home massager and other easily supplied materials.

RESULTS

The sperm flowback (simulated) was measured using a technique that can be used in a home setting. There was a significant difference in simulant retention between the orgasm (M=4.08, SD=0.17) and non-orgasm (M=3.30, SD=0.22) conditions; t (5)=7.02, p=0.001. Cohen's d=3.97, effect size r=0.89. This indicates a medium to small effect size.

CONCLUSIONS

This method could allow females to test an aspect of sexual response that has been linked to lowered fertility in a home setting with minimal training. It needs to be replicated with a larger sample size.

An evolutionary behaviorist perspective on orgasm

Evolutionary explanations for sexual behavior and orgasm most often posit facilitating reproduction as the primary function (i.e. greater rate of fertilization). Other reproductive benefits of sexual pleasure and orgasm such as improved bonding of parents have also been discussed but not thoroughly. Although sex is known to be highly reinforcing, behaviorist principles are rarely invoked alongside evolutionary psychology in order to account for human sexual and social behavior. In this paper, I will argue that intense sexual pleasure, especially orgasm, can be understood as a primary reinforcer shaped by evolution to reinforce behavior that facilitates reproductive success (i.e. conception through copulation). Next, I will describe an evolutionary account of social shaping. In particular, I will focus on how humans evolved to use orgasm and sexual arousal to shape the social behavior and emotional states of others through both classical and operant conditioning and through both reproductive and non-reproductive forms of sexual behavior. Finally, I will describe how orgasm is a signal of sensitivity to reinforcement that is itself reinforcing.

Using ecological momentary assessment to investigate short-term variations in sexual functioning in a sample of peri-menopausal women from Iran

The investigation of short-term changes in female sexual functioning has received little attention so far. The aims of the study were to gain empirical knowledge on within-subject and within- and across-variable fluctuations in women’s sexual functioning over time. More specifically, to investigate the stability of women´s self-reported sexual functioning and the moderating effects of contextual and interpersonal factors. A convenience sample of 206 women, recruited across eight Health care Clinics in Rasht, Iran. Ecological momentary assessment was used to examine fluctuations of sexual functioning over a six week period. A shortened version of the Female Sexual Function Index (FSFI) was applied to assess sexual functioning. Self-constructed questions were included to assess relationship satisfaction, partner’s sexual performance and stress levels. Mixed linear two-level model analyses revealed a link between orgasm and relationship satisfaction (Beta = 0.125, P = 0.074) with this link varying significantly between women. Analyses further revealed a significant negative association between stress and all six domains of women’s sexual functioning. Women not only reported differing levels of stress over the course of the assessment period, but further differed from each other in how much stress they experienced and how much this influenced their sexual response. Orgasm and sexual satisfaction were both significantly associated with all other domains of sexual function (P<0.001). And finally, a link between partner performance and all domains of women`s sexual functioning (P<0.001) could be detected. Except for lubrication (P = 0.717), relationship satisfaction had a significant effect on all domains of the sexual response (P<0.001). Overall, our findings support the new group of criteria introduced in the DSM-5, called “associated features” such as partner factors and relationship factors. Consideration of these criteria is important and necessary for clinicians when diagnosing FSD.

Sexual selection and the evolution of behavior, morphology, neuroanatomy and genes in humans and other primates

Explaining human evolution means developing hypotheses about the occurrence of sex differences in the brain. Neuroanatomy is significantly influenced by sexual selection, involving the cognitive domain through competition for mates and mate choice. Male neuroanatomy emphasizes subcortical brain areas and visual-spatial skills whereas that of females emphasizes the neocortex and social cognitive areas. In primate species with high degrees of male competition, areas of the brain dealing with aggression are emphasized. Females have higher mirror neuron activity scores than males. Hundreds of genes differ in expression profiles between males and females. Sexually selected differences in gene expression can produce neuroanatomical sex differences. A feedback system links genes, gene expression, hormones, morphology, social structure and behavior. Sex differences, often through female choice, can be rapidly modulated by socialization. Human evolution is a dramatic case of how a trend toward pair bonding and monogamy lowered male competition and increased female choice as a necessary step in releasing the cognitive potential of our species.

Functional variation in sensitivity to cues that a partner is cheating with a rival

The costs imposed by a romantic partner's mixed reproductive strategy (MRS) generate selection pressures for anticipatory responses to mitigate or avoid those costs. People will differ in their vulnerability to those costs, based in part on the qualities of their romantic rivals. Thus, we predicted that individuals at high risk of a partner's MRS--women with many sexually accessible rivals and men with many rivals more physically attractive than themselves--would be more attentive to cues that an MRS was being employed than those at lower risk. Based on similarity judgments derived from a successive-pile-sort method, this prediction was supported in a study involving over 1,300 students and community members. These results complement a growing body of research on selection pressures generated by romantic rivals.

Does menstrual cycle phase influence the gender specificity of heterosexual women's genital and subjective sexual arousal?

Unlike men, heterosexual women's genital arousal is gender nonspecific, such that heterosexual women show relatively similar genital arousal to sexual stimuli depicting men and women but typically report greater subjective arousal to male stimuli. Based on the ovulatory-shift hypothesis-that women show a mid-cycle shift in preferences towards more masculine features during peak fertility-we predicted that heterosexual women's genital and subjective arousal would be gender specific (more arousal towards male stimuli) during peak fertility. Twenty-two naturally-cycling heterosexual women were assessed during the follicular and luteal phases of their menstrual cycle to examine the role of menstrual cycle phase in gender specificity of genital and subjective sexual arousal. Menstrual cycle phase was confirmed with salivary hormone assays; phase at the time of first testing was counterbalanced. Women's genital and subjective sexual arousal patterns were gender nonspecific, irrespective of cycle phase. Cycle phase at first testing session did not influence genital or subjective arousal in the second testing session. Similar to previous research, women's genital and subjective sexual arousal varied with cues of sexual activity, but neither genital nor subjective sexual arousal varied by gender cues, with the exception of masturbation stimuli, where women showed higher genital arousal to the stimuli depicting male compared to female actors. These data suggest that menstrual cycle phase does not influence the gender specificity of heterosexual women's genital and subjective sexual arousal.

Female extra-pair mating: adaptation or genetic constraint?

Why do females of so many socially monogamous species regularly engage in matings outside the pair bond? This question has puzzled behavioural ecologists for more than two decades. Until recently, an adaptionist's point of view prevailed: if females actively seek extra-pair copulations, as has been observed in several species, they must somehow benefit from this behaviour. However, do they? In this review, we argue that adaptive scenarios have received disproportionate research attention, whereas nonadaptive phenomena, such as pathological polyspermy, de novo mutations, and genetic constraints, have been neglected by empiricists and theoreticians alike. We suggest that these topics deserve to be taken seriously and that future work would benefit from combining classical behavioural ecology with reproductive physiology and evolutionary genetics.

The pharmacology of the human female orgasm - its biological and physiological backgrounds

The female orgasm has been examined over the years by numerous scientific disciplines yet it still has many secrets to be disclosed. Because its physiology, especially its neurophysiology, is sparingly understood its pharmacology is necessarily limited based mainly on the side effects of drugs. Few published studies have used a placebo group as controls. The paucity of focussed studies is well illustrated by the fact that there still is no approved medication to treat female orgasmic dysfunction. The present brief overview examines the most important aspects of its biology and especially its physiology highlighting the many questions that need answering if we are to have a comprehensive pharmacology of the female orgasm.

Human female orgasm as evolved signal: a test of two hypotheses

We present the results of a study designed to empirically test predictions derived from two hypotheses regarding human female orgasm behavior as an evolved communicative trait or signal. One hypothesis tested was the female fidelity hypothesis, which posits that human female orgasm signals a woman's sexual satisfaction and therefore her likelihood of future fidelity to a partner. The other was sire choice hypothesis, which posits that women's orgasm behavior signals increased chances of fertilization. To test the two hypotheses of human female orgasm, we administered a questionnaire to 138 females and 121 males who reported that they were currently in a romantic relationship. Key predictions of the female fidelity hypothesis were not supported. In particular, orgasm was not associated with female sexual fidelity nor was orgasm associated with male perceptions of partner sexual fidelity. However, faked orgasm was associated with female sexual infidelity and lower male relationship satisfaction. Overall, results were in greater support of the sire choice signaling hypothesis than the female fidelity hypothesis. Results also suggest that male satisfaction with, investment in, and sexual fidelity to a mate are benefits that favored the selection of orgasmic signaling in ancestral females.

Is Cunnilingus-Assisted Orgasm a Male Sperm-Retention Strategy?

We secured data from 243 men in committed, sexual, heterosexual relationships to test the sperm retention hypothesis of oral sex. We predicted that, among men who perform cunnilingus on their partner, those at greater risk of sperm competition are more likely to perform cunnilingus until their partner achieves orgasm (Prediction 1), and that, among men who ejaculate during penile-vaginal intercourse and whose partner experiences a cunnilingus-assisted orgasm, ejaculation will occur during the brief period in which female orgasm might function to retain sperm (Prediction 2). The results support Prediction 1 but not Prediction 2. We discuss limitations of the current research and discuss how these results may be more consistent with alternative hypotheses regarding female orgasm and oral sex.

Changes in women's feelings about their romantic relationships across the ovulatory cycle

According to the dual mating hypothesis, women possess two overlapping suites of mate-choice mechanisms: one leading to preferences for sexually desirable men who have high-fitness genes and one leading to preferences for men who are able to invest in a woman and her children. Evidence increasingly demonstrates that women's preference for sexual desirability (but not investment attractiveness) increases when women are most fertile within the ovulatory cycle. Little is known, however, about the implications of these preference shifts for women's relationships with their long-term partners. Using luteinizing hormone tests to verify ovulation, across two studies (Samples 1 and 2), we found that women whose partners were relatively low in sexual desirability felt less close to their partner (Samples 1 and 2) and were more critical of their partner's faults (Sample 2) on high-fertility days of the cycle just prior to ovulation compared with low-fertility days of the cycle. Women whose partners were relatively high in sexual desirability felt closer to their partner (Sample 1) and more satisfied with their relationship (Sample 2) on high- than low-fertility days of the cycle. There were no such shifts in women's commitment to their relationship. Therefore, partner sexual desirability predicts women's high-fertility assessments of relationship quality but not their intentions to stay in their relationship, consistent with the dual mating hypothesis. These findings suggest that variations across the ovulation cycle in women's reproductive hormones play an important role in relationship dynamics.