THE FEMALE ORGASM: TESTING AN EVOLUTIONARY ADAPTATION FOR PAIR-BONDING REINFORCEMENT IN POTENTIALLY CONCEPTIVE AND NON- CONCEPTIVE PAIRS ______

A Thesis

Presented to the

Faculty of

California State University, Fullerton ______

In Partial Fulfillment

of the Requirements for the Degree

Master of Arts

in

Anthropology ______

By

Juanita P. Jackson

Thesis Committee Approval:

Elizabeth G. Pillsworth, Division of Anthropology, Chair John Patton, Division of Anthropology Aaron Lukaszewski, Department of Psychology

Fall, 2017

ABSTRACT

The human female orgasm, has often been a topic of debate in evolutionary scholarship. Some scholars argue that it evolved to aid in sperm selection of high quality males, others argue that it evolved as part of a pair-bond maintenance system, and some propose that it’s simply a byproduct of the male orgasm. This study compares predictors of female orgasm based on mate qualities, between heterosexual and non-heterosexual women. We predict that if the female orgasm evolved to favor conception with genetically fit males, then female sexual response should be more sensitive to cues of genetic quality in male partners, predicting, to a greater extent, orgasm frequency among heterosexual women. Also, heterosexual women should be more likely to report deep orgasm and orgasms that produce an internal sucking sensation, as these are argued to enhance sperm retention. Also, if female orgasm evolved to reinforce pair-bonds, long- term investing and resource qualities in either male or female partners should predict orgasm frequency. We surveyed 93 heterosexual women and 20 non-heterosexual women, who were romantically and sexually involved with a partner. We found that partner’s physical attractiveness predicted frequency to a greater extent in non- heterosexual women; orgasm centrality and presence of internal sucking sensation was not predicted by sexual orientation. Women experienced marginally more frequency with more compatible partners, and compatibility was marginally greater for heterosexual women. Partner’s resources did not predict frequency in either group.

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TABLE OF CONTENTS

ABSTRACT ...... ii

LIST OF TABLES ...... vi

LIST OF FIGURES ...... vii

ACKNOWLEDGMENTS ...... viii

Chapter 1. INTRODUCTION ...... 1

Testing the Byproduct Hypothesis ...... 4 Testing the Good Genes Hypothesis ...... 6 Testing the Pair-Bonding Hypothesis ...... 12 Current Study ...... 15 Hypothesis 1 ...... 17 Hypothesis 2 ...... 17

2. METHODS ...... 19

Materials ...... 19 Procedure ...... 19 Measures ...... 19 Outcome Variables ...... 19 Predictor Variables ...... 20 Genetic Quality ...... 20 Resource Qualities and Investing Qualities ...... 21 Control Variables ...... 22

3. RESULTS ...... 23

Participants...... 23 Analyses ...... 24 Tests of Hypotheses ...... 25 Prediction 1 ...... 25 Predictions 2-3 ...... 25 Predictions 4-5 ...... 29

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4. CONCLUSION ...... 31

5. DISCUSSION ...... 33

Limitations ...... 37 Future Direction ...... 37

APPENDIX: QUESTIONNAIRE ...... 39

REFERENCES ...... 59

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LIST OF TABLES

Table Page

1. Predictions Based on Three Hypotheses ...... 18

2. Descriptive Statistics ...... 24

3. Frequency of Orgasm with Different Stimuli ...... 25

4. Two Sample t-test Reporting Between Group Difference in How They Rate Their Partners ...... 26

5. Main Effect and Interaction of Variables Predicting Frequency of Orgasm ...... 27

6. Logistic Regression for Variables Predicting Likelihood of Orgasm Centrality and Internal Sucking Sensation ...... 30

7. Results Compared to Predictions ...... 32

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LIST OF FIGURES

Figure Page

1. Orgasm frequency as as function of partner physical attractiveness, by participant sexual orientation ...... 28

2. Orgasm frequency as a function of relationship duration, by participant sexual orientation ...... 28

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ACKNOWLEDGMENTS

I would like to acknowledge Dr. Elizabeth Pillsworth for all of her support, guidance and kindness throughout my tenure as a graduate student; I am truly grateful to have had Dr. Pillsworth as my mentor. I would also like to acknowledge my thesis committee Dr. John Patton and Dr. Aaron Lukaszewski for their help and insight in this process. Additionally, I would like to acknowledge my family and friends for their unwavering encouragement, love and support.

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CHAPTER 1

INTRODUCTION

While most women report having been able to achieve orgasm at some point in their lives as a result of some sort of sexual stimulation, the majority of women do not regularly achieve orgasm during sexual intercourse, and some never do (Wallen & Lloyd,

2011). In many ways, female orgasm appears to be analogous to male orgasm: both are characterized by feelings of strong and intense pleasure, followed by a feeling of release once climax occurs (Meston, Levin, Sipski, Hull, & Heiman, 2004), and include physiological changes such as an increase in heart rate, respiration, and blood pressure, and corresponding muscle contractions (Alwaall, Breyer, & Lue, 2015; Komisaruk,

Beyer-Flores, & Whipple, 2006). But scholars have generally approached the topic of male orgasm as fairly non-mysterious, as it has an apparently clear link with the biological function of ejaculation. While ejaculation and orgasm are physiologically distinct processes (Alwall et al., 2015), raising some questions concerning the inherent necessity of male orgasm, orgasm is generally coupled with ejaculation, making it subject to strong selective pressures as contributing to reproductive success (Wallen & Lloyd,

2011). Ejaculation during intercourse serves a clear evolutionary function, it helps direct sperm into the reproductive tract of a woman, and occurs in nearly 100% of men during sexual intercourse (Wallen & Lloyd, 2011). In contrast, women’s orgasms are shown to be far more variable. According to Zietsch and Santtilla (2011), 10% of women have

2 never experienced an orgasm, while in a study by Dunn, Cherkas, and Spector (2005),

32% of women claimed that they never or only infrequently experienced orgasm as a result of sexual intercourse. Given that female orgasm appears to be far less consistent and reliable than male orgasm or ejaculation, scholars have debated whether the female orgasm serves an adaptive function—such as increasing sperm retention with partners of high genetic quality or maintaining pair-bonds—or whether it might simply be a byproduct that arose in conjunction with the adaptation of male ejaculation.

In order to evaluate the possible adaptive functions of female orgasm, it is useful first to consider the features of a trait that we would expect to see in an adaptation as opposed to a byproduct. An adaptation is defined as a feature that appears to have been designed for a specific function having adequate “efficiency, precision and economy”

(Williams, 1966). This function may have a complex structure with a clear design toward increasing reproductive success, and can be compared with other species having similar traits, to see if they could have, at some point in their evolutionary history, shared similar selective pressures for that trait (Williams, 1966). Byproducts, on the other hand, are features that share a common developmental origin with an adaptation, but themselves serve no function. Byproducts have an apparently deficient functional design and they often appear rudimentary or reduced relative to the adaptive feature (Puts, 2006). An oft- cited example of a byproduct is the male nipple. While the female nipple serves the obvious function of allowing a mother to provide milk to her offspring, the male nipple, though present, does not serve any such purpose (Symons, 1979). It appears as a reduced version of the female nipple, both in size and elaboration (Puts et al., 2006).

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Based on these expectations regarding adaptations and byproducts, we can evaluate the trait of female orgasm as either a likely adaptation or a likely byproduct.

The female orgasm does not reveal an obvious adaptive function, yet it also does not appear to be a “reduced” version of the male orgasm. In fact, female orgasm is generally considered more complex than male orgasm, with women reporting significantly greater intensity and more frequent back-to-back orgasms than men (Mah & Binik, 2001, 2002;

Masters & Johnson, 1966). In addition, while female orgasm may be less consistent than male orgasm, it does not appear to simply be less present, rather the expression of the trait appears to be patterned, with some women experiencing orgasm only during specific sexual activities, others only with specific partners, and others based on the quality of the sexual experience (Leeners et al., 2013). If the female orgasm is a byproduct, we would expect it to be a vestigial version of the male adaptation, and this does not appear to be the case. Given the psychological complexity and variability of orgasm experience, it appears to have been designed for a specific function.

Another common feature of adaptions is that we expect to see analogous features in other species that have arisen due to similar adaptive challenges. For example, behaviorally freezing or playing dead is a common response to predator threat this is favored in different species. In the case of male orgasm, sperm transfer utilizing some sort of ejaculatory mechanism is a common adaptation found in a wide range of species and taxa (Puts, 2006). Human female orgasm may also have analogs in non-human species, though the data on this is much less substantiated. There is evidence among female non-human primates of sudden changes in behavior observed during copulation, such as body spasms and a characteristic vocalization with facial expression (Chevalier-

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Skolnikoff, 1974), that appear similar to the phenomenon of human female orgasm.

Although sparse, the possible evidence of orgasm in female non-human primates suggests that it is plausible that female orgasm serves an adaptive function. There are two broad classes of adaptive function that have been proposed regarding female orgasm: the good genes hypothesis and the pair-bonding hypothesis. According to the good genes hypothesis, the female orgasm is an adaptation to selectively transport and retain sperm from mates with high genetic quality to increase the probability of a woman conceiving offspring with good genes. The pair-bonding hypothesis, in contrast, suggests that the female orgasm is an adaptation that aids with the selection and/or maintenance of long- term bonding.

Testing the Byproduct Hypothesis

Wallen & Lloyd (2011) have argued that the relationship between female orgasm experience and the distance between a woman’s clitoris and urethra meatus (CUMD), a feature controlled by exposure to prenatal androgens, supports the hypothesis that female orgasm is a byproduct of male orgasm and exists solely due to shared ontogeny.

Analyzing raw data from two previous studies, Wallen & Lloyd found that in each of the two study samples, women who reported experiencing orgasm frequently during intercourse (67% of the time or more), as well as those women who reported ever experiencing orgasm during intercourse, had significantly shorter CUMD distances

(CUMD = 2.0 ± 0.1 cm) than women who had never reported experiencing orgasm during intercourse (CUMD = 2.8 ± 0.1 cm). The researchers in this study argue that because women who have shorter CUMD report higher occurrence of orgasm during sexual intercourse, the female orgasm has more to do with a woman’s anatomical

5 structure than anything else, and that this finding is most consistent with the byproduct hypothesis. This method fails to account for orgasm achieved in any manner other than by penile-vaginal intercourse, however, and would thus miss any patterns that may be relevant if female orgasm is an adaptive function that is not related to conception.

Zietsch and Santtila (2011) attempted to more directly test the byproduct hypothesis by looking at orgasmic function among same- and opposite-sex twins and siblings. If female orgasm is a byproduct of shared ontogeny with males, then, Zietsch and Santtila reasoned, there should be a substantial correlation in orgasm function among opposite sex siblings, with sisters’ orgasm functioning being a reflection of that of their brothers. The researchers assessed the degree of similarity in orgasm function and experience among monozygotic (MZ) male twins, MZ female twins, dizygotic (DZ) male twins, DZ female twins, opposite-sex twins, and non-twin sibling pairs. While the researchers determined that there was a significant degree of heritability in orgasm function based on similarity among MZ male and female twin pairs, the patterns of results suggested that different genes may be involved in determining male and female orgasm function, as there was less correlation between male-female twins or sibling pairs than among DZ twins or non-twin sibling pairs of either sex. These findings, present a major challenge to the byproduct hypothesis.

Although it is particularly hard to rule out a byproduct hypothesis since many of the predictions derived from adaptive hypotheses would also be consistent with a byproduct—for example, the good genes hypothesis might predict that women are more likely to orgasm with men who are more physically attractive, but this would also be the

6 case if female orgasm were a byproduct of male orgasm—the findings from Zietsch &

Santtila present a serious challenge to this idea.

Testing the Good Genes Hypothesis

Some researchers have proposed that the female orgasm serves as a mechanism aiding in the retention of sperm from high quality males. It has been proposed that the ancestral environment of human mating is likely to have included a relatively high rate of sperm competition, in which multiple males may copulate with a female within a given time frame, thus leading to competition for fertilization of the egg among different male’s sperm (see, e.g., Shackelford et al., 2002; Simmons, Firman, Rhodes, & Peters, 2004;

Smith, 1984). Within a context of sperm competition, females are generally expected to have evolved mechanisms of cryptic mate choice, in which the female reproductive system favors fertilization by some sperm over others (see, e.g., Birkhead, 1998;

Birkhead & Møller, 1998; Eberhard, 1996). In birds and other animals, such cryptic choice has been shown to involve mechanisms such as differential sperm retention or expulsion (see, e.g., Pizarri & Birkhead, 2000). If humans also faced an environment in which sperm competition was common, natural selection may have favored the female orgasm as a means of increasing the probability of fertilization of sperm from a specific male (Thornhill & Gangestad, 2008). If the good genes hypothesis is correct, we should expect female orgasm to be correlated with cues to genetic quality of male partners. We might also expect orgasm frequency to be greater during the ovulatory phase of women’s menstrual cycles, when they are most likely to conceive, and to be directly related to the probability of conception. Not all predictions have been tested, and for some, it would be difficult to do so; however, it is important to note some of the evidence we’d expect to

7 see, if the female orgasm was indeed an adaptation for selecting high quality sperm.

Multiple studies have suggested that an individual’s physical, and particularly his sexual, attractiveness is based on features such as low fluctuating asymmetry (FA), muscularity, and other masculine features, and can be used as a reliable cue to genetic quality (see, e.g., Barber, 1995; Gangestad, Garver-Apgar, & Simpson; 2007; Larson, Haselton,

Gildersleeve, & Pillsworth, 2013; Symons, 1980; Thornhill & Gangestad, 1993).

To test whether female coital orgasm may have evolved to aid in selecting the sperm of males with good genes, Shackelford et al. (2000) conducted a study collecting self-reported data from 340 heterosexual women in the United States and Germany.

Participants were asked to rate their partners based on physical and sexual attractiveness and to indicate whether or not they experienced orgasm during their last intercourse with their partner. They were also asked to report how often, on average, they experienced orgasm during sexual intercourse with their partner. The results indicated that, after controlling for age, relationship length and satisfaction, women who rated their partner as more attractive were more likely to have experienced orgasm at last intercourse

(ß = .2071) (SE = 0.833) (Wald = 6.1832) compared to those women who rated their partners as less attractive [insert stats], a pattern the authors interpreted as providing support for the good genes hypothesis.

In 1995, Thornhill, Gangestad, and Comer more directly tested the good genes hypothesis by measuring the bilateral symmetry of the face and body of women’s male sex partners. Bilateral symmetry of the face and body are proposed phenotypic indicators of overall gene quality and developmental health, and could also, according to the authors, be substantially affected by parasite load. Thornhill et al. suggested that favoring

8 individuals with low fluctuating asymmetry (FA) of the face and body is a parasite-driven selective tool of human attractiveness that assists in avoiding parasite prone potential mates. To measure the frequency of female orgasm and its association with male FA, questionnaires were administered to 86 sexually active couples from the University of

New Mexico. The questionnaire addressed self and partner potential future earnings, social potency, investing behaviors, self-professed love for partner, sexual behavior and attitudes, female orgasm and contraceptive use. FA was measured by comparing measurements across multiple bilateral features, such as foot width, ankle width, hand width, ear length, ear width, and elbow width. Photos were also taken and independently rated for physical attractiveness. The researchers found that women with male partners who were more symmetrical, were reported, by both partners, to have experienced more copulatory orgasms. Of the ten predictor variables, male FA was the only variable that significantly predicted orgasm (ß = 0.30, t = -2.54, p < 0.01), indicating that other male features such as access to resources, investing behaviors, and professed love were not related to orgasm frequency. These findings appear to support a sperm selection function of female orgasm over a possible pair-bonding function.

In line with Thornhill et al.’s (1995) predictions of mate attractiveness and orgasm, Puts, Wellin, Burriss, and Dawood’s (2012) study also provided evidence in support of the good genes hypothesis, by testing female reported orgasm frequency and timing in relation to her partner’s masculinity and attractiveness. The good genes hypothesis predicts that not only will women orgasm more frequently during copulation with men with proposed good genetic markers, but that the timing of the woman’s orgasm relative to the man’s orgasm should occur within a specific window of time to

9 increase conceptive potential and the likelihood of obtaining good genes for her offspring

(Baker & Bellis, 1993; Darling, Davidson, & Cox, 1991). In the study conducted by Puts et al., in a sample of 110 sexually active heterosexual couples, men and women were photographed and issued a questionnaire that asked about their own and their partner’s attractiveness. Women were asked about their partner’s masculinity and dominance, and men were asked to rate their own dominance, masculinity and their partner’s femininity; each were also asked questions regarding frequency of orgasm during various sexual activities. The results showed that women partnered with men who were rated as more attractive were more likely to experience orgasm in the purported conceptive window during or after male orgasm than women whose partners were rated as less attractive

(ß = 0.5, S.E. = .0833, Wald = 6.1832). These findings, as well as those of Shackelford et al., (2000) and Thornhill et al. (1995) described above, provide compelling evidence that, within pairs, women’s frequency of orgasm is related to the expression of purported cues of genetic quality by their male partners.

In addition to the correlations of orgasm frequency with partner genetic qualities, researchers have also investigated the physiological mechanism by which cryptic female choice may be occurring in humans. In 1993, Baker and Bellis set out to address the relationship between female orgasm and sperm retention. From the good genes perspective, greater amounts of ejaculate from males with good genes should be retained in the female reproductive tract compared to that of males with lesser genetic quality. For this type of manipulation to take place, we must first look for evidence that supports a mechanism, by which preferential sperm, could be retained. Baker and Bellis asked 32 sexually active heterosexual couples to collect the flowback of seminal fluid that was

10 ejected from the women’s vagina post-copulation, and to also record the timing of her orgasm relative to the timing of her partner’s ejaculation. According to Baker and Bellis, lesser quantities of sperm were expelled if the woman’s orgasm occurred no more than one minute prior to the male’s ejaculation and no more than 45 minutes after the male’s ejaculation. Greater amounts of sperm were expelled if the woman’s orgasm occurred more than one minute before ejaculation by the male, suggesting that timing of female orgasm and male ejaculation influenced the quantity of sperm retained after insemination.

Because greater ejaculate amounts house a greater number of sperm, Baker and Bellis argued that the greater amount of ejaculate retained, the greater the opportunity for conception. They proposed that the method by which this could occur is via a blow-suck mechanism, created by the orgasm, that aids in the transportation of sperm from the vagina into the cervix (Baker & Bellis, 1993). It is important to note that, while the results reported in this study are often interpreted as evidence supporting sperm retention, the volume of the ejaculate itself is not known for these data. As there is high within- subject variation in ejaculate size, based on numerous factors (Schwartz, Laplanche,

Jouannet, & David, 1979), it is uncertain that simply measuring the volume of flowback can provide an accurate account of the amount of sperm retained. Because of this, accuracy of the volume inseminated is questioned, and because methods are of concern, the evidence supporting the argument are weak.

Other evidence that has been suggested as supporting the sperm selection hypothesis is a typology of orgasms constructed by King, Belsky, Mah, and Binik (2010).

These researchers conducted a study with 503 women, in which the participants provided descriptions of orgasms experienced both with a partner and through self-stimulation,

11 using previously developed scale of orgasm experience. The participants were asked to rate a number of adjectives for how well they described their most recent orgasm experience. Each of the adjectives were rated on a six-point scale and were combined to create 10 composite scores: including sensations of building, flooding, flushing, shooting, throbbing, general spasms, pleasurable satisfaction, relaxation, emotional intimacy and ecstasy. From this analysis, four orgasm types for pleasure and sensations were revealed.

Type I were marked by high pleasure and high sensations of building, flooding, flushing, spurting, and throbbing, and involved general spasm, emotional intimacy and relaxation.

Type II orgasms were defined by high pleasure with medium sensations relating to pleasure but lower feelings of relaxation and internal sensations. Type III labeled medium pleasure and medium sensations received low scores in sensations associated with pleasure, satisfaction and internal sensations. Lastly, Type IV orgasms received low scores in adjectives describing pleasure and sensation Type I and II orgasms were grouped to form the orgasms that were labeled “good sex” as they received high pleasure and sensations scores; Type III and IV were considered “not-as-good-sex” orgasms for their lower ratings. It was concluded that spasming was typical during “good sex,” and it was proposed that spasming may be related to the quality of insuck described by Baker and Bellis (King et al., 2010). Subsequently, in 2012, King and Belsky conducted a follow up study to the 2010 research. They surveyed 265 females between the ages of 18 and 76, about their orgasm experience and their partners’ characteristics, as well as orgasm sensations and location. It was found that Type I orgasms were characterized by having a greater internal sucking sensation (70%) than Type II (28.3%), and more likely to be described as originating deep inside (Type I = 70.2%, Type II = 28.3%).

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Additionally, Type I orgasms were more likely to happen during sexual intercourse with a partner (70.7%) whereas Type II orgasms were more likely to occur during self- stimulation (48.8%). Although the relationship between these experienced sensations and any physical effect of sperm transport or retention is as yet unknown, the authors suggested that it may be possible to use self-assessed orgasm sensations to indicate orgasms that might assist in the sperm selection.

The good genes hypothesis is surrounded by some weakness in addition to those already mentioned. These additional weaknesses include the fact that no study has produced evidence that it is directly linked to conception or any reliable measure of how much orgasm can, or might increase probability of conception. Moreover, if orgasm perpetuates sperm selection, we would expect to see some correlation to orgasm occurrence with regard to ovulation and support for that is yet to be documented in the literature.

Testing the Pair-bonding Hypothesis

The Pair-bonding Hypothesis suggests that the female orgasm could be an evolutionary adaptive feature that facilitates pair-bonding, however there is a great deal of inconsistency in how that phrase is used. Some researchers have argued that orgasm may serve to reinforce the social bond and should therefore be related to the value of the relationship (see, e.g., Costa, Brody, 2007). Others suggest that the female orgasm may indicate to a woman that she is in a relationship with a good investing partner, which then motivates the women to remain in the relationship (see, e.g., Gentle, 2011). Common to both of these perspectives, however, is the idea that female orgasm, like human female sexual behavior more broadly, is likely to serve functions beyond conception.

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Humans sexuality is characterized, among other things, by an extremely extended sexuality, that is, humans regularly have sex at times when conception is not possible

(Symons, 1980). This is not completely unique to humans. Females in many primate species, do not restrict sexual activity to when they are fertile (see, e.g., Fürtbauer,

Heistermann, Schülk, & Ostner, 2011; Grebe, Gangestad, Garver-Apgar, & Thornhill,

2013; Manson, Perry, & Parish, 1997). Hrdy (1996) showed that sexual solicitations in monkey and apes were observed not only during female estrus, but also during non-peak fertility times.

These studies suggest that sex is used for purposes outside of conception, and has been hypothesized to serve a social bond function. In bonobos, for example, females engage in sexual activity not only outside of the fertile window, but also with other females and sometime with juveniles, partners with whom conception is not possible

(Kuhle, 2014). It has been suggested that engaging in these behaviors could have facilitated relationships that made alloparental care possible (Kuhle, 2013). It is of particular note that alloparents need not be biological parents, and, in fact, other females are likely to be the best source of alloparental care among bonobos, among whom sexual behavior clearly serves a social function.

The hormone oxytocin has been shown to play an important role in both the experience of orgasm and in pair-bonding. In a 1987 study, Carmichael et al. assessed oxytocin levels in men and women prior to self-induced orgasm, and again during orgasm/ejaculation. Results showed higher levels of oxytocin during arousal, and a significant increase in levels, among women, during orgasm. In another study, a connection between oxytocin and pair-bonding has been shown in monogamous prairie

14 voles (Insel & Hulihan, 1995). Researchers injected female prairie voles with oxytocin, and found that 10 of 11 oxytocin-injected females, showed an increase in the amount of contact (side-by-side sitting) with a particular male vole, spending twice as much time with her preferred partner than with a novel mate. partner preference. With this evidence,

Insel and Hulihan argue that there is a connection between the release of oxytocin in the female vole, and partner preference. Together, these results point towards a possibility that during the female orgasm, the release of increased levels of oxytocin can induce or strengthen a pair-bond with a particular male partner.

If female orgasm plays a role in maintaining pair-bonds, then female orgasm should also be related to qualities of the dyad, such as the degree to which the two partners can understand one another, and/or relationship-related qualities of the partner, such as his generosity or kindness. To test orgasm as a potential signal of good relationship quality, Costa and Brody surveyed 30 Portuguese women on their orgasm rates, frequency of different sexual behaviors and perceived relationship quality. They hypothesized that only sexual behavior that is relevant to potential gene propagation would be correlated with better physiological and psychological functioning; meaning that only penile-vaginal intercourse orgasm would produce the most significant correlation with relationship quality, as it is the method for potential reproduction. The results of the study found that penile-vaginal orgasm frequency was indeed positively correlated with perceived relationship quality components (satisfaction, intimacy, passion, and love) (all r ≥ .44) and non-coital orgasm experiences with a partner were uncorrelated with relationship quality.

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Another version of the pair-bonding hypothesis suggests that orgasm may be a response to cues of a sexual partner’s investing qualities. Many studies have shown that a partner’s access to resources is of greater importance to women when choosing a long- term romantic partner than it is to men, and this pattern has been interpreted as the result of differential costs of reproduction (Buss, 1989; Buss & Barnes, 1986; Li, Bailey,

Kenrick, Lisenmeier, 2002; Trivers, 1972). In 2009, Pollett and Nettle tested the relationship between reported orgasm and partner investing qualities in 1534 Chinese

Women (Pollett & Nettle, 2009a). They initially reported that partner’s income significantly predicted orgasm frequency among women, however, that same year, Pollett and Nettle published a correction. The correction reveals that the model used did not correctly fit the study, and once the proper control variables were included in the analysis, partner’s income no longer significantly predicted orgasm frequency (Pollett &

Nettle, 2009b).

The literature on the pair-bonding hypothesis has some substantial overall weaknesses. The lack of clarity regarding the hypothesis makes it difficult to determine differences between characteristics that are considered good dyadic qualities (partnering or compatibility) and those that are related to resources.

Current Study

Research on female orgasm to date has focused almost exclusively on the good genes hypothesis, and has focused on establishing a correlation between orgasm frequency and a partner’s cues to genetic quality. One way to differentiate between a conceptive function of orgasm and a non-conceptive function, such as pair-bond

16 maintenance, is to compare orgasm experience between potentially conceptive pairs (i.e., heterosexual couples) and non-potentially conceptive pairs (i.e., homosexual couples).

The evidence for the good genes hypothesis has not addressed a direct link between orgasm and conception, and because there are several other predictions that testing either has not yet addressed or has not yet been supported, the hypothesis is not adequately substantiated. Among these predictions, include orgasm in non-heterosexual sex. Given the lack of evidence supporting orgasm as a mechanism for sperm retention and the byproduct hypothesis, I predict that the female orgasm likely serves to reinforce or strengthen a pair bond. Its role in facilitating oxytocin release, has been proven to increase partnering behaviors in humans and other species. Additionally, the supporting evidence addressing orgasm occurrence in association with investing qualities that are linked to things like social and material resources is also lacking.

The purpose of this study is to provide a test between the good genes hypothesis and the pair-bonding hypothesis by examining the experience of orgasm in potentially conceptive pairs (heterosexual couples) and non-potentially conceptive pairs

(homosexual couples), and its relationship to different partner qualities.

Hypothesis

This study will test predictions from two hypotheses:

1. The female orgasm evolved as a sperm selection mechanism (good genes

hypothesis).

2. The female orgasm evolved as a pair-bond maintenance mechanism (pair-

bonding hypothesis).

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Predictions

Hypothesis 1.

Prediction 1. If the female orgasm evolved as a sperm selection device, then heterosexual women should orgasm with more frequency than non-heterosexual women.

Prediction 2. If the female orgasm evolved as a sperm selection device, then partner’s genetic qualities (physical attractiveness) will predict orgasm frequency in heterosexual women, to a greater extent than in non-heterosexual women.

Prediction 3. If female orgasm evolved as a sperm selection device, then non- genetic partner qualities should be less related to orgasm frequency than partner’s genetic qualities (attractiveness).

Prediction 4. If female orgasm evolved as a sperm selection device, heterosexual women should be more likely to report deep orgasm and orgasm the produces an internal sucking sensation.

Prediction 5. If female orgasm evolved as a sperm selection device, then deep orgasm and internal sucking sensations should be predicted by partner genetic quality.

Hypothesis 2.

Prediction 1. If female orgasm evolved to reinforce or maintain pair-bonding, then heterosexual and non-heterosexual women should orgasm with similar frequency.

Prediction 2. If female orgasm evolved to reinforce or maintain pair-bonding, then investing qualities should be more related to orgasm frequency than genetic or resource quality.

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Prediction 3. If female orgasm evolved to reinforce or maintain pair-bonding, then partner investing qualities should predict orgasm frequency similarly among heterosexual and non-heterosexual women.

Prediction 4. If female orgasm evolved to reinforce or maintain pair-bonding, then deep orgasm and internal sucking sensation should be of similar frequency among heterosexual and non-heterosexual women.

Prediction 5. If female orgasm evolved to reinforce or maintain pair-bonding, then deep orgasm and internal sucking sensation need not be predicted by partner’s genetic qualities.

Table 1. Predictions Based on Three Hypotheses

Byproduct Sperm Selection Pairbonding Hypothesis Hypothesis Hypothesis

Non- Non- Hetero Non-Hetero Hetero Hetero Hetero Hetero Orgasm Frequency - -   - - Predictors of Orgasm Frequency Partner physical attractiveness    - - - Partner resources ------Partner investing quality - - - -   Experience of Type I Orgasm - -   - - Predictors of Type I Orgasm Partner physical attractiveness - -  - - - Partner resources ------Partner investing quality ------

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CHAPTER 2

METHODS

Materials

Participants took an online survey which asked questions concerning their sexual orientation and relationship type, sexual response history, perception of partner’s physical attractiveness and investing qualities, sexual, emotional and overall satisfaction with their partner, perception of self, sociosexuality (SOI-R) and demographic information. To control for variation in orgasm produced by intercourse as opposed to external stimulation, we asked participants to respond separately regarding penetrative and non- penetrative sexual activities. Participants who identified as non-heterosexual were not provided questions addressing penile vaginal intercourse.

Procedure

Participants were provided a link to the Qualtrics website (a web based survey tool) address which gave them access to the survey. Respondents were given a code at the end of the survey, which could be used in an opportunity drawing for a gift card. The submission of the code was optional.

Measures

Outcome Variables

Orgasm frequency, orgasm centrality, internal sucking sensation and duration of the relationship were used as outcome variables for this study. Participants were asked to

20 rate the frequency with which they experienced orgasm when engaging in various sexual activities (i.e. self-stimulation with no penetration, self-stimulation with penetration, sex with another person with no penetration, sex with another person with penetration (non- penis), and penile-vaginal sex (for heterosexual women only)), using a 100-point sliding scale from “never” (0) to “always” (100). Questions addressing orgasm centrality and presence of internal sucking sensation were based on King & Belsky (2012) and included the following: “Did you experience any internal sucking sensations?” with multiple choice options of “none”, “weak”, “moderate” strong,” and “Where was your orgasm centered?” with multiple choice options being “on the surface of the genitals” or “deep inside.” For the purposes of examining orgasm frequency between the two groups, we decided to combine variables for orgasm frequency during non-penetrative sex with partner, and orgasm frequency during penetrative sex with partner, to create an overall frequency of orgasm during sex with a partner.

Predictor Variables

The predictor variables for this study included partner’s genetic, resource and long-term investing qualities.

Genetic Quality. As mentioned previously, we do not measure genetic quality directly, but we use physical attractiveness to measure genetic quality, as it has been suggested that physical attractiveness can serve as a reliable cue to genetic quality (see, e.g., Gangestad et al., 2007) To measure partner’s physical attractiveness, a composite measure was created using the following survey questions: “How attractive would you rate your partner’s body?” “How attractive would you rate your partner’s face?” and

“How attractive would you rate your partner’s sexual desirability?” The same questions

21 were asked with respect to how other women would rate the participant’s partner’s face, body and sexual desirability. Each question was presented to the participant using a slider scale where the minimum value (0) represented “Not at all attractive” and the maximum value (100) represented “Extremely attractive.” To produce an overall measure for partner’s genetic quality, these six questions were averaged together to create a single composite variable (α = 0.9194), labeled “physical attractiveness.”

Resource and Investing Qualities. Partner resource and investing qualities were assessed with a single scale that included 14 items. Factor analysis confirmed two distinct subscales, which corresponded to partner’s financial and social status (resources) and partner’s kindness, generosity, and parenting qualities (investment).

Partner’s resource qualities were assessed with the following questions: “How would you rate your partner’s current social status?” “How would you rate your partner’s potential future social status?” “How would you rate your partner’s current financial resources?” and “How would you rate your partner’s future potential financial resources?” The same questions were asked with respect to how other women would rate the participant’s partner’s resource qualities and social status. Each question was presented to the participant using a slider scale, where the minimum value (0) represented

“Extremely low” and the maximum value (100), represented “Extremely High.” To produce an overall measure for partner’s resources, all questions concerning partner’s financial resources and social status were combined and averaged together to create the variable “resource qualities” (α = 0.9132).

Partner’s qualities as an investing partner were assessed by asking “How caring is your partner?” “How good with children is your partner?” “How kind is your partner?”

22 and “How would you rate your partner’s social dominance?” The same questions were asked with respect to how other women would rate the participant’s partner’s caring qualities. Each question was presented to the participant using as slider scale, where the minimum value (0) represented “not at all”, and the maximum value (100) represented

“extremely.” To produce an overall measure for partner’s long-term investing qualities, all questions concerning partner’s investing qualities were combined and averaged together to create the variable “caring qualities” (α = 0.8455).

Control Variables. In addition to the central predictor variables, we also assessed potential covariates to use as control variables the statistical model. One of these was relationship length, which has been shown to correspond to orgasm experience.

The other was sociosexuality, assessed using the SOI-R (Penke, 2011). Sociosexuality is a measure of orientation toward short- or long-term mating strategies and includes measures of both attitudes and behaviors regarding uncommitted sex and sexual variety

(Simpson & Gangestad, 1991). This measure was included because it is possible that orgasm experience is related to women’s openness with sexuality, however since women’s responses on the SOI-R did not correlate with any of the other predictor or outcome measures of interest, it was not included in the statistical models.

23

CHAPTER 3

RESULTS

Participants

The protocol used for this study was approved by the Institutional Review Board of California State University at Fullerton. Participants included a total of 113 women

(Mage = 32.12, SDage =.839) 93 heterosexual women (Mage = 32.51, SDage, = 8.73) and 20 non-heterosexual women (Mage = 30.3, SDage, = 9.81), who were all 18 years or older and currently involved in a sexual relationship. 55.66% of the respondents identified as

Caucasian, 21.70% as Hispanic or Latino/a/x, 17.92% as African American, 1.89%

Asian, 1.89% indicated “Other” and 0.94% identified as Native Hawaiian or Other

Pacific Islander.

Participants were recruited via Instagram and Facebook (social networking outlets) and flyers that were passed out and posted on California State University

Fullerton’s campus, as well as University of California Riverside’s campus. Prior to being directed to the survey, all participants were informed that their participation in the research study was completely voluntary, and that they may choose to not answer specific questions or stop participation at any time during the survey, without penalty.

For the purposes of this study, frequency of orgasm was used to test predictions; however, we looked at preference and ease of orgasm via different activities as well, and found a significant difference between heterosexual and non-heterosexual women in the

24 ease of orgasm, during self-stimulation with penetration. We also found a marginal difference in ease of orgasm during sex with a partner (penetrative & non-penetrative).

Table 2. Descriptive Statistics

Hetero Non-hetero Difference Stimuli (SD) (SD) t (p) Ease of orgasm self-stimulation, no 78.79 67.116 1.511 (0.13) penetration (28.53) (34.56) Ease of orgasm self-stimulation, 51.74 71.31 (34.6) 1.868 (0.06)* w/penetration (36.78) Ease of orgasm w/partner, no 64.97 75.68 -1.591 (0.11) penetration (25.77) (26.62) Ease of orgasm—combined 65.77 76.47 penetration & non-penetration -1.80 (0.07)* (19.09) (27.24) orgasm with other person) Preferred Orgasm Experience Non-Hetero (mean ranking Hetero (mean (ranking order) value) ranking value) Penile Vaginal Penetration 1.8 Sex w/partner, w/penetration 2.3 2.6 Sex w/partner, no penetration 1.9 2.8 Self-stimulation, no penetration 2.3 3.1 Self-Stimulation, w/penetration 3.5 3.7

Note: for preferred orgasm (in ranking order) 1 = most preferred, 5 = least preferred. * p < .1*

Analyses

All analyses were conducted using Stata14 (StataCorp. 2015. Stata Statistical

Software: Release 14. College Station, TX: StataCorp LP). Because respondents were allowed to stop participating at any time, or choose to not answer specific questions, not all women in the study provided responses to each question, so n’s are reported for each analysis.

25

Tests of Hypotheses

Prediction 1: Orgasm Frequency in Heterosexual and Non-Heterosexual Women

We found very few differences in frequency of orgasm between heterosexual and non-heterosexual women, with the exception of frequency of non-penetrative sex (see

Table 2).

Table 3. Frequency of Orgasm with Different Stimuli

Non- Hetero hetero Difference Stimuli (SD) (SD) t (p) Frequency of orgasm self-stimulation, no 82.71 79.884 0.383 penetration (28.47) (29.01) (0.702) 72.35 55.806 1.471 Frequency of self-stimulation, w/penetration (4.95) (.806) (0.146) Frequency of orgasm w/partner, no 69.13 86.066 -2.303 penetration (29.84) (17.43) (0.02)** 74.26 73.98 0.035 Frequency of orgasm w/partner, w/penetration (3.04) (7.98) (0.971) Frequency of orgasm- combined penetration 72.72 79.63 0.035 & non-penetration orgasm with other person (19.99) (21.88) (0.225)

** p < .05

Predictions 2-3: Effects of Partner Qualities on Orgasm Frequency

Before testing the effects of partner qualities on orgasm frequency, we first ran a series of two-sample t-tests to examine mean variance in the two groups’ evaluations of their partner’s physical attractiveness, resource qualities, and long-term investing qualities. We found no differences in how heterosexual and non-heterosexual women evaluated their partner’s physical attractiveness (t = -1.1, p = 0.28), resource qualities

(t = -0.36, p = 0.72), or investing qualities (t = -0.42 p = 0.68; see Table 4).

26

Table 4. Two-Sample t-Tests Reporting between Group Difference in How They Rate Their Partners

Hetero Non-hetero Difference (SD) (SD) t (p) Physical Attractiveness 78.5 (17.97) 83.6 (16.5) -1.1 (0.28) Resources 69.4 (19.6) 71.2 (14.3) -0.36 (0.72) Long-term investing (compatibility) 85.4 (17.0) 87.3 (16.0) 0.42 (0.68) Time Involved w/partner 8.7 (8.44) 2.74 (2.54) 3.11 (0.002)*** SOI_R 3.44 (1.4) 3.6 (1.37) -0.4 (0.68) Orgasm center .582 (.496) .411 (.51) 1.28 (0.20) Internal Sucking .610 (.490) 0.647 (.49) -0.279 (0.78) ** p < .05, *** p < .01

We then ran a single multiple regression model with orgasm frequency as the outcome variable, and partner attractiveness, partner resources, and partner investing qualities as predictors, as well as the interaction of each predictor with sexual orientation.

Relationship length was included in the model as a control variable. There was a significant difference between heterosexual (M = 8.7, SD = 8.44) and non-heterosexual women (M = 2.74, SD = 2.54) in our sample for time involved in the relationship (t =

3.11, p = 0.002). Because of this significant difference, we chose to include it as a control variable in the test of main effect and interaction. There was a positive main effect of time involved on orgasm frequency (t = 2.41, p = 0.019), as well as an interaction of time involved and sexual orientation on the effect of relationship length (t = 2.01, p = 0.049)

(see Figure 2).

Partner Physical Attractiveness

Across sexual orientation, partner’s physical attractiveness had no main effect on frequency of orgasm (t = -0.29, p = 0.77); however, there was an interaction of genetic

27 quality and sexual orientation on orgasm frequency, such that the effect of partner attractiveness significantly predicted orgasm frequency for non-heterosexual women, but not for heterosexual women (t = 2.51, p = 0.01). This interaction is in the opposite direction from what was predicted (see Figure 1).

Partner Resource Qualities

There was no main effect of partner resources on orgasm frequency (t = 0.75, p = 0.45), and no interaction of orientation and partner resources on orgasm frequency

(t = -0.61, p = 0.54).

Partner Long-term Investing Qualities

There was a positive, marginal, main effect of partner investing qualities on orgasm frequency. Across orientations women experience more orgasm frequency with more compatible partner’s. We found a marginal interaction of sexual orientation and partner investing qualities on orgasm frequency (t = -1.71, p = 0.091). The effect of partner’s investing qualities on orgasm frequency is marginally greater for heterosexual women than non-heterosexual women (t = -1.78, p = 0.08).

Table 5. Main Effect and Interaction of Variables Predicting Frequency of Orgasm

Frequency of orgasm during penetrative or non- penetrative sex with a partner. Main Effect Interaction Good Genes 0.29 (0.77) 2.51 (0.01)** Investing -1.78 (0.08)* -1.71 (0.09)* Resources -0.75 (0.45) -0.61 (0.54) Time Involved in the relationship 2.41 (0.019)** 2.01 (0.04)**

* p < .1, ** p < .05

28 120 100 80 60 Orgasm Frequency (predicted values) (predicted Frequency Orgasm 40

0 20 40 60 80 100 Partner Physical Attractiveness

Hetero Non-Hetero Hetero Non-Hetero

Figure 1. Orgasm frequency as as function of partner physical attractiveness, by participant sexual orientation

120 100 80 60 Orgasm Frequency (predicted values) (predicted Frequency Orgasm 40

0 2 4 6 8 10 Relationship Length in Years

Hetero Non-Hetero Non-heterosexual Heterosexual

Figure 2. Orgasm frequency as a function of relationship duration, by participant sexual orientation

29

Predictions 4-5: Effects of Sexual Orientation and Partner Qualities on Type I Orgasms

To test whether heterosexual women in our sample were more likely to experience orgasms that were characterized by sensations that could potentially be associated with sperm retention, we first ran an independent t-test comparing heterosexual and non-heterosexual women’s responses to orgasm location (deep vs. surface) and experience of internal sucking sensation. Because location of orgasm center

(deep or surface) and presence of internal sucking sensation, are both binary variables, for each we ran a logistic regression with the presence or absence of the orgasm feature as the outcome variable, and sexual orientation, partner physical attractiveness, partner resource qualities, partner investing qualities, and the interaction of sexual orientation with each of the partner quality measures as predictor variables. Relationship length was again included as a control variable.

Deep Orgasm

In comparing heterosexual and non-heterosexual women’s responses for orgasm location, the results produced no significant difference in reported orgasm location, between the two groups for deep orgasm (deep vs. surface t = 1.28, p = 0.20). The results of the logistic regression, showed that none of our variables of interest predicted orgasm centrality (see Table 6).

Internal Sucking Sensation

In comparing heterosexual and non-heterosexual women’s responses for internal sucking sensations (presence of internal sucking t = -0.28, p = 0.78). The results of the logistic regression, showed that none of our variables of interest predicted the presence or absence of an internal sucking sensation (see Table 6).

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Table 6. Logistic Regression for Variables Predicting Likelihood of Orgasm Centrality and Internal Sucking Sensation.

Deep vs Surface Odds Internal Sucking Sensation Odds Predictor Variables Ratio (p) Ratio (p) Partner .984 (0.31) 1.02 (0.16) Physical 1 (0.62) .973 (0.11) Attractiveness Resources 1.01 (0.37) 1.01 (0.46) Time Involved 1.01 (0.54) .952 (0.15)

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CHAPTER 4

CONCLUSIONS

In conclusion, the results from this study provided more support for the pair- bonding hypothesis than there is for the sperm selection hypothesis, but were only able to modestly differentiate between the pair-bonding hypothesis and the byproduct hypothesis

(see Table 7). There was no overall difference between heterosexual and non- heterosexual women in either the frequency of orgasm in general (Prediction 1) or the experience of Type I orgasms purported to be related to increased sperm retention

(Prediction 4). There was also no evidence in support of the prediction that partner’s physical attractiveness would be a better predictor of either orgasm frequency (Prediction

2) or Type I orgasm (Prediction 5) in heterosexual women. In fact, partner physical attractiveness had a greater effect on orgasm frequency in non-heterosexual women than heterosexual women, a result that was not predicted by any of the hypotheses.

In contrast, the pattern of effects regarding partner investing qualities provided marginal support for the pair-bonding hypothesis. There was a marginally significant main effect of partner investing qualities showing that, across sexual orientations, women experience more frequent orgasms with partners rated more highly on features related to relationship quality, such as kindness and generosity (Prediction 3). There was a significant interaction of sexual orientation and partner investing quality such that the

32 effect of partner investing qualities on orgasm frequency was marginally greater for heterosexual women compared to non-heterosexual women.

Table 7. Results Compared to Predictions

Byproduct Sperm Selection Pairbonding Hypothesis Hypothesis Hypothesis Results

Non- Non- Non- Non- Hetero Hetero Hetero Hetero Hetero Hetero Hetero Hetero Orgasm Frequency - -   - - - - Predictors of Orgasm

Frequency Partner physical - - - - attractiveness     Partner resources ------Partner investing - - - - quality     Experience of Type I ------Orgasm   Predictors of Type I

Orgasm Partner physical - - - - - attractiveness - -  Partner resources ------Partner investing - - - - quality - - - -

Partner’s resources, a quality that has been predicted by other studies to correlate with female orgasm if orgasm serves a pair-bonding function, did not predict orgasm frequency in either sample group, and there was no interaction of sexual orientation and partner’s resources on orgasm frequency. Relationship length, which was included in all tests as a control variable, was positively correlated with orgasm frequency across sexual orientation, but this effect also interacted with sexual orientation such that the effect of relationship length was stronger among heterosexual women than among non- heterosexual women in the sample.

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CHAPTER 5

DISCUSSION

The good genes hypothesis suggests that the female orgasm is an evolutionary adaption preferential transport and retention of sperm from partners with high genetic quality (Baker & Bellis 1993; Shackelford et al., 2000; Thornhill & Gangestad, 2008).

We tested this hypothesis in two different ways: (1) looking at orgasm frequency in potentially conceptive and non-conceptive pairs, based on partner’s physical attractiveness (a purported indicator of good genes); and (2) by determining the likelihood of reported deep orgasm and the presence of internal sucking sensations during orgasm (Type I orgasms), in heterosexual and non-heterosexual women. If the good genes hypothesis is correct, and orgasm is an adaptation for retaining the sperm of males with high genetic quality, then we predicted partner’s physical attractiveness would predict frequency of orgasm, and do so to a greater extent in heterosexual compared to non-heterosexual women, as the potential genetic benefit differs between the two groups.

In contrast to these predictions, we found that partner’s physical attractiveness had no effect on orgasm frequency among heterosexual women, but did positively predict orgasm frequency among non-heterosexual women. This pattern was not predicted a priori, by any of the three hypotheses being tested, but could provide support for the byproduct hypothesis. Several studies have suggested that an effect of partner attractiveness on orgasm frequency could support the byproduct hypothesis as well as the

34 sperm retention hypothesis since partner attractiveness is generally expected to be of relevance to male mate preferences (e.g., Buss & Barnes, 1986) and therefore an effect of physical attractiveness on female orgasm could also be explained as a byproduct of the male pattern (see, e.g., Wallen & Lloyd, 2012). We suggest that the pattern that we observed, whereby the physical attractiveness of female sexual partners (i.e., the partners of non-heterosexual women) had a greater effect on women’s orgasm than the physical attractiveness of male sexual partners (i.e. the partners of heterosexual women) may actually be a stronger argument in favor of the byproduct hypothesis than a general effect of partner physical attractiveness on orgasm frequency. If female orgasm is a byproduct of male orgasm, then it seems likely that it would be influenced by features of a partner’s physical attractiveness that would be related to male reproductive success, that is, feminine characteristics of physical attractiveness. No previous studies have investigated the effect of female physical attractiveness on women’s experience of orgasm. This pattern should be interpreted with caution, however, due to the small number of non- heterosexual women in our sample.

If the characteristics of deep centered orgasms are consistent with possible oxytocin action (King, Belsky, Mah, & Binik; 2010), and a potential mediator of the peristaltic mechanism associated with creating insuck sensations (King & Belsky, 2012) and thus potentially related to likelihood of conception, then we should predict that heterosexual women should be more likely to experience deep orgasms than non- heterosexual women if female orgasm evolved as a sperm selection mechanism.

Additionally, the presence of internal sucking sensation should be more often reported in heterosexual women. What we found in our sample of women, did not support this

35 prediction, as it showed that heterosexual women were no more likely to experience deep orgasm or internal sucking sensations than were non-heterosexual women. This prediction, however, is founded a number of as-yet unsubstantiated assumptions. There is no direct evidence that these orgasm sensations are indeed related to any sort of

“upsuck” mechanism, nor is there any direct evidence that such an “upsuck” phenomenon increases conception probability. In addition, the possible relationship between orgasm sensations and the release of oxytocin could mean that such sensations could be just as easily related to a pair-bonding function of female orgasm. Further research is needed to make a more refined examination of this; however, in our sample, neither sensations could be correlated to orgasm frequency or sexual orientation.

Many of the predictions of the study regarding the pair-bonding hypothesis are actually predictions of null effects (contrasted to the positive predictions made by the sperm selection hypothesis). In particular, we suggest that a lack of difference in orgasm frequency between heterosexual and non-heterosexual women is more consistent with the pair-bonding hypothesis than with the sperm selection hypothesis, and that the physical attractiveness of a sexual partner should not be more relevant than other features in predicting orgasm frequency if orgasm is related to pair-bonding. The one positive prediction based on the pair-bonding hypothesis is that partner investing qualities should be more predictive of orgasm frequency than potential indicators of genetic quality, and that this effect should not vary substantially by sexual orientation. We found support for this positive prediction, in that across sexual orientation, partner investing qualities positively predicted orgasm frequency. We did observe a marginal interaction of partner investing qualities and sexual orientation with partner investing qualities having a

36 marginally greater effect on orgasm frequency among heterosexual as opposed to non- heterosexual women. Again, these results in general are supportive of the pair-bonding hypothesis, but suffer from a very small sample of non-heterosexual women. Further investigation, with a larger sample of non-heterosexual women, might yield more detailed results, particularly because main effect and interactions for partner quality were both marginal.

In previous studies, partner resources have been predicted to be related to orgasm frequency if female orgasm serves a pair-bonding function (see, e.g., Pollett & Nettle,

2009a, 2009b). This prediction has been based on the characterization of partner resources as an important “long-term” mate quality (see, e.g., Buss, 1989; Gildersleeve,

Haselton, & Pillsworth, 2013) We suggest that this prediction is based on an inaccurate interpretation of both the importance of resources in a long-term mate and the role of orgasm in pair-bonding. While resources have been shown many times to weigh more heavily in women’s long-term mate preferences compared to men’s long-term mate preferences (see, e.g., everything), this is not the feature that is most predictive of either relationship quality or longevity (see, e.g., Buss, 1989). We suggest that if female orgasm serves a pair-bonding maintenance function, then it should be more closely related to dyadic qualities, that is, features related to the long-term prospects of the relationship (which we operationalized as partner investing qualities). Future studies could further disambiguate these ideas by more directly assessing dyadic qualities, such as compatibility, shared world-view, or ratings of partner personality and sense of humor

(as suggested by Pillsworth, 2008).

37

Finally, in our study as in previous studies, we find only weak support for the pair-bonding hypothesis over the byproduct hypothesis. This is in part because of the difficulty in identifying discriminating predictions as many of the predictions from either the sperm selection hypothesis or the pair-bonding hypothesis would also be consistent with what we should expect to see if female orgasm is a byproduct of adaptive features of male orgasm. In sum, while the results of this study provide somewhat stronger support for the pair-bonding hypothesis over the sperm selection hypothesis of female orgasm, there are still many areas that require further investigation.

Future Direction

In our opinion, the areas most in need of further investigation are 1) directly testing whether or not orgasm increases conception probability, 2) more carefully defining the pair-bonding hypothesis and delineating proper predictions, and 3) finding predictions that will more clearly differentiate between either of the adaptive hypotheses and the byproduct hypothesis.

Limitations

There are a several limitations to this study. Because the questionnaire did not ask questions concerning menstrual cycle or ovulatory cycle, we could not control for this in the data. Because conception is not possible during the entire month, being able to account for timing of a woman’s cycle, would have been beneficial to help strengthen and narrow predictive variables. Additionally, there are limitations to working with self- reported data, as there is often a small margin for subjectivity, when the participant is interpreting the question. Also, asking a respondent to recollect information about their past sexual behaviors could be cause for the incorrect reporting of data; it may be

38 difficult for the participant to provide truly correct answers when trying to recall details of these instances and behaviors.

Furthermore, it is important to recognize that while predictions 1-5 for hypothesis

1, assumes there would be differences between non-conceptive and potentially conceptive pairs, these women, biologically, are capable of conceiving, so the psychological mechanisms surrounding the female orgasm, may not have “caught up” evolutionarily enough, to produce differences in response patterns, between heterosexual and non-heterosexual women. Lastly, the most restricting limitation to this research project, is the sample size of non-heterosexual women obtained. Because we were only able to recruit 30 non-heterosexual women, with an even smaller amount who completed most of the questions on the survey, we should remain mindful of this when considering the interpretation and results produced.

39

APPENDIX

QUESTIONNAIRE

1. What is your age?

2. How would you describe your sexual orientation? (check one)

 Heterosexual (primarily attracted to the opposite sex)  Homosexual (primarily attracted to the same sex)  Bisexual (equally attracted to both sexes)  Unsure  Other

2a. If you selected "bisexual," "unsure," or "other" as your sexual orientation, please indicate the sex of the person with whom you most recently had a sexual relationship.

o Female o Male

3. Are you currently involved in a romantic relationship in which you are sexually active? ("Sexually active" can refer to any sort of sexual activity, including kissing, heavy petting, manual stimulation, etc., and does not need to include sexual intercourse.)  Yes  No

4. How long have you been romantically involved with this person?

Days ____

Months ____

Years ____

5. How serious or committed is this relationship?

         Not at all serious Extremely serious

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6. How exclusive is this relationship?

        

Not at all exclusive Extremely exclusive

7. How likely is it that you will still be involved with this person in:

(Probability (0% chance to 100% chance)

0 20 40 60 80 100 6 Months 1 Year 5 Years 10 Years

8. Do you currently live with this person?  Yes  No

9. How many children do you have with this person?  0  1  2  3  4  5 or more

10. Have you ever taken any form of hormonal birth control (such as the "pill," injection, implant, patch, NuvaRing, etc.)?  No  Yes, I am currently taking hormonal birth control Yes, I have taken hormonal birth control in the past, but am not currently taking it

11. Were you taking hormonal birth control when you first became romantically involved with your current partner?  No  Yes

***Beginning of Non-hetero sexual response questions***

41

12. Have you ever experienced an orgasm (alone or with a partner)?  Yes  No  I don't know

13. Please select all of the following activities in which you have engaged in the last 12 months.

 Self-stimulation, no penetration  Self-stimulation with penetration  Sex with another person, no penetration  Sex with another person, with penetration

14. How FREQUENTLY do you experience orgasm when engaging in each of the following activities? (Do not answer for any activities that you do not engage in)

______Self-stimulation, no penetration ______Self-stimulation with penetration ______Sex with another person, no penetration (e.g.: oral sex, anal sex, touching, caressing etc.) ______Sex with another person, with penetration (e.g.: a vibrator or sex toy etc.)

15. How EASY is it for you to orgasm during each of the following activities? (Do not answer for any activities that you do not engage in)

______Self-stimulation, no penetration ______Self-stimulation with penetration ______Sex with another person, no penetration (e.g.: oral sex, anal sex, touching, caressing etc.) ______Sex with another person, with penetration (e.g.: a vibrator or sex toy etc.)

16. How SATISFYING are orgasms you experience during each of the following activities? (Do not answer for any activities that you do not engage in)

______Self-stimulation, no penetration ______Self-stimulation with penetration ______Sex with another person, no penetration (e.g.: oral sex, anal sex, touching, caressing etc.) ______Sex with another person, with penetration (e.g.: a vibrator or sex toy etc.)

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17. How do you PREFER to experience orgasm? (please drag the following items into your preferred ranking order)

______Self-stimulation without penetration ______Self-stimulation with penetration ______Sex with partner without penetration ______Sex with partner with penetration

Please think of the last time that you experienced an orgasm during sexual activity with your partner. Please rate the degree to which each of the following sensations describe your experience during that orgasm.

18. Did that orgasm occur during sexual activity that included penetration?  Yes  No

19. Did you experience any internal sucking sensations?

 None  Weak  Moderate  Strong

20. How clear was your thinking after orgasm?

 Total loss of clarity  Somewhat foggy  Clear thought as normally experienced  Clearer-than-normal thinking

21. How relaxed did you feel following orgasm?

 Very relaxed  Somewhat relaxed  Somewhat excited  Very excited

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22. How relaxed did you feel prior to orgasm?

 Very relaxed  Somewhat relaxed  Somewhat anxious  Very anxious

23. How localized was your orgasm?

 Very localized (experienced in only a small area of your body)  Somewhat localized  Somewhat distributed  Whole body involved

24. How noisy were you during orgasm?

 Not at all noisy / silent  Somewhat noisy  Very noisy

24. Where was your orgasm centered?

 On the surface of the genitals  Deep inside

25. Did you experience any floating sensations following orgasm?

 Yes  No

26. Did you experience any apnea (catching of breath; holding breath) during orgasm?

 Yes  No

27. Did you experience any sense of loss-of-self following orgasm?

 Yes  No

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28. Did you ejaculate during orgasm (the expulsion or "squirting")?

 Yes  No

29. Did you experience a sensation like a desire to urinate (pee) prior to or during orgasm?  Yes  No

30. How long from the start of sexual intimacy did it take for orgasm to occur?

 A few minutes  More than a few minutes but less than 10  More than 10 minutes but less than half an hour  More than 30 minutes but less than 60 minutes  An hour or more

*** End of non-hetero sexual response portion of survey *** 31. Have you ever experienced an orgasm (alone or with a partner)?

 Yes  No  I don't know

32. Please select all of the following activities in which you have engaged in the last 12 months.

 Self-stimulation, no penetration  Self-stimulation with penetration  Sex with another person, no penetration  Sex with another person, non-penis penetration  Sex with another person, penile-vaginal penetration

33. How FREQUENTLY do you experience orgasm when engaging in each of the following activities? (Do not answer for any activities that you do not engage in)

45

______Self-stimulation, no penetration ______Self-stimulation with penetration ______Sex with another person, no vaginal penetration (e.g.: oral sex, anal sex, touching, caressing) ______Sex with another person, non-penis penetration (e.g.: a vibrator, sex toy etc.) ______Sex with another person, penile-vaginal penetration

34. How EASY is it for you to orgasm during each of the following activities? (Do not answer for any activities that you do not engage in)

______Self-stimulation, no penetration ______Self-stimulation with penetration ______Sex with another person, no vaginal penetration (e.g.: oral sex, anal sex, touching, caressing) ______Sex with another person, non-penis penetration (e.g.: a vibrator, sex toy etc.) ______Sex with another person, penile-vaginal penetration

35. How SATISFYING are orgasms you experience during each of the following activities? (Do not answer for any activities that you do not engage in)

______Self-stimulation, no penetration ______Self-stimulation with penetration ______Sex with another person, no vaginal penetration (e.g.: oral sex, anal sex, touching, caressing) ______Sex with another person, non-penis penetration ______Sex with another person, penile-vaginal penetration

36. How do you PREFER to experience orgasm (please drag the following items into your preferred ranking order)?

______Self-stimulation without penetration ______Self-stimulation with penetration ______Sex with partner without penetration ______Sex with partner with non-penis penetration ______Penile-vaginal intercourse

46

37. Did that orgasm occur during sexual activity that included penetration?

 Yes: penile-vaginal intercourse  Yes: penetration with non-penis object  No

38. Did you experience any internal sucking sensations?

 None  Weak  Moderate  Strong

39. How clear was your thinking after orgasm?

 Total loss of clarity  Somewhat foggy  Clear thought as normally experienced  Clearer-than-normal thinking

40. How relaxed did you feel following orgasm?

 Very relaxed  Somewhat relaxed  Somewhat excited  Very excited

41. How relaxed did you feel prior to orgasm?

 Very relaxed  Somewhat relaxed  Somewhat anxious  Very anxious

42. How localized was your orgasm?

 Very localized (experienced in only a small area of your body)  Somewhat localized  Somewhat distributed  Whole body involved

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43. How noisy were you during orgasm?

 Not at all noisy / silent  Somewhat noisy  Very noisy

44. Where was your orgasm centered?

 On the surface of the genitals  Deep inside

45. Did you experience any floating sensations following orgasm?

 Yes  No

46. Did you experience any apnea (catching of breath; holding breath) during orgasm?

 Yes  No

47. Did you experience any sense of loss-of-self following orgasm?

 Yes  No

48. Did you ejaculate during orgasm (the expulsion or "squirting")?

 Yes  No

49. Did you experience a sensation like a desire to urinate (pee) prior to or during orgasm?

 Yes  No

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50. How long from the start of sexual intimacy did it take for orgasm to occur?

 A few minutes  More than a few minutes but less than 10  More than 10 minutes but less than half an hour  More than 30 minutes but less than 60 minutes  An hour or more

51. Compared to others around the same age, how attractive do you think other women would rate your partner on each of the following characteristics?

Body         

Not at all attractive Extremely Attractive

Face         

Not at all attractive Extremely Attractive

Sexual desirability         

Not at all attractive Extremely Attractive

52. How would other women rate your partner on each of the following characteristics?

Kind         

Not at all Extremely

Socially dominant         

Not at all Extremely

Caring         

Not at all Extremely

Good with children         

Not at all Extremely

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53. How would other women rate your partner on each of the following characteristics?

Current social status         

Extremely low Extremely high

Potential future social status         

Extremely low Extremely high

54. How would other women rate your partner on each of the following characteristics?

Current financial resources         

Extremely low Extremely high

Potential future financial resources         

Extremely low Extremely high

55. How attractive would you rate your partner on each of the following characteristics?

Body         

Not at all attractive Extremely Attractive

Face         

Not at all attractive Extremely Attractive

Sexual desirability         

Not at all attractive Extremely Attractive

56. How would you rate your partner on each of the following characteristics?

Kind         

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Not at all Extremely

Socially dominant         

Not at all Extremely

Caring         

Not at all Extremely

Good with children         

Not at all Extremely

57. How would you rate your partner on each of the following characteristics?

Current social status         

Extremely low Extremely high

Potential future social status         

Extremely low Extremely high

58. How would you rate your partner on each of the following characteristics?

Current financial resources         

Extremely low Extremely high

Potential future financial resources         

Extremely low Extremely high

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59. How sexually, emotionally and overall satisfied are you with your partner?

Sexually         

Not at all satisfied Extremely satisfied

Emotionally         

Not at all satisfied Extremely satisfied

Overall         

Not at all satisfied Extremely satisfied

60. How sexually experienced is this person?

This person is

        

Not at all sexually experienced Extremely sexually experienced

61. Compared to yourself, how physically attractive is your partner?

Relative attractiveness

        

Much less than me Much more than me

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62. Consider yourself and your partner, and what you both offer to the relationship; who is the better overall partner? (has more to offer in overall attractiveness, financial resources, kindness, intelligence etc.)

Overall

        

I have more to offer My partner has more to offer

63. With how many different partners have you had sex within the last 12 months?

 0  1  2  3  4  5-6  7-9  10-19  20 or more

64. With how many different partners have you had sexual intercourse on one and only one occasion?

 0  1  2  3  4  5-6  7-9  10-19  20 or more

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65. With how many different partners have you had sexual intercourse without having an interest in a long-term committed relationship with the person?

 0  1  2  3  4  5-6  7-9  10-19  20 or more

66. Please indicate how much you agree with each of the following statements.

Strongly Strongly

disagree agree Sex without love is OK         

I can imagine myself being comfortable and          enjoying "casual" sex with different partners.

I do not want to have sex with a person until I am sure          that we will have a long- term, serious relationship.

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67. How often do you fantasize about having sex with someone other than your current romantic partner?

 Never  Very Seldom  Once every two or three months  Once a month  Once every two weeks  Once a week  Several times per week  Nearly every day  At least once a day

68. How often do you experience sexual arousal when you are in contact with someone you are not in a committed romantic relationship with?

 Never  Very Seldom  Once every two or three months  Once a month  Once every two weeks  Once a week  Several times per week  Nearly every day  At least once a day

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69. In everyday life, how often do you have spontaneous fantasies about having sex with someone you have just met?

 Never  Very Seldom  Once every two or three months  Once a month  Once every two weeks  Once a week  Several times per week  Nearly every day  At least once a day

70.Please select the ethnic category that best represents you.

 American Indian or Alaska Native  Asian  Black or African American  Hispanic or Latino/a/x  Native Hawaiian or Other Pacific Islander  White or Caucasian  Other (please specify) ______

71. Do you live in the U.S.?

 Yes  No

72. What is your zip code?

73. In what country do you live?

74. How would you define your current socio-economic status?

 Upper  Upper Middle  Lower Middle  Upper Lower  Lower

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76. What is your education level?

 Some high school  High School diploma or GED  Some college  College degree  Post-graduate or professional degree

77. What is your annual household income (if living in your parent’s household-- excluding your parents income)?

 Under $15,000  $15,000—$24,999  $25,000—$34,999  $35,000—$49,999  $50,000—$74,999  $75,000—$99,999  $100,000—$149,999  $150,000—$199,999  $200,000 and over

78. What is your political affiliation?

 Democrat  Republican  Libertarian  Independent  None

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75. How would you define the socio-economic status of the household you grew up in?

 Upper  Upper Middle  Lower Middle  Upper Lower  Lower

79. What is your religious affiliation?

 Christian  Catholic  Islam  Jewish  Buddhist  Hindu  Other  Secular  None

80. How orthodox or devout, to your religion, would you consider yourself to be?

I would consider myself to be

        

Not at all devout or orthodox Extremely devout or orthodox

81. How many total number of children do you have?

 0  1  2  3  4  5  6 or more

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82. Are you currently pregnant?

 Yes  No

83. Are you currently breastfeeding?

 Yes No

59

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