Abstract
A joke holds that women need a reason to have sex, whereas men just need a place. While the reality of male sexual behavior is at least slightly more complex, research in evolutionary psychology over the past two decades has confirmed that the joke contains a kernel of truth—human females, as predicted by straightforward evolutionary logic, do seem to be the more picky sex when deciding to have intercourse. However, as Cindy Meston and David Buss argue in their new book Why Women Have Sex, the varied reasons actual women give—rather than statistical representations of them—are numerous, their range of associated emotions wider, and the implications for evolutionary models potentially more complicated than has been outlined over the course of several decades of research. Why Women Have Sex offers a popularized review of the existing evolutionary and developmental literature regarding female sexual motivation and strategies, but it does so by weaving together personal, first-person accounts of women's sexual motivations and experiences.
As the authors explain in the introduction, the book is based on a previous study they conducted called “Why Humans Have Sex” that elicited both sexes' personal accounts of sexual motivations. Then Meston, a sexual psychophysiologist, and Buss, an evolutionary psychologist—both at the University of Texas at Austin—compiled a list of 237 distinct motivations from this initial population and used statistical methods to combine them into major groupings. In researching the book, they asked over one thousand women to give a description of actual sexual encounters associated with any of these 237 reasons, mostly via online survey. These reasons are discussed in relation to the underlying motivations they point to and the likely evolutionary benefits they gave our ancestral mothers. The result is a well-written book that provides a glimpse into the subjective motivations women give for their actual sexual decisions, discussions about how these various motivations combine to achieve strategic goals key for reproduction (such as procuring a mate of high genetic quality or high commitment and resource acquisition ability, jockeying for social status, capitalizing on more attractive mating opportunities, etc.), brief explanations of how present day female sexual motivations reflect recurrent survival and reproductive problems faced by our ancestral mothers, and a reminder that these may not necessarily be adaptive or happiness-promoting in the modern world. Importantly, it accomplishes these feats without becoming preachy or taking an authoritative stance, and does it with a healthy sense of humor.
In chapter 1, “What Turns Women On?: Scent, Body, Face, Voice, Movement, Personality, and—Yes—Humor,” Meston and Buss survey the recent findings of the proximate mechanisms that motivate women to have sex—the traits males possess that succeed in turning women on. Much of what has come to light through evolutionary studies of sexual behavior in the past few decades is reviewed in this and the following few chapters. This review affords a nice summary for anyone new to the field, including, as one of us (Lynn) found, a good introduction to the evolutionary psychology of sexuality to students in a more general anthropology course on human sexuality. Among the many factors the authors report as underlying women's sexual motivations, sheer proximity is listed first, with women generally attracted to men to whom they have even briefly been exposed—whether or not they actually speak! Apparently, it is not that women tend to fall for guys they've gotten to know but simply ones they've been proximally exposed to before. Scent is discussed in terms of providing women with cues to a potential mate's genetic compatibility, such as heterozygosity in major histocompatibility complex genes (as revealed in the now classic “smelly t-shirt” studies), which are thought to yield offspring with immune systems capable of guarding against a wide range of pathogens. Evidence suggests that women prefer male bodies with the classic V-shaped torso with a high shoulder-to-hip ratio, which are hypothesized to have signaled good hunting and protection ability in the ancestral environment. Faces (as well as other body parts) of males have varying degrees of bilateral symmetry, and females have been shown to find symmetrical traits more attractive. Symmetry is thought to provide cues about a potential mate's genetic quality and developmental stability. In addition to symmetry, the authors review evidence that “conventionally handsome” male faces are those that are “composite” in the sense of being near the population average. The book also reviews the relatively newer data on voice attractiveness. Women seem to prefer certain vocal qualities, namely a deeper resonance, which has been related to bilateral symmetry, facial attractiveness, digit ratios, and other features theoretically optimized by testosterone. Elegant movement, interesting personality, and a good sense of humor are also preferred by human females, as such traits can function as fitness indicators. The authors review the evidence that human females choose mates based on what animal behaviorists call “mate-copying,” in which certain males who are known to be successful with women are judged more attractive than those who are not. According to this “sexy-sons” hypothesis (Weatherhead and Robertson, 1979), by mating with males who are seen to possess the ability to attract females, a female unites her genes with male genes good at building bodies of sons and grandsons attractive to the next generation of females, and thus getting those genes into future descendants.
Chapter 2, “The Pleasure of It: Sexual Gratification and Orgasm,” is a forum for women to describe in their own words the obvious proximal motivation for engaging in sex—i.e., sheer physical gratification. The authors summarize clinical findings from the Meston lab and other studies that document the nature of sexual stimulation and how it relates to arousal, masturbation, the G-spot, and orgasm—and introduce readers to the delightful image of unstimulated vagina as cooked cannelloni noodle…Female orgasm is, they report, still somewhat mysterious (though Meston admittedly headed the 2003 Women's Orgasm Committee for the World Health Organization!)—more elusive than male orgasm—and human females appear to vary enormously in this respect. Some females report orgasm frequently while having sex with a partner, and others reporting it as rare or absent. The authors discuss several biocultural and evolutionary explanations for this, including the possibility that female orgasm is a byproduct of male orgasm and thus not adaptive, as well as the idea that it is adaptive and a way for a woman's body to reinforce mating with a quality male. As an indication of a disparity in genital-centrism that might also be influential, the authors point out that males are more likely to name their penis than women are their vagina. They cite evidence indicating that a large fraction of women complaining of inability to achieve orgasm are in fact physiologically capable of doing so after “directed masturbation.” One study apparently found that 100% of non-orgasmic women were able to achieve orgasm during masturbation and 47% during subsequent intercourse with partners. Why the numbers are comparatively low prior to such direction is, the authors argue, due to lack of knowledge on the part of individual women and cultural teachings that bring guilt to bear on the sexual response—a known orgasm-killer. Meston and Buss cite evidence suggesting that women in cultures that encourage female orgasm successfully attain them more than in cultures that do not. The authors do not, however, mention the hypothesis that if orgasm is an adaptive mate choice mechanism that provides cues to partner quality, then monogamy, even serial monogamy, likely limits the range of partners many women encounter, thus potentially resulting in an apparent “inability” of many women to experience orgasm.
Notably absent in this discussion is the role that details of male genitalia may play in the female orgasm response, including male circumcision. Male genitalia have long been thought (erroneously) to serve as mere sperm transfer devices, but current theory and evidence suggests that male genitalia may serve as courtship devices sensitive to sexual selection via female choice or, in other cases, evolve antagonistically to female genitalia (Eberhard, 1996; Hosken and Stockley, 2004; Short, 1979). As Meston and Buss summarize, there is a range of post-copulation measures females can take to bias paternity in favor of particular males, including truncating copulation before insemination, manipulating body postures to influence sperm rejection/retention, destroying sperm via douching or other procedures, prevention of zygote implantation, and spontaneous abortion, among others. Orgasm is an obvious candidate as a mediator in these key events, but, as the authors point out, the evidence is fragmentary and contradictory. For instance, the timing of female orgasm with respect to male ejaculation and the permeability of the cervical mucus plug is still not fully understood. Do certain penis shapes stimulate particular vaginas better than others? In what sexual position is the penis designed to penetrate the vagina? Did the foreskin evolve to affect male copulatory ability or directly stimulate female sexual anatomy? Given the heavy focus of proximate mechanisms discussed in this chapter, the book would have been improved with a more thorough discussion of these topics, though this would have necessarily extended its discussion to male sexual morphology and behavior, perhaps taking the reader too far afield. In any case, readers will appreciate that the jury is still out on the intriguing phenomenon of female orgasm.
In chapter 3, “The Thing Called Love: An Emotional and Spiritual Connection,” love is described as a combination of intimacy, passion, and commitment and reported to cement the pair bond and provide what evolutionary psychologists refer to as “long-term commitment insurance.” This chapter, though beginning with a quote from Marjorie Shostak's Nisa (1981), the anthropological classic that rendered modern forager sexuality resonantly human and upon which Helen Fisher drew much for her 1992 treatment of the evolution of love, the chapter is largely a homage to the Euro-American psychological conception of love, even considering the Buss et al. (1990) analysis of data from 37 cultures. Nevertheless, some of the psychological insights reviewed were found broadly applicable in modeling cross-cultural conceptions of love, including the outlining of seven types of love and three criteria for “consummate love.” Additionally, some women in the Meston and Buss study report using sex to attain or express love and commitment. At the physiological level, researchers have been able to peer into the minds of people in love and discover that emotional love has various drug-like effects on certain parts of the brain. Early on in romantic relationships, there is a decrease of serotonin, whereas the latter stages of attachment are characterized by vasopressin and oxytocin changes. The actual women surveyed for the book consistently ranked expressing and feeling love as being among the top ten reasons for having sex. Some women reported that it allowed them to achieve a transcendental experience. Important personality differences also seem to play a role in the love-sex connection, with more extroverted women being more open to sex without love. Finally, an interesting factoid culled from this chapter is that, contra to a simplistic version of the “Coolidge effect” (wherein males show high sexual performance given novel, receptive partners), committed men often appear to stay in love longer, are less likely to break up a relationship, and find breaking up more traumatic than females.
Chapter 4, “The Thrill of Conquest: From Capturing a Mate to Poaching One,” deals with competition in the mating market. The authors explain why there is a kind of marketplace in which women, as well as men, compete for quality mates, both for short- and long-term. Women sometimes report that they have sex to give them an edge over the competition for high-quality men and that they find it thrilling to succeed in this competition. To the degree to which the targeted males are already in a committed relationship, capturing a mate on the open market can become mate poaching. Not surprisingly many of the women reported using sex as an especially effective tactic in this regard, and some cited desire for revenge as a motivation for doing so. The authors suggest that mate poaching may be more common in cultures that forbid polygyny, such that women are forced to poach desirable males away from other women or settle for a low-status male. Data that may surprise some readers indicates the double-standard that judges promiscuous women more harshly than promiscuous men is often enforced more nowadays by women rather than by men as a dimension of this intrasexual rivalry. Another discussion that is often fodder for the tabloids but falls under the radar of simplistic evolutionary models is the “cad/dad” vs. “cad/cad” phenomenon. The former is an evolutionary model in which high quality males are sought for short-term affairs, while more resource-stable but lower quality males are chosen for long-term partners; the cad/cad model is in some ways equivalent to the “bass-player effect,” wherein groupies “collect” or serially seek high status musicians (i.e., the singer or guitarist, not the bass player) or athletes, except that it is without recourse to a stable “dad.” Unlike the cad/dad model, women who pursue these high status males ostensibly do not have to worry about a “dad” because these males can afford to allocate resources for multiple offspring and their mothers, as in polygynous societies—i.e., the “polygyny threshold hypothesis.” This was also formulated as “pre-reproductive investment” by Elizabeth Cashdan (1993), who found that women utilizing such a strategy flaunt their sexuality, as opposed to those expecting post-reproductive investment, who are more likely to conceal it.
On the other hand, this chapter also confirms some conventional wisdom, such as that pornography actually undermines male spousal attraction and that fashion imagery undermines female self-esteem. Though not real-life sexual rivals, these images can supply the standards by which males and females appraise themselves and each other. Realistic or not, sexual rivalry motivates crimes of passion, and one study cited in the book found that 91% of men and 84% of women had experienced at least one vivid homicidal fantasy, most of them motivated by sexual competition.
Chapter 5, “Green-Eyed Desire: From Guarding a Mate to Trading Up,” deals with other economic constraints relating to the human mating market. Women appear to use sex to help guard male mates by keeping them satisfied, reminding men what they stand to loose should they defect—or as many women in the study put it, “keep[ing] his mind off other women.” Women also seem to be motivated to sometimes have sex with other men as a way of gaining information about their mate value or to obtain a better partner—i.e., to “trade-up” in the mating market. Attracting a high-quality mate can allow a woman to enhance and evaluate her mate value, and many women cited this as a reason to have sex. The authors refer to research showing that women do this more often around ovulation.
Chapter 6, “A Sense of Duty: When Responsibility or Guilt Calls,” describes duty-bound or obligatory motivations behind sex, especially in the context of long-term relationships. Much of this chapter seems redundant, but among interesting points made are that, for a variety of reasons, men in relationships often report desiring more sex than women, and apparently women sometimes are motivated to have sex out of a sense of obligation or in exchange for male commitment as a “wifely duty.” Evolutionary theory predicts that maintaining sexual access is a central reason why males forgo mating opportunities with other women and enter committed relationships with women, so it is not surprising that this is among the main reasons women give for having sex. As the authors note, women are often socialized to be nurturers, and this too may sometimes motivate women to have sex out of a sense of duty. Also, in contrast to the bulk of this book, which paints a picture of female sexuality as not dissimilar to that of males, there truly is a gender disparity in preoccupation with sex. For instance, male sexual fantasy rates range from one to five times per day, whereas women range from three times per day to once a month! (The preceding exclamation point indicates that, as males unfamiliar with this data, once a month is simply stunning to us and, according to a completely informal survey one of us conducted among facebook friends, to many women as well.) Unsurprisingly, this disparity appears to be mediated by the same biochemical force implicated in so many other sexual discontinuities—testosterone. While it is the ratio to estrogen that mediates the development of masculine and feminine features, it appears that the absolute level may mediate sex drive.
Like the previous chapter, chapter 7, “A Sense of Adventure: When Curiosity, Variety—and Mate Evaluation—Beckon,” largely quotes from women regarding their sexual motivation in terms of exploration and adventure without the rigorous empirical substantiation of earlier chapters. It may seem puzzling that women sometimes have sex out of a sense of sheer adventure given significant potential costs such as reputational damage and sexually transmitted diseases, but, as the authors point out, sexual variety is a way to survey the sexual landscape and find out more about one's own sexual abilities and that of others (indeed, an informal survey of largely female undergraduates conducted by one of us [Lynn] in a human sexuality course indicated a significant proportion have used the withdraw and “morning after pill” methods of birth control despite being previously educated about the risks of pregnancy and sexually transmitted infections). Not surprisingly, penis size is one of the factors many women report being curious about. Also, women reported that they sometimes had sexual adventures simply to gain greater experience through practice, which may be employed later to impress a quality mate. Certain personality traits, namely extraversion and impulsivity, also correlate with ability to separate sex from love and thus motivate sexual adventurousness. It is surprising that, given previous work of Buss and his collaborators on “sexual strategies theory” (Buss and Schmitt, 1993), more attention was not given to the theoretical background on this topic. Also surprising is the lack of mention of the possibility that females mate with multiple males over a lifetime as a kind of genetic bet-hedging (i.e., multiple paternity as a way of not putting all of one's eggs in the same genetic basket).
In chapter 8, “Barter and Trade: The Value of Sex—Literally and Figuratively,” Meston and Buss tackle the controversial subject of the female use of sex for direct material gain, whether in formal exchange as found in prostitution or in more conventional arrangements, and argue that courtship in general often consists of gift-giving on the part of the male—a fact which has cross-cultural support. It is no secret that some women are attracted to rich men, and it should come as no surprise that they are sometimes motivated to have sex to get resources from such men. While the authors make it clear that some forms of prostitution are unfavorable options for poor, desperate women, other forms may reflect sound decision making—some women reported that they could make more money, and avoid the drudgery of marriage, by engaging in prostitution. As the women in the study report, sometimes the motivation to have sex comes from a desire to leverage favors or favorable treatment from men. One study among undergraduates at an elite Midwestern institution found an astonishing 9% of women had initiated a barter of sex for a tangible benefit and 82% of those women did so outside of an ongoing romantic relationship. Sometimes women don't even have to have sex at all, but can, as the authors state, exploit the “male overperception bias” (the tendency of the male mind to interpret non-sexual interaction with a woman as conveying the promise of sexual opportunity) to leverage resources out of men—as the authors note, women can employ a “bait-and-switch” tactic. This tactic is common and can be confidently employed given other facts about the mating market, namely that most men find most women at least somewhat attractive, whereas most women do not find most men at all attractive! Simply the sight of an attractive woman can lead to male sexual arousal (quickly ticking up the one to five sexual fantasies a day rate!). The same is not true of women, report Meston and Buss, who also have a higher tolerance for sexual abstinence.
Meston and Buss discuss sexual barter as it is perhaps more commonly conceived and practiced as well. The “sexual economy of prostitution” extends not only from street prostitution to high priced call girls and sexual slave trafficking, but encompasses the “sugar daddy/sugar baby” phenomenon, though not all sugar babies consider their behavior prostitution. The ubiquity of this phenomenon in the United States is signified, say the authors, by the proliferation of websites that bill themselves as dating services but with such titles as Sugardaddie.com or SugarDaddyForMe.com, though cross-cultural research has yet to confirm this practice elsewhere.
Chapter 9, “The Ego Boost: Body Image, Attention, Power, and Submission,” discusses women's desire to enjoy ego boosts by having sex to enhance or gauge their attractiveness in terms of body image and elicitations of attention from a partner, which sometimes include exerting sexual power over a male. Data suggests that female self-esteem is more associated with sexual attractiveness than is that of males, which is not surprising given the male mating preference for feminine youth and fertility. Yet what is problematical is that the self-perception of attractiveness is positively correlated with sexual activity, creating positive feedback loops and inhibiting healthy sexuality among women with low self-esteem. As previously indicated, this is further hampered by glamour magazine standards, since, according to studies reviewed by the authors, only 5% of women even have the genetic potential to look like a runway model. However, a considerable amount of sexual power is also exerted by females in contrast to prevailing stereotypes. For instance, dominant women, like dominant men, tend to have sexual submission fantasies. Other examples portray submission as the deployment of power. As one woman put it: “In many ways sex is about power, power to give your partner pleasure and take it away from them, and power to feel attractive and desirable” (p. 204). Women sometimes report that this can be achieved, paradoxically, by relinquishing power in the form of sexual submission. By so doing, it seems that a woman can sometimes gain the added benefits of being the full recipient of sexual pleasure without having to reciprocate directly. The reiteration of this scenario rings suspiciously of rationalization. Interesting, this scenario statistically clusters with the opposite possibility, that sometimes people just like to submit because they want to relinquish (or are not capable of being in) control. Disturbingly, some women report a desire to be sexually submissive out of feeling a need to be punished, which leads to the next chapter.
Chapter 10, “The Dark Side: Sexual Deception, Punishment, and Abuse,” covers unpleasant ground, and Meston and Buss should be praised for having the courage to address controversial topics of sexual coercion, though they seem to go heavy on the “horrible crime” moralizing, as if cautious about being perceived as coldly objective. As they indicate, the book would have been incomplete without this chapter because, “These are not ways in which women want to have sex. But they are nonetheless some of the reasons women end up having sex” (p. 211). Furthermore, knowing more about sexual deception and abuse and hearing about the damaging effects of it in women's own words could potentially let other women who have suffered abuse know that they are not alone and hopefully provide stronger defenses against it. As the authors summarize, since there has evidently been an evolutionary arms race between male attempts to copulate with women and female defenses against unwanted sex, sexual conflict theory predicts that males will sometimes use deceptive tactics to gain sexual access. Since women are hypothesized to demand some level of commitment before consenting to sex, men frequently deceive women in this regard. One way a woman can accurately gauge a man's actual level of commitment is by delaying sex. Predictably, this is a source of conflict between the sexes. Another defense is by erring on the side of assuming that a man's level of commitment is actually lower than it may be, and here readers are introduced to the “commitment skepticism bias.” Other anti-rape mechanisms mentioned by the authors include the occurrence of aversive rape fantasies by women who do not literally wish to fulfill such fantasies. They may be a form of scenario-building, the normal abstractions humans engage in to imagine potential outcomes (Alexander, 1989), that in this case prepare women by instilling them with caution or fearfulness. The concept of evolutionary arms races and evidence that some aspects of human psychology may be the result of such is an exciting part of the new science of evolutionary psychology, and the book shares of this excitement with readers.
Chapter 11, “Sexual Medicine: The Health Rewards of a Sex Life,” surveys the myriad findings suggesting a connection between a satisfying sex life and potential health benefits. Women report having sex to relieve headaches, the pain associated with menstruation, and stress, as well as to aid sleep, ward off depression and anxiety, enhance mood, combat loneliness, and get exercise. The authors also summarize the evidence suggesting improved immune function of sexual intercourse. The treatment provided this collection of data suggest that sexual analgesia should be included in any course or text on Darwinian or evolutionary medicine. Far from simply converging on the extraordinary “semen as an anti-depressant” data that came out of the Gallup lab a few years ago (admission of partiality: one of us [Lynn] received graduate training in the Gallup lab), this chapter surveys the numerous strategies by which evolutionary forces have encouraged humans to fulfill the biological imperative to have sex and to have it often. Theoretically, its numerous physiological benefits maximize the probability of fertilization, but, fortunately, most of these benefits accrue irrespective of fertility. However, the lifecycle perspective is largely ignored. The problem with this is that penile-vaginal intercourse becomes more problematical for women after menopause, due to a reduction in vaginal wall thickness, elasticity, and lubrication, among other things. The emphasis over the past few decades on maintaining an active sex life has overemphasized intercourse, resulting in a view of menopause and reduced penetrative intercourse as pathological. Obviously, this phallocentric view undermines the health rewards that accrue to the variety of sexual behaviors humans can engage in throughout our lives (Hartley, 2006; Tiefer, 2006).
This book is not simply a collection of Panglossian or “just so” stories, a criticism frequently leveled at evolutionary psychology. As reiterated in the conclusion, “Women's Sexual Complexities,” the book's first-person accounts often do not support the prevailing heuristic models. Rather, they represent the exceptions that are normal aspects of human variation. This is important information, as many readers, and, indeed, many whose vocations are the study of human evolution, do not see themselves in these models. For instance, contrary to a “picky choosers” model, a quote in the introduction reads, “I had sex with a couple of guys because I felt sorry for them. These guys were virgins and I felt bad that they had never had sex before so I had sex with them” (p. xxi), and another participant notes, “I once had sex with a man because he was looking at me longingly but wouldn't say much” (p. 4). By collecting women's accounts of their own motivations for having sex and how each of these motivations yield both successful and unsuccessful encounters, and the sometimes contradictory motivations involved (to gain high status by mating with a particular male in one story, and then suffering reputational damage from sex in another story), the authors may invite criticism among some of the book's intended audience, namely those readers most accustomed to searching for the ultimate, evolutionary reasons for having sex. Those readers with only a very cursory understanding of sexual selection and mate choice theory may read the huge array of sexual accounts, along with the authors' proximate and evolutionary explanations, and argue that a body of theory that can explain everything explains nothing. All that can be said to counter that claim is that the book is mostly designed to examine the proximate motivations in light of probable ultimate explanations. In any case, readers will come away with an understanding that female mating psychology is turning out to be exquisitely tuned to numerous cues and environmental factors and that women are able to adjust their mating tactics according to a wide array of sometimes conflicting strategies.
While the format of the book perhaps glosses over certain complications—namely the lumping together of the self-reports of both gay, straight, and bisexual women—the volume makes for a well-written and interesting read, especially for the lay audience, and will serve as a useful compilation of citations for more advanced readers.