We’ve seen how men and women sometimes differ in what they find attractive. It turns out they differ in attitudes and behavior regarding sex as well. Most of us are familiar with the common stereotypes: Men, it is often said, want sex all the time, whereas women typically play the role of gatekeeper, deciding if and when sex begins in a relationship. Is there some truth to these stereotypes? Although there is important variation within each gender, many findings support the idea that, compared with women, men have more permissive attitudes about sexuality in and out of relationships:

Men are much more likely than women to say that they would enjoy casual sex outside the context of a committed relationship, whereas women prefer to engage in sexual activities as part of an emotionally intimate relationship (Hendrick et al., 2006; Oliver & Hyde, 1993; Ostovich & Sabini, 2004).

If you ask teenagers how they feel about having sex for the first time, most of the young men cannot wait to lose their virginity, and only one third of them view the prospect with a mix of positive and negative feelings. Young women have a different view: Most are ambivalent about having sex, some are opposed, and only a third of them are looking forward to their first experience of sex (Abma et al., 2004).

If you went on a date with someone and didn’t have sex, would you regret it? Men report regretting not pursuing a sexual opportunity much more often than women do (Roese et al., 2006).

Once in a romantic relationship, men want to begin having sex sooner than women do, they want sex more often, and they are more likely to express dissatisfaction with the amount of sex they have (Sprecher, 2002).

The differences between men and women go beyond what they say. When we look at what people are actually doing, men on average have higher sex drives than women do:

Men experience sexual desire more frequently and intensely than do women, and they are more motivated to seek out sexual activity (Vohs et al., 2004). Young men experience sexual desire on average 37 times per week, whereas women experience sexual desire only about 9 times per week (Regan & Atkins, 2006). Men also spend more time fantasizing about sex than women do: Sex crosses men’s minds about 60 times per week; for women, only about 15 times (Leitenberg & Henning, 1995; Regan & Atkins, 2006).

Men spend more money on sex. Not only do men spend a lot of money on sexual toys and pornography (Laumann et al., 2004), men are much more likely than women to pay for sex. One study found that, among Australians, 23 percent of men said that they paid for sex at least once, but almost none of the women had (Pitts et al., 2004).

Men masturbate more frequently than women do (Oliver & Hyde, 1993). Among people who have a regular sexual partner, about half of the men still masturbate more than once a week, whereas only 16 percent of women pleasure themselves as frequently (Klusmann, 2002).

Men are more likely to be sexually unfaithful to their romantic partners. Although most husbands and wives never have sex with someone other than their partner after they marry, about one out of every three husbands, compared with only one out of five wives, has an extramarital affair (Tafoya & Spitzberg, 2007).

Where polygamy is practiced, such as in some African cultures, it is almost always men who have the multiple spouses (Zeitzen, 2008).

These and other facts paint a pretty clear picture: On average, men are more sex driven than women, and are interested in more frequent sex with more partners. A big question, of course, is why these differences exist.

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Evolutionary psychology gives us one way to understand these sex differences. Robert Trivers (1972) proposed that reproductive success means different things to men and women because the sexes differ in their inherent parental investment, that is, the time and effort that they necessarily have to invest in each child they produce. Men’s parental investment can be relatively low. If a man has sex with 100 different women in a year, he can, in theory, father as many as 100 children with little more time and effort than it takes to ejaculate. Women have a much higher level of parental investment. The number of children they can bear and raise in a lifetime is limited, and they have to commit enormous time and energy to each child lest it die before reaching maturity.

Trivers argued that because men and women differ in the necessity of their parental investment, they evolved to have different mating strategies, or overall approaches to mating, that helped them to reproduce successfully (Buss, 2003; Geary, 2010). For men, there may be some benefit to a mating strategy of pursuing every available sexual opportunity and to focus more on a short-term mating strategy. If a man mates with as many women as possible in short-term relationships, he probably won’t be able to provide high-quality parenting to every child he fathers, and so many of those children will not thrive as well as they would with high investment from both parents (Allen & Daly, 2007). But what a man lacks in parental quality he might make up in sheer quantity: Chances are that at least some of those children will survive to propagate the man’s genes.

Women, in contrast, would get no reproductive benefit from being highly promiscuous. If they flitted from partner to partner, mating indiscriminately, they would not be able to produce any more children than they would by having sex with only one fertile man for a lifetime. Instead, women would benefit from a mating strategy of choosing their mates carefully, seeking out partners with good genes who would contribute resources to protect and feed their offspring. In other words, women might prefer a long-term mating strategy.

This evolutionary perspective could explain many of the systematic gender differences in sexual attitudes and behavior that we listed above. Given the evolutionary explanation, it is not surprising that men all over the world show a greater desire than women for brief affairs with a variety of partners, and that when they enter a new romantic relationship, they are more eager than women to jump in the sack (Schmitt, 2005). What’s more, women are indeed more careful and deliberate than men in their choice of sexual partners. They are less interested than men are in casual, uncommitted sex (Gangestad & Simpson, 1990). They will not have sex with a partner unless he meets a fairly high bar of intelligence, friendliness, prestige, and emotional security, whereas men set the bar much lower for the personal qualities they demand in a potential sexual partner (Kenrick et al., 1990).

It is important to note, however, that the evolutionary perspective does not imply that men and women employ a single mating strategy across all situations and periods in their lives, or, for that matter, that all men and women will employ the same strategy. For one thing, the mating strategies that men and women adopt depend on whether they are looking for a short-term fling or a long-term partnership (Buss & Schmitt, 1993). For example, when men are in the market for a short-term partner—someone with whom to have a casual sexual encounter—they adjust their radar to look for women who appear sexually available, or “easy” (Schmitt et al., 2001). But men do not always act like dogs on the hunt for promiscuous women. When they are looking for a longer, more committed relationship, they seek out women who appear chaste (Buss, 2000).

It is also important to emphasize that any strategy has its costs and benefits. The social, cultural, and physical environment can alter the way these balance out (Geary, 2010). Some of these trade-offs are listed in Table 14.1.

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Thus, even if certain mating strategies were adaptive in our distant evolutionary past, they should not be viewed as natural or preferable ways to act. For example, although mating with as many women as possible brings a man some elements of advantage, it also brings potential costs: conflict with and violent reactions by other men in the man’s vicinity; development of a negative reputation among women in the vicinity; and lack of contribution to the survival of the children he does father. All of these factors would favor a more monogamous approach. In certain contexts, then—such as where the sex ratio is male dominated, or where infant mortality is a particular concern—men may benefit more from greater monogamy and parental investment (e.g., Pollet & Nettle, 2008). Thus, David Geary (2010) suggests that one way to think about it is that biology and evolutionary pressures may create an ideal preference (i.e., for men to have sex with as many attractive women as possible and for women to selectively choose high-investment men), but the actual strategy is informed by cultural and social contexts. The challenge for research, then, is to be able to specify which social and cultural factors interact with generalized preferences for evolved mating strategies.

Consider today’s modern world. Do you think these strategies would be advantageous in the contemporary mating landscape? In the modern environment we inhabit now, male promiscuity and female chastity might not necessarily help people reproduce more effectively. For one thing, many women now use birth control to prevent fertility. Also, many casual sexual encounters involve the use of prophylactics to prevent the spread of sexually transmitted diseases (as well as pregnancy). In fact, in this environment, men might be able to reproduce more successfully if, instead of pursuing multiple partners, they consistently showed love and commitment to one partner and increased their parental investment. Geary (2010) notes, for example, that humans are quite different from nearly all other mammals in the relatively high degree of involvement that fathers have in child rearing. Furthermore, as women gain more equal footing with men in terms of economic and social power, and because technology has potentially reduced the burdens of infant care (e.g., formula as a substitute for breast milk, the ability to pump and store breast milk), women may benefit from a less selective approach (Schmitt, 2005). These are just a few of the cultural factors influencing people’s views of sex and their sexual behavior. Next we briefly consider additional factors that play a role in sexual attitudes and behavior.

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It is important to recognize that although sex obviously serves the biological function of reproduction, many psychological motives influence people’s decisions to have sex. When college students were asked to list all of the reasons why they or someone they know had recently engaged in sexual intercourse, they mentioned 237 reasons (Meston & Buss, 2007). Most of these reasons had to do with seeking positive states such as pleasure, affection, love, emotional closeness, adventure, and excitement. Students also mentioned more calculating and callous reasons, albeit less frequently. Some used sex as a way to aggress against someone (“I was mad at my partner, so I had sex with someone else”), to gain some advantage (“I wanted a raise”), or to enhance their social status (“I wanted to impress my friends”).

Lynne Cooper and colleagues (1998) have shown that many of these reasons for sex boil down to five core motives. Specifically, she finds that the among both college-student and community samples, the most frequently endorsed motives for sex are (in descending order) to enhance physical or emotional pleasure, to foster intimacy, to affirm one’s sense of self-worth, to cope with negative emotions, and to gain partner or peer approval. A number of factors can influence which motive tends to affect sexual behavior.

Whether a person has sex is influenced by the prevailing cultural norms about what is and what is not permissible. Whether you are a man or a woman, you probably are more accepting of premarital sexual intercourse than your grandparents were. Sixty or so years ago, most Americans disapproved of sex before marriage; these days, fewer than a third of Americans think that premarital sex is wrong (Wells & Twenge, 2005; Willetts et al., 2004). At the same time, most people generally disapprove of sex between unmarried partners who are not emotionally committed to each other, and they look more favorably on sexually active partners who are in a “serious” rather than a “casual” relationship (Bettor et al., 1995; Willetts et al., 2004). In short, although people today generally are not expected to “save themselves for marriage” in the same way that your grandparents were expected to do, most of us still believe that sex outside of marriage is more acceptable if it occurs in the context of a committed, affectionate relationship (Sprecher et al., 2006).

These changes in norms over the past few decades are also reflected in people’s sexual behavior. In today’s United States, by the age of 44, almost everyone—95 percent of the population—has had sexual intercourse before marriage (Finer, 2007). Although on average American men and women do not marry until their mid- to late 20s, they usually have sex for the first time around the age of 17. In fact, by the time Americans reach 20 years of age, only 15 percent have not yet had sex (Fryar et al., 2007). These are very different patterns than those researchers see in the first half of the twentieth century. Most people back then waited two to three years longer to begin having sex (Wells & Twenge, 2005).

Cultural norms influence not only whether people engage in sex, but how comfortable they feel about reporting permissive sexual attitudes and behavior. Consider this puzzle: The average middle-aged man reports that he has had seven sexual partners during his lifetime, whereas the average woman has had only four (Fryar et al., 2007). Shouldn’t these numbers be the same (given the survey’s focus on heterosexual encounters)? If a partner is required for sex, it would seem that each time a man engages in heterosexual sex, his female partner does, too. There are several possible explanations for this common sex difference. For example, men are more likely than women to have sex with prostitutes, but prostitutes rarely respond to these surveys. Also, men and women tend to hold different definitions of what constitutes “sex.” For example, in heterosexual couples, men are more likely than women to say that oral sex qualifies as sex (Sanders & Reinisch, 1999).

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But another explanation is that men tend to exaggerate the number of partners they’ve been with, whereas women tend to minimize that number (Willetts et al., 2004). When men are asked about their number of partners, they tend to estimate the number rather than counting diligently, and when in doubt, they round up. As a result, they almost always report round numbers, such as 10 or 30, and almost never provide seemingly exact counts such as 14 or 27 (Brown & Sinclair, 1999). Women, on the other hand, respond to researchers’ inquiries into their sex lives by counting their partners more accurately and then fudging by subtracting a partner or two from their reported total (Wiederman, 2004).

How do we know that norms play a role in men’s and women’s biased reporting? You might expect that if, for impression-management purposes, men exaggerate their numbers to appear like studs, and women downplay their numbers to appear chaste, then the difference between men and women would be especially pronounced if men and women were told that an experimenter would view their responses. That is exactly what a study by Alexander and Fisher (2003) found. But this study produced an even more interesting result: If men and women were put into a “bogus pipeline” condition in which they were led to believe that lying could be detected, sex differences in reported sexual behavior were almost nonexistent. So here we clearly see that cultural gender norms influence not only people’s sexual behavior but also their willingness to report on it.

More generally, cultures vary in the permissiveness of their attitudes regarding sex, presumably as a result of particular historical, political, and religious influences. Americans have more conservative sexual attitudes than people in many other technologically advanced countries (Widmer et al., 1998). For example, when asked about their attitudes about sex before marriage, sex before age 16, extramarital sex, and same-sex relations, Americans are stricter than respondents in a variety of other countries, as Table 14.2 shows.

One general point to take from all this is that although some of the reasons people pursue sex certainly involve biological tendencies toward pleasure seeking and reproduction, many others reflect how a person is shaped by, and interacts with, his or her social and cultural environment.

Let’s do a little thought experiment, shall we? Imagine you are in a committed relationship with someone whom you love very deeply. If you are lucky, maybe you already are there, and not much imagination is required. Now imagine that you learn that your partner has been carrying on secretly with another person. In one version of this dark scenario, you learn that the affair is about wild, passionate sex. In an alternative version, it is about a deep emotional attachment. If you were forced to choose between these two tragic turns in your relationship, which would seem to be the lesser of two evils?

Early Research

When researchers first examined how people react to infidelity, they found evidence of a significant difference between men and women. In an early set of studies, 49% of men but only 19% of women said they would be more upset if they caught their partner sleeping around than if their partner had fallen for another person (Buss et al., 1992). Of course, this means that 81% of women, compared with only 51% of men, said they would be more bothered by learning that their partner had fallen in love with someone else. Do men and women really have such different views of disloyalty? If so, why? The next two decades of research sought to answer these two questions.

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Despite humans’ monogamous tendencies, cases of infidelity in committed couples do occur with some frequency, as previously noted (Tafoya & Spitzberg, 2007). From an evolutionary standpoint, people have a lot to lose from their partner’s extrarelational affairs. The emotion of jealousy might have evolved to be an affective warning light signaling our partner’s real or imagined indiscretions. Jealousy might cue us to be alert to possible rivals who could catch our partner’s eye and woo him or her away (Buss, 2000). But an evolutionary perspective claims that infidelity carries different meanings for men and women because it differentially affected their ability to reproduce.

Of course, marriages do happen and men stay around to change diapers, attend dance recitals, and coach little Susie’s soccer league. These monogamous tendencies are thought to have evolved, and led to cultural rituals that sanction them, because there was an adaptive advantage to having the proud papa available to provide resources, protection, and a role model for developing kids (Geary, 2010). Romantic attachments provide the emotional glue to bond couples together. From this theory of evolved cost-benefit analysis, women could have evolved a greater sensitivity than men to any suggestion of that emotional bond’s dissipating, and their partners’ leaving them with the burden of child rearing. For a man, mate guarding would have served the propagation of his genes by keeping his mate from cheating on him, leading to a situation in which he expended a lot of resources raising some other man’s offspring. Thus women may have evolved to experience jealousy primarily in response to emotional infidelity, whereas men may have evolved to experience jealousy primarily in response to sexual infidelity.

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Modern Perspectives

This evolutionary argument for gender differences in jealousy fits the findings of those early studies, but theorists soon raised questions both about the data themselves as well as the conclusions that might be drawn from them. Some research fits the original view. Some does not.

First, following up on Buss’s original research, studies have replicated his pattern of sex differences. Men’s greater worry over sexual infidelity and women’s greater concern with emotional infidelity have been found across cultures (Buss et al., 1999; Buunk et al., 1996; Geary et al., 1995) and also show up when people consider online relationships (Groothof et al., 2009). A meta-analysis of studies that have presented participants with the choice between sexual and emotional infidelity shows this sex difference to be of moderate size, although stronger among college-age, heterosexual participants (Harris, 2003). The sex difference goes beyond what people say. When male and female college students imagined these two types of infidelity, their bodies reacted somewhat differently depending on their gender. Male participants imagining their partners sexually cheating on them had elevated skin conductance, indicative of an increased sympathetic response of the fight-or-flight type. Women showed higher levels of skin conductance when imagining that their partners had become emotionally attached to someone else (Buss et al., 1992).

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The story might have ended here, with the field concluding that we have an evolved tendency to feel jealous and that these mental modules of jealousy are distinct for men and women. However, other researchers have had problems with this interpretation and the data on which it has relied. One argument is that the existence of these sex differences actually has been overstated (Harris, 2003). Forcing people to choose between a love affair and a lustful liaison is a rather contrived scenario, a bit like asking whether someone would prefer a kick in the head or a punch in the stomach. Neither is particularly desirable, and by focusing on sex differences in preferring one choice over the other, we might be ignoring a rather obvious but important point: that both sexes would experience jealousy in either case. When people are asked about each kind of infidelity independently rather than being forced to choose between one or the other, the normally observed sex difference seems to disappear (DeSteno & Salovey, 1996; Harris, 2003; Sagarin et al., 2003).

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Other methodological aspects of the original studies have been questioned. For example, studies of actual infidelity rather than imagined infidelity sometimes replicate the sex difference, but not always (Edlund et al., 2006; Harris, 2002). It also might be difficult to draw conclusions about the greater sympathetic activation when men imagine sexual versus emotional infidelity. It turns out that men generally show greater sympathetic activation when imagining their partner having sex instead of becoming emotionally attached, regardless of whether this imagined relationship is actually with themselves instead of with someone else (Harris, 2000). These critiques of the methods used in the original studies have led some researchers to question how large or meaningful this purported sex difference really is.

If we do accept that men tend to bristle at a wife’s one-night stand, whereas women fret that a husband is confiding his deepest feelings to a secret pen pal, controversy also arises over how to explain this difference. Perhaps these differences are more a function of cultural learning than evolved propensities. For example, women tend to assume that a man in love will also be having sex, whereas men assume that a woman having sex will also be in love (DeSteno & Salovey, 1996; Harris & Christenfeld, 1996). So women might be more bothered than men by emotional infidelity because they are more likely to assume that their partner has or is very likely to consummate the affair (DeSteno et al., 2002).

Another culturally based argument is that men derive more self-esteem from their sex lives than women do, whereas women derive more self-esteem from being emotionally bonded to a partner than men do (Goldenberg et al., 2003). Therefore, it’s no surprise that a partner’s emotional disloyalty would trigger greater self-esteem concerns for women, whereas a partner’s sexual disloyalty would trigger greater self-esteem concerns for men. For example, when participants are asked to think about death, a condition known to elevate efforts to defend self-esteem, men become even more threatened by imagining their partner sleeping with someone else, whereas women become even more threatened by imagining their partner falling in love with someone else. In further support of a self-esteem-based argument, research that actually induces jealousy in the laboratory (as opposed to measuring it by having participants imagine hypothetical scenarios) finds that situations that increase jealousy do so by threatening self-esteem (DeSteno et al., 2006). For example, seeing a desirable person choose to work with someone else decreases a person’s self-esteem. This decrease in self-esteem fuels increases in jealousy.

A third critique is that certain aspects of the data just don’t seem to fit with an evolutionary account. For example, if differences in jealous reactions truly are sex linked, then gay men should show the same patterns of response found in straight men—they simply desire partners of their same sex (Symons, 1979). This does not appear to be the case. In a study of both gay and straight men and women, straight men reported greater relative concern about sexual than about emotional infidelity, but gay men did not. In addition, every group reported greater concerns about emotional infidelity. When asked to recollect a time when a partner actually cheated on them, people were more upset about the emotional rather than the sexual aspects of the affair (Harris, 2002). In fact, most studies using the “choose your infidelity” method find that the percentage of men (typically straight) who say they would be more bothered by sexual infidelity is at or near 50%. If a sex-specific mechanism had evolved such that men could detect and react to sexual infidelity in their mates, perhaps we would expect men’s aversion to sexual infidelity to be stronger than a coin toss (DeSteno & Salovey, 1996).

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In sum, the evolutionary account offers a provocative explanation of gender differences in jealousy, but different studies point to other explanations for when and why men and women feel jealous. As scientists continue to examine these processes, we think it is important to get some perspective on these debates. On the one hand, there is general agreement that our current psychology is influenced by our evolutionary past, but that rarely if ever means any particular propensity is rigidly determined by it. If you think about the differences between men and women as a pie, one slice of that pie is our evolved tendencies. Another slice might be cultural upbringing. Yet other slices might be gender differences in other relevant personality traits or the person’s experiences in the immediate social context. The argument about men’s and women’s jealousies might be framed better as what kinds of explanations are the bigger pieces of the pie, not whether the entire pie belongs to evolution or to culture. Maybe the biggest lesson we learn from this line of research is that even scientists get jealous if they worry that a single explanation is getting more than its fair share of attention.

Regarding the sex-difference issue, it is also worth noting that research finds that both men and women report feeling angry when they think about a partner sleeping with someone else, but feel sad and hurt if they imagine their partner having an emotional connection with someone else (Green & Sabini, 2006; Sabini & Green, 2004). One explanation for these reactions is that we all get angry when someone fails to control his or her impulses, but we feel a sense of loss if we imagine that our partner could leave us for another.

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