Chapter 11
Fundamentals of Human Mating Strategies

David P. Schmitt

Primates are a diverse lot…some are monogamous, some polygynous, and some promiscuous…at least one—the human primate—is all of these.

—Mealey, 2000, p. 262

Evolutionary psychologists continue to debate the most fundamental mating strategy of humans. Some maintain that humans are solely designed for lifelong monogamy (Hazan & Zeifman, 1999; Lovejoy, 1981). Others argue that humans are designed for mating with more than one person during their lifetime, either through polygynous, polyandrous, or promiscuous mating (Baker & Bellis, 1995; Ryan & Jethá, 2011). Still others posit that humans possess a “pluralistic” mating repertoire (Barash & Lipton, 2001; Gangestad & Simpson, 2000), and that men and women have evolved facultative, context sensitive strategies of reproduction (Buss & Schmitt, 1993; Kenrick, Sadalla, Groth, & Trost, 1990). Cross-species and cross-cultural comparisons by anthropologists, biologists, and behavioral ecologists have produced conflicting accounts of human mating adaptations (Dixson, 2009; Mealey, 2000). As a result, a definitive characterization of humanity's fundamental mating strategy remains elusive.

In this chapter, evidence is reviewed regarding the reproductive strategies—and specialized mating psychologies—fundamental to humans. Cross-species comparisons and ethnological patterns observed across foraging cultures—cultures that practice the hunting and gathering lifestyle prevalent for 99% of human history—help to clarify our most basic human mating adaptations (Brown, 1991; Marlowe, 2003). Overall, extant evidence suggests there is no single mating strategy in humans. Humans evolved a pluralistic mating repertoire that is facultatively responsive to sex, temporal contexts, personal characteristics such as mate value and ovulatory status, and evocative features of culture and local ecology (Buss, 1994).

Sex and Temporal Context Differences in Human Mating Strategies

Humans appear to have a menu of mating strategies at their disposal, or a pluralistic mating repertoire (Gangestad & Simpson, 2000). According to this line of reasoning, humans come equipped with specialized mating adaptations for both long-term and short-term mating (Buss & Schmitt, 1993). Not all people pursue both mating strategies at all times. Instead, design features for long-term and short-term mating are differentially triggered depending on the mating strategy being actively pursued (see Schmitt, 2014).

Polygynous mating strategies, for instance, could be explained as arising from both long-term and short-term mating adaptations in men. In polygynous unions, men engage both the long-term adaptations of pair-bonding that are inherent in their monogamous mating psychology (Fisher, 1998) while also satisfying the desires for sexual variety so central to men's short-term mating psychology (Symons, 1979). Polyandrous mating strategies, on the other hand, activate the long-term pair-bonding adaptations of women, and in some cases may satisfy their short-term desires for genetic quality and diversity (see Thornhill & Gangestad, 2008), especially in the case of nonadelphic polyandry. Patterns of extra-pair copulation, or infidelity, may follow from the sex-specific short-term mating adaptations of both sexes (Schmitt, 2005a). Premarital sexuality could psychologically function as preparatory to long-term mating (e.g., evaluating the quality of a potential monogamous partner over a long temporal span) or as means of precocious reproduction in the context of a lifelong life history strategy of short-term promiscuity (Lancaster, 1994).

Most pluralistic theories of human mating evolution argue that a flexible, facultative mating design—comprised of both long-term monogamous adaptations and short-term promiscuous adaptations—would have provided reproductive benefits to humans in our ancestral past, allowing individuals to functionally respond to a wide range of familial, cultural, and ecological contexts (Del Giudice, 2009; Pedersen, 1991; Schmitt, 2005b). Pluralistic theories further acknowledge humans can benefit from shifting between long-term and short-term mating strategies during their lifespan and when in different stages of romantic relationships (Schmitt et al., 2002; Schwarz & Hassebrauck, 2012). Humans also facultatively shift mating strategies depending on hormonal status, ovulatory status, and relative mate value (Bale & Archer, 2013; Camargo, Geher, Fisher, & Arrabaca, 2013; Frederick & Haselton, 2007). In short, humans have evolved a mix of different strategies calibrated to adaptively respond to local reproductive contingencies.

Most pluralistic approaches also postulate that men and women possess sex-specific design features that reliably generate sex differences in human mating (Buss & Schmitt, 1993; Gangestad & Simpson, 2000). For example, men appear motivated by evolved desires for sexual variety—desires that lead men to functionally pursue numerous mating partners and to consent to sex relatively quickly within certain cost-benefit contexts (Buss & Schmitt, 2011; R. D. Clark & Hatfield, 1989; Schmitt, Alcalay, Allik, et al., 2003). In contrast, women's short-term mating motivations appear not to be rooted in the desire for numerous sexual partners per se, and seem focused, instead, on other factors such as obtaining men of high status, who impart immediate resources, who display social dominance, intelligence, or otherwise show genetic quality (Greengross & Miller, 2011; Jonason, Tost, & Koenig, 2012; Schmitt, 2014). As a consequence, pluralistic approaches predict men's and women's intersexual mate choices and intrasexual competition tactics will differ in important ways. Most evolutionary theories of human mating strategies are based on this assumption, which can be traced partly to the seminal logic of Parental Investment Theory.

Parental Investment Theory

According to Parental Investment Theory (Trivers, 1972), the relative proportion of parental investment—the time and energy devoted to the care of individual offspring (at the expense of other offspring)—varies across males and females. In some species, males provide more parental investment (e.g., the Mormon cricket). In other species, females possess the heavy-investing parental burdens (e.g., most mammals). Importantly, sex differences in parental investment burdens are systematically linked to the intrasexual and intersexual processes of sexual selection (Darwin, 1871). The sex that invests less in offspring is intrasexually more competitive, especially over gaining reproductive access to the opposite sex. The lesser-investing sex is willing to mate more quickly, at lower cost, and with more partners than is the heavier-investing sex. The lesser-investing sex also is reliably more aggressive, dies earlier, matures later, and generally competes for mates with more vigor (see Alcock, 2001).

Much evidence in favor of Parental Investment Theory comes from species where males are the lesser-investing sex. Males of these species display much more competitiveness with each other over sexual access to heavier-investing females, and to exhibit more intrasexual competition through greater aggressiveness, riskier life history strategies, and earlier death (Archer & Lloyd, 2002; Trivers, 1985). Lesser-investing males also discriminate less in mate choice, often seeking multiple partners and requiring less time before consenting to sex (see Alcock, 2001).

Perhaps the most compelling support for Parental Investment Theory has come from “sex-role reversed” species. In species where males are the heavy-investing parent (e.g., the red-necked phalarope), females are expected to vie more ferociously for sexual access to heavy-investing males and to require little from males before consenting to sex. This form of sexual differentiation exists among many sex-role reversed species including the red-necked phalarope, the Mormon cricket, katydids, dance flies, water bugs, seahorses, and a variety of fish species (Alcock, 2001). Parental Investment Theory, therefore, is not a theory about males always having more interest in low-cost, indiscriminate sex than females. Instead, it is a theory about sex differences in parental investment tendencies systematically relating to sex differences in mating strategies.

Among humans, many males invest heavily as parents (Lovejoy, 1981). Nevertheless, men incur lower levels of obligatory or minimum parental investment in offspring than women do (Symons, 1979). Women are obligated to incur the costs of internal fertilization, placentation, and gestation in order to reproduce. The minimum physiological obligations of men are considerably less—requiring only the contribution of sperm. Furthermore, all female mammals, including ancestral women, carry the obligations of lactation. Lactation can last several years in human foraging environments, years during which it is harder for women to reproduce and invest in additional offspring than it is for men (Blurton Jones, 1986). Finally, across all known cultures men typically invest less in active parenting effort than women (Low, 2000).

This human asymmetry in parental investment should result in the lesser investing sex (i.e., men) displaying greater intrasexual competitiveness and lower intersexual choosiness in mate preferences. Numerous studies have shown that men exhibit greater physical size and competitive aggression (Puts, Chapter 13, this volume), riskier life history strategies (Daly & Wilson, 1988), relatively delayed maturation (Geary, 1998), and earlier death than women do across cultures (Kruger, 2009). In addition, men's mate preferences are, as predicted, almost always less choosy or discriminating than women's, primarily in the context of short-term mating (Buss & Schmitt, 1993).

Because men are the lesser investing sex of our species, they also should be more inclined toward low cost, short-term mating than women. Human sex differences in the desire for short-term sex have been observed in studies of sociosexual attitudes and behaviors (Lippa, 2009), motivations for and prevalence of extramarital mating (Wiederman, 1997), quality and quantity of sexual fantasies (B. J. Ellis & Symons, 1990), quality and quantity of pornography consumption (Ogas & Gaddam, 2011), motivations for and use of prostitution (McGuire & Gruter, 2003), willingness to have sex with strangers (R. D. Clark & Hatfield, 1989), affective reactions to short-term mating (Galperin et al., 2013), and in fundamental differences between the mating experiences of gay males and lesbians (Lippa, 2007). Sex differences in parental investment obligations appear to have profoundly influenced the evolution of men and women's fundamental mating strategies.

Sexual Strategies Theory

Buss and Schmitt (1993) extended Trivers' (1972) theory by proposing Sexual Strategies Theory. According to Sexual Strategies Theory, men and women have evolved a complex repertoire of mating strategies. One strategy within this repertoire is “long-term” mating. Long-term mating is typically marked by extended courtship, heavy investment, pair bonding, the emotion of love, and the dedication of resources over a long temporal span to the mating relationship and any offspring that ensue. Another strategy within this repertoire is “short-term” mating, defined as a fleeting sexual encounter such as a hook-up or one-night stand. Between the ends of this temporal continuum are brief affairs, prolonged romances, and other intermediate-term relationships. Which sexual strategy or mix of strategies an individual pursues is predicted to be contingent on factors such as opportunity, personal mate value, sex ratio in the relevant mating pool, parental influences, regnant cultural norms, and other features of social and personal context (see also Buss, 1994).

Sex Differences in Long-Term Mating

Although Sexual Strategies Theory views both sexes as having long-term and short-term mating strategies, men and women are predicted to psychologically differ in what they desire and how they tactically pursue these strategies. In long-term mating, for example, the sexes are predicted to differ in their psychological adaptations of mate choice. Men are hypothesized to place a greater mate choice premium on signals of fertility and reproductive value, such as a woman's youth and physical appearance (Buss, 1989; Cloud & Perilloux, 2014; Grillot, Simmons, Lukaszewski, & Roney, 2014). Women, in contrast, are hypothesized to place a greater premium on a man's status, resources, ambition, and maturity—cues relevant to his ability for long-term provisioning—as well as his kindness, generosity, and emotional openness—cues to his willingness to provision women and their children (B. J. Ellis, 1992; Feingold, 1992).

Numerous studies have replicated or confirmed Sexual Strategies Theory related findings using nationally representative, cross-cultural, or multicultural samples (see Schmitt, 2014). Lippa (2007), for example, conducted an Internet survey of samples from 53 nations and confirmed across 100% of cultures that women demonstrate heightened long-term mate preferences for good financial prospects, social status, ambition, and older age, whereas men demonstrate heightened long-term mate preferences for good looks. In a recent review of sex differences in long-term mate preferences, Eastwick, Luchies, Finkel, and Hunt (2014) concluded, “It is currently uncontroversial that these sex differences describe the average stated preferences of men and women in complex modern societies” (p. 4). Other investigators have used nonsurvey techniques to study courtship effectiveness, marital choice, marital conflict, and divorce—including experimental, behavioral, and naturalistic methodologies—and have validated key Sexual Strategies Theory hypotheses concerning sex differences in long-term mate preferences (Cantú et al., 2014; Li et al., 2013; Maestripieri, Klimczuk, Traficonte, & Wilson, 2014a; Yong & Li, 2012). Men who display cues to long-term provisioning, and women who display cues to youth and fertility, tend to be the ones that are most effective at attracting monogamous long-term mating partners (Guéguen & Lamy, 2012; Schmitt, 2002). Most importantly, the ultimate functionality of Sexual Strategies Theory predicted mate preferences has been documented in studies showing marriages of older, higher-status men and marriages of younger and more physically attractive women tend to produce increased numbers and survival of offspring (Bereczkei & Csanaky, 1996; Fieder & Huber, 2007; Nettle & Pollet, 2008; von Rueden, Gurven, & Kaplan, 2011).

Sex Differences in Short-Term Mating

According to Sexual Strategies Theory, both sexes are hypothesized to pursue short-term mateships in certain contexts, but for different reproductive reasons that reflect sex-specific adaptive problems of short-term mating (Buss & Schmitt, 1993). For women, the asymmetry in obligatory parental investment leaves them little to gain in reproductive output by engaging in indiscriminate, short-term sex with numerous partners. However, for men, the potential reproductive benefits from promiscuous mating can be profound (Symons, 1979). A man can produce as many as 100 offspring by mating with 100 fertile women over the course of a year, whereas a man who is monogamous will tend to have only one child with his partner during that time. In evolutionary currencies, this represents a strong selective pressure—and a potent adaptive problem—for men's short-term mating strategy to favor a desire for sexual variety. Of course, 100 instances of only one-time mating between a man and 100 women would rarely, if ever, produce precisely 100 offspring. However, this selective pressure remains potent because a man mating with 100 women over the course of a year—particularly repeated matings when the women are nearing ovulation and are especially interested in short-term mating (Thornhill & Gangestad, 2008)—would likely have significantly more offspring than a man mating with only one woman over the course of a year.

Whether a woman mates with 100 men or is monogamously bonded with only one man, she will still tend to produce only one child in a given year. The potential reproductive benefits from indiscriminate mating with numerous partners, therefore, are much higher for men than women (Symons, 1979). It is important to note that women can reap evolutionary benefits from short-term mating as well (Greiling & Buss, 2000). A key caveat, though, is that women's psychology of short-term mating appears to center more on obtaining men of high quality rather than numerous men in high-volume quantity (Thornhill & Gangestad, 2008).

A key premise of Sexual Strategies Theory, therefore, is that both sexes can reap reproductive rewards from engaging in short-term mating under certain circumstances. Even though both sexes may adaptively pursue brief mateships, however, men and women are hypothesized by Sexual Strategies Theory to differ in the evolved psychological design of their short-term mating strategies. According to Sexual Strategies Theory, three of the more distinctive design features of men's short-term mating psychology are: (1) Men possess a greater desire than women do for a variety of sexual partners, (2) men require less time to elapse than women do before consenting to sexual intercourse, and (3) men tend to more actively seek short-term mateships than women do (Buss & Schmitt, 1993, p. 210). In each case, these hypothesized desires function to help solve men's adaptive problem of obtaining large numbers of short-term partners.

This suite of hypothesized sex differences has been well supported among studies of college student and community samples (Fenigstein & Preston, 2007; Kennair, Schmitt, Fjeldavli, & Harlem, 2009; McBurney, Zapp, & Streeter, 2005). Schmitt and his colleagues (Schmitt, Alcalay, Allik, et al., 2003) replicated these fundamental sex differences across 10 major regions of the world. When people from North America were asked “Ideally, how many different sexual partners would you like to have in the next month?” over 23% of men, but only 3% of women, indicated that they would like more than one sexual partner in the next month. This finding confirmed that many men desire sexual variety in the form of multiple sexual partners over brief time intervals, whereas very few women express such desires. Similar degrees of sexual differentiation were found all around the world. Moreover, when men and women actively pursuing short-term mates were asked whether they wanted more than one partner in the next month, over 50% of men, but less than 20% of women, expressed desires for multiple sexual partners. This finding supports the key Sexual Strategies Theory hypothesis that men's short-term mating strategy is very different from women's and is based, in part, on obtaining large numbers of sexual partners.

Schmitt and his colleagues (Schmitt, Alcalay, Allik, et al., 2003) also documented that men universally agree to have sex after less time has elapsed than women do, and that men from all world regions expend more effort on seeking brief sexual relationships than women do. For example, across all cultures nearly 25% of married men, but only 10% of married women, reported that they are actively seeking short-term, extramarital relationships. These culturally universal findings support the view that men evolved to seek large numbers of sex partners when they pursue a short-term mating strategy. It is critical to note that many men and women focus solely on long-term mating (Stewart-Williams & Thomas, 2013), and some women also pursue short-term sexual relationships as a key mating strategy (Lancaster, 1994). However, when women seek short-term mates they are more selective and tend to seek out men who are physically attractive, symmetrical, masculine, and/or possess other hypothesized markers of good quality genes (Thornhill & Gangestad, 2008).

As noted earlier, the special design of men's short-term mating psychology—desire for partner variety, quick to consent to sex, and actively seeking short-term mates—has been confirmed in studies of sex differences in sociosexuality (Lippa, 2009; Simpson & Gangestad, 1991). Schmitt (2005b) assessed the sociosexuality of men and women across 48 nations and found men were more unrestricted than women in every culture (average d = .74). Lippa (2009) replicated Schmitt's results across a larger sample of 53 nations, including exactly replicating the overall sex difference of d = .74. Men's specialized design of short-term mating has been revealed in studies of extra-pair mating, sexual fantasies, pornography consumption, prostitution consumption, affective reactions to short-term mating, and in fundamental differences between mating psychologies of gay males and lesbians (see Buss & Schmitt, 2011).

Perhaps most compelling are real world behavioral tests of hypothesized sex differences in short-term mating. In the 1970s, R. D. Clark and Hatfield (1989) had experimental confederates approach college students on American campuses and ask if they would like to have sex. Around 75% of men agreed to have sex with a complete stranger, whereas no women (0%) agreed to sex with a stranger. R. D. Clark (1990) found nearly identical results in a replication attempt in the 1980s. More than 20 years later, Hald and Høgh-Olesen (2010) largely replicated these findings in Denmark, with 59% of single men and 0% of single women agreeing to the proposition, “Would you go to bed with me?”

Schützwohl, Fuchs, McKibbin, and Shackelford (2009) asked participants to estimate what men and women would do in a similar situation, but they also manipulated the physical attractiveness of the confederate. Men were thought to agree to sex with a stranger if she was highly attractive 54% of the time, whereas women were thought to agree to sex with a stranger if he was highly attractive 8% of the time. Guéguen (2011) had confederates of various levels of physical attractiveness actually approach real-life strangers and ask if they would have sex, finding 83% of men agreed to have sex with a highly attractive woman and 60% of men agreed to sex with a woman of average attractiveness. For women, 3% agreed to have sex with a highly attractive man, but no women (0%) agreed to sex with a man of average attractiveness. It appears men of high physical attractiveness are most able to successfully pursue a short-term sexual strategy, given women's specially designed psychology of short-term mating. For the average-looking man, short-term mating may not represent a viable reproductive option (see also Greitemeyer, 2005).

Individual Differences in Human Mating Strategies

The previous section addressed the evolutionary psychology of how men and women pursue short-term and long-term mating strategies. Another important question is why an individual man or woman would opt to pursue a long-term monogamous strategy versus a short-term promiscuous strategy. Several theories have suggested personal circumstances—including stage of life, personal characteristics, and physical attributes—play an adaptive role in shaping or evoking people's strategic mating choices (Buss & Schmitt, 1993; Gangestad & Simpson, 2000). Among the more important sex-specific features affecting mating strategies are mate value, age, and, among women, their ovulatory status.

Sexual Strategy Pluralism

According to Sexual Strategies Theory (Buss & Schmitt, 1993), whether a man pursues a short-term or long-term mating strategy depends, in part, on his status and prestige. In foraging cultures, men with higher status and prestige tend to marry multiple women and reap fitness benefits from doing so (Betzig, 2012; Gurven & Hill, 2009). In modern cultures, men with high status are usually unable to legally marry more than one woman. Some evidence suggests modern men with high status—whether due to hunting ability, physical strength, or other locally-relevant attributes—still manifest a greater potential for fertility by copulating more often (Kanazawa, 2003), having sex with more partners (Gallup, White, & Gallup, 2007), engaging in more extra-pair copulations or affairs (Schmitt et al., 2004), and practicing legalized de facto polygyny (or “effective polygyny”) via divorcing and remarrying a series of highly fertile women over time (i.e., serial monogamy; Nettle & Pollet, 2008). Of course, given an equal sex ratio of men and women in a given culture, this results in other men—namely those with low status and prestige—being limited to monogamy. In addition, some low-status men are left with no wives at all, and may be forced to resort to coercive, promiscuous mating strategies (McKibbin, Shackelford, Goetz, & Starratt, 2008; Thornhill & Palmer, 2000). Consequently, one important source of individual variation in mating strategy is male status.

Mating Differences Within Men

Men's expressed mate preferences and pursued sexual strategies depend on other factors as well, including their overall value in the mating marketplace (Bailey, Durante, & Geary, 2011; Lukaszewski, Larson, Gildersleeve, Roney, & Haselton, 2014; Saad & Gill, 2014). A man's “mate value” is determined, in part, by his status and prestige. It is also affected by his current resource holdings, long-term ambition, intelligence, interpersonal dominance, social popularity, sense of humor, reputation for kindness, maturity, height, strength, and athleticism (B. J. Ellis, 1992).

Most studies of men in modern cultures find that, when they are able to do so as a result of high mate value, men opt for short-term mating strategies (Penke & Denissen, 2008; Surbey & Brice, 2007). For example, Lalumière and his colleagues (Lalumière, Seto, & Quinsey, 1995) designed a scale to measure overall mating opportunities. This scale, similar to overall mate value, included items such as “relative to my peer group, I can get dates with ease.” They found among North American men that those with higher mate value tended to have sex at an earlier age, to have a larger number of sexual partners, and to follow a more promiscuous mating strategy overall (see also von Rueden et al., 2011).

Another indicator of overall mate value is the social barometer of self-esteem (Kirkpatrick, Waugh, Valencia, & Webster, 2002). Similar to the results with mating opportunities, North American men who score higher on self-esteem scales tend to engage in more short-term mating strategies (Camargo et al., 2013). In a cross-cultural study involving over 50 nations, Schmitt (2005b) revealed this trend was evident around the world. The same relationship was usually not evident, and was often reversed, among women in modern nations (see also Mikach & Bailey, 1999). Women with high self-esteem were more likely to pursue monogamous, long-term mating strategies. These findings would seem to support Parental Investment Theory (Trivers, 1972), in that when mate value is high and people are given greater choices, men prefer frequent short-term mating whereas women strategically opt for more monogamous mateships.

According to Strategic Pluralism Theory (Gangestad & Simpson, 2000), men should also be more likely to engage in short-term mating strategies when they exhibit the physical characteristics most preferred by women, especially traits indicative of low genetic mutation load (Lukaszewski et al., 2014; Thornhill & Gangestad, 2008). Evidence that physically attractive men adaptively respond to women's desires and become more promiscuous comes from several sources. Rhodes, Simmons, and Peters (2005) found, for example, that attractive men have more short-term, but not long-term, partners; whereas attractive women have more long-term, but not short-term, partners. Men who possess broad and muscular shoulders, a physical attribute preferred by short-term oriented women (Frederick & Haselton, 2007), tend toward short-term mating as reflected in an earlier age of first intercourse, more sexual partners, and more extra-pair copulations (Hughes & Gallup, 2003). In numerous studies of North American college students, Gangestad and his colleagues have shown that women who seek short-term mates place special importance on the physical attractiveness of their partners, and that physically attractive men are more likely to pursue short-term mating strategies (Gangestad & Cousins, 2001; Simpson, Gangestad, Christensen, & Leck, 1999). In a cross-cultural study of several dozen nations, Schmitt et al. (2004) replicated these results and found that men who consider themselves attractive in nearly all cultures are more likely than other men to engage in short-term mating strategies. Among women, physical attractiveness was generally associated with more monogamous mating desires (Buss & Shackelford, 2008), though this trend was not evident in Eastern Europe and Southern Europe (Schmitt, 2005a). In sum, several findings suggest that when men have the opportunity to pursue a short-term mating strategy, due in part to their physical attractiveness, they tend to do so.

Some research suggests that genetic and hormonal predispositions may affect men's mating strategies (Garcia et al., 2010; Hönekopp, Voracek, & Manning, 2006). Much of this research focuses on the moderating effects of testosterone (Dabbs & Dabbs, 2000; Welling et al., 2008). For example, married men, compared to their same-age single peers, tend to have lower levels of testosterone (Burnham et al., 2003), and men who are expectant fathers and hope to parent children only with their current partner have lower testosterone yet (Gray, Kahlenberg, Barrett, Lipson, & Ellison, 2002; Hirschenhauser, Frigerio, Grammer, & Magnusson, 2002; van Anders & Watson, 2006). Married men who maintain interest in additional mating and those who exert no effort at parenting, however, do not experience testosterone declines (Edelstein, Chopik, & Kean, 2011; McIntyre et al., 2006). Men who are especially high in testosterone and possess high testosterone-related traits (e.g., enhanced muscularity, prominent browridge, wide jaw, deep voice) tend to have more sexual partners (Hill et al., 2013; Maestripieri, Klimczuk, Traficonte, & Wilson, 2014b), to start having sex earlier (Udry & Campbell, 1994), to exert more effort at mating (Gray et al., 2004), to be more likely to have affairs in adulthood (Booth & Dabbs, 1993), to divorce more frequently (Mazur & Booth, 1998), to have more wives in polygynous cultures (Alvergne, Jokela, Faurie, & Lumma, 2010), to have higher sperm counts (Manning, 2002), and to have more children (Apicella, Feinberg, & Marlowe, 2007; Jasienska, Jasienski, & Ellison, 2012).

Related findings involving testosterone and variability in men's mating strategies may lie in prenatal testosterone exposure and its organizational effects on the human brain. Exposure to heightened levels of testosterone in utero around the second month of gestation typically causes increased masculinization of the human male brain (L. Ellis, 2011; Manning, 2002). If men's brains are designed to produce a mating psychology that, when short-term mating is pursued, is rooted in relatively indiscriminate mating (Symons, 1979), this would lead to the hypothesis that those human males who are exposed to higher testosterone in utero would be more likely to develop indiscriminate short-term mating strategies in adulthood.

One clue to testosterone exposure can be found in the relative length of human fingers (Manning, 2002). Essentially, if one's ring fingers (fourth digits or “4D”) are longer than one's pointer fingers (second digits or “2D”), high levels of in utero testosterone exposure and high circulating levels of testosterone in adulthood are implicated. Men with especially long ring fingers (i.e., those with a low 2D:4D ratio) have been found to follow faster life history pathways and more short-term oriented mating strategies (Schwarz, Mustafić, Hassebrauck, & Jörg, 2011). Men with low 2D:4D ratios are also likely to have more children overall, to have more sperm motility, to be more competitive and assertive, and to be perceived as more attractive than other men (Manning, 2002; Stenstrom, Saad, Nepomuceno, & Mendenhall, 2011). These findings further implicate testosterone as an activating factor in men's short-term strategies. Importantly, most of these relationships are not typically found among women (though masculine women have been found to engage in more short-term mating; A. P. Clark, 2004; Mikach & Bailey, 1999). In women, other factors appear much more relevant to the adaptive evocation of evoke mating strategy choice.

Mating Differences Within Women

Women's desires for sex tend to peak during the late follicular phase, just before ovulation when the odds of conceptive sex are maximized (Regan, 1996). It was once thought this shift in sexual desire evolved because it increased the probability of having conceptive intercourse in our monogamous female ancestors. However, several studies have documented that many design features of women's mating strategies change over the cycle, with short-term desires for men with high quality genes peaking in the highly fertile days just before ovulation (Cantú et al., 2014; Durante, Griskevicius, Simpson, Cantú, & Li, 2012; Durante, Li, & Haselton, 2008; Gildersleeve, Haselton, & Fales, 2014).

Women who are interested in short-term mating, for example, tend to prefer men who are high in dominance and masculinity (Buss & Schmitt, 1993), as indicated by testosterone-related attributes such as prominent brows, large chins, and other features of facial, bodily, and behavioral masculinity (Mueller & Mazur, 1998; O'Connor et al., 2012; Perrett et al., 1998). Short-term oriented women may prefer these attributes as “sexy son” markers of testosterone that are honest indicators of immunocompetence quality in men (Thornhill & Gangestad, 2008). During the late follicular phase, women's preferences for men with masculine traits reliably increase (Gildersleeve et al., 2014), precisely as though women are shifting their mating psychology to follow a more short-term oriented strategy (see Cantú et al., 2014; Durante et al., 2012).

Overall, there is compelling evidence that women's mating strategies—both their desires and behaviors—strategically shift, from a long-term mating psychology to a more short-term oriented mating psychology, precisely when they are most fertile (Grammer, Renninger, & Fischer, 2004). It is possible these shifts function, for some women, as a mechanism to obtain high-quality genes from extra-pair copulations while maintaining a long-term relationship with a heavily investing partner (Thornhill & Gangestad, 2008).

In addition to ovulatory shifts, there is evidence that women's mating strategies change across their lifespan. For example, an early-30s peak in sexual desire may have been functional for our female ancestors. The percentage of fertile ovulatory cycles—cycles that include an ovulation that could lead to pregnancy—varies tremendously over a woman's lifespan, peaking at 70% in women during their early 30s (see Baker & Bellis, 1995). In a study of 1,400 women from the United States and Canada, Schmitt and his colleagues (2002) found that women in their early 30s experience a peak in sexual desire, as measured by subjective feelings of lust and behavioral manifestations of seductiveness and increased sexual activity. Along with evidence from orgasmic output, the cognitive emotional focus of sex, and social perceptions of sexual peak (see Barr, Bryan, & Kenrick, 2002), it appears that women's sexual desire peaks in their early 30s and may have the specific evolutionary function of either increasing reproduction with one's primary long-term mating partner, or leading women in their early 30s to engage in more extramarital affairs or more promiscuous sex, perhaps in an effort to increase the genetic quality or diversity of their offspring.

Several other individual differences and personal situations seem linked to adaptive variability in women's mating strategies. For example, short-term mating strategies are more likely to occur during adolescence, when one's partner is of low mate value, when one desires to get rid of a mate, and after divorce—all situations where short-term mating may serve specially-designed adaptive functions (Greiling & Buss, 2000). In some cases, short-term mating seems to emerge as an adaptive reaction to early developmental experiences within the family (Belsky, Steinberg, & Draper, 1991). For example, short-term mating strategies are more likely to occur among women growing up in father absent homes (Webster, Graber, Gesselman, Crosier, & Schember, 2014) especially in homes where a stepfather is present (B. J. Ellis, 2004). In these cases, the absence of a father, and presence of a stepfather, may indicate to young women that mating age men are unreliable. In such environments, short-term mating may serve as the more viable mating strategy in adulthood (Belsky, 1999; Lancaster, 1994; Sheppard, Garcia, & Sear, 2014; also see Comings, Muhleman, Johnson, & MacMurray, 2002).

Finally, some have argued that frequency-dependent or other forms of selection have resulted in different heritable tendencies toward long-term versus short-term mating (Gangestad & Simpson, 2000). There is behavioral genetic evidence that age at first intercourse, lifetime number of sex partners, mate preferences, and sociosexuality—a general trait that varies from restricted long-term mating to unrestricted short-term mating—are somewhat heritable (Lyons et al., 2004; Verweij, Burri, & Zietsch, 2012) and hormone dependent (Grant & France, 2001; Law Smith et al., 2012).

Cultural Differences in Human Mating Strategies

In addition to sex and individual differences, evolutionary psychologists expect human mating strategies to vary in adaptive ways across cultures (Gangestad, Haselton, & Buss, 2006; Gaulin, 1997). Indeed, evolutionary psychologists, anthropologists, and behavioral ecologists have long demonstrated that many aspects of culture—particularly ecological harshness, warfare, kinship, residence, and inheritance patterns—are systematically related to mating strategies, as well as to rules governing premarital sex (Barber, 2000), jealousy and adultery (Korotayev & Kazankov, 2003), love (Schmitt et al., 2009), marital dynamics (Weisfeld & Weisfeld, 2002), mate preferences (Marcinkowska et al., 2014; Moore et al., 2013), and sexual issues such as postpartum sex taboo and incest avoidance (Hartung, 1985; Pasternak, Ember, & Ember, 1997). Evolutionary psychologists clearly expect culture to play an important role in activating and evoking human mating adaptations (see Pirlott & Schmitt, 2014). Even so, some critics persist in ignoring this feature of evolutionary psychology, asserting that, “By relying on outmoded theories that emphasize biology to the exclusion of culture, evolutionary psychologists may be missing some of the most important, characteristically human, evolutionary processes” (Wood, Kressel, Joshi, & Louie, 2014, p. 17). Such statements reveal an astounding lack of knowledge regarding the foundation of evolutionary psychology and its emphasis on culture (Tooby & Cosmides, 1992).

Among the earliest and most well documented links between culture and human mating are those involving adaptive variation in polygynous versus monogamous marriage systems (Ember, Ember, & Low, 2007; Henrich, Boyd, & Richerson, 2012; Marlowe, 2003). For example, Low (1990) documented that tribal cultures with high pathogen stress are more likely to have polygynous marriage systems. Monogamous systems, in contrast, are relatively absent in high-pathogen environments (Dow & Eff, 2013). This pattern of mating pluralism can be explained, in part, by high pathogen ecologies causing men to prefer genetic diversity in their offspring (diversity that would protect against pathogens and could be achieved through polygyny) while women prefer particularly healthy men who can support multiple wives, of which there are few in high pathogen areas of the world—a pattern also related to the polygyny threshold model (Low, 2000). Mating adaptations designed to respond to pathogen levels may also give rise to different forms of polygyny. For example, in high pathogen environments, polygynous men tend to marry exogamously, outside their local tribe, which further increases their offspring diversity. Sororal polygyny, when men marry women who are sisters, would provide less genetic diversity and rarely occurs in high pathogen environments (Low, 2000).

Operational Sex Ratios and Mating Dynamics

Another well-researched aspect of culture that appears to differentially evoke human mating adaptations is operational sex ratio (Guttentag & Secord, 1983; Pedersen, 1991). Operational sex ratio can be defined as the relative balance of marriage-age men versus marriage-age women in the local mating pool, though other formulations have been proposed (Hardy, 2002). When computing operational sex ratios, marriage age is usually treated as between 15 and 49 years (Guttentag & Secord, 1983). Sex ratios are considered “high” when the number of men significantly outsizes the number of women in a local culture. Conversely, sex ratios are considered “low” when there are relatively more women than men in the mating market. In most cultures women tend to slightly outnumber men, largely because of men's polygynous tendency to have a higher mortality rate (Daly & Wilson, 1988). Nevertheless, significant variation often exists in sex ratios across cultures, across ages, and within cultures when viewed over historical time (Kruger, 2009; Marlowe & Berbesque, 2012; Pollet & Nettle, 2008).

Pedersen (1991) argued that a combination of Sexual Selection Theory (Darwin, 1871) and Parental Investment Theory (Trivers, 1972) leads to a series of predictions concerning the effects of sex ratios on human mating strategies. According to sexual selection theory, when males desire a particular attribute in potential mating partners, females of that species tend to respond by competing in the expression and provision of that desired attribute. Among humans, when sex ratios are especially low and there are many more women than men, men should become an especially scarce resource that women compete for with even more intensity than normal (see also Griskevicius et al., 2012; Stone, Shackelford, & Buss, 2007).

When combined with the parental investment notion described earlier in which men tend to desire indiscriminate short-term mating (Buss & Schmitt, 1993), this leads to the hypothesis that humans in cultures with lower sex ratios (i.e., more women than men; traditionally ratios below 100) should pursue more short-term oriented mating strategies. The logic of Pedersen's (1991) theory is that in cultures with many more women than men, men are scarce and can afford to demand from interested women that men's greater desires for short-term sex be fulfilled. As a result of these mating market forces, the culture as a whole should become more oriented toward short-term mating.

Conversely, when sex ratios are high and men greatly outnumber women, men must enter into more intense intrasexual competition for the limited number of potential female partners (see also Hudson & Den Boer, 2004; cf. Schacht, Rauch, & Borgerhoff Mulder, 2014). Women's preferences for long-term monogamous relationships become the key desires that must be responded to if men are to remain competitive in the courtship marketplace. In this case, Pedersen's (1991) logic suggests that humans in cultures with higher sex ratios (i.e., more men than women; ratios above 100) should possess more monogamous mating proclivities.

Using data from sex ratio fluctuations over time within the United States, Pedersen (1991) marshaled a compelling case for causal links between sex ratios, sexual selection processes, and human mating strategies. For example, high sex ratio fluctuations have been historically associated with increases in monogamy, as evidenced by lower divorce rates and men's greater willingness to invest in their children. Low sex ratios have been historically associated with indexes of short-term mating, such as an increase in divorce rates and a reduction in what he termed female “sexual coyness.” In a cross-cultural study of over 40 nations, Schmitt (2005a) examined whether national sex ratios were correlated with direct measures of basic human mating strategies in an attempt to test Pedersen's (1991) theory. As expected, cultures with more men than women tended toward long-term mating, whereas cultures with more women than men tended toward short-term mating (see also Barber, 2000; Schmitt & Rohde, 2013). As shown in Figure 11.1, women's sociosexuality tends to increase (i.e., become more unrestricted or short-term oriented) as the operational sex ratio decreases (i.e., more women than men in the mating pool; scores below 100), r(46) = –0.50, p < .001. Overall, it appears that human mating strategies are facultatively responsive to the balance of men versus women in the local mating pool, supporting the fundamental postulate of strategic pluralism in human mating (see also Barber, 2008; Chipman & Morrison, 2013).

Figure 11.1 National Levels of Women's Sociosexuality Related to Operational Sex Ratios Across 48 Nations of the International Sexuality Description Project. Source: Schmitt, 2005b.

Psychosocial Acceleration Theory

Combining aspects of life history theory (Low, 1998), attachment theory (Bowlby, 1982), and concepts such as reaction norms, phenotypic plasticity, gene-environment interactions, and prepared learning (Figueredo et al., 2008; West-Eberhard, 2003)—several researchers have suggested experiences during childhood play a pivotal role in the facultative development of human mating strategies. Perhaps most prominent among these is a lifespan model developed by Belsky et al. (1991). According to this model, early social experiences adaptively channel children down one of two reproductive pathways. Children who are socially exposed to high levels of stress—especially insensitive/inconsistent parenting, harsh physical environments, and economic hardship—tend to develop insecure attachment styles. These children also tend to physically mature earlier than those children who are exposed to less stress. According to Belsky and his colleagues, attachment insecurity and early physical maturity subsequently lead to the evolutionary adaptive development of what is called an opportunistic reproductive strategy in adulthood (i.e., short-term mating). In cultures with unpredictable social environments, it is therefore argued, children adaptively respond to stressful cues via phenotypic plasticity by developing the more viable strategy of short-term mating (see also Del Giudice, 2009).

Conversely, those children exposed to lower levels of stress and less environmental hardship tend to be more emotionally secure and to physically mature later. These children are thought to develop a more “investing” reproductive strategy in adulthood (i.e., long-term mating) that pays evolutionary dividends in low stress environments. Although the causal mechanisms that influence strategic mating are most prominently located within the family, this model also suggests that certain aspects of culture may be related to mating strategy variation.

A closely related theory has been proposed by Chisholm (1996). Chisholm argues that local mortality rates—presumably related to high stress and inadequate resources—act as cues that facultatively shift human mating strategies in evolutionary adaptive ways (see also Griskevicius, Delton, Robertson, & Tybur, 2011). In cultures with high mortality rates and unpredictable resources, the optimal mating strategy is to reproduce early and often, a strategy related to insecure attachment, short-term temporal orientations, and promiscuous mating strategies. In cultures that are physically safe and have abundant resources, mortality rates are lower and the optimal strategy is to invest heavily in fewer numbers of offspring. In safer environments, therefore, one should pursue a long-term strategy associated with more monogamous mating. Collectively, the Belsky et al. (1991) and Chisholm (1996) theories can be referred to as a “psychosocial acceleration theory” of human mating strategies.

Numerous studies have provided support for psychosocial acceleration theory (Cohen & Belsky, 2008; Figueredo et al., 2008). In an attempt to test psychosocial acceleration theory, Schmitt and his colleagues (Schmitt, Alcalay, Allensworth, et al., 2003) measured the romantic attachment styles of over 17,000 people from 56 nations. They related insecure attachment styles to various indexes of familial stress, economic resources, mortality, and fertility. They found overwhelming support for psychosocial acceleration theory. For example, nations with higher fertility rates, higher mortality rates, higher levels of stress (e.g., poor health and education), and lower levels of resources tended to have higher levels of insecure romantic attachment. Schmitt (2005b) also found that short-term mating was related to insecure attachment across cultures. As expected, the dismissing form of insecure attachment was linked to short-term mating in men and fearful/preoccupied forms of insecure attachment were linked to short-term mating in women. These findings support the view that stressful environments cause increases in insecure romantic attachment—increases presumably linked to short-term mating strategies (Figueredo et al., 2006).

Conclusions: Evolution and Human Mating Strategies

Humans possess a pluralistic mating repertoire, organized in terms of basic long-term/high-investment and short-term/low-investment mating psychologies. The activation and pursuit of these mating psychologies differs in adaptive ways across sex, personal circumstance, and cultural context. Men's short-term mating strategy, for example, is based on opportunistic mating, including the relatively indiscriminate acquisition of numerous partners. Women's short-term strategy, in contrast, is more heavily rooted in obtaining men of high genetic quality (including men who possess masculine and symmetrical facial features), securing additional resources, using short-term mating to secure a long-term mate, or “mate switching” to a different partner. High mate value men tend to pursue short-term mating strategies more than other men, and, when possible, strive for polygynous or serial marriages. Women nearing ovulation express desires indicative of their short-term mating psychology, including being more sensitive to the symmetry and masculinity of men. Men who fulfill these desires are successful as short-term sexual strategists. In cultures with high stress and fertility, insecure attachment and short-term mating adaptively emerge, and female-biased sex ratios appear to adaptively generate short-term mating strategies as well.

An important area for future research will be to more precisely gauge the adaptive ways in which different cultures constrain or permit the expression of one or more strategies within the human repertoire, and to find ways of applying these results to solving social problems and informing public policies. For example, based on the cross-cultural relationship between sex ratio and women's sociosexuality (see Figure 11.1), once women outnumber men at a sex ratio of about 95, women's sociosexuality conspicuously increases. In many American urban environments, women significantly outnumber men as a result of gang-related homicides and high rates of male imprisonment. Public policies that exacerbate excesses of women (e.g., drug laws that place large numbers of local men in prison) may well serve to increase the short-term mating of local populations. Such a shift could have unintended secondary effects on single-parenting (Lancaster, 1994) and sexual aggression (Thornhill & Palmer, 2000). Utilizing new knowledge about the facultative nature of mating strategy deployment and its adaptive calibration to local ecologies should prove useful for evolutionary-minded policy makers (Crawford & Salmon, 2004; Roberts, 2011).

In the future, evolutionary perspectives on human mating strategies need to be better integrated with other perspectives, including religious, historical, and feminist scholarship (see Buss & Schmitt, 2011; Vandermassen, 2005). Religious teachings frequently address sexual and reproductive behavior, often in evolutionary-relevant ways (Kirkpatrick, 2005; Weeden, Cohen, & Kenrick, 2008). The same may be true for other aspects of life that, at first glance, seem disconnected from human evolution. Political ideology, sexual orientation, gender identity, gender equality, education, climate, geography, ethnicity, and linguistic heritage may all impact human mating strategies (Barber, 2002; Pirlott & Schmitt, 2014), yet none of these topics were adequately addressed in this chapter. The adaptationist perspective emphasized here represents a starting point for future theorizing and research on the fundamental nature of human mating strategies. With a strong foundation in evolutionary psychology, future efforts at improving human sexual science will be faster in coming and more effective in execution.

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