Human mating strategies

Research on human mating strategies is guided by the theory of sexual selection, and in particular, Robert Trivers' concept of parental investment. Trivers defines parental investment as “any investment by the parent in an individual offspring that increases the offspring's chance of surviving (and hence reproductive success) at the cost of the parent's ability to invest in other offspring.”[2] The support given to each offspring typically differs between the male and female parents, which is called differential parental investment. Trivers posited that differential parental investment between males and females drives the process of sexual selection. In turn, sexual selection leads to the evolution of sexual dimorphism in mate choice, competitive ability, and courtship displays (see also secondary sex characteristics).

Minimum parental investment is the least required care needed to reproduce. In humans, females have a higher minimum parental investment. They have to invest in internal fertilization, placentation, and gestation, followed by childbirth and lactation. However, males do not have to invest as much, but many males contribute high investment to their offspring.[3] While human males can invest heavily in their offspring as well, their minimum parental investment is still lower than that of females.[4] While females have to at least invest in pregnancy, the minimum parental investment of a male is his sperm cells.

This same concept can be looked at from an economic perspective regarding the costs of engaging in sexual relations. Females incur the higher costs, as they carry the possibility of becoming pregnant among other costs.[5] Conversely, males have comparatively minimal costs of having a sexual encounter. Therefore, evolutionary psychologists have predicted a number of sex differences in human mating psychologies.

Life history theory helps to explain differences in timing of sexual relationships, quantity of sexual partners, and parental investment.[6] According to this theory, organisms have a limited supply of energy, which they use to develop their bodies. This energy is put on a theoretical spectrum of how organisms prioritize energy use. At one end of the spectrum, the organism prioritizes speeding up physical development and reaching sexual maturation quickly, which is deemed a fast strategy.[7] Additionally, fast strategy organisms seek to have sexual relationships earlier, several mates, and invest little in their offspring. On the other end of the spectrum, is slow strategy, where the organism prioritizes development of a high quality body. Slow strategy organisms seek to have sexual relationships later, few mates, and invest more heavily in their offspring.

These strategies are unconscious and help increase the organism’s reproductive success in a given environment. Early childhood environments dictate which strategy a person unconsciously pursues.[8] In a hostile environment, risks and unpredictability are increased and therefore survival is less likely than in safe environments. A fast strategy is more likely to be pursued by an organism in a hostile environment in order to reach maturity and reproduce quickly.[9] In safe environments, an organism is likely to pursue a slow strategy to develop its body first and then reproduce. Each strategy is optimized for their specific environmental characteristics. Therefore, the life history strategy influences the mating strategy of the individual animal. This concept has been applied to humans as well.[7] Additionally, there are differences in life history strategies both between and within species.

To bond or express sexual interest, people flirt. Kate Fox, a social anthropologist, posits two main types of flirting: flirting for fun and flirting with intent. Flirting for fun can take place between friends, co-workers, or total strangers who wish to get to know each other. This type of flirting does not seek sexual intercourse or romantic relationship, but increases the bonds between two people.

Flirting with intent plays a role in mate-selection. The person flirting sends out signals of sexual availability to another, and hopes to see the interest returned to encourage continued flirting. Flirting can involve non-verbal signs, such as an exchange of glances, hand-touching, hair-touching, or verbal signs, such as chatting up, flattering comments, and exchange of telephone numbers to enable further contact.

People date to assess each other's suitability as a partner in an intimate relationship or as a spouse. Dating rules may vary across different cultures, and some societies may even replace the dating process by a courtship instead.

In many cultural traditions, a date may be arranged by a third party, who may be a family member, acquaintance, or professional matchmaker. In some cultures, a marriage may be arranged by the couple's parents or an outside party. In the 2000s, internet dating has become popular.

Due to differential parental investment, the less investing sex should display more intrasexual competitiveness.[2] This is because they can invest less in each offspring and therefore can reproduce at a higher frequency, which allows them to compete for more mates. Additionally, the higher investing sex should be more choosy in their mate.[2]  Since they have a higher minimum parental investment, they carry greater costs with each sexual encounter. These costs lead them to have higher selection standards and therefore are more choosy. In humans, males are typically the less investing sex and females are the more investing sex.

Since males are the less investing sex in humans, they should pursue a short-term mating strategy more than females.[5] Short term mating is characterized by casual, low commitment sexual relationships with many partners that do not last a long time. Additionally, males benefit more from short-term mating than females do.[10] Because males generally pursue short-term mating strategies, their overall reproductive success is higher than females, however it is also more variable. This means that males are able to have more offspring on average, however only relatively few males are able to have a very large number of offspring. Due to this short-mating strategy, males have a greater desire for sexual variety, need less time to consent to intercourse, and seek short-term mates more than females.[5] [11]

However, females also pursue short-term mates, but the motivations differ from males. Females can benefit from short-term mating in numerous ways.[12][13] First, it allows for a quick extraction of resources. Women in a stressed situation may benefit from protection from a male and short term mating is a way to achieve this as is seen in contemporary asylum seeker anthropological studies.[14] Additionally, they mate with a high mate value male that they would not be able to if they pursued a long-term strategy. This allows them to get access to higher quality genes.

One prominent hypothesis is that ancestral women selectively engaged in short-term mating with men capable of transmitting genetic benefits to their offspring such as health, disease resistance, or attractiveness (see good genes theory and sexy son hypothesis). Since women cannot inspect men's genes directly, they may have evolved to infer genetic quality from certain observable characteristics (see indicator traits). One prominent candidate for a "good genes" indicator includes fluctuating asymmetry, or the degree to which men deviate from perfect bodily symmetry. Other candidates include masculine facial features,[15] behavioral dominance,[16] and low vocal pitch.[17] Evolutionary psychologists have therefore indicated that women pursuing a short-term mating strategy have higher preferences for these good gene indicators, and men who possess good genes indicators are more successful in pursuing short-term mating strategies than men who do not. Indeed, research indicates that self-perceived physical attractiveness,[18] fluctuating asymmetry,[19] and low vocal pitch[20] are positively related to short-term mating success in men but not in women. Women prefer purported good genes indicators more for a short-term mate than for a long-term mate, and a related line of research, known as the ovulatory shift hypothesis, shows that women's preferences for good genes indicators in short-term mates tends to increase during peak fertility in the menstrual cycle just prior to ovulation.[21]

Conversely, long-term mating is marked by serious committed sexual relationships with relatively few partners. While males generally pursue a short-term mating strategy when possible, females typically pursue a long-term mating strategy.[5] Long-term strategies are characterized by extended courtships, high investment, and few sexual partners. While pursuing a long-term strategy, females are able to get resources from males over the course of the relationship. Female mating psychology is generally more focused on finding high quality mates rather than increasing the quantity of their mates, which is reflected in their pursuit of a long-term strategy.[22] Additionally, they also benefit from higher parental investment by males. Women are thought to seek long-term partners with resources (such as shelter and food) that provide aid and support survival of offspring.[23] To achieve this, women are thought to have evolved extended sexuality. The key benefit for males pursuing a long-term strategy is higher parental certainty.[5] However, both sexes pursue both strategies and get benefits from both strategies.[24] Additionally, humans typically do not pursue the extremes of either short or long-term mating strategies.

Mate values correspond to future reproductive success likelihood of an individual.[25] Mate value contains the ability of the individual to produce healthy offspring in the future, based on the individual's age and sex.[25] The mate value of each sex is determined by what the opposite sex desires in a mate, so male mate values is determined by what females desire and vice versa.[5] Over time, the individuals who had higher mate values had higher reproductive success. These qualities that make up mate value evolved into what is consider physically attractive.[26] Thus individuals with a high mate value are perceived to be more attractive by the opposite sex than those with low mate value.[26] Additionally, individuals with a high mate value are more able to be more choosy in their mates and reproduce more often than those with a low mate value. Due to biological differences between the sexes, it is predicted that there are differences in what the sexes desire in a mate.[5] Therefore, it is thought that there are differences between male and female mate values.

Mate value is perceived through signals and cues. Signals are characteristics that have been selected for because they offer reliable changes in receiver behavior that lead to higher reproductive success for the receiver.[27] Conversely, cues have not been selected for to carry meaning, instead they are byproducts.[27] However, with sexual selection, cues can become signals over time.[26] Costly signals are ones that require intense effort for the signaler to send. Because they require high investment, costly signals are typically honest signals of underlying genetic qualities.[28] However, signals that are not costly enough can be faked and therefore are not associated with the underlying benefits.

Evolutionary psychologists have predicted that men generally place a greater value on youth and physical attractiveness in a mate than do women. Youth is associated with reproductive value in women, because their ability to have offspring decrease dramatically over time compared to men. Therefore, males typically prefer to mate with females who are younger than themselves, except when they are maturing in their teens. [29] The features that men find physically attractive in women are thought to signal health and fertility.[5] Additionally, physical attractiveness signals genetic quality for both males and females. Men who preferentially mated with healthy, fertile, and reproductively valuable women would have left more descendants than men who did not. Since men's reproductive value does not decline as steeply with age as does women's, women are not expected to exhibit as strong of a preference for youth in a mate.

However, male mate value is partly based upon his ability to acquire resources.[30] This is because one of the costs of pregnancy is the limited ability to get resources for oneself.[31] Additionally, it signals ability of the male to commitment and invest in the female and her offspring.[30] Male resource investment increases the likelihood the offspring will survive and reproduce itself. Due to this, females are typically attracted to older males, since they are likely to have a greater ability to provide resources and have a higher social status.[29] Evolutionary psychologists have speculated that women are relatively more attracted to ambition and social status in a mate because they associate these characteristics with men's access to resources.[30][32] Women who preferentially mated with men capable of investing resources in themselves and their offspring, thereby ensuring their offspring's survival, would have left more descendants than women who did not. Male mate value is also determined by his physical and social dominance, which are signals to high quality genes.[5]

Sexual selection theory states that because of their lower minimum parental investment, men can achieve greater reproductive success by mating with multiple women than women can achieve by mating with multiple men.[33] Evolutionary psychologists therefore argue that ancestral men who possessed a desire for multiple short-term sex partners, to the extent that they were capable of attracting them, would have left more descendants than men without such a desire. Ancestral women, by contrast, would have maximized reproductive success not by mating with as many men as possible, but by selectively mating with those men who were most able and willing to invest resources in their offspring. Gradually in a bid to compete to get resources from potential men, women have evolved to show extended sexuality.

One classic study of college students at Florida State University found that among 96 subjects chosen for attractiveness, approached on campus by opposite-sex confederates and asked if they wanted to "go to bed" with him/her, 75% of the men said yes while 0% percent of the women said yes.[34] Evidence also indicates that, across cultures, men report a greater openness to casual sex,[35] a larger desired number of sexual partners,[36] and a greater desire to have sex sooner in a relationship.[36] These sex differences have been shown to be reliable across various studies and methodologies.[37][38] However, there is some controversy as to the scope and interpretation of these sex differences.[39][40]

Evolutionary research often indicates that men have a strong desire for casual sex, unlike women. Men are often depicted as wanting numerous female sexual partners to maximize reproductive success.[41] Evolutionary mechanisms for short-term mating are evident today. Mate-guarding behaviors and sexual jealousy point to an evolutionary history in which sexual relations with multiple partners became a recurrent adaptive problem,[42] while the willingness of modern-day men to have sex with attractive strangers,[43] and the prevalence of extramarital affairs in similar frequencies cross-culturally, are evidence of an ancestral past in which polygamous mating strategies were adopted.[44] By contrast, journalist Daniel Bergner, who dismisses evolutionary biology, argues that monogamy has been used to control human female sexual behavior and that the human female sex drive is not lower than the human male sex drive.[45]

Flanagan and Cardwell argue[41] that men could not pursue this ideology without willing female partners. Every time a man has a new sexual partner, the woman also has a new sexual partner. It has been proposed, therefore, that casual sex and numerous sexual partners may also confer some benefit to females. That is, they would produce more genetically diverse offspring as a result, which would increase their chances of successfully rearing children to adolescence, or independence.[41]

Error management theory states that psychological processes should be biased to minimize costs of making incorrect judgments and decisions.[46] Since males generally pursue a short-term mating strategy, the costs of not having sexual intercourse is higher than having sexual intercourse. Therefore, the cost for a male thinking a female does not desire to engage in sexual intercourse when if fact she does is higher than perceiving a female does want to have sexual intercourse when she does want to engage in intercourse. Conversely, since females generally pursue a long-term strategy, the costs of having sexual intercourse is higher than not having sexual intercourse. Therefore, the cost for a female of perceiving a male wants to invest when is does not is higher than perceiving a male doesn't not want to invest when in fact he does want to invest. Due to these costs, males and females have developed separate psychological mechanisms where males over perceive female desire for sex and females under perceive male commitment. However, males accurately perceive female commitment and females accurately perceive male sexual interests.

In addition to acquiring and attracting mates, humans need to retain their mate over a certain period of time. This is especially important in long-term, pair-bonded relationships.[47] It has been hypothesized that feelings of love have evolved to keep humans in their mating relationship.[48] It has been shown that feelings of love motivate individuals to pursue their current partner and stray away from alternatives. Additionally, proclaiming feelings of love increases the attachment and commitment to the current partner.[49] Further, when proclaiming recalling love and commitment, Oxytocin, a hormone associated with pair-bonding activities, increases in the bloodstream.[50] This links physiological indicators with mate retention behaviors.

Despite this link, maintaining a pair-bonded relationship can be difficult, especially around alternative mates. When presented with alternative mates with a high mate value, humans tend to view their current relationship less favorably. This occurs when males are presented with physically attractive females, and it occurs for females when they are present with socially dominant males.[51] However, there are psychological counter-measures to these processes. First, individuals in a committed relationship tend to devalue alternative mate options, thus finding them less attractive.[52] Second, these individuals don’t always consider potential alternatives. Instead they pay less attention to alternative mates and therefore don’t undergo the devaluation process.[53] These mechanisms tend to happen unconsciously and help the individual maintain their current relationship.

There are several strategies that an individual can do to retain their mate. First off, individuals should engage in more mate retention strategies when their mate is of high value. Therefore, males with more physically attractive mates and females with males that have more resources engage in more mate retention behaviors.[47] Additionally, to retain their mates, males undertake resource displays and females enhance their physical appearance.[54] Finally, jealousy helps maintain relationships. Jealousy is associated with the threat of mate loss and helps individuals engage in behaviors to keep their current mate.[55] However, males and females differ on what cues jealousy.[56] Since males have issues confirming parental certainty, they become more jealous than females for sexual cheating. However, historically females needed male resources for offspring investment. Therefore females become more jealous over emotional cheating, as it threatens the devotion of resources to her and her offspring.

Just as there are differences between the sexes in mating strategies, there are differences within the sexes and such within-sex variation is substantial.[57] Individual differences in mating strategies are commonly measured using the Sociosexual Orientation Inventory (SOI), a questionnaire that includes items assessing past sexual behavior, anticipated future sexual behavior, and openness to casual sex.[58] Higher scores on the SOI indicate a sexually unrestricted mating strategy, which indicates an openness to casual sex and more partners. Conversely, lower scores on the SOI indicate a sexually restricted mating strategy, which a focus on higher commitment and less partners.

Several studies have found that scores on the SOI are related to mate preferences, with more sexually restricted individuals preferring personal/parenting qualities in a mate (e.g. responsibility and loyalty), and with less sexual restricted individual preferring qualities related to physical attractiveness and social visibility.[59] Other studies have shown that SOI scores are related to personality traits (i.e. extraversion, erotophilia, and low agreeableness),[60] conspicuous consumption in men as a means to attract women,[61] and increased allocation of visual attention to attractive opposite-sex faces.[62]

Evolutionary psychologists have proposed that individuals adopt conditional mating strategies in which they adjust their mating tactics to relevant environmental or internal conditions, which is called strategic pluralism.[57] The concept of sexual pluralism states that humans do not pursue the same mating strategy all of the time. There are different motivations and environmental influences that determine the mating strategy which a person will adopt. The long-term and short-term mating behaviors are trigger in the individual by the current strategy being pursued.[12] Therefore, not only are there differences between the sexes in long-term and short-term mating, but there are also differences within the sexes. To the extent that ancestral men were capable of pursuing short-term mating strategies with multiple women, they tend to do so. However, not every male is able to pursue this option. Additionally, even though most women pursue a long term mating strategy, some females pursue a short-term strategy.

When possible, males will typically pursue a short-term mating strategy.[5] The ability to do this depends upon their mate value, so males with a high mate value are more likely to pursue a short-term mating strategy.[63] High mate value males have been shown to have sexual intercourse earlier and more often than low mate value males. Self-esteem and physical attractiveness have been shown to be related to male pursuing a short term mating strategy.[64] Additionally, males with more testosterone have been shown to pursue more short-term strategies.[65]

However, not all males pursue a short-term mating strategy. There are several reasons for this. First, long-term mating has its own advantages that have already been discussed. Second, while males of higher mate value and status have opportunities to pursue short-term mates, low mate value males typically do not have the same opportunities. Since females generally prefer long-term mating strategies, the few who would mate in the short-term are already paired with the high mate value males. Additionally, the benefits of short-term mating for females are only obtained through high mate value males. Therefore, low status males are more likely to pursue long-term mating strategy.

While more attractive males tend to pursue a short-term mating strategy, more attractive females tend to pursue a more long-term mating strategy. Additionally, younger females are more likely to pursue a short-term mating strategy, as well as those who are not satisfied with their current partner.[66]

The ovulatory cycle has been shown to influence a female’s mating strategy. In the late follicular phase, women are the most fertile in the ovulatory cycle.[67] During this time, there is evidence that females tend to pursue a short-term oriented mating strategy over a long-term one.[68][69] Additionally, female sexual desires increase as well as their attraction towards more masculine males.[5]

Additionally, female mating strategies can change across their lifetime. In their early thirties, females experience a peak in sexual desire.[70] In turn, this increase influences females to pursue a more long or short term oriented strategy depending on the mate value of their current partner.[71]

Research on the conditional nature of mating strategies has revealed that long-term and short-term mating preferences can be fairly plastic. Following exposure to cues that would have been affected mating in the ancestral past, both men and women appear to adjust their mating preferences in ways that would have historically enhanced their fitness. Such cues include the need to care for young, danger from animals and other humans, and resource availability.[72] Additionally, there is evidence that the female sex drive is more plastic than male sex drive, because they are the selecting sex.[73] Since females typically chose when and with whom to engage in sex, this sex drive plasticity could be an affect of female mate choice.

Evolutionary psychologists have investigated different strategies and environmental influences across different cultures and confirmed that men tend to report a greater preference for youth and physical attractiveness in a mate than do women. Additionally, women tend to report a greater preference for ambition and social status in a mate than do men.[30][32] The specific role that culture plays in modulating sex differences in mate preferences is subject to debate.[74][75] Cultural variations in mate preference can be due to the evolved differences between males and females in a given culture.

Culture also has a link to mating strategies in the form of marriage systems in the society. Specifically, pathogens have been linked to whether a society is more likely to have polygynous or monogamous marriage systems. Cultures with high pathogen stress are more likely to have polygynous marriage systems, especially exogamous polygamy systems.[76] This is helpful for both males and females, as males obtain greater genetic diversity for their offspring and females have access to healthy males, which are typically lacking in high pathogen societies.[4] Conversely, monogamy is often absent from high pathogen environments, but common in low pathogen environments.[77]

Further, since physical attractiveness is thought to signal health and disease resistance, evolutionary psychologists have predicted that, in societies high in pathogen prevalence, people value attractiveness more in a mate. Indeed, research has confirmed that pathogen prevalence is associated with preferences for attractiveness across nations.[78] Women in nations with high pathogen prevalence also show greater preferences for facial masculinity.[79] Researchers have also reasoned that sexual contact with multiple individuals increases the risk of disease transmission, thereby increasing the costs of pursuing a short-term mating strategy. Consistent with this reasoning, higher pathogen prevalence is associated with lower national SOI scores.[80] Finally, several studies have found that experimentally manipulating disease salience has a causal influence on attractiveness preferences and SOI scores in predicted directions.[81][82][83]

The local operational sex ratio has been shown to have an impact on mating strategies.[84] This is defined as the ratio of marriage-age males to marriage age females, with a high ratio representing more males and a low ratio representing more females in the local area. When there is a imbalance of sexes, the rare sex typically has more choice, while the plentiful sex has to compete more strategically for the rare sex. This leads to the plentiful sex competing on specific areas that the rare sex finds attractive.[85] Additionally, the plentiful sex will adopt more of the rare sex’s mating strategy. For example, with a low sex ratio, females will adopt a more short term mating strategy and will compete more intense on things like physical attractiveness. However, with a high sex ratio, males will adopt a more long term strategy to attractive females.

In 2005, the evolutionary psychologist David Schmitt conducted a multinational survey of sexual attitudes and behaviors involving 48 countries called the International Sexual Description Project (ISSR).[35] Schmitt assessed relationships between several societal-level variables and average scores on the SOI. One variable that was shown to significantly predict a nation's average SOI score was the Operational Sex Ratio (OSR). This prediction was confirmed; OSR was significantly positively correlated with national SOI scores.[35] Another variable that Schmitt predicted would influence SOI scores was the need for biparental care. In societies where extensive care from both parents is needed to ensure offspring survival, the costs of having sex with an uncommitted partner are much higher. Schmitt found significant negative correlations between several indices of need for biparental care (e.g. infant mortality, child malnutrition, and low birth-weight infants) and national SOI scores.

Some sex differences in mate preferences may be attenuated by national levels of gender equity and gender empowerment.[86][87] For example, as women gain more access to resources their mate preferences change. Finding a mate with resources becomes less of a priority and a mate with domestic skills is more important. As women's access to resources varies between cultures, so does mate preference.[88] In light of these findings, it has been suggested that both female physical attractiveness and male access to resources be thought of as “necessities” in a mate.[89] Other qualities, such as humor, are thought of as “luxuries.” Therefore humans first look for the necessities in a mate. After they have obtained the specific necessities, individuals can then  place value on the luxury qualities. This helps to explain some of the debate of the role of resources and attractiveness in mate value.