Mate choice in humans

One of the earliest theories posited to explain mate preferences was Darwin's Theory of Sexual Selection. This theory came about when he noticed that certain characteristics (most famously, the feathers of a male peacock) appeared to have no survival value. Unsatisfied with his theory of natural selection as the primary driver of evolution, he proposed that sexual selection was at play. As a result of success in such competitions, the victors are able to mate, meaning that their heritable traits are passed down to offspring with greater frequency. Those who lost do not gain access to mates and have less reproductive success. Over many generations, this differential reproductive success causes the qualities that contribute to winning these competitions (like upper body strength, formidability, or intelligence, for example) to become more common in the population. This pattern shapes preferences because individuals who choose mates with successful, competitive traits have a greater chance of producing children who survive and are reproductively successful themselves. As a result, preferences for such advantageous traits are passed down along with the traits themselves. The second mechanism, intersexual selection (also called epigamic selection), represents one sex's propensity to prefer and, in turn, select specific members of the opposite sex that embody preferred characteristics. Because desired qualities (like physical attractiveness or intelligence, for instance) are notably heritable, individuals who select mates who display such qualities are more likely to have children who also possess them. Over time, this process increases the frequency of preferred traits in the population and also strengthens the preferences themselves (offspring inherit both the desired traits and the preference for them). Thus, this preferential mate choice directly influences one's reproductive success. Both processes work together to select for qualities that enhance an individual's reproductive success, favoring characteristics that improve mating opportunities (even if those characteristics do not directly improve survival) and, importantly, shaping what we deem to be preferable in a mate. These mechanisms have been substantiated across virtually every species that reproduces sexually, highlighting sexual selection theory as a pervasive evolutionary force. == Consensual mate preferences ==

During human evolution, there was a selection pressure to pursue mates who had traits that could yield reproductive success. Those who successfully mated with reproductively fit individuals passed their genes onto the next generation with greater frequency. This sexual selection strengthened the presence of the reproductively beneficial traits themselves as well as the preference for them. The resulting consensual mate preferences refer to the widely shared, cross-cultural judgments regarding the desirable mate qualities that most people, regardless of sex or culture, tend to value. Physical qualities Physical attractiveness and symmetry Physical attractiveness is highly desired among men and women because it functions as a cue to fertility and health. Moreover, a very attractive mate would likely produce offspring that are also attractive, enhancing their fitness. Though men tend to prioritize and prefer physical attractiveness more so than women, it is still a quality that is highly desired by both sexes. Symmetry is one of the many aspects that factors into attractiveness for both men and women. Both facial and bodily symmetry are considered to be very attractive because they essentially act as a certificate of good health and reproductive potential (developmental stability, genetic diversity, and parasite resistance, for example). Fluctuating asymmetry, or deviation from perfect bilateral evenness, can indicate poor genetic quality and is thus deemed undesirable in a mate. Preference for symmetry in a mate is observed cross-culturally, indicating its robustness as a cue to good health. Research shows that physically attractive individuals have better sex lives. Symmetry in particular is a good predictor of the number of sex partners one has. Furthermore, more symmetrical men tend to have their first intercourse at an earlier age than do less symmetrical men. Visible indicators of health include bilateral symmetry, skin condition, and sexual dimorphism. For example, clear skin tone and complexion is broadly considered to be desirable in a mate, functioning as a signal of health and high quality genetics. The presence of sexually dimorphic traits also indicates health, as both estrogen and testosterone (hormones that produce sexually dimorphic traits) are known immunosuppressants. However, women on contraceptive pills rate the odor of MHC-similar men as being more pleasant, it is unknown why women on contraceptive pills rate smell in this way. It was found that when processing MHC-similar smells were processed faster. Contrary to these findings, other studies have found that there is no correlation between attraction and odor by testing males' odor preferences on women's odors. The study concludes that there is no correlation in attraction between men and women of dissimilar HLA proteins. Research completed on a Southern Brazilian student population resulted in similar findings that found significant differences in the attraction ratings of giving to male sweat and MHC-difference. Facial preferences Human facial preferences have been shown to correlate with both MHC-similarity and MHC-heterozygosity. Research into MHC-similarity with regards to facial attractiveness is limited. One study found that women may prefer mates with MHC-similar faces, despite evidence that they prefer men with dissimilar body odors. While facial asymmetry hasn't been correlated with MHC-heterozygosity, the perceived healthiness of skin appears to be. It appears to be that only MHC-heterozygosity and no other genetic markers are correlated with facial attractiveness in males and it has been shown that so far that there is no correlation that has been found in females. Slightly different from facial attractiveness, facial masculinity is not shown to correlate with MHC heterogeneity (a common measure of immunocompetence). Criticisms A review article published in June 2018 concluded that there is no correlation between HLA and mate choice. In addition to assessing previous studies on HLA-Mate choice analysis to identify errors in their research methods (such as small population sizes), the study collects a larger set of data and re-runs the analysis of the previous studies. By using the larger data set to conduct analysis on 30 couples of European descent, they generate findings contrary to previous studies that identified significant divergence in the mate choice with accordance to HLA genotyping. Additional studies have been conducted simultaneously on African and European populations that only show correlation of MHC divergence in European but not African populations. Other qualities Traits such as kindness, dependability, intelligence, and honesty are highly valued among men and women alike. These traits are cues to adaptive behaviors that would highly benefit one's partner and family. Kindness and empathy Kindness, the quality of being nice or friendly, is consistently ranked as one of the top priorities in a mate. Intelligence Intelligence is also consistently ranked by men and women as a top priority for a mate. A mate who is highly respected by others in their social network would be able to gain access to resources and, in turn, confer upon their family. It is a human universal and has been suggested to act as a commitment device designed to promote stable pair bonding, cooperation in parenting, and reproductive success. Honesty A mate's honesty is highly valued and preferred by both men and women. Explanations for consensual preferences Relationship satisfaction One prominent theory as to why these preferences are rated as very desirable and important for many people is their association with relationship satisfaction. This theory posits that some qualities (such as kindness or empathy) greatly contribute happiness within the relationship. Unkind or unempathetic partners may decrease relationship satisfaction and, as a result, increase the likelihood of relationship dissolution. Other trivial qualities (such as good housekeeping skills) are deemed less important in a relationship simply because they don't have a significant effect on relationship satisfaction or maintenance. Evolutionary biology Another theory as to why some qualities are consistently desired among men and women is the traits' association with reproductive investment capability. Essentially, this theory states that mate qualities like physical attractiveness or intelligence are considered important and desirable because they are more greatly correlated with parental investment abilities than are traits like good housekeeping skills. As a result, minor traits (such as good housekeeping skills) are not widely desired or prioritized. Ancestral humans who prioritized mate preferences that served proximate cues to reproductive investment capabilities were able to have more offspring and thus propagate their genes with a greater frequency. Both of these theories are not incompatible. They likely, in fact, work together to strengthen the importance of certain mate preferences from two different angles. == Sex-differentiated mate preferences ==

In ancestral environments, men and women faced different selection pressures. Women are highly constrained in their reproductive output because they are limited by gestation and lactation, therefore having significant obligatory parental investment. Men do not have such constraints– they are only limited by the number of fertile mates they have access to and are thus able to sire several children in a year. These asymmetries in parental investment led to differing optimal strategies for maximizing fitness and reproductive success. As such, men and women evolved diverging mate preferences which remain prevalent to this day. == Female mate choice ==

Although human males and females are both selective in deciding with whom to mate, females exhibit more mate choice selectivity than males, as is seen in nature. Relative to most other animals however, female and male mating strategies are found to be more similar to each other. According to Bateman's principle of Lifespan Reproductive Success (LRS), human females display the least variance of the two sexes in their LRS due to their high obligatory parental investment, that is a nine-month gestational period, as well as lactation following birth in order to feed offspring so that their brain can grow to the required size. Human female sexual selection can be examined by looking at ways in which males and females are sexually dimorphic, especially in traits that serve little other evolutionary purpose. For example, male traits such as the presence of beards, overall lower voice pitch, and average greater height are thought to be sexually selected traits as they confer benefits to either the women selecting for them, or to their offspring. Experimentally, women have reported a preference for men with beards and lower voices. Female mate choice hinges on many different coinciding male traits, and the trade-off between many of these traits must be assessed. The ultimate traits most salient to female human mate choice, however, are parental investment, resource provision and the provision of good genes to offspring. Many phenotypic traits are thought to be selected for as they act as an indication of one of these three major traits. The relative importance of these traits when considering mate selection differ depending on the type of mating arrangement females engage in. Human women typically employ long-term mating strategies when choosing a mate, however they also engage in short-term mating arrangements, so their mate choice preferences change depending on the function of the type of arrangement. This is partly explained by the fact that short-term mating is a profitable mating tactic for highly masculine men, and research has found correlations between high levels of masculinity and low levels of romantic/parental investment. Since men who have such cues of high genetic quality may be more inclined to engage in short-term mating, women who want to secure good genes for her offspring must also engage in short-term mating. • Genetic benefit hypothesis: Women may choose to engage in short-term mating arrangements in order to aid conception if her long-term partner is infertile, to gain superior genes to those of her long-term partner, or to acquire different genes to those of her partner and increase the genetic diversity of her offspring. This relates to what is known as the sexy son hypothesis; if a woman acquires genes from a high quality male, her offspring will likely have higher mate value, resulting in their increased reproductive success. One indicator of high genetic quality is physical attractiveness and the presence of sexually dimorphic features. For instance, high testosterone men are less likely to get married, and when they do, they tend to have more marital problems and higher rates of divorce than low testosterone men. Because the presence of masculine features in men is indicative of a good immune system, exposure to pathogen cues is shown to be associated with stronger preferences for male facial masculinity among women. Across a variety of cultures, it has been found that pathogen load is positively correlated with importance of partner physical attractiveness. Research shows that men with broad shoulders relative to hips (a highly sexually dimorphic quality correlated with testosterone) tend to lose their virginity at a younger age, have more sex mates, have more affairs, and have more sex with other people's mates as compared to men with lower shoulder-to-hip ratios. Long-term mating preferences Resources and financial prospects A man's reproductive investment is highly tied to his ability to attain and confer benefits for the family. Today, this translates to a man's ability to bring in economic resources and provide for the family monetarily. Monetary privilege allows access to resources that may provide material and social advantages to offspring. Another study found that women in Kenya preferentially select mates who have lots of land. Indeed, married men consistently have higher levels of income than single men of the same age. Divorce due to a lack of economic support never occurred among males. Ambition, industry, and social status In line with female preference for a mate's economic resources and financial prospects, women cross-culturally have shown preference for a mate's ambition, industriousness, and social status. For example, one study found that women rated high-status men as significantly more attractive than lower-status men. These qualities would have, again, signaled the ability of a mate to provide for a woman and her offspring. There is lots of evidence that this preference translates into real life mating behavior. For instance, mail-order brides from a variety of countries were more likely to select men who had higher levels of status and ambition. Another study found that women were more likely to seek out mates who owned a car and placed importance on their career. Protection Because ancestral women were more susceptible to dangerous others, they evolved preferences for mates that signal both the ability and willingness to protect. Qualities such as dominance, a larger body size, physical formidability, athleticism, and bravery are all highly valued among women. Tall men are more likely to date, get responses on dating ads, and acquire highly attractive partners. Age Cross-culturally, women have shown a strong preference for men who are older than themselves. One prominent reason for this is that older men typically have greater economic security and social status than younger men. Costs The primary cost of employing a long-term mating strategy among women is having to forgo short-term mating opportunities and the previously described benefits they might bring. Benefits There are many benefits of using a long-term mating strategy for women. Namely, a woman's long-term mate can secure status and resources for herself and her offspring. Also, having a long-term mate can ensure the physical protection of herself and her family. Lastly, employing a long-term mating strategy can ensure enhanced mating success of the offspring by means of the material and social benefits acquired from a father. == Men ==

Short-term mating preferences Physical attractiveness When finding a short-term mate, males highly value women with sexual experience and physical attractiveness. Men who are interested in a short-term sexual relationship are more likely to prioritise information about the body of potential partners, rather than their faces. In comparison to women, men prefer to have sex sooner and are more willing to loosen their preference standards while seeking casual sex. In addition, men are more likely than women to feel regret regarding missed sexual opportunities. Substantially more men than women will agree to have sex with a stranger, a finding that has been replicated across many countries. Cross-culturally, men solicit prostitutes far more than women do, with 99% of sex worker patrons being male. Men seeking short-term sexual relationships are likely to avoid women who are interested in commitment or require investment. In short-term sexual relationships, men are less choosy because of low parental investment. When looking for short-term sexual relationships, men may wish for there to be as little time as possible between each partner. Appearing to be immature, under the influence, flirtatious, sleepy, and wearing revealing clothing are preferred by men seeking casual sex because they are believed to be cues that a woman can be easily seduced. In fact, these sexual exploitability indicators are not preferred (and are found to be unattractive) by men employing a long-term mating strategy. In fact, physical appearance contains lots of information about a person, like their age and health status. Most men today are attracted to women who signal high reproductive value, inferred through her age and physically healthy/attractive appearance. Attractiveness Indicators of relative youth and health are substantial predictors of female attractiveness judgments by men. Other physical qualities preferred by men are healthy hair, lively gait, bodily symmetry, and firm/symmetrical breasts. One prominent mate preference among men is a low waist-to-hip ratio (hourglass figure). In fact, it has been found that congenitally blind men show preference for a low waist-to-hip ratio in a mate, indicating that the hourglass figure is a robust indicator of reproductive value. Observable characteristics of a woman can indicate good health and the ability to reproduce, qualities which are likely to be desired by a male. This may include smooth skin, absence of lesions, muscle tone, long hair and high energy levels. A Waist-to-hip ratio of 0.7 is an indicator of fertility, lower long-term health risks and suggests that the woman isn't already pregnant. Breasts of medium cup size were found to be the most attractive, however authors noted that men focused primarily on the coloration of nipples and areola rather than breast size. In addition, cross-cultural marriage statistics throughout time show that women are typically younger than their partners by anywhere from 3 to 10 years. Furthermore, data from foreign bride purchases showed that men tended to select considerably younger mates for marriage. Other behavioral data also points to a preference fulfillment for younger mates among men. For example, in cultures that take part in bridewealth practices, the age of a potential wife impacts the amount of money spent, with younger wives getting higher amounts of money. Research also indicates that mate guarding tactics are more strongly employed for younger women. Both young and old men are attracted to women in their twenties. Faces that appear younger are usually rated as more attractive by males. Such loyalty indicates a woman's commitment to the relationship, reducing the likelihood of partner defection. Unlike many animals, humans are not able to consciously display physical changes to their body when they are ready to mate, so they have to rely on other forms of communication before engaging in a consensual relationship. Romantic love is the mechanism through which long-term mate choice occurs in human males. Furthermore, he may enhance the fitness of his offspring via parental investment and strengthen social power via his alliances with his partner's family. Given the fact that many women require commitment prior to engaging in a sexual relationship, a man may benefit from employing a long-term mating strategy by simply increasing the chance of attaining a mate at all. == Parasite stress on mate choice ==

The parasite-stress theory, otherwise known as pathogen stress, states that parasites or diseases put stress on the life development of an organism, leading to a change in the appearance of their sexually attractive traits. The initial research on the Hamilton–Zuk hypothesis (see indicator traits) showed that, within one species (brightly colored birds), there was greater sexual selection for males that had brighter plumage (feathers). In addition, Hamilton and Zuk showed that, comparing across multiple species, there is greater selection for physical attributes in species under greater parasitic stress. This has influenced research regarding human mate choice. In societies with a high prevalence of parasites or pathogens, members would derive greater evolutionary advantage from selecting for physical attractiveness/good looks in mate choice compared to that derived by members of societies with lower prevalence. Humans could use physical attractiveness to determine resistance to parasites and diseases, which are believed to lower their sufferers' ability to portray attractive traits from then on and limit the number of high-quality pathogen-resistant mates. In cultures where parasitic infection is especially high, members could use cues available to them to determine the physical health status of the potential mate. Regardless of the wealth or ideology, the females in areas that are more at risk or have higher rates of parasites and diseases would weigh masculinity more highly when rating potential mates. • Scarification: In pre-industrial societies, body markings such as tattoos or scarifications are predicted to have been a way in which individuals could attract potential mates, by indicating the reproductive quality of a person. Meaning, scars on the body could be viewed by prospective mates as evidence that a person has overcome parasites and is thus more attractive to potential mates. Research investigating this hypothesis (Singh and Bronstad 1997) found that in instances of increased pathogen prevalence, the only anatomical area with evidence of scarification in females was found on the stomach, with no evidence found for male scarification. • Masculinity: In societies where there are high levels of parasites or diseases, the females, as the overall health of members decreases, are predicted to increasingly emphasize masculinity in their mate preferences. Women look for signs of masculinity in areas such as the voice, face and body shape of males. The face, in particular, may hold several cues for parasitic resistance and has been the subject of most attractiveness research. • Polygamy: Tropical areas were originally associated with polygynous societies as a result of the surrounding environment being both ecologically richer and homogeneous. However, whilst tropical areas were associated with polygamy, pathogen stress is predicted as a better indicator of polygamy and has been positively correlated with it. Furthermore, over the course of human evolution, areas which had high levels of parasite-stress may have shifted the polygamy threshold and increased the presence of certain types of polygamy in a society. Criticisms Gangested and Buss (2009) say that research indicates that parasite stress may have only influenced mate choice through females searching for "good genes" which show parasite resistance, in areas which have high prevalence of parasites. John Cartwright also points out that females may be simply avoiding the transmission of parasites to themselves rather than it being them choosing males with good genes and that females look for more than just parasite-resistant genes. Mate preference priorities Mate preference priorities are often measured using budget allocation, a method in which research participants are given a limited number of "dollars" they must distribute to various mate traits, a paradigm which forces them to make decisions about which characteristics are most important to them. This method generally yields two categories of preferences: necessities and luxuries. Necessities One study showed that, when given a small budget, people prioritize mate traits that were ancestrally significant for reproductive success. These traits are thought to be necessities, meaning they are considered essential in a mate. Cross-cultural and sex-differentiated necessities The traits that were viewed as necessities differed among men and women in both Eastern and Western samples. • Western women placed a higher priority on a partner having good financial prospects, a sense of humor, and a desire for children. • Western men viewed humor as a necessity. • Eastern women and men saw good financial opportunities as a necessity in a partner. • Eastern men rated a partner's religiosity as a necessity. Consensual necessities Despite the observed differences, men and women from various cultural backgrounds consistently placed a high value on kindness and physical attractiveness (though men did allocate a slightly higher amount toward attractiveness). Luxuries When given a large budget, participants allotted resources to traits considered luxuries – qualities that are desirable but nonessential in a partner. Cross-cultural and sex-differentiated luxuries • Western men tended to rate good financial prospects in a mate as a luxury. • Eastern men and women viewed humor as a luxury. • Eastern men and women, as well as Western men saw a partner's desire for children as a luxury. • Eastern women and Western women and men saw religiosity in a mate as a luxury. Consensual luxuries Regardless of sex or cultural background, the participants in this study frequently rated creativity and chastity as luxuries. == See also ==