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David buss evolution of human_mating_2007

  1. 1. 心 理 学 报 2007,39(3):502~512Acta Psychologica Sinica The Evolution of Human Mating David M. Buss University of Texas, AustinMating is close to the engine of the evolutionary process—differential reproductive success. As descendants ofreproductively successful ancestors, modern humans have inherited the mating strategies that led to our ancestor’ssuccess. These strategies include long-term committed mating (e.g., marriage), short-term mating (e.g., a briefsexual encounter), extra-pair mating (e.g., infidelity), mate poaching (luring another person’s mate), and mateguarding (effort devoted to keeping a mate). Since men and women historically confronted different adaptiveproblems in the mating domain, the sexes differ profoundly in evolved psychology of mating solutions. Thesepsychological sex differences include possessing distinct mate preferences, dissimilar desires for short-termmating, and distinct triggers that evoke sexual jealousy. This article reviews empirical evidence supportingevolution-based hypotheses about these mating strategies. The study of human mating is one of the true “successstories” of evolutionary psychology.Keywords: mating, adaptive problems, sexual jealousy, evolutionary psychology. 人类“性交往”的进化性交往是人类繁衍出现差异的进化“引擎”。现代人继承了祖先成功繁衍后代的性交往策略。这些策略涵盖长期守诺的性交往(如婚姻)、短期性交往(如短暂的外遇)、婚姻外的性交往(如不忠)、私通他人配偶(引诱别人的配偶)以及配偶维持(与单一配偶性交往)等。两性在性交往过程中面临不同的适应问题,性交往问题的进化机制存在极大的性别差异。配偶偏好不同、短期性交往的愿望不同以及性嫉妒的诱因不同等都是性交往具有性别差异的表现。很多实证研究都证实了性交往策略的存在,人类性交往研究是进化心理学研究中较为成熟的一个研究领域。关键词:性交往,适应性问题,性嫉妒,进化心理学。分类号:B84-069 Mating is close to the heart of the evolutionary from leaving, and engaging in all of the necessarilyprocess responsible for creating adaptations—the sexual and social behaviors required for successfuldifferential reproductive success of individuals as a conception, child-birth, and child-rearing to take place.consequence of heritable differences in corresponding As a consequence of the number and complexity oftraits. Simply put, those who fail to mate fail to mating problems humans have recurrently faced overbecome ancestors. If any one of our ancestors failed the long expanse of human evolutionary history, itto select an appropriate mate, failed to successfully follows logically that humans have evolved a largeattract a mate, or failed to retain a mate for enough and complex array of psychological adaptationstime needed for reproduction, we would not be here to specifically dedicated to the task of mating.contemplate the successful strategies that led to our Nowhere do people have an equal desire to mateexistence. Modern humans are all descendants of a with all people. Everywhere, some people arelong and unbroken line of ancestors who succeeded in preferred as mates, others shunned. Desires are centralthe complex tasks required to mate successfully. As to all facets of mating. Desires determine who we aretheir descendants, modern humans have inherited the attracted to, and who is attracted to us. They influencemating strategies that led to their success. which attraction tactics will be successful (those that Successful mating requires solutions of a number of fulfill desires) and which attraction tactics will faildifficult adaptive problems. These include selecting a (those that violate desires). Successful mate retentionfertile mate, out-competing same-sex rivals in tactics involve continuing to provide theattracting a mate, fending off mate poachers (those reproductively-relevant resources that fulfill thewho try to lure one’s mate away), preventing the mate desires of one’s mate. From mate selection to desertion, these desires influence every step of theReceived 2006-08-30 mating process.Correspondence should be addressed to David M. Buss, University ofTexas at Austin, Department of Psychology, Austin, TX 78712, USA;e-mail: dbuss@psy.utexas.edu 502
  2. 2. 3期 David M. Buss. The Evolution of Human Mating 503 Parental Investment and Sexual Selection succeeding generations. The result is evolution Although Charles Darwin (1859) recognized that through sexual selection.survival was central to the evolutionary process, many The second process through which sexual selectionnatural phenomena he observed seemed baffling on occurs is intersexual selection. This process involvesthe theory of “survival selection”. He noticed the preferences of members of one sex for membersphenomena such as the brilliant plumage of peacocks, of the opposite sex who possess certain qualities.the flamboyant feathers of cardinals, and the Hypothetically, if all women preferred to mate withenormous antlers of deer. How could these men who had green eyes, those with green eyes wouldmetabolically costly features possibly have evolved? have a mating advantage. Over time, we wouldMany seemed like open lures to predators, and hence witness an increase in the frequency of green eyes indetrimental to survival. Darwin also noticed that the population. The key point is that the desires of onemales and females of many species are different in sex for certain qualities in a mate can createsize and shape. Male elephant seals, for example, evolutionary change—either an increase in theweigh roughly 4,000 pounds; female elephant seals frequency of desired qualities or a decrease in theweigh only 1,000 pounds. Among baboons, males are frequency of undesired qualities. Although Darwintwice the size of females. Among humans, males are called this process “female choice,” it is clear that in12 percent taller than females, on average. Since both many species, and certainly in humans, males alsosexes have faced roughly the same survival problems, exert considerable mate choice.why would they differ in size and morphology? And Theoretically, the mate preferences of one sex canwhat could account for variation on the degree of determine over evolutionary time the domains insexual dimorphism across species? which the opposite sex competes (see Figure 1). If Darwin’s answer to these empirical puzzles was the females desire males who build sturdy nests, thentheory of sexual selection (Darwin, 1859; 1871). The males will compete with each other to construct neststheory of sexual selection dealt with the evolution of that embody the female preferences. Conversely, thecharacteristics due to mating, rather than survival, domains in which one sex competes can influence theadvantage. Darwin described two component evolution of mate preferences in the other sex. Ifprocesses through which sexual selection could take males compete with other males to monopolizeplace. In the first, called intrasexual competition, resource-rich territories that females need to supportmembers of one sex (often, but not always, the males) their young, for example, females might subsequentlyengaged in competitive battles with each other. Two evolve a mate preference for males that control largestags locking horns in combat is an excellent example territories. Thus, mate preferences and patterns ofof intrasexual competition. The victors in these battles intrasexual competition can co-evolve, eachgain preferential sexual access to females. The losers influencing the other.fail to mate. The qualities that lead to success insame-sex contests, therefore, are passed down ingreater numbers (assuming that these qualities are Intersexual Selection: Intrasexualpartly heritable). Whatever qualities are linked with Preferential Mate Competition:losing fail to get passed down. Evolution--that is Choice Same-Sex Rivalry for Matechange over time--occurs as a result of the differentialreproduction of the winners and losers in same-sexcontests. Figure 1. Sexual selection subsumes the processes of It is important to note that intrasexual competition intrasexual competition and intersexual selection. The mateneed not always be direct physical combat. Males in preferences of one sex determine the domains in which thesome species compete for position in the status or opposite sex will compete. The ways in which one sexdominance hierarchy through non-physical means, competes can infuence the evolution of mate preferences.and position in the hierarchy can be linked withpreferential access to mates (e.g., Betzig, 1986; Buss, Darwin’s (1871) theory of sexual selection was1994/2003). Males in other species scramble for initially designed to explain the various empiricalaccess to territory, and access to territory often gives puzzles he had observed—things like the brilliantits owners preferential access to mates. Males in still plumage of peacocks (preferred by peahens) and theother species compete for access to position in the larger size of males in some species (explained by thestatus or dominance hierarchy, which can give those advantage that size gives males in intrasexualwho rise preferential access to mates. The key point is competition, or by female preferences for males whothat whatever heritable qualities lead to success in are large). Indeed, the theory of sexual selectionintrasexual competition—be they physical strength, provides that most powerful theory known to explainability to acquire territory, or skills as hierarchy the many ways in which men and women differnegotiation--are passed on in greater numbers in psychologically and behaviorally (Buss, 1995; Geary,
  3. 3. 504 心 理 学 报 39 卷1998). But many puzzles remained. Darwin observed Not all mating, however, lasts a long time. Humanthat females were often the choosy sex, but he did not matings can last a few months, a few weeks, a fewknow why. He also observed that males were often days, or even a few minutes. This end of the temporalthe competitive sex, but he did not know why. continuum may be called short-term mating (Buss &Roughly a century would pass before evolutionary Schmitt, 1993). The temporal dimension turns out tobiologists devised a powerful theory to explain which be critical to many components of mating, perhapssex will compete and which sex will exercise choice, none more central than the qualities desired.that is, what drives the operation of the two Furthermore, humans display remarkable creativity incomponent processes of sexual selection. their ability to mix and match mating strategies. It is Trivers’s (1972) answer to these questions was the not uncommon, for example, for a person to engage intheory of parental investment. According to this one long-term committed mateship with heavytheory, the sex that invests more than the other in investment in children, while simultaneously pursuingoffspring would be more choosy about mates. In an extramarital affair, or series of affairs, on the side.species with internal female fertilization, the greater Humans, in short, are neither solely monogamous,parental investment by females makes them a nor solely promiscuous; neither polygynous norvaluable reproductive resource. Gestating, bearing, polyandrous. Which strategies from the menu aand breast feeding a child, for example, are costly particular person chooses is heavily dependent onendeavors. A nine-month pregnancy is the minimum circumstances. These include the sex ratio in theobligatory investment needed by a woman to produce mating pool (i.e., the ratio of males to females that area child, whereas one act of sex is the minimum looking for a mate), a person’s mate value (howinvestment needed by a man to produce that same desirable they are to members of the opposite sex),child. and even prevailing cultural norms (Buss, 2004). Elementary economics tells us that those who hold These contextual factors will be discussed later, butvaluable resources do not give them away first, we must outline the central desires of men andindiscriminately. Evolution favored women who were women in their pursuit of long-term and short-termhighly selective about their mates. Women who were mates.not choosy would have suffered lower reproductivesuccess. Those who engaged in careful mate selection, What Women and Men Desire in a Marriagefor example preferring a man who would stay around, Partnerinvest in her, and protect her children, enjoyed Because women have a large obligatory parentalreproductive benefits. The more an individual devotes investment to produce children, and therefore areeffort to parental investment, according to Trivers predicted to be discriminating in their mate choice, on(1972), the greater the benefits of exercising careful what qualities should they base their desires?mate choice. The sex that invests less in offspring, Potential mates vary in thousands of ways, fromaccording to this theory, should be more competitive height and weight to social skills, from athletic abilitywith each other for access to the high-investing sex. to hair color. Adaptationist thinking provides a guideIn summary, the relative investment of the two sexes to hypotheses about the evolution of what womendrives the operative components of sexual selection, want. Women are predicted to desire characteristicswith the high investing sex being selected to be more that reliably lead to an increase in women’schoosy and the lower investing sex being the most reproductive success. These include selecting a matecompetitive with members of their own sex for who (1) is able to invest resources in her and hermating access to the more valuable high-investing sex. children, (2) is able to physically protect her and her children, (3) shows promise as a good parent, and (4) Humans Have a Menu of Mating Strategies will be sufficiently compatible in goals and values to One of the intriguing features of human mating is enable strategic alignment without inflicting too manythat it cannot be characterized by a single strategy. costs on her and her children (Buss, 1994/2003).One strategy on the menu is long-term committed In a large-scale cross-cultural study, Buss and hismating, often, but not always, characterized by a colleagues (Buss, 1989; Buss et al., 1990) exploredformal public commitment such as marriage. In long- how much women and men desired each of 32term mating, both sexes typically invest heavily in qualities in a potential long-term mate. The studyany resultant offspring. As a consequence, and in involved samples from 37 cultures located on sixaccordance with the theory of parental investment, continents and five islands. The samples includedsexual selection should favor in both sexes high levels Gujarati Indians, Estonians, Chinese from bothof choosiness or selectivity. Poor long-term mate Taiwan and the Mainland of China, Santa Catarinachoices would have been costly for either women or Brazilians, and South African Zulu. The samplemen because they would have risked wasting their included tremendous diversity of ethnic, religious,heavy investments. political, and economic groups. The total sample size
  4. 4. 3期 David M. Buss. The Evolution of Human Mating 505was 10,047, with an average of 272 from each of the and healthy. Similarly, mutual attraction/love37 cultures. emerged as one of the most valued qualities in aCulturally variable desires. Cultures varied spouse worldwide. Both sexes also valued potentialtremendously in the value placed on some spouses who were similar to themselves in theircharacteristics. The desire for chastity or virginity political orientation and religious beliefs. Intelligence(lack of prior sexual intercourse) proved to be the is linked with many positive qualities, including skillmost cross-culturally variable, as shown in Figure 2. at parenting and longevity. Kindness is linked with aMainland Chinese and individuals from the island of cooperative disposition, interest in long-termTaiwan placed tremendous value on virginity, as did relationships, ability to form social alliances, andparticipants living in India and Iran. At the other end empathy in rearing children. Dependability is linkedof the scale, those from Finland placed little with reliability, sustained cooperation, andimportance on chastity, as did those from most willingness to help a mate consistently through timesWestern European countries such as Denmark, of trouble. Good health is linked with longevity andSweden, France, and Germany. lack of diseases that might be transmitted to a mate or children. Similarity of the couple helps to minimize social conflict within their relationship and leads to greater long-term happiness in marriage (see Buss, 1994/2003 for an extended discussion of these qualities). Universal sex differences in desires. Despite these cultural variations and cross-cultural universals, women and men differed across the globe on their desire for some qualities, precisely as predicted in advance by the evolutionary hypotheses. Women, significantly more than men, desired “good financial prospect” in a mate (see Figure 3). The sex differences were larger in some cultures such as Japan and Zambia, and smaller in other cultures such asFigure 2. The rating scale ranged from 3 (indispensable) to 0(irrelevant or unimportant) in a marriage partner. Sex China and Croatia, but these differences are universal.differences are statistically significant (p < .05) for India, Japan, Women also tended to value qualities that are knownUSA, and Croatia, but not for mainland China, Taiwan, or to be linked to resource acquisition, such as ambition,Finland. industriousness, social status, and somewhat older age. Overall, 62% of the cultures showed a significantsex difference, always in the direction of men valuingvirginity more than women. There were no reversalsof this pattern. On the other hand, 38% of the culturesshowed no significant sex difference. These findingssuggest that the importance placed on chastity ishighly susceptible to cultural input, with culturesdiffering from each other both in the absolute valueplaced on chastity as well as in the presence orabsence of sex differences. Nonetheless, the fact thatin many countries men valued virginity more thanwomen, with no single reversal, indicates that thevalue placed on virginity is not an infinitely culturally Figure 3. Women universally place greater importance on good financial prospects in a marriage partner. Rating scalevariable. Evolutionary psychologists have proposed ranged from 3 (indispensable) to 0 (irrelevant or unimportant)that concern about a woman’s sexual contact with in a marriage partner. Sex differences are statisticallyother men represents facing the recurrent adaptive significant (p < .05) in all cultures.problem of uncertainty of paternity. Researchsuggests that men’s desire for sexual fidelity of a mate, Physical appearance, as voluminous research hasrather than premarital virginity, may indeed be a shown, provides a wealth of cues to a woman’s health,human universal (Buss, 2000; 2004). fertility, and reproductive value (see Figure 4). Cross-cultural universal desires in both sexes. Contrary to long-held beliefs among social scientists,Many characteristics were universally desired by both standards of beauty are not arbitrary or infinitelysexes. Worldwide, women and men wanted mates culturally variable. Evolutionary psychology provideswho were intelligent, kind, understanding, dependable, a powerful theory for the evolution of standards of female beauty—whatever observable cues are linked
  5. 5. 506 心 理 学 报 39 卷with fertility (immediate probability of conception) or attractiveness or “good looks,” supporting thereproductive value (future reproductive potential) will evolutionary psychological prediction. It is importantevolve to become part what humans find attractive in to note that women still value physical attractiveness,females. These include cues to youth, such as full lips, but the importance they place on this quality is not assmooth skin, lustrous hair, and a low ratio of hips to great as the importance that men place on it.waist (WHR). They also include cues to health, suchas clear skin, absence of sores, white teeth, andsymmetrical features. Beauty, in short, is in the“psychological adaptations of the beholder,” and menvalue physical appearance because of the wealth ofinformation it provides about a woman’s youth, health,and hence reproductive capacity. Cues Fertility or Full lips Reproductive Clear skin Standards of Value Clear eyes Attractiveness Lustrous hair Figure 5. Participants reported in years their preferred age Long hair difference between self and spouse, expressed in number of Muscle tone Sprightly gait years older or younger. Men universally preferred younger Symmetry partners, whereas women universally preferred older partners. Facial femininity In China, for example, women wanted men nearly roughly Feminine voice three and a half years older than themselves, whereas men Low WHR wanted women roughly two years younger than themselves. Etc. The sex differences are statistically significant (p < .001) in all cultures.Figure 4. Graph depicts the logic of the hypothesis of evolvedstandards of beauty. Observable cues such as full lips and clearskin are hypothesized to become part of evolved standards offemale attractiveness because of their link with fertility(immediate probability of reproduction) or reproductive value(future reproductive potential). WHR = waist-to-hip ratio. Men universally wanted mates who were youngerthan themselves, confirming the hypothesis that mendesire this powerful fertility cue (see Figure 5). Thisproved to be the strongest sex difference in the 37culture study. Nonetheless, there was some cross-cultural variability. In China, for example, young mendesired spouses to be more than two years younger; inTaiwan and Venezuela more than three years younger; Figure 6. Men universally place greater importance onand Zambia and Nigeria, more than six years younger. physical attractiveness (“good looks”) in a long-term mate, Because of the wealth of information a woman’s supporting the evolutionary hypothesis.appearance provides about her fertility and In summary, universal sex differences occurred inreproductive value, men were predicted to place a precisely those domains predicted to involve sex-greater premium on physical appearance or physical differentiated adaptive problems, notably the desireattractiveness than do women in mate selection. for mates who have the ability to invest resourcesAlthough physical appearance was still predicted to (women prefer more than men) and mates whobe important for women in their choice of a mate display cues to youth and physical attractiveness,because of its link to health, many qualities that known signals of fertility (men prefer more thanwomen desire such as resources and status are not women). Despite these universal sex differences,easily evaluated by physical appearance. Therefore, many mate preferences show great similarity betweenthe evolutionary hypothesis predicted that men would the sexes (e.g., kind and understanding, intelligent,value physical attractiveness more than women. healthy), and there are also important culturalFigure 6 shows representative results from six differences in some desires such as the desire for acountries from the 37 culture study. In all cases, men mate who is a virgin.more than women indeed value physical
  6. 6. 3期 David M. Buss. The Evolution of Human Mating 507 It is important, of course, to obtain independent fundamental desires differ for men and women andconfirmation of these findings from alternative affect actual mating behavior in precisely the waysmethods that do not rely on expressed preferences. predicted.And indeed, many alternative methods support thevalidity of the methods used to obtain expressed Short-Term Mating Desirespreferences. A study of actual marriages in 29 Trivers’s (1972) theory of parental investmentdifferent cultures, for example, confirmed that men do provides a powerful logical basis for predicting sex-choose younger women (Buss, 1989). Grooms were differentiated adaptations for the pursuit of short-termolder than brides in each one of the 29 cultures, with matings. Men, more than women, are predicted toan average age difference of three years. Furthermore, have evolved a greater desire for casual sex (Buss &as men get older, if they get divorced and remarry, Schmitt, 1993; Symons, 1979). The same act of sexthey tend to marry women who are increasingly that causes a woman to invest nine months inyounger than they are. The age gap is three years at pregnancy obligates the man to little or no investment.first marriage, five years at second marriage, and Over a one-year period, an ancestral man whoeight years at third marriage (Buss, 1994/2003; managed to have short-term sex with dozens ofKenrick & Keefe, 1992). women would have caused multiple pregnancies. An Studies of the content and response rates to ancestral woman who had sex with dozens of men inpersonals ads also confirm the results found with the same year would produce only a single child. Theexpressed preferences. Women mentioning physical reproductive benefits to men of short-term mating, inattractiveness and young age as part of their self- sum, would have been a direct increase in thedescription in their ads receive significantly higher production of children. A married man with tworesponse rates than women who are older or who fail children, for example, would have increased histo mention anything about their physical reproductive success by 50% by one short-termattractiveness. Conversely, men who mention copulation or affair that resulted in conception andexcellent financial resources in their self-descriptions birth.in their ads received a higher response rate from The empirical evidence for a sex difference inwomen than men who fail to mention this attribute desire for short-term mating is extensive, supported(Baize & Schroeder, 1995). by hundreds of scientific studies (Buss, 2004). When Finally, studies of the behavioral tactics that men asked how many sex partners they would ideally like,and women use to attract mates, retain mates, and men state that they would like an average of 18 inderogate their rivals all correspond closely to the their lifetime, whereas women average around 4.5, asexpressed desires of the opposite sex. Women, for shown in Figure 7 (Buss & Schmitt, 1993). Theseexample, tend to put more effort into appearance large sex differences have been replicated usingenhancement in mate attraction and mate retention, different statistical methods of calculating centraland when they derogate their rivals they focus on the tendency (e.g., medians rather than means) onrival’s physical flaws (e.g., mentioning that the other samples diverse in age (Schmitt et al., 2003).woman’s thighs are heavy). Conversely, men tend todisplay and bestow resources on the women they aretrying to attract and retain. They tend to denigratetheir rivals by impugning the rival’s professionalprospects, such as mentioning that the rival is lazy,lacks ambition, or lacks clear goals in life (see Buss,2004, for detailed summaries of these studies). Whenmen and women attempt to deceive each other, theydo so precisely along the lines of the desiresexpressed by the opposite sex (Tooke & Camire,1991). It is worth noting that, conceptually, we do notexpect a perfect correspondence between expresseddesires and actual mating behavior for the simplereason that people cannot always get what they want. Figure 7. Number of sexual partners desired. ParticipantsA person’s own limited “mate value” or level of recorded in blank spaces provided how many sexual partners they ideally would like to have for each specified time intervaldesirability, for example, will limit their ability to (data from Buss and Schmitt, 1993).attract the most desirable mates. Most people mustsettle for someone who is less than what they ideally Another psychological solution to the problem ofwant. Nonetheless, the available evidence converges gaining sexual access to a variety of partners is to letfrom a variety of different methods that these little time elapse between meeting a desired female
  7. 7. 508 心 理 学 报 39 卷and seeking sexual intercourse. The less time a man In summary, the evidence is strong that men havepermits to elapse before seeking sexual intercourse, evolved psychological mechanisms dedicated tothe larger the number of women with whom he can solving the complex problems posed by success atsucceed in copulating. In one study that has been short-term mating. These include a desire for sexualextensively replicated, men and women rated how variety, the tendency to let little time elapse beforelikely they would be to consent to sex with someone seeking sexual intercourse, and the behavioralthey viewed as desirable if they had known the person willingness to consent to sex with strangers. Infor only an hour, a day, a week, a month, and so on. addition, men, but not women, appear to lower theirBoth men and women say that they would probably standards dramatically in the context of short-termhave sex after knowing a desirable potential mate for mating (Buss & Schmitt, 1993); show a markedfive years (see Figure 8). At every shorter interval, decrease in attraction to a sex partner immediatelymen exceeded women in the reported likelihood of following sexual intercourse with a short-term sexhaving sex. These large sex differences have been partner, a psychological phenomenon hypothesized toreplicated in a study of 52 cultures (Schmitt et al., facilitate a hasty post-copulation departure (Haselton2003). & Buss, 2001); report exaggerating the depth of their A behavioral study confirmed this large sex feelings to gain sexual access (Haselton, Buss, Oubaid,difference (Clarke & Hatfield, 1989). Men and & Angleitner, 2005); and report that they would havewomen experimenters approached total strangers on a an extramarital affair if they knew that no one wouldcollege campus, and said “Hi, I’ve been noticing you find out (for reviews of this evidence, see Buss,around campus, and I find you very attractive.” Then 1994/2003). In sum, the evidence for evolvedthey asked one of three questions: Would you go out psychological adaptations in men for short-termon a date with me? Would you go back to my mating is substantial.apartment with me? Would you have sex with me?The experimenters recorded the percentage who The Puzzle of Women’s Short-Term Matingagreed to each request, and also any verbal comments Strategiesthey made. Although the empirical evidence is clear that men, Of the women approached by the male far more than women, have a great desire for a varietyexperimenters, 50% agreed to go out on a date with of sex partners, men could never have evolved thishim; 6% agreed to go back to his apartment; and 0% desire in the absence of willing women (barringagreed to have sex. Some women who were asked for deception or forced intercourse). Indeed,sex were insulted, and some thought this is bizarre. Of mathematically, the mean number of sex partners forthe men approached by the female experimenters, men and women must be identical, assuming an equal50% agreed to go out on a date, similar to the sex ratio in the population. Every time a man has sexwomen’s responses. However, 69% agreed to go back with a woman with whom he has not previously hadto her apartment. And 75% agreed to have sex with sex, a woman is simultaneously having sex with aher. Of the men who declined the sexual request, man with whom she has never had sex.some were apologetic, citing for instance a prior Perhaps because the evolutionary logic for mencommitment with parents or a fiancée. These sex having evolved a strong desire for sexual variety is sodifferences have been replicated in subsequent studies clear—a direct increase in reproductive output—the(see Buss, 2000, for a summary). evolutionary logic for women having evolved a short- term mating psychology remained relatively neglected until recently. The puzzle is deepened by the fact that short-term mating often carries substantial costs for women. Women, more than men, risk damage to their reputations, a lowering of perceptions of their mate value, and if mated, the possibility of violence at the hands of a jealous boyfriend or husband (Buss, 2000). Given these costs, it is unlikely that selection would have forged a female short-term mating psychology in the absence of substantial benefits that outweigh those costs. In an effort to explore what those benefits might be, Greiling and Buss (2000) both formulated andFigure 8. Participants indicated how likely they would be to extracted from the literature a number of hypotheseshave sex with someone they found attractive as a function of about potential benefits that women might possiblyhow much time they had known the individual. The scale obtain from short-term mating. These includeranged from +3 (highly likely) to -3 (highly unlikely). resource hypotheses (e.g., immediate resource
  8. 8. 3期 David M. Buss. The Evolution of Human Mating 509accrual), genetic hypotheses (e.g., producing more summary, resource acquisition, mate switching, andgenetically diverse offspring), mate switching good genes are the three most viable hypotheses forhypotheses (e.g., using a short-term mating as a means the evolved functions of women’s short-term mating.to exit a poor mateship), mate skill acquisition Further research, of course, is needed to test thesehypotheses (e.g., clarifying mate preferences), and hypotheses.mate manipulation hypotheses (e.g., deterring a The existence of already mated women whopartner’s future infidelity). sometimes engage in sexual intercourse with other Greiling and Buss (2000) conducted a series of four men points to an adaptive problem that men aroundempirical studies to identify which hypotheses the world past and present confront—the problem ofappeared promising and which did not. Although mate poachers.limited in scope, these studies were designed toexamine (1) the perceived likelihood that a woman Mate Poachingwould receive particular benefits through a short-term Mate poaching is defined as behavior designed tomating; (2) the perceived magnitude of benefits if attract someone who is already in a romanticreceived; (3) the contexts in which women engage in relationship, either temporarily for a brief sexualshort-term mating; and (4) individual differences encounter or more permanently for a long-termamong women in proclivity to engage in short-term mateship. Until recently, practically nothing wasmating. Below are reported only the result of short- known scientifically about the phenomenon of mateterm extra-pair mating (EPC). poaching (Schmitt & Buss, 2001). Mate poaching The hypotheses that received the most empirical turns out to be a prevalent phenomenon. Using asupport across studies were those of resource relatively mature sample of American participants,acquisition and mate switching. For example, women averaging 41 years of age (range = 30 – 65), 60% ofjudge it to be highly likely that they will receive the men and 53% of the women reported havingjewelry, money, free dinners, or clothing by engaging attempted to poach someone as a long-term mate whoin short-term mating. Furthermore, a critical context was already in an existing committed relationship atin which women consider short-term affairs is when least once. The comparable figures for attempting tothe partner cannot hold down a job. Women who attract an already-mated person for a short-termactively engage in short-term mating, in contrast to sexual liaison were 60% for men and 38% for women,their more monogamous counterparts, judge the another piece of evidence supporting the greaterresource benefits to be “more beneficial.” desire men compared to women have for short-term The hypothesized mate-switching function of mating.women’s short-term mating would, of course, only The majority of this sample also reported beingapply to context in which the short-term mating is an recipients of mate poaching attempts by others whileaffair or an extra-pair copulation (EPC). Contexts in they were in a committed romantic relationship. Thewhich women judge it to be highly likely that they figures for the long-term mating context were 93% forwill have an affair include “feeling that she could find men and 82% for women. Eighty-seven percent of thesomeone with whom she is more compatible than her men and 94% of the women reported being recipientscurrent partner.” Furthermore, women perceive it to of mate poaching attempts for brief sexual matings.be highly beneficial to discover a sexual partner who Attempted mate poaching is one issue; successfulis interested in making a commitment to them, willing mate poaching is another. When asked whether theyto spend a lot of time with them, and able to replace have been successfully lured away from an existingtheir current partner. relationship, 67% of the men and 41% of the women Other research, however, also supports the good responded affirmatively for the long-term context.genes hypothesis (Gangestad, Thornhill, & Garver- And 40% of the men and 31% of the women reportApgar, 2005; Gangestad & Thornhill, 1997). having been successfully seduced by a mate poacherSymmetry of features and masculine facial features, for a short-term sexual liaison. Similar findings havefor example, are hypothesized to be markers of good been obtained cross-culturally in samples fromgenes. This signals a strong immunocompetence Taiwan and Mainland of China, Israel, Turkey,system and resistance to environmental insults during Greece, Croatia, Slovenia, Poland, Portugal, Germany,development—healthy qualities that could get passed France, England, and Canada (Schmitt et al., 2004).on to children. Women show a special preference for It is likely that mate poaching is an evolved matingmen who are symmetrical and masculine when they strategy for the simple reason that desirable matesare ovulating—precisely the time when they are most attract many suitors and consequently end up inlikely to conceive a child (Gangestad et al., 2005). mating relationships. Desirable individuals typicallyFurthermore, mated women experience sexual do not remain unmated for long. Thus, in order tofantasies about these other men when they are obtain a desirable mate, it is often necessary to seekovulating, more than when they are not ovulating. In those who are already “taken.” The unique mate
  9. 9. 510 心 理 学 报 39 卷poaching tactics, such as befriending the couple and these reasons, evolutionary psychologists havewaiting in the wings for an opportunity, or attempting predicted that men, more than women, would getto drive a wedge in the relationship, reveal the lengths upset about signals of sexual infidelity. In contrast,to which people will go in order to mate poach. women, more than men were predicted to get upset about signals of emotional infidelity, since emotional Mate Retention Strategies involvement is a leading indicator of the diversion of Infidelity and mate poaching as mating strategies these resources and commitments (Buss et al., 1992).pose serious adaptive problems for the “victims,” that Although both sexes are predicted to become upset atis the mates of the individuals who are committing both forms of infidelity, since they both signal theinfidelity or being tempted by a mate poacher. If these loss of reproductively-relevant resources, themating strategies have recurred over the long course hypothesis predicts a sex difference in theof human evolutionary history, as the evidence “weighting” of the cues to infidelity.suggests, the principle of co-evolution dictates that Dozens of empirical studies, using a variety ofstrategies will almost certainly evolve to defend methodologies, have now been conducted to test foragainst these problems and the costs they impose. this sex difference (Buss & Haselton, 2005). In oneInfidelity, which inflicts a cost on the reproductive study, participants were asked to imagine that theirsuccess (fitness) of the partner, will in turn select for romantic partner had become both sexually anddefenses to prevent infidelity such as jealousy and emotionally involved with someone else (Buss et al.,mate guarding. These defenses, in turn, make 1999). Then they were asked to indicate which aspectinfidelity less reproductively successful as a strategy, of the betrayal was more upsetting. In an Americanwhich creates selection pressure for additional sample, 61% of the men, but only 13% of the womeninfidelity adaptations, such as those that evade the judged the sexual infidelity aspect of the betrayal tojealous eyes of the mate guarder. These infidelity be the most upsetting. Conversely, only 39% of theadaptations, in turn, select for more sophisticated men, but 87% of the women, judged the emotionaldefenses. One possible solution involved the attachment to the other person as more upsetting.evolution of jealousy (Buss, Larsen, Westen, & Similar sex differences have been obtained in KoreaSemmelroth, 1992; Daly, Wilson & Weghorst, 1982; and Japan (Buss et al., 1999), China (Geary, Rumsey,Symons, 1979). Jealousy is an emotion that is Bow-Thomas, & Hoard, 1995), and Swedenactivated whenever there is a threat to a valued (Wiederman & Kendall, 1999). In studies of memory,relationship (Daly et al., 1982). Threats can come in men can more easily recall cues to sexual infidelity,many forms, such as the loss of a partner’s sexual, whereas women can more easily recall cues tofinancial, or emotional resources to a rival. Threats emotional infidelity.can come from within the relationship from a partner In summary, men and women differ, as originallywho might have the urge to stray, or from outside the predicted in advance by evolutionary psychologists, inrelationship in the form of mate poachers attempting the weighting given to the events that activateto lure a partner away. jealousy. Men, more than women, tend to become Over the past decade, a substantial amount of extremely distressed over signals of sexual infidelity;research has been devoted to exploring jealousy as an women more than men tend to become moreevolved solution to the problems of infidelity and distressed over signals of emotional infidelity. Ofmate poaching (see Buss, 2000, for an in-depth course, both sexes typically get extremely upset bydiscussion). The specifics of the adaptive problems both forms of infidelity, as they should because bothdiffer for men and women, according to evolutionary forms threaten key reproductively relevant resources.psychologists (Buss, 2000; Daly et al., 1982; Symons, Furthermore, the two forms of infidelity are positively1979). Because fertilization occurs internally within correlated in everyday life—people tend to becomewomen, men can suffer a lack of certainty in their sexually involved with those with whom they arepaternity. They can never be 100% certain that a child emotionally involved and vice-versa. Nonetheless, theis genetically their own (barring modern forms of findings are clear in supporting the originalpaternity testing). In contrast, women are always predictions about the psychological design of jealousy100% certain that their offspring are their own. Sexual as an evolved defense against infidelity and theinfidelity, of course, is the action that can compromise threats posed by mate poachers.a man’s paternity in offspring. Men and women also appear to be threatened by Although women have never confronted the somewhat different qualities in intrasexual rivals.problem of maternity uncertainty, an infidelity by a Specific evolution-based predictions were tested in awoman’s mate can be extremely damaging. The cross-cultural study that included Korea, thewoman whose husband is unfaithful risks losing his Netherlands, and the United States (Buss, Shackelford,time, resources, and commitments, all of which could Choe, Buunk, & Dijkstra, 2000). Korean, Dutch, andget channeled to a rival female and her children. For American men, more than corresponding women,
  10. 10. 3期 David M. Buss. The Evolution of Human Mating 511reported greater distress when a rival who was expressed preferences, as well as in studies of actualinterested in their partner surpassed them on financial marriages, responses to personals ads, and tactics ofprospects, job prospects, and physical strength. In mate attraction, mate retention, competitor derogation,contrast, Korean, Dutch, and American women report and intersexual deception.greater distress when a rival surpasses them on facial The empirical evidence supports the evolutionaryand bodily attractiveness. Although both sexes are psychological hypothesis that men have evolved aequally jealous overall, the sexes differ in the more powerful desire for a variety of sex partners thanweighting given to sexual versus emotional infidelity have women. The evolutionary logic for this sexas well as in the qualities of rivals that they find difference is straightforward—men who succeeded inthreatening. securing sexual access to a variety of women would If jealousy is an evolved emotion, and the empirical have achieved greater reproductive success than menevidence so far appears to support this proposition, who did not. Ancestral women, in contrast, could notthen the next step is to explore the behavioral output increase their reproductive output by having sex withof this emotion. Three different studies have explored many men. Nonetheless, there is a hidden side to“mate retention tactics” of men and women, using female sexuality, and some women some of the timeboth married couples and dating couples as also pursue short-term matings. Because women’sparticipants (Buss, 1988; Buss & Shackelford, 1997; short-term mating can be risky, it is reasonable toShackelford, Goetz, Buss, Euler, & Hoier, 2005). hypothesize that ancestral women received benefitsMate retention tactics are specific behaviors designed from short-term mating that outweighed the costs.to ward off rivals or to deter a mate from straying. The leading hypotheses for why women engage inThe specific tactics range from vigilance (e.g., He short-term mating, especially extra-pair mating, arecalled her at unexpected times to see who she was the possibility of acquiring good genes that can bewith) to violence (e.g., He hit the guy who made a passed to her offspring, increasing her access topass at her). material resources, and switching to a better mate. Married men tend to engage in especially vigorous Women who cuckolded their husbands historicallymate retention efforts when their spouse is young in have inflicted large reproductive costs on their regularage and physically attractive. In contrast, women tend mates. Cuckolded men risk diverting years or decadesto engage in especially vigorous mate retention efforts of parental resources to a rival’s offspring. Thewhen married to men who have good jobs, high principle of co-evolution predicts that men haveincomes, and devote a lot of time to status striving. In evolved adaptations designed to defend against theaddition, men and women differ in the types of mate diversion of their mate’s sexual and reproductiveretention tactics they use. Men, more than women, resources.tend to display resources to their mate, as well as Jealousy as an emotion has been proposed as onethreaten and commit violence on intrasexual rivals. evolved defense mechanism. The empirical evidenceWomen, more than men, tend to enhance their strongly supports several evolution-based hypothesesphysical appearance as a mate retention strategy, as about the psychological design of jealousy. Malewell as intentionally evoking their partner’s jealousy. jealousy, more than women’s, is triggered by signalsIntentionally evoking jealousy, for example by flirting of sexual infidelity and rivals to exceed them on thewith other men and eliciting their interest, appears to qualities that women are known to want in a matebe a strategy women use to increase their mate’s such as good financial prospects. Women’s jealousy,perceptions of their desirability (Buss, 2000). more than men’s, is activated by signals of emotional infidelity (and hence potential long-term diversion of Conclusions commitments) as well as by rivals who exceed them Humans have evolved a complex menu of mating on facial and bodily attractiveness.strategies. These include long-term committed mating, Much more research needs to be conducted on thebrief sexual encounters, infidelity, mate poaching, and complexities of human mating strategies. At this pointmate guarding. Long-term mate preferences are in the evolutionary psychology, however, scientistscomplex, reflecting desires for many different now have some of the broad outlines of thequalities such as kindness, intelligence, mutual fundamentals of human mating strategies and theattraction, love, dependability, and good health. Some ways in which they are designed differently in menare cross-culturally variable, such as the desire for and women.virgin spouses. Two universal clusters of sex Additional research is needed on the context-differences are the desire for youth and beauty (men sensitive nature of human mating strategies. Preciselyvalue more than women) and the desire for a mate which circumstances might cause a person to shiftwho has good financial prospects and elevated social from a long-term mating strategy to a short-termstatus (women value more than men). These profound mating strategy or vice-versa? Which circumstancessex differences have been documented in studies of might trigger an extramarital affair, or conversely,
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