Sex Differences in Sex Drive, Sociosexuality, and Height across 53 ...

Arch Sex BehavDOI 10.1007/s10508-007-9242-8ORIGINAL PAPERSex Differences in Sex Drive, Sociosexuality, and Height across53 Nations: Testing Evolutionary and Social Structural TheoriesRichard A. LippaReceived: 4 September 2006 / Revised: 14 June 2007 / Accepted: 14 June 2007Ó Springer Science+Business Media, LLC 2007Abstract By analyzing cross-cultural patterns in fiveparameters—sex differences, male and female trait means,male and female trait standard deviations—researchers canbetter test evolutionary and social structural models of sexdifferences. Five models of biological and social structuralinfluence are presented that illustrate this proposal. Usingdata from 53 nations and from over 200,000 participantssurveyed in a recent BBC Internet survey, I examinedcross-cultural patterns in these five parameters for twosexual traits—sex drive and sociosexuality—and forheight, a physical trait with a biologically based sex difference.Sex drive, sociosexuality, and height all showedconsistent sex differences across nations (mean ds = .62,.74, and 1.63). Women were consistently more variable thanmen in sex drive (mean female to male variance ratio =1.64). Gender equality and economic development tendedto predict, across nations, sex differences in sociosexuality,but not sex differences in sex drive or height. Parameters forsociosexuality tended to vary across nations more thanparameters for sex drive and height did. The results forsociosexuality were most consistent with a hybrid model—thatboth biological and social structural influencescontribute to sex differences, whereas the results for sexdrive and height were most consistent with a biologicalmodel—that evolved biological factors are the primarycause of sex differences. The model testing proposed hereencourages evolutionary and social structural theorists tomake more precise and nuanced predictions about the patterningof sex differences across cultures.R. A. Lippa (&)Department of Psychology, California State University,Fullerton, Fullerton, CA 92834, USAe-mail: rlippa@fullerton.eduKeywords Evolutionary theory BBC Internet study Sex differences Sex drive Sociosexuality Socialstructural theoryIntroductionCross-cultural research provides an important testingground for both evolutionary and social structural theoriesof sex differences in sexuality. Proponents of evolutionarytheories argue that cross-culturally consistent sex differencesin traits such as sociosexuality (i.e., restricted versusunrestricted sexual attitudes and behavior), sexual activitylevels, and the characteristics preferred in mates (e.g.,physical attractiveness) constitute strong evidence thatevolved biological dispositions underlie these sex differences—dispositionsthat show through the ‘‘noise’’ ofcultural variations (Buss, 1989, 2005; Schmitt, 2005). Inresponse, proponents of social structural theories note thatthere are strong associations, across societies, betweenindices of gender equality and sex differences in sexuality,and these associations constitute powerful evidence thatsocial and cultural factors contribute to these sex differences(Eagly & Wood, 1999, 2005; Wood & Eagly, 2002).Despite the either-or tone that often colors the debatebetween evolutionary and social structural theorists, thesetwo approaches are not necessarily mutually exclusive, andit is likely that both have valid domains of application(Lippa, 2007; Schmitt, 2005). Cross-cultural consistenciesin sex differences (e.g., in all countries and cultures studiedto date, men score higher than women on sociosexuality)may indeed constitute evidence that there are biologicalcomponents to these sex differences. At the same time, thepower of indices of gender equality to predict sex differencesin sexuality across cultures suggests that some sex123

Arch Sex Behavdifferences are highly sensitive to cultural ideologies andsocial ecologies. In a sense, what constitutes the ‘‘figure’’to one theoretical approach (e.g., explaining systematiccross-cultural variation in sex differences is of primaryinterest to social structural theory) is background noise tothe other (cross-cultural variation is sometimes regarded byevolutionary theory as error variance masking the ‘‘maineffect’’ of evolved sex differences).Recent attempts to test the relative power of evolutionaryand social structural theories to account for crossculturaldata on sex differences have been inconclusive, inpart because the data to be explained do not decisivelydistinguish between the two theoretical approaches. To usea statistical metaphor, the models proposed by the twoapproaches are under-identified by the data that have beenused to test them. For example, evolutionary theoristsargue that the consistent finding that men score higher thanwomen on sociosexuality in all cultures surveyed to date isstrong evidence for evolved sex differences in sociosexuality(Buss, 2005; Schmitt, 2005). Social structural theoristscounter that all modern societies display patriarchalsocial structures, albeit to varying degrees, and thus it is notsurprising that all societies show unidirectional sex differencesin traits such as sociosexuality, sexual activitylevels, and preferences for particular traits in mates (Eagly& Wood, 2005). Thus, the very same findings—unidirectionalsex differences in sociosexuality that vary acrosscultures—can be explained, post-hoc, by both evolutionaryand social structural theories.One goal of the current research was to generate betteridentified models that could more clearly distinguishbetween the predictions of evolutionary and social structuraltheories. One route to achieving this goal is to providemore ‘‘data points’’ to be fitted to the theories’ proposedmodels. To accomplish this goal, in the research reportedhere I focused not only on the ability of evolutionary andsocial structural theories to predict sex differences acrosscultures, but also on their ability to predict the pattern ofmale and female mean trait levels and the pattern of maleand female trait standard deviations (SDs) across cultures.By attempting to predict the patterns of these additionalparameters, researchers may be able to generate betteridentified models that can discriminate more conclusivelybetween evolutionary and social structural theories.Researchers can also evaluate the predictive power ofhybrid models that assume both biological and socialstructural contributions to sex differences.To illustrate the promise of these methods, I analyzed alarge cross-cultural dataset generated by a recent BBCInternet survey of over 200,000 participants, and I focusedparticularly on two sexual traits—sex drive and sociosexuality.My goal was to demonstrate that cross-culturalpatterns of sex differences, male and female trait means,and male and female trait SDs were different for these twotraits. I argue, based on these findings, that different modelsof biological and social structural influence are needed toaccount for the cross-cultural patterns of results for thesetwo sexual traits. Thus, in addition to applying newmethods to the cross-cultural study of sex differences, Ialso examine the possibility that the relative power ofevolutionary and social structural theories to explain sexdifferences may vary depending on the trait underconsideration.In addition to analyzing data on sex drive and sociosexuality,I also conducted parallel analyses on a third,nonsexual trait—self-reported height. Because it seemsnoncontroversial to assume that sex differences in heightare largely determined by evolved genetic differencesbetween the sexes (see Gaulin & Boster, 1985), results forheight provide a pure example of the pattern of results thatmight be expected for a sex difference that is largely biologicalin origin. This pattern of results can then be comparedwith the corresponding patterns of results for sexdrive and sociosexuality.Five Hypothetical Cross-National Patterns of SexDifferences, Male and Female Means, and Maleand Female SDsThe following sections present five models of how biologicaland cultural factors might contribute to sex differences,trait means, and trait SDs in psychological traits. Itis important to note that these models are not exhaustive.Rather, they constitute a small subset of a large universe ofpossible models.The Pure Biological Causation ModelSome sex differences result largely from biological causes.Possible examples are sex differences in height, fundamentalvoice frequency, waist-to-hip ratios, and individuals’degree of sexual attraction to men and to women. Inthe pure biological model, sex differences are constantacross cultures and countries, and male and female traitSDs are assumed not to vary across cultures. Male andfemale trait means may vary across cultures—for example,men’s and women’s mean heights could vary across culturesas a result of biological factors (e.g., genetic differencesbetween ethnic groups) and environmental factors(national and cultural differences in diet and health care).However, if men’s and women’s means vary across cultures,they are assumed to do so in a parallel fashion (e.g.,genetic or nutritional factors in given cultures wouldequally depress or elevate male and female mean heights).Because men’s and women’s means vary in a parallelfashion and men’s and women’s SDs are constant across123

Arch Sex Behavparticularly low variability in unrestricted societies and particularlyhigh variability in restricted societies, whose culturalpressures conflict with their innate dispositions. Similarly,women may show particularly low variability in restrictedsocieties and particularly high variability in unrestrictedsocieties, whose cultural pressures conflict with their innatedispositions (or, alternately, whose liberal ideologies allowwomen freer rein to express individual differences in sociosexuality).When we superimpose the pattern in Fig. 3 (greatercultural influence on women’s than on men’s SDs) with thebiology-culture interaction just hypothesized, the net resultis the following: Women show strongly decreased SDsin sociosexuality in restrictive cultures, because they aregenerally more influenced by cultural pressures than menare and, simultaneously, the cultural press in restrictivecultures is congruent with their innate disposition, so thetwo influences superimpose and reinforce one another. Effectsfor men should be weaker, because the effect of culture (restrictedcultures reduce variance in sociosexuality) opposes thehypothesized biology-culture interaction (men will showmore variable sociosexuality in restrictive cultures, because inthese cultures they are subject to the countervailing pushes andpulls of cultural pressures and innate dispositions).Previous Research on Sex Drive and SociosexualityTo place the current research on sex differences in sex driveand sociosexuality in a broader context, in the followingsections I briefly review previous work on the assessment ofthese traits and existing evidence on sex differences in sexdrive and sociosexuality.Measurement of Sex Drive and SociosexualityA number of self-report measures of sex drive have appearedin recent years (Lippa, 2006; Ostovich & Sabini, 2004;Spector, Carey, & Steinberg, 1996).Thesescalestypicallyassess respondents’ desire for sex, their frequency of sexualactivity, their degree of thinking about and fantasizing aboutsex, and their evaluation of the rewardingness of sex. Forexample, in a recent study of the relation between sex driveand same-sex and other-sex attractions (Lippa, 2006), I useda five-item sex drive scale that asked participants to rate howmuch they agreed with the following statements: (1) ‘‘I havea strong sex drive;’’ (2) ‘‘I frequently think about sex;’’ (3) ‘‘Itdoesn’t take much to get me sexually excited;’’ (4) ‘‘I thinkabout sex almost every day;’’ (5) ‘‘Sexual pleasure is themost intense pleasure a person can have.’’The most commonly used instrument used to assesssociosexuality is the Sociosexuality Orientation Inventory(SOI; Simpson & Gangestad, 1991), a 7-item scale thatincludes three overt behavior items (e.g., ‘‘With how manydifferent partners have you had sex within the past year?),one covert behavior item (‘‘How often do [did] you fantasizeabout having sex with someone other than yourcurrent [most recent] dating partner?’’), and three attitudinalitems (e.g., ‘‘Sex without love is ok.’’). Because thebehavior items have different response formats from attitudinaland covert behavioral items, Simpson and Gangestadproposed a complex weighting system to combineSOI items (see Simpson & Gangestad, 1991, Appendix A).Although the SOI shows good internal consistency,highly skewed response distributions for some items andthe complex weighting system proposed by Simpson andGangestad for scoring the SOI have led some researchersto question its psychometric soundness (Voracek, 2005).Another concern is that responses to some items (e.g., thosethat assess number of sexual partners in the past year andnumber of one-night stands) depend too much on participants’relationship status. One item (fantasizing about sexwith someone other than one’s current or most recentdating partner) does not readily apply to married people orto people in committed relationships, and thus it may notbe appropriate for studies that assess non-college students.Finally, behavioral items may tend to confound the constructsof sex drive and sociosexuality.Sex Differences in Sex Drive and SociosexualityIn a comprehensive review, Baumeister, Catanese, and Vohs(2001) surveyed a broad range of research results indicatingthat, on average, men’s sex drive is higher than women’s. Insummarizing their findings, they observed that ‘‘[t]here wereno measures that showed women having stronger drives thanmen’’ (p. 264). As part of their review, Baumeister et al.examined research results from several non-western societies,and they concluded that these studies were consistent withother studies showing that men have higher sex drive thanwomen. However, they acknowledged that ‘‘[r]igorous datafrom other cultures are difficult to find…’’ (p. 268).There is little quantitative information on the magnitudeof sex differences in sex drive. In a recent study (Lippa,2006, Study 3), I computed a reliable (a = .82) multi-itemself-report measure of sex drive, and in a sample of over1,700 participants, heterosexual men and women showed alarge difference in their self-reported sex drive (d = .82).Furthermore, women were more variable than men in theirsex drive (female to male variance ratios were 1.43 forheterosexual participants). Using a less reliable one-itemmeasure of sex drive to assess more than 1,700 college123

Arch Sex Behavstudents (Lippa, 2006, Study 1), I found a smaller but stillsubstantial difference in heterosexual men’s and women’ssex drives (d = .58) and, once again, women’s self-reportedsex drive was significantly more variable than men’s(female to male variance ratio = 1.30). Ostavich and Sabini(2004) used a four-item scale to assess sex drive in 129college men and 148 college women, and their statisticstranslated to a very large sex difference (d = 1.17). Theirdata also showed women to be more variable than men insex drive (female to male variance ratio = 1.60).An ambitious study by Schmitt (2005) has provided thecurrent gold standard for estimates of sex differences insociosexuality. Using SOI data collected in 48 nations,Schmitt found d values for sex differences that ranged from.30 to 1.24 in various nations, with an overall mean valueof .74. Schmitt concluded that ‘‘[t]hese results…place sexdifferences in sociosexuality…among the largest and culturallymost robust ever documented in the domain of sexand human mating’’ (p. 262). Schmitt further noted that‘‘[w]ithin the constraints of the current methodology andsampling limitations, it can be concluded from these resultsthat sex differences in sociosexuality are a cultural universal,supporting the basic tenets of parental investmenttheory…’’ (p. 265).Social Structural Factors that Correlate with SexDifferences in Sociosexuality across CulturesIn addition to documenting cross-culturally consistent sexdifferences in sociosexuality, Schmitt (2005) identified anumber of cultural, economic, and demographic factors thatwere associated, across nations, with men’s and women’slevels of sociosexuality and with sex differences in sociosexuality.For example, indices of nations’ degree of genderequality tended to be associated with women’s levels ofsociosexuality and with sex differences in sociosexuality,with greater gender equality associated with higher levelsof sociosexuality in women and smaller sex differences.Measures of economic and environmental stress (e.g., asassessed by infant mortality rates, life expectancy, and grossdomestic product) were associated, across nations, withlower levels of sociosexuality in both men and women.Schmitt viewed these findings as providing strong supportfor strategic pluralism theory, which proposes that humanshave evolved a menu of mating strategies, which are triggeredby environmental contingencies (Gangestad &Simpson, 2000). Finally, higher sex ratios (more men thanwomen) were associated with lower national levels ofsociosexuality, supporting some of the predictions of sexratio theory (Guttentag & Secord, 1983; Lazarus, 2002;Pedersen, 1991). The results that follow will, among otherthings, test whether Schmitt’s findings replicate in anotherlarge international sample.MethodParticipants and ProcedureFrom February through May 2005, the British BroadcastingCorporation (BBC) conducted an English-languageInternet survey, which focused on human sex differences incognition, motivation, personality, and sexuality. The survey,designed to produce data for use in the BBC documentarySecrets of the Sexes, was advertised on the BBCwebsite and participants responded online. Because of thebroad reach of the BBC as an international news source,survey participants came from all over the world. Participantscould complete a variety of psychological tests andquestionnaires, which were arranged in six modules, eachof which took about five minutes to complete. A total of255,114 people responded to at least some items in everymodule. In the course of responding to approximately200 questions, most participants reported their sex andheight and completed a two-item sex drive scale and athree-item scale that assessed the attitudinal component ofsociosexuality.For the entire BBC sample, men’s median age was 30(M = 32.26, SD = 11.26), and women’s median age was 28(M = 31.11, SD = 10.83). The current analyses focused onparticipants whose ages were ‡18 and £80 years. Thebreakdown of participants by reported relationship statuswas: 29% married, 29% single, 16% living together in aserious relationship, 15% living apart in a serious relationship,8% in a causal relationship, 3% divorced, and under 1%widowed. Participants came from countries across the world,but the largest numbers were from the United Kingdom(45%), the United States (29%), Canada (5%), and Australia(4%). Participants from continental Western Europe madeup about 6% of the sample.Fifty-three nations in the BBC dataset had samples of 90or more participants. In many of the national samples, therewere roughly equal numbers of men and women, althoughthere was a tendency for men to outnumber women. Inall national samples but two, both male and female samplesizes were larger than 40. The two exceptions wereVenezuela (female n = 32 for sociosexuality and sex drivescores) and Saudi Arabia (female n = 20 for sociosexualityand sex drive scores). In his 48-nation study of sociosexuality,Schmitt (2005) noted that ‘‘[a]t least 25 men and 25women were needed to achieve the necessary statisticalpower for evaluating sex differences…(when settingb = .80, a = .05, and looking for an effect moderate tolarge in size…)’’ (p. 253). All of the male and femalesamples in the current study achieved this criterion, exceptfor the sample of Saudi women. For additional demographicinformation about the BBC sample, see Lippa(2007) andReimers(2007).123

Arch Sex BehavMeasuresDemographicDemographic information collected by the BBC Internetsurvey included age, relationship status, country of residence,ethnicity, education level, and income level. For anoverview of the BBC Internet survey, its questions, andtheir response formats, see Reimers (2007).Nations’ Dominant ReligionsMost of the 53 nations studied in the current study wereclassified, based on their majority religions, as Buddhist,Catholic, Eastern Orthodox, Hindu, Jewish, Moslem, Protestant,or Taoist. Information about dominant religions wasobtained from the US Department of State InternationalReligious Freedom Report 2004. If Catholics or Protestantsdid not constitute a majority in a given country, but Christiansnonetheless formed a majority of the population, thennations were classified as ‘‘mixed Christian.’’ The five religiousgroupings that included the most nations were: Catholic(Argentina, Austria, Belgium, Brazil, Chile, Croatia,France, Hungary, Italy, Ireland, Lithuania, Malta, Mexico,the Philippines, Poland, Portugal, Slovenia, Spain, andVenezuela); Eastern Orthodox (Bulgaria, Cyprus, Greece,Romania, and Russia); Moslem (Egypt, Pakistan, Turkey,Saudi Arabia, and the United Arab Emirates); Protestant(Denmark, Finland, Iceland, Norway, South Africa, Sweden,the United Kingdom, and the United States); and mixedChristian (Australia, Canada, Germany, the Netherlands,New Zealand, Switzerland, and Trinidad and Tobago).Sex Drive, Sociosexuality, and HeightIn one section of the BBC survey, participants were askedabout their romantic and sexual relationships, and there weretwo items that assessed sex drive: ‘‘I have a strong sex drive’’and ‘‘It doesn’t take much to get me sexually excited.’’Participants responded to these items using a 7-point scalethat ranged from ‘‘disagree’’ to ‘‘agree.’’ This section alsoincluded three items that assessed the attitudinal componentof sociosexuality: ‘‘Sex without love is OK.’’ ‘‘I can imaginemyself being comfortable and enjoying casual sex withmultiple partners.’’ ‘‘I would have to be closely attached(emotionally and psychologically) to someone before I’dfeel comfortable and fully enjoy having sex with him/her.’’Response formats were the same as for sex drive items. Sexdrive and sociosexuality scores were computed from theseitems, with appropriate items reversed.The decision to use just attitudinal sociosexuality itemswas based on three considerations. First, although a numberof behavioral SOI items were included in the BBC survey,their wording was sometimes different from that in theoriginal SOI and some were targeted at only a subset of theBBC participants (e.g., single participants). Second, computingsociosexuality from just the attitudinal items sidesteppedsome of the psychometric problems that affect thefull sociosexuality scale. Third, the current research soughtto compare and contrast results for sex drive and sociosexuality.Because sex drive and attitudinal sociosexualityitems in the BBC survey used exactly the same responseformat and because the sex drive and sociosexuality scaleswere both short (a two-item and a three-item scale), the twomeasures were psychometrically similar—a major virtue inthe current analyses.The BBC survey assessed participants’ height by askingthem to type in, as string variables, their height in feet andinches or in meters. In the final data files, heights wereconverted to feet and inches. To exclude implausibly lowor high values for height, I included in my analyses onlyheights that ranged from 56 to 84 inches (four feet eightinches to seven feet). The number of participants who haduseable height information was somewhat smaller than thenumber who had valid sex drive and sociosexuality scores.Gender Equality, Economic Development, and Sex RatiosStatistics for United Nations gender-related developmentand gender empowerment indices were taken from theUnited Nations 2005 and 2001 Human Development Reports(available at: http://www.hdr.undp.org/statistics/data/, see the section on ‘‘data by indicator’’). The UN genderrelateddevelopment index assesses nations’ gender equityon three dimensions: health and longevity, standard ofliving, and knowledge and education. The UN genderempowerment measure assesses nations’ gender equity onthree power dimensions: power over economic resources,participation in economic decision making, and participationin political decision making. In several cases, when2005 statistics were not available for given nations, I used2001 statistics instead. United Nations gender empowermentstatistics were not available for six of the 53 nationsstudied here.Indices of economic development were also obtainedfrom UN Human Development reports. These includednations’ per capita income in U.S. dollars, life expectancy,infant mortality per thousand live births, fertility rates, andrates of contraception use. A final variable, national sexratios for people aged 15–64 years of age, was obtainedfrom the World Fact Book 2005, a publication of the UnitedStates Central Intelligence Agency (http://www.odci.gov/cia/publications/factbook/index.html).123

Arch Sex BehavResultsReliability of Sex Drive and SociosexualityAcross Nations and the Correlation of SexDrive and SociosexualityMean reliabilities (a) over all 53 nations for sex drive andsociosexuality were .72 and .78, respectively. Reliabilities forsex drive and sociosexuality computed over all participantswere .79 and .81, respectively. Over all participants, sex driveand sociosexuality were modestly correlated, r(210277) =.28, p < .001. The correlation of sex drive and sociosexualitywas lower when computed separately for men, r(115923)=.21,p < .001, and for women, r(94253) = .20, p < .001,suggesting that the association between sex drive andsociosexuality in the entire sample was partly due to thefact that both variables were correlated with sex.Intercorrelation of Indices of Gender Equality,Economic Development, and Sex RatiosTable 1 presents intercorrelations of indices of gender equality,economic development, and sex ratios. The two UNindices (gender development and gender empowerment) werehighly correlated (r = .82) and they were also substantiallycorrelated with indices of economic development. In general,the correlations in Table 1 show that countries that weregender egalitarian also tended to be high on economicdevelopment, whereas countries that were gender nonegalitariantended to be low on economic development. The onlymeasure that was relatively independent of other measureswas that of national sex ratios.Sex DriveThe following sections present the core analyses of thecurrent study, with one section devoted to each of the threetraits under study: sex drive, sociosexuality, and height. Ineach section, I first examine the intercorrelations of maleand female means, male and female SDs, and sex differencesfor the trait under study. The goal was to see whichfactor contributed most to sex differences: male means,female means, male SDs, or female SDs. A second goalwas to see whether there were national traits of sex drive,sociosexuality, and height. To the extent that male andfemale means correlated strongly across nations, then thisprovided evidence for national traits (e.g., if male andfemale heights strongly correlated across nations, then thiswould indicate there were consistently ‘‘shorter’’ and‘‘taller’’ nations, on average).To investigate the power of cultural and social structuralfactors to predict sex differences and other parameters, ITable 1 Intercorrelations across nations of United Nations indices of gender development and gender empowerment, indices of economic development, and sex ratiosUN gender development UN gender empowerment Per capital income Life expectancy Infant mortality Fertility Contraception Sex ratiosUN gender development –UN gender empowerment .82*** (47) –Per capital income .78*** (52) .79*** (47) –Life expectancy .84*** (53) .69*** (47) .68*** (52) –Infant mortality –.91*** (53) –.60*** (47) –.57*** (52) –.82*** (53) –Fertility –.67*** (53) –.49** (47) –.34* (52) –.46*** (53) .70*** (53) –Contraception .59*** (45) .59** (39) .50** (44) .39** (45) –.43** (45) –.51*** (45) –Sex ratios –.13 (53) –.19 (47) .09 (52) .10 (53) .03 (53) .34 (53) –.46** (45) –Note:*p < .05, ** p < .01, *** p < .001. Numbers in parentheses are sample sizes. All indices are taken from 2005 and 2001 United Nations Human Development Reports, except for measuresof sex ratios, which come from the CIA World Fact Book, 2005123

Arch Sex Behavpresent for each trait the correlations between social indicesand the five parameters of interest: male means, femalemeans, male SDs, female SDs, and sex differences. To theextent that social indices predict parameters strongly (e.g.,UN indices of gender equality predict sex differences insociosexuality), then this provides evidence that there issystematic variation across nations in the parameters. However,if social indices do not predict parameters, then there islittle evidence for systematic national and cultural variation,and the likelihood increases that sex differences—particularlythose that are consistent across nations—have biologicalcauses.To elucidate the observed patterns of correlations, I presentfor each trait graphs of the five parameters of interest: malemeans, female means, male SDs, female SDs, and sex differences.In these graphs, nations were arrayed along the x-axis in the order of the magnitude of their sex differences.These graphs correspond closely to the graphs presented forthe hypothetical models presented in the introduction. In afinal set of analyses, I use regression analyses to compare thepower of sex, gender equality as assessed by UN indices, andtheir interaction to predict male and female trait means across53 nations.Intercorrelations of Male and Female means, Maleand Female SDs, and Sex Differences in Sex DriveFor sex drive, sex differences as assessed by the raw differencebetween male and female means correlated .97(p < .001) with d scores, and thus these two measures ofsex differences were essentially the same. Because d valuesare the conventional way to assess sex differences, I usedthem in the current analyses.Male and female SDs correlated relatively weakly with dstatistics (r =–.36,p

Arch Sex BehavSex Drive Means and SDs and Sex Differences (d's)6.005.004.003.002.001.000.00male meansfemale meansmale SDsfemale SDsd'sVenezuelaCyprusIndiaMaltaSaudi ArabiaTrinidad, Tobag.PakistanPortugalThailandSingaporeHungaryPhilippinesNew ZealandSloveniaAustraliaMalaysiaUnited Arab Em.BelgiumIcelandIrelandGermanyUKIsraelNetherlandsLithuaniaMexicoRomaniaSouth AfricaUSACanadaFinlandAustriaFranceCroatiaJapanSpainItalySwitzerlandPolandSwedenBulgariaTurkeyNorwayGreeceEgyptChinaChileDenmarkArgentinaBrazilEstoniaCzech Rep.RussiaCountriesFig. 5 Sex drive parameters across 53 nations presented in order of their sex differences in sex drived = 4.24. The very large d value may seem puzzling, giventhat the mean d for sex drive, across nations, was .62.However, d values for nations were computed with individualsas the unit of analysis, whereas in the paired-datat-test, nations was the unit of analysis and the data pointswere national means. Thus, at the level of nations, men’smean sex drive levels were consistently much higher thanwomen’s mean sex drive levels.Examination of Fig. 5 also reveals a second dramaticsex difference: Across nations, female SDs in sex drivewere consistently higher than male SDs. This differencewas also significant and strong, paired-data t(52) = –20.75,p < .001, d = –2.85, mean female-to-male variance ratioacross nations = 1.64.As noted earlier, nations were arranged along the x-axisin order of their sex differences in sex drive in Fig. 5.Because the graph of sex differences increased in such anorderly fashion, it is tempting to see this increase asreflecting systematic factors. However, this was not thecase. The ordering of nations in Fig. 5 did not show anyculturally or demographically coherent pattern. Furthermore,the largest-sample nations (e.g., the United Kingdom,the United States, Canada, Australia, and a number ofEuropean nations) tended to be in the middle of the list,whereas many small-sample nations were to the left andright sides of the array. This suggests that variations ineffect sizes resulted from sampling error, not from systematicfactors. Figure 6 makes this point more apparentby plotting effect sizes as a function of the log of samplesizes.The scatter plot shows that, for large-sample nations,effect sizes were stable, clustering around .60 whereas, forsmall-sample nations, effect size values scattered considerablyabout this mean level. Indeed, when effect sizes wereregressed on the log of sample sizes, the regression line wasessentially flat (b = .05, ns), indicating that mean effect sizesdid not vary across samples of various sizes. However,log sample size correlated significantly with the absolutevalue of residuals, r = –.46, p = .001—that is, larger samplesizes were associated with less variable effect sizes. Thus,much of the variation in d values, across nations, appeared toresult from sampling error, not from systematic differencesacross nations and cultures.Sex and Gender Equality as Predictors of Mean Levelsof Sex DriveUsing regression analysis, I examined the power of sex andgender equality to predict male and female means acrosscultures. The data points were the 53 male means and the 53female means for sex drive. The predictor variables weresex, coded as ‘‘1’’ for males and ‘‘2’’ for females, and genderequality (the mean of the two highly correlated UN indices).An interaction term was also entered into the regression—theproduct of the standardized sex and genderequality variables.These three orthogonal variables significantly predictedmale and female sex drive means, multiple r =.93,r 2 = .86,p < .001, with sex the strongest predictor: b for sex = –.92,p

Arch Sex BehavSex Differences in Sex DriveSizes forEffect1.000.800.600.400.20the interaction = .01, ns. These results are consistent with thegraphs of male and female sex drive means in Fig. 5, whichshow a highly consistent sex difference across nations, notmuch variation in men’s and women’s sex drive levels acrossnations, and quite parallel graph lines for men and women(i.e., no interaction).When a corresponding regression was run on men’s andwomen’s SDs, the prediction was again strong, multipler =.88,r 2 =.78,p < .001, and again sex proved to be thestrongest predictor: b for sex = .88, p

Arch Sex BehavTable 3 Correlations, across nations, between social indices and sociosexuality parametersMen’s means,sociosexualityWomen’s means,sociosexualityMen’s SDs Women’s SDs Sex differences (ds)UN gender development .64*** (53) .76*** (53) –.19 (53) .67*** (53) –.58*** (53)UN gender empowerment .48** (47) .71** (47) .04 (47) .62*** (47) –.67*** (47)Per capita income .32* (52) .58*** (52) –.02 (52) .48*** (52) –.63*** (52)Life expectancy .38** (53) .55*** (53) –.21 (53) .47*** (53) –.50*** (53)Infant mortality –.55*** (53) –.62*** (53) .24 (53 –.57*** (53) .42** (53)Fertility –.63*** (53) –.62*** (53) .33* (53) –.55*** (53) .32* (53)Contraception .55*** (45) .71*** (45) –.15 (45) .64*** (45) –.60*** (45)Sex ratios –.25 (53) –.27 (53) .24 (53) –.25 (53) .14 (53)Note:p < .1, * p < .05, ** p < .01, *** p < .001. Numbers in parentheses are sample sizesSociosexuality Means and SDs and Sex Differences (d's)5.004.003.002.001.000.00male meansfemale meansmale SDsfemale SDsd's for sex diffPhilippinesTrinidad, Tobag.PakistanSaudi ArabiaMalaysiaThailandTurkeyVenezuelaHungaryMaltaIndiaRussiaRomaniaIrelandUnited Arab Em.SingaporeLithuaniaJapanSloveniaEstoniaPolandArgentinaCyprusPortugalGreeceBulgariaSouth AfricaBrazilBelgiumAustraliaCroatiaCzech Rep.UKChinaUSACanadaSpainMexicoChileEgyptIsraelGermanyItalyNew ZealandNorwayNetherlandsFranceFinlandSwedenSwitzerlandDenmarkAustriaIcelandCountriesFig. 7 Sociosexuality parameters across 53 nations presented in order of their sex differences in sociosexualitylevels decrease as we move from left to right, from small tolarge sex differences in sociosexuality. Superimposed on thedownward slope of male and female means was a consistentsex difference in sociosexuality, with men higher than women.A paired-data t-test showed that this sex difference wassignificant and strong, t(52) = 27.60, p < .001, d = 3.79.The mean d-value for sex differences in sociosexualityacross 53 nations was .74.Women’s SDs in sociosexuality decreased as we movefrom left to right, whereas men’s SDs were more stable. Theresult was a crossover in female and male SDs. To the leftside of the graph women’s SDs tended to be larger thanmen’s, whereas to the right side of the graph men’s SDstended to be larger than women’s. This crossover effect wassignificant: across nations, the difference between women’sand men’s SDs correlated significantly with sex differencesin sociosexuality, r = –.70, p < .001.There were systematic differences between the low-sexdifferencenations to the left and the high-sex-differencenations to the right of Fig. 7. On the left side are Iceland,Austria, Denmark, Switzerland, Sweden, Finland, France,and the Netherlands, and on the right side are the Philippines,Trinidad and Tobago, Pakistan, Saudi Arabia, Malaysia,Thailand, Turkey, and Venezuela. As the correlations inTable 6 suggest, nations to the left side of the x-axis tendedto be high on gender equality and economic development,whereas nations to the right side of the x-axis tended to below on gender equality and economic development.123

Arch Sex BehavSex and Gender Equality as Predictors of Mean Levelsof SociosexualityAs in the analyses of sex drive, I examined the power ofsex and gender equality to predict male and female meansacross cultures. The data points were the 53 male meansand the 53 female means for sociosexuality The predictorvariables were sex, gender equality (the mean of the twoUN indices), and an interaction term.These three orthogonal variables significantly predictedmale and female sociosexuality means, multiple r = .90,r 2 = .81, p < .001: b for sex = –.79, p < .001; b for genderequality = .41, p < .001; and b for the interaction = .14,p = .002. These results are consistent with the graph of maleand female means for sociosexuality presented in Fig. 7,which shows a highly consistent sex difference across nations,a systematic decline across nations in both men’s andwomen’s mean sociosexuality levels, and a steeper decline inwomen’s than in men’s sociosexuality across nations (i.e., aninteraction effect).Note that the interaction between sex and genderequality in the current analysis tapped the same phenomenathat the correlations between UN indices and sex differencesdid in Table 3. However, the current analysis remindsus that although the power of culture (i.e., structural measuresof gender equality) to moderate sex differences wasreal and substantial for sociosexuality, when one predictsthe overall pattern of male and female means, the maineffects for sex (b 2 =.62)andforculture(b 2 =.17)weremuch stronger than the moderating effect of culture on sexdifferences (b 2 = .02 for the interaction). Stated anotherway, although culture moderated the magnitude of sexdifferences, it was never the case that culture eliminatedthese sex differences, which remained quite powerfuloverall, despite the presence of significant cultural maineffects and interactions.When a similar regression was conducted on men’s andwomen’s SDs for sociosexuality, the prediction was not asstrong, but still substantial, multiple r = .68, r 2 = .47,p < .001: b for sex = –.28, p < .001; b for gender equality= .43, p < .001; and b for the interaction = .45,p < .001. The interaction effect once again indicated thatthere was a crossover of women’s and men’s SDs as wemove from gender egalitarian to gender nonegalitarian nations.The main effect for sex reflected the fact that, ingeneral, men’s SDs were a bit higher than women’s, paireddatat(52) = 2.84, p = .006, d = .39, and the main effect forculture reflected the fact that SDs in sociosexuality tended tobe smaller in gender nonegalitarian than in gender egalitariansocieties. It is interesting to note that the sex differencein sociosexuality SDs, to the extent it was present, wasopposite in direction to the sex difference in sex drive SDs.HeightIn the following sections, I report analyses for height thatcorrespond to the analyses reported in the previous sectionsfor sex drive and sociosexuality. Recall that I assumed atthe start that sex differences in height are largely caused bybiological factors, and thus the results that follow shouldillustrate the patterns of results expected for a trait with abiologically caused sex difference.Intercorrelations of Male and Female means, Maleand Female SDs, and Sex Differences in HeightUnlike the corresponding results for sex drive and sociosexuality,difference scores and d statistics for height wereonly moderately correlated (r = .51, p < .001). The reasonfor this relatively weak correlation was that d statistics forheight correlated strongly with men’s and women’s SDs(r = –.79 and –.57, respectively), but only weakly withmen’s and women’s mean heights (r = –.04 and –.27,respectively), and thus variations in d scores for height weremuch more a function of SDs than of means. Variations inmen’s and women’s SDs in height were, in turn, largely afunction of sample size, as illustrated by Fig. 8, whichpresents a scatter plot of male and female SDs as a functionof the logarithm of male and female sample sizes. In thisplot, SDs clustered narrowly around a value of three inchesin large samples, but they were much more scattered in smallsamples. The net result was that sex differences in height, asStandard Deviations in Height for Men and Wome n5.004.003.002.001.002.00 4.00 6.00 8.00 10.00 12.00Log Sample SizeFig. 8 SDs of men’s and women’s height in 53 nations as a functionof the logarithm of sample sizes123

Arch Sex Behavassessed by d statistics, were greatly influenced by randomerror in the estimation of SDs. Consequently, raw differencescores provide a better measure of sex differences in heightthan d statistics do and, therefore, raw difference scoreswere used in the analyses that follow.Men’s and women’s mean heights were strongly correlated,across nations (r = .93, p < .001), indicating thatthere were consistent national levels of heights—i.e., therewere ‘‘shorter’’ nations (e.g., India, Pakistan, the Philippines,Singapore) and there were ‘‘taller’’ nations (Estonia,Lithuania, the Netherlands, Norway).Correlations between Social Indices and HeightParametersWere sex differences in height predicted, across nations, bycultural and social structural factors? Table 4 presentscorrelations between societal indices and the five parametersof interest: men’s means, women’s means, men’s SDs,women’s SDs, and sex differences in height. The rightmostcolumn of Table 4 shows that sex differences inheight did not correlate significantly with any index. Therewere, however, significant correlations between indices andmen’s and women’s mean heights across nations. In general,gender equality and economic development wereassociated with greater height. This may seem surprising atfirst glance, but upon reflection the finding makes sense.Countries high on gender equality tend to be affluentcountries with good nutrition and good health care, both ofwhich may serve to increase the average height of citizens.In general, indices of gender equality and economicdevelopment were not associated with men’s and women’sSDs in height.The pattern of correlations in Table 4 is clarified byFig. 9, which graphically portrays the five parameters ofinterest across the 53 nations, arrayed in order of themagnitude of their sex differences. The most striking featureof Fig. 9 is the consistency of sex differences in heightacross nations. The graphs of men’s means and women’smeans tended to be quite parallel across the 53 nations, withmen’s means always higher than women’s means. A paireddatat-test showed that sex differences in height were highlysignificant across nations and very strong, t(52) = 101.08,p < .001, d = 13.88, mean sex difference = 5.26 inches,mean of 53 national ds = 1.63.Examination of Fig. 9 also shows that men’s and women’sSDs appear not to differ much—all SDs were clusteredaround 3 inches. Although it is not visually apparent, men’sSDs (M = 3.37) were slightly larger than women’s SDs(M = 3.03), paired-data t(52) = 4.42, p

Arch Sex BehavHeight Means and SDs (in Feet)and Sex Differences (Raw Differences)7.006.005.004.003.002.001.00male meansfemale meansraw differencesmale SDsfemale SDs0.00GreeceRomaniaNetherlandsChinaSaudi ArabiaArgentinaIcelandUSAJapanHungaryUKLithuaniaRussiaPakistanFinlandPolandBelgiumTrinidad, TobagoCanadaSwedenDenmarkIrelandSloveniaSouth AfricaTurkeyAustraliaCroatiaNew ZealandIndiaNorwayAustriaPortugalGermanyCzech RepBulgariaEstoniaFranceBrazilCyprusItalyChileSingaporeSpainMalaysiaSwitzerlandUnited Arab EmiratesMaltaEgyptMexicoVenezuelaIsraelPhilippinesThailandCountriesFig. 9 Height parameters across 53 nations presented in order of their sex differences in heightFig. 9, which show a highly consistent sex difference acrossnations, not much variation in men’s and women’s heightacross nations, and quite parallel graph lines for men andwomen (i.e., no interaction).When a corresponding regression was run on men’s andwomen’s SDs in height, the prediction was weak, multipler = .36, r 2 = .13, p = .003, and there was only one significantpredictor: b for sex = –.33, p = .001; b for genderequality = .07, ns; and b for the interaction = .12, ns. Thesignificant effect for sex showed again that men’s SDswere significantly larger than women’s, which I hypothesizedmight be due to a scaling effect. The low multipler was consistent with earlier evidence suggesting thatvariation in height SDs resulted largely from samplingerror, not from systematic factors.Religion, Sex Drive, and SociosexualityAs noted earlier, the five religious groupings that comprisedthe most nations in the total set of 53 nations were: Catholicnations (n = 18), Eastern Orthodox nations (n = 5), Moslemnations (n = 5), Protestant nations (n = 8), and mixedChristian nations (n = 7). To probe the effect of religion onsex differences in sex drive and sociosexuality, I conductedtwo one-way ANOVAs—the first on sex differences in sexdrive and the second on sex differences in sociosexuality.The groups of nations compared in the ANOVAs were thefive religious groupings just described. The ANOVA on sexdifferences in sex drive did not show a significant differenceacross religions, F(4, 39) = 1.03, ns. However, the ANOVAon sex differences in sociosexuality did show a significantdifference, F(4, 39) = 4.34, p = .005. Group means, orderedfrom smallest to largest sex differences in sociosexuality,were: Protestant nations (mean d = .53), mixed Christiannations (mean d = .64), Catholic nations (mean d = .76),Eastern Orthodox nations (mean d = .83), and Moslem nations(mean d = .92). This spectrum could be characterizedas ranging from more liberal, individualistic, and ‘‘western’’religions (although it should be noted that Protestantdenominations vary considerably on the ‘‘liberal’’ dimension)to more conservative, collectivist, and ‘‘eastern’’religions.Religions might influence sex differences in sociosexualityvia the gender ideologies and social structures theypromote. To test this hypothesis, I ran the one-way ANOVAon sex differences in sociosexuality again, this time treatingsocietal gender equality (as assessed by the mean of the twoUN indices) as a covariate. After controlling for genderequality, the five groups of nations no longer differed significantly,F(4, 38) = .81, ns. This result was consistent withthe hypothesis that religions had their impact via themediating route of gender ideologies and social structure,although it did not prove the hypothesis.DiscussionIn the current research, measures of sex drive, sociosexuality,and height served as useful controls to one another. In123

Arch Sex Behavparticular, sex drive and sociosexuality measures were wellmatched in terms of their response formats and scalelengths. Because of this, it is unlikely that the reportedfindings resulted from response sets or from the idiosyncraticways that people in different countries used ratingscales. If this were so, then the findings for sex drive andsociosexuality would have shown similarities cross-culturally,which they did not. Indeed, if there is a centraltake-home message that emerges from the current results, itis how different the results were for sex drive and sociosexuality.These two traits showed different patterns of sexdifferences, different patterns of within-sex variability,different patterns of cross-cultural consistency, and differentpatterns of association with outside criteria. Thus, onone level, the current research could be viewed as a complexdemonstration of the discriminant validity of theconstructs of sex drive and sociosexuality (see Ostovich &Sabini, 2004; Simpson & Gangestad, 1991).At the start of this article, I offered five hypotheticalmodels of how male and female trait means, male andfemale trait SDs, and sex differences might vary acrossnations, depending on various assumptions about biologicaland socio-cultural influences on men’s and women’sbehavior. The results presented in the previous sections canbe summarized succinctly in terms of these models. Thefindings for sex drive and height were most consistent withthe pure biological causation model, whereas the results forsociosexuality were most consistent with the hybrid model,which assumes cultural influences superimposed on biologicalpredispositions.For both sex drive and height, sex differences wereextremely consistent across nations and they were notmoderated by gender equality or associated with economicdevelopment. Regression analyses that probed the power ofsex, gender equality, and their interaction to predict maleand female trait means yielded very similar results for sexdrive and height: bs for sex were –.92 and –.94, respectively;bs for gender equality were –.11 and .17, respectively,and bs for interactions were .01 and –.01,respectively. Thus, for these two traits, sex accounted for85–88% of the variance in male and female trait means,gender equality accounted for one to three percent of thevariance, and sex-by-culture interactions accounted forinsignificant amounts of variance.At the same time, there were several noteworthy differencesbetween the results for sex drive and height. Forone, height was more trait-like across nations than sexdrive was, and this probably resulted from both geneticfactors (ethnic differences in stature) and biologically activeenvironmental factors (national differences in nutritionand health care). A second important finding that distinguishedsex drive from height (and from sociosexuality aswell) was that, across nations, women were consistentlymore variable than men in sex drive. Sex drive was theonly trait to show such a powerful sex difference in traitvariability. Although there was a weak sex difference inSDs for height, this may have resulted from scaling effects,and the weak sex difference in sociosexuality SDs wasopposite in direction to the sex difference in sex drive SDs.While many of the results for sex drive and height weresimilar, the results for sociosexuality, in contrast, differedin many ways from corresponding results for sex drive andheight. Although men were consistently higher in sociosexualitythan women, this sex difference was moderatelymoderated by nations’ levels of gender equality and economicdevelopment. Sex differences in sociosexualityproved to be smallest in nations that were high on genderequality and economic development and largest in nationsthat were low on gender equality and economic development.Both men’s and women’s mean levels of sociosexualitydecreased as nations’ levels of gender equalitydecreased, but the decrease was steeper for women thanfor men.Furthermore, women’s, but not men’s, variability in sociosexualitydecreased as levels of gender equality decreasedacross nations. This resulted in a crossover effect for men’sand women’s SDs in sociosexuality: in gender egalitariancountries, women tended to be more variable than men, but ingender nonegalitarian countries men tended to be more variablethan women. This crossover effect is an important pieceof evidence supporting the hybrid model. Social structuraltheorists have argued that all modern societies are patriarchalto varying degrees, and this explains why women’s sociosexualityis lower than men’s in all modern societies.Extending this argument to men’s and women’s variability insociosexuality, social structural theorists might be expected tosimilarly argue that if patriarchal culture restricts the variabilityof women’s sociosexuality compared to men’s, thenthis effect should be consistent in direction across cultures, butvariable in magnitude. However, this was not the case. Theobserved crossover effect was consistent with the hybridmodel’s prediction that men’s and women’s biological predispositionsinteract with ‘‘cultural presses’’ to influence thevariability of men’s and women’s sociosexuality differentlyacross cultures.The Current Results and Those of Schmitt (2005)Thirty of the 53 nations assessed in the current study werealso assessed in Schmitt’s (2005) 48-nation study of sociosexuality.Across these 30 nations, Schmitt’s estimatedeffect sizes for sex differences in sociosexuality correlatedmoderately with the current study’s estimates, r = .49,p = .006. The relatively modest size of this correlation mayhave resulted from the different scales used to assess123

Arch Sex Behavsociosexuality in the two studies and from the differentsamples obtained in the two studies.In summarizing the results of his study, Schmitt (2005)wrote, ‘‘the most consistent finding was that men scoredhigher on sociosexuality than women across cultures’’ (p.273). According to Schmitt, this cross-cultural consistencyprovided strong support for sexual selection theory andparental investment theory, which imply that the sex thatinvests more in offspring (i.e., women), will show morerestricted sociosexuality than the sex that invests less inoffspring (men). The current results constituted a strongreplication of Schmitt’s findings on the strength and crossculturalconsistency of sex differences in sociosexuality.Indeed, the overall mean effect size for sex differences insociosexuality was identical in the two studies, d = .74.After correcting the effect size in the current study forattenuation due the unreliability of the three-item sociosexualityscale, the estimate was even larger, d = .85, andbecause scale reliability represents just a portion of measurementerror and does not address other sources ofattenuation, such as restrictions in range, this was verylikely an under-correction (see Baugh, 2002; Bobko, Roth,& Bobko, 2001).The current research identified two additional sex differencesthat were remarkably consistent across cultures. Inall nations, men reported having higher sex drives thanwomen (mean d = .62; when corrected for unreliability,d = .74), and in all nations women had more variable sexdrives than men did (in a paired t-test with nations as theunits of analysis, d = 2.85; mean female-to-male varianceratio = 1.64). These findings also seem interpretable interms of sexual selection and parental investment theory.Because women are the ‘‘choosier’’ sex and becausewomen often offer mating privileges to men in exchangefor resources, protection, and commitment, it seems reasonableto hypothesize that sexual selection would endowwomen, on average, with less urgent sex drives that aremore subject to rational control. As the limiting resource inreproduction, women typically do not have to worry aboutfinding men to impregnate them, although they may haveto worry about inducing men to stay around after impregnation.In contrast, men’s success at mating and reproductiontends to be more variable than women’s, and thehighest levels of male success (defined here in terms oftransmission of genes to future generations) may sometimesresult from promiscuous sexual activity with multiplepartners. Thus, sexual selection likely has led men, onaverage, to have stronger and more consistently ‘‘turnedon’’ sex drives than women.The current research replicated a number of additionalfindings reported in Schmitt (2005), and in several casesthe current findings were stronger than Schmitt’s. Forexample, stressed reproductive environments were associatedwith lower levels of sociosexuality in both men andwomen, and these associations tended to be stronger forwomen than men. Associations between societal stress andsociosexuality were generally stronger in the current studythan in Schmitt’s study. Schmitt reported only weak evidencethat societal stress and low economic developmentwere linked to sex differences in sociosexuality. In contrast,the current study found stronger evidence, with socialstress associated with larger sex differences in sociosexuality.Schmitt reported fairly strong associations betweenUN indices of gender equality and women’s levels ofsociosexuality. The current research replicated these findingsand further documented substantial associationsbetween UN indices and men’s sociosexuality and betweenUN indices and sex differences in sociosexuality.Why were results in the current study often stronger thancorresponding results in Schmitt’s (2005) study? One possibleanswer is that the current study used a shortsociosexuality scale consisting of just attitudinal items,whereas Schmitt’s research used the full SOI. Apropos ofthis possibility, one reason why men consistently showedgreater variability in sociosexuality than women did inSchmitt’s study (see commentary by Eagly & Wood, 2005,p. 283) may be that the behavioral items in the SOI acted toinflate male variability, because of the extreme behavioralresponses of a relatively small subset of men. A secondreason for stronger results in the current study is that Schmitt’snational samples may have been, on average, smallerand more restricted than the samples obtained in the currentresearch (see below).There was one finding in the current study that proved tobe weaker than the corresponding finding in Schmitt’sreport—namely, the association between national sex ratiosand sociosexuality. Table 3 showed that correlations betweensex ratios and men’s sociosexuality (r = –.25) andbetween sex ratios and women’s sociosexuality (r = –.27)were only marginally significant. When I computed theaverage of men’s and women’s sociosexuality for eachnation (a measure of overall national sociosexuality levels),this average, unlike its components, did correlate significantlywith national sex ratios, r(52) = –.27, p < .05.However, the corresponding correlation from Schmitt’sstudy was larger, r(46) = –.45, p < .001. As others havenoted, local sex ratios are likely to be more importantdeterminants of men’s and women’s mating strategies thannational sex ratios (Bond, 2005), and this is particularlytrue for geographically large and diverse nations. Given thecrudeness of the sex ratio measures used in both Schmitt’sstudy and the current one, it is remarkable that there wereany significant correlations between sex ratios and sociosexuality.To the extent that these correlations were significant,they tended to support the predictions of sex ratiotheory (Guttentag & Secord, 1983; Pedersen, 1991), that123

Arch Sex Behavhigh sex ratios (more men than women) are associated withreduced levels of sociosexuality, because in societies withsurplus males the sexual ‘‘marketplace’’ is driven more bywomen’s than by men’s desires.The current results extended Schmitt’s findings onsociosexuality by investigating the impact of nations’dominant religion on sex differences in sociosexuality (andon sex drive as well). The results indicated that religioncovaried with national sex differences in sociosexuality, butnot with sex differences in sex drive. In general, nations withmore conservative and collectivist religions tended to showlarger sex differences in sociosexuality. These differencesdisappeared, however, when UN gender equality was enteredas a covariate, and this provided at least circumstantialevidence that religion had its impact via the mediating routeof gender ideologies and social structure.Limitations and Strengths of the BBC DataThe BBC data had a number of limitations that are worthnoting. For one, they were not drawn from a probabilitysample. As described in the method section, BBC Internetsurvey participants were self-selected—they tended to berelatively young, well educated, affluent, and Internet savvy.Thus, on average, BBC participants may have representedtheir nations’ educated elites. Furthermore, the BBC surveywas administered in English, and this undoubtedly restrictedwho could participate in the survey, particularly in non-English-speaking countries. As Schmitt (2005) has observed,it is difficult to obtain large, representative crossculturalsamples. A limitation of the BBC sex drive andsociosexuality measures was their brevity, which may haveresulted in reduced reliability. Finally, the BBC data werecollected by an Internet survey, and such data may be subjectto unique kinds of error variance (see Gosling, Vazire,Srivastava, & John, 2004).The BBC data also had strengths. One was the size anddiversity of the BBC sample. It is virtually unheard of forresearchers to have access to self-report data on sex driveand sociosexuality from an international sample comprisingover 200,000 people. The only study comparable inscope to the current one was Schmitt’s (2005) ambitiousanalysis of International Sexuality Description Project data.In a number of ways, however, the BBC data are likelysuperior in quality to ISDP data. Schmitt’s data came largelyfrom college students, who were young and ofteninexperienced with long-term relationships. In contrast, themajority of BBC participants were not college students; theaverage age of BBC participants ensured that most BBCparticipants were older than the typical college student andin their prime reproductive years. Furthermore, becausemost BBC participants were either married or in seriousrelationships, they likely responded to sexuality-relatedquestions based on more extensive and varied real-lifeexperience than the average college student would. The factthat the BBC data were collected via an Internet surveyvirtually guaranteed that samples from various nations weremore geographically diverse, within each nation, than Schmitt’ssamples, which often consisted of college studentssurveyed at particular universities. Finally, many of the nationalsamples in the BBC dataset were larger than correspondingsamples in Schmitt’s study. All of these factorstaken together suggest that parameter estimates in the currentresearch (e.g., estimates of national means and national SDsin sociosexuality) may have been more reliable and morerepresentative of their respective nations than correspondingestimates from Schmitt’s study.Setting a More Demanding Standard of Predictionfor Both Evolutionary and Social Structural TheoriesSpecific results in this article are likely to please both socialstructural and evolutionary theorists. Social structural theorywas successful in predicting that sex differences in sociosexualitywould be moderated by societies’ levels of genderequality and economic development. Consistent with socialstructural theory, societies with higher levels of genderequality and economic development tended to display weakersex differences in sociosexuality. Furthermore, across nations,gender egalitarianism was associated with higher levels ofsociosexuality in both men and women, though the associationwas stronger for women than for men. The greater associationbetween ‘‘culture’’ and female sociosexuality provides newevidence supporting Baumeister’s (2000) claim that women’ssexuality is, in some ways, more influenced than men’s bysocial and cultural factors.In its most strongly stated form, Eagly and Wood’s(1999, 2005) social structural theory proposes that sex differencesin psychological traits and behaviors do not at allresult from evolved psychological dispositions in men andwomen. Rather, they result from the social roles that haveevolved in some societies—particularly modern agriculturaland industrial societies—as a result of physical differencesbetween the sexes (e.g., greater male upper bodystrength, female gestation and lactation), and the economicdivisions of labor and social structures that followed fromthese physical differences. Thus, according to Eagly andWood’s theory, the proximate causes of sex differences aresocial structure (e.g., greater male than female power, patriarchy),social roles (men as workers, women as housekeepers),and the gender ideologies that accompany andsustain these patriarchal social structures and social roles.The current results offer at best partial support for thisstrong version of social structural theory, and this partial123

Arch Sex Behavsupport was present for only one trait—sociosexuality. Theresults offered no support for social structural theory inrelation to sex differences in sex drive. Even in the case ofsociosexuality, it is important to note that regressionanalyses of male and female national means indicated thatsex differences were much more powerful than culturemain effects or sex-by-culture interactions. Although sexdifferences in sociosexuality could plausibly result fromboth biological and cultural factors, it is important to notethat the ‘‘main effect’’ of gender equality on men’s andwomen’s levels of sociosexuality (b 2 = .17), was muchstronger than the interaction between gender equality andsex (b 2 = .02). In other words, both men’s and women’smean sociosexuality levels tended to covary in a parallelfashion with nations’ levels of gender equality, and genderequality did not strongly moderate sex differences insociosexuality. The overall pattern of results for sociosexuality,i.e., the cross-cultural patterns of sex differences,male and female means, and male and female SDs, seemsmost consistent with the hybrid model portrayed in Fig. 4.Although social role theory has not much addressed theissue of within-sex variation, it seems to imply that societiescharacterized by strong gender roles and nonegalitariangender ideologies will show less within-sex variationin gender-linked traits and behaviors (e.g., occupationalchoices) than societies characterized by weak gender rolesand egalitarian gender ideologies (Lippa, 2005; see thepure social structural model presented in Fig. 1). In thecurrent results, this prediction held for women’s sociosexuality,but it did not hold for men’s sociosexuality, nordid it hold for women’s or men’s sex drive. Again, thisprovides at best partial support for social structural theory.Furthermore, social role theory does not offer an obviousexplanation for the interaction between gender equality andmen’s and women’s SDs in sociosexuality. This interactioncan, however, be readily explained by assuming that biologicalpredispositions interact with cultural ‘‘presses.’’A major weakness of social structural theory is that itoften seems to make a generic ‘‘strong gender roles lead tolarge sex differences’’ prediction for psychological traitsthat show sex differences. Although this prediction appearsto be true for sex differences in sociosexuality, it does notappear to be true for sex differences in other traits. Forexample, the strength of societal gender roles is unrelatedto observed sex differences in the value assigned to amate’s physical attractiveness (Eagly & Wood, 1999;Lippa, 2007), and it is unrelated to sex differences in themean levels and variability of sex drive (as reported here).Also contrary to social role’s generic hypothesis, stronggender roles are associated with smaller sex differences inthe value assigned to a mate’s niceness (Lippa, 2007), andstrong versus weak gender roles are associated with differencesin the direction of sex differences in valuing amate’s intelligence (Lippa, 2007). To demonstrate trueexplanatory power, social structural theory must accountfor such variations in the relation between social roles andsex differences, and ideally it should predict, not postdict,such variations. In addition, social role theory must predictthe magnitudes as well as direction of sex differences forvarious traits.The current results present explanatory challenges toevolutionary theories as well. Mean levels of sociosexualityand national SDs in sociosexuality, particularly mean levelsand SDs for women, were strongly associated with societalmeasures of gender equality and economic developmentand, as a result, sex differences in sociosexuality were alsostrongly associated with gender equality and economicdevelopment. In commenting upon similar findings inSchmitt’s (2005) study, Buss (2005) wrote that ‘‘…althoughthe modest cultural variation in the magnitude of sex differencesin the SOI is theoretically important, I suggest thatit is not adequately explained by nebulous theoretical constructssuch a structural powerlessness, gender empowerment,patriarchy, or social structural roles…’’ (p. 279). Bussproposed instead that ‘‘…both men and women possess anevolved menu of mating strategies, selectively activated byparticular features of the personal, social, and ecologicalcontext…’’ (p. 279). In relation to the current results, thetask that confronts theorists like Buss is to explain whymen’s and women’s sociosexuality covaried with featuresof the social and ecological context, whereas their sex drivedid not. Furthermore, evolutionary theories must explainwhy gender equality and gender empowerment measurescovaried so strongly with sex differences in sociosexuality,but not at all with sex differences in sex drive. Like socialstructural theories, evolutionary theories should predict, notpostdic, such findings.Setting the Stage for More Complex and InteractiveTheoriesBecause the findings reported here for sex drive andsociosexuality differed so strongly, we now know that noneof the models presented at the start of this article is necessarilyor uniquely true. The future task facing those whostudy psychological sex differences is to do the hardempirical work of testing various models, for various traits,with hard-to-get cross-cultural data. I predict that empiricalreality will prove to be sufficiently complex so as to confoundmany theorists’ unitary notions about the etiologyand cross-cultural consistency of sex differences. UnlikeSchmitt (2005), who expressed dissatisfaction with thepossibility that several different theoretical perspectivesmight be necessary to explain sex differences in sociosexuality,I am not disappointed by this prospect. The news thatemerges from both Schmitt’s study and the current one—-123

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