Arch Sex Behav DOI 10.1007/s10508-015-0535-z

ORIGINAL PAPER

The Relationship Between Digit Ratio (2D:4D) and Sexual Orientation in Men from China Yin Xu • Yong Zheng

Received: 11 July 2014 / Revised: 9 March 2015 / Accepted: 19 March 2015  Springer Science+Business Media New York 2015

Abstract We examined the relationship between 2D:4D digit ratio and sexual orientation in men from China and analyzed the influences of the components used to assess sexual orientation andthecriteriaused toclassify individualsashomosexual on this relationship. A total of 309 male and 110 female participants took part in a web-based survey. Our results showed that heterosexual men had a significantly lower 2D:4D than heterosexual women and exclusively homosexual men had a significantly higher left 2D:4D than heterosexual men whereas only exclusively homosexual men had a significantly higher right 2D: 4D than heterosexual men when sexual orientation was assessed via sexual attraction. The left 2D:4D showed a significant positive correlation with sexual identity, sexual attraction, and sexual behavior, and the right 2D:4D showed a significant positive correlation with sexual attraction. The effect sizes for differences in2D:4Dbetweenhomosexualand heterosexual men varied according to criteria used to classify individuals as homosexual and sexual orientation components; the more stringent the criteria (scores closer to the homosexual category), the larger the effect sizes; further, sexual attraction yielded the largest effect size. There were no significant effects of age and latitudeon Chinese 2D:4D. This studycontributes to the current understanding of the relationship between 2D:4D and male sexual orientation. Keywords Chinese

2D:4D  Sexual orientation  Latitude 

Y. Xu  Y. Zheng (&) Key Laboratory of Cognition and Personality, School of Psychology, Southwest University, No. 1 Tiansheng, Beibei, Chongqing 400715, China e-mail: [email protected]

Introduction The digit ratio (2D:4D) is defined as the ratio of the lengths of thesecondandfourthdigitsofthehand.Severallinesofevidence suggest that 2D:4D is a possible marker of prenatal exposure to androgens, such as testosterone, with low 2D:4D indicating high prenatal testosterone and low estrogen, and high 2D:4D conversely indicating low prenatal testosterone and high estrogen (Manning, Scutt, Wilson, & Lewis-Jones, 1998). Analysis of samples from routine amniocentesis have shown that low 2D:4D correlates with high concentrations of testosterone relative to estrogen (Lutchmaya, Baron-Cohen, Raggatt, Knickmeyer, & Manning, 2004), and hormones such as androgens can transfer from males to females in utero, with females from opposite-sex twins having lower 2D:4D than females from samesex twins (van Anders, Vernon, & Wilbur, 2006). Moreover, females with congenital adrenal hyperplasia have been shown to have a lower 2D:4D than healthy control females (Brown, Hines, Fane, & Breedlove, 2002; Honekopp & Watson, 2010; Okten, Kalyoncu, & Yaris, 2002; Rivas et al., 2014). Additionally, several other studies have found that males have a significantly lower 2D:4D than females (Branas-Garza, Kova´rˇ´ık, & Neyse, 2013; Grimbos, Dawood, Burriss, Zucker, & Puts, 2010; Honekopp & Watson, 2010; Manning et al., 2000; Manning & Fink, 2011). Neurohormonal theories of human sexual orientation have speculated and proposed high prenatal androgen exposure during critical periods of development may be related to heterosexualityinmen,whereaslowandrogenexposuremaybeassociated withhomosexuality inmen (Collaer& Hines,1995; Ellis& Ames, 1987; Rahman & Wilson, 2003a).Sinceboth 2D:4Dand sexual orientation are associated with prenatal androgen exposure, some studies have focused on the relationship between 2D:4D and sexual orientation. However, the results of studies in this field are inconsistent. Some studies have found that there is no significant difference in 2D:4D between heterosexual and

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homosexual men (e.g., Miller, Hoffmann, & Mustanski, 2008; Voracek,Manning,&Ponocny,2005;Wallien,Zucker,Steensma, & Cohen-Kettenis, 2008). Others have found that homosexual men have a significantly higher 2D:4D (e.g., Hiraishi, Sasaki, Shikishima,&Ando,2012;Kangassalo,Polkki,&Rantala,2011; Manning,Churchill,&Peters,2007)orlower2D:4D(e.g.,Rahman, 2005; Rahman & Wilson, 2003b; Robinson & Manning, 2000) than heterosexual men. Reviewing studies on the relationship between 2D:4D and sexual orientation, we found differences in the components (sexual identity, sexual attraction or sexual fantasy, and sexual behavior) used to assess sexual orientation. For instance, some studies only assessed sexual identity (e.g., Lippa, 2003; Williams et al., 2000), whereas others examined both sexual identity and sexual fantasy (e.g., Manning, 2005), sexual fantasy and sexual behavior (e.g., Robinson & Manning, 2000), or assessed a combination of sexual identity, sexual fantasy, and sexual behavior (e.g., Hall & Schaeff, 2008; McFadden & Shubel, 2002). Such studies also differed in the criteria (the cut-off values for homosexuals) used to classify individuals as homosexual. For instance, some studies using the 5-point Kinsey-like scale (which ranges from 1 to 5) to assess sexual orientation classified individuals with a score of 4 and 5 as homosexuals (e.g., Manning, 2005; Putz, Gaulin, Sporter, & McBurney, 2004). Among studies using a 7-point Kinsey-like scale (which ranges from 0 to 6) to assess sexual orientation, homosexuals have been categorized as those with a score of 6 (e.g., Hall & Schaeff, 2008), with a score of 5 and 6 (e.g., Rahman, 2005), or with a score equal to or higher than 2 (e.g., Kangassalo et al., 2011; Rahman & Wilson, 2003a, b). Studies using the 9-point Kinsey-like scale (which ranges from 1 to 9) to assess sexual orientation have classified individuals with a total score of 11 or less on three items as homosexuals (Kraemer et al., 2006, 2009). Additionally, some studies categorized individuals according to participants’ own choice of descriptor: heterosexual, homosexual, or bisexual (e.g., Lippa, 2003; Manning et al., 2007). Savin-Williams (2006) has pointed out that the assumed prevalence of homosexuals depends on which component is used to assess sexual orientation, and which criteria are used to classify individuals as homosexuals, which perhaps explains the heterogeneity of homosexual samples among studies of 2D:4D and male sexual orientation, and the conflicting results on this topic. Importantly, a number of studies have reported that ethnicity may affect 2D:4D (Lippa, 2003; Manning, Stewart, Bundred, & Trivers, 2004; Manning & Robinson, 2003). However, most studies on the relationship between 2D:4D and male sexual orientation have been carried out using Western populations, and few digit ratio studies have been conducted on Chinese populations to date (however, see Manning et al., 2007, who investigated the relationship between 2D:4D and sexual orientation in Chinese participants). Additional studies on 2D:4D

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in Chinesepopulations would not only allow exploration of the differences in 2D:4D across sexual orientation groups in nonWestern societies, but also extend the findings and generalizability of the previous work on the influence of ethnicity on 2D:4D. Several studies have suggested that there are some variations in 2D:4D among countries with the same ethnicity (McFaddenetal.,2005)orindifferentregionsofthesamecountry(Loehlin, McFadden, Medland, & Martin, 2006). Accordingly, Loehlin et al. suggested that genetic pool differences rather than latitude-related environmental variables contribute to the population differences in 2D:4D. However, the results of studies investigating the relationship between 2D:4D and latitude have not yet been properly compiled. Manning and Fink (2011) found that there tended to be a negative relationship between 2D:4D and latitude among Caucasian participants of nations that were predominantly Caucasian.Hurd andvanAnders(2007) showed that higher 2D:4D appears to be more common at intermediate latitudes and suggested that the association between 2D:4D and latitude might be explained by the allometric relationship between height and 2D:4D across populations, while Helle and Laaksonen (2009) found that there appears to be a convex association between 2D:4D and latitude. However, prior studies on the relationship between 2D:4D and latitude have notable limitations. Loehlin et al. (2006) failed to show that the 2D:4D of Australian females was similar to that reported in the British studies and dissimilar to that observed in the United States. Part of the samples analyzed by Hurd andvanAnders(2007)andHelleandLaaksonen(2009)werethe nine populations first described by Manning et al. (2000). These nine populations included samples from Spain, England, Hungary,and Jamaica, among others; thus, thepopulations consisted of different ethnicities. Since some studies have shown that ethnicity affects the 2D:4D (e.g., Lippa, 2003; Manning et al., 2007), the studies by Hurd and van Anders (2007) and Helle and Laaksonen (2009) were likely biased by the influences of ethnicity and latitude on 2D:4D. Thus, the findings of the studies on the relationship between 2D:4D and latitude in China, in which the study subjects were of the same ethnicity, can be considered more persuasive. Accordingly, the objective of the study reported here was to examine the relationship between 2D:4D and sexual orientation in men from China and to analyze the influences of the components used to assess sexual orientation, the criteria used to classify individuals as homosexuals, and the effect of latitude on Chinese 2D:4D. We predicted that homosexual men would have a higher 2D:4D than heterosexual men and the differences in 2D:4D between homosexual and heterosexual men would vary according to the components used to assess sexual orientation and the different criteria used to classify individuals as homosexual.

Arch Sex Behav

Method

Demographic Information

Participants and Procedure

Demographic information included participants’ gender, age, education level (junior high school or less, senior high school, college, and postgraduate or higher), nationality (Han or the ethnic minorities), and province of residence.

The sample consisted of 309 Chinese men and 110 heterosexual women from 28 provinces/regions of China. Ninety-five men and 110 women with a score of 0 and 1 were heterosexual and 183 men with a score between 4 and 6 were homosexual based on their answers the question: ‘‘What is your sexual orientation?’’Data were collected via a web-based survey hosted by Wenjuanxing (a Chinese survey website). Gay participants were recruited via notices (including the website and purpose of the questionnaire) placed on some Chinese web sites that serve gay individuals, including homosexual forums and chat rooms. Potential participants were told that participation in this project would provide them with the chance to learn more about the causes of homosexuality, and they were assured that their information would be kept strictly confidential. The process of recruiting heterosexual individuals was similar, except that they were recruited via notices posted on general Internet forums and websites that serve all people, such as Zhangshulin Forum and Tianya.cn. Participants were required to complete a questionnaire which comprised the measures of sexual orientation, finger lengths, and demographic information.

Measures Sexual Orientation Sexual orientation was assessed by three items pertaining to sexual identity, sexual attraction, and sexual behavior on a 7-point Kinsey-like scale. Participants were required to answer the question: ‘‘What is your sexual orientation’’ (0 = exclusively heterosexual; 6 = exclusively homosexual). Participants were also asked the gender they felt sexually attracted to (0 = exclusively females; 6 = exclusively males) and the gender of their lifetime sexual partners (0 = exclusively females; 6 = exclusively males; 7 = no sexual experience) Finger Lengths Participants were required to measure their finger lengths following the instructions (using the ring finger of the right hand as an example): ‘‘Hold your right hand in front of you. Look at where your ring finger joins the palm of your hand. Find the bottom crease. Go to the middle of this crease. Put the 0 of your ruler (such as plastic or steel ruler in mm increments) exactly on the middle of the bottom crease. Make sure the ruler runs straight up the middle of your finger. Measure to the tip of your finger (not your nail) in millimeters’’ (Manning et al., 2007). Participants were required to provide the 2nd and 4th digit length for both hands.

Results Preliminary Analyses 2D:4D was computed as the ratio of the lengths of the second and fourth digits of the hand. Given that there is a significant gender difference in 2D:4D (e.g., Honekopp & Watson, 2010), men and women were separated to detect the possible outliers. First, we used the box plot to detect the possible outliers for each hand separately, which are values that are higher than Q3 (the 75th percentile) ? 1.5IQR (interquartile range) or lower than Q1 (the 25th percentile) - 1.5IQR. Participants were excluded if either left or right 2D:4D was an outlier. Thus, the range of 2D:4D in men and women was restricted to all values from .807 to 1.116 and from .820 to 1.134, respectively, and 11.46 % (48/419) of the participants were excluded from our analyses. As a result, this study consisted of 309 Chinese men and 110 women.In addition, therange of2D:4D in this studywas similar to that in previous studies that used direct measurement (e.g., Caswell & Manning, 2009); thus, outliers may represent measurement error rather than natural variation. Second, province values for average latitude were calculated according to the province of residence that the participants provided. Demographic Information The mean age of this sample was 23.82 years (SD = 7.10 years), ranging from 15 to 58 years. Twenty (4.77 %) participants reported a junior high school education or less, 69 (16.47 %) a senior high school education, 249 (59.43 %) a college education, and 81 (19.33 %) postgraduate education or higher. A total of 390 (93.08 %) participants were the Han and 29 (6.92 %) participants were the ethnic minorities. Correlations Between Age, Latitude, and Sexual Orientation Components with 2D:4D by Hand Only men were included in this analysis. Table 1 shows the correlation between age, latitude, and sexual orientation components with 2D:4D by hand. For both hands, there were no significant correlations between age and 2D:4D, and between latitude and the 2D:4D in Han population. Weak positive correlations were obtained between sexual orientations components and 2D:4D in this study, ranging from .09 to .15. There were significant positive correlations between sexual identity,

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sexual attraction, and sexual behavior with left 2D:4D. Moreover, there was a significant positive correlation between sexual attraction and right 2D:4D, but no significant correlations between sexual identity and sexual behavior with right 2D:4D. Sexual Orientation and 2D:4D Men and heterosexual women were included in this analysis. Men were classified into three groups based on their scores on each component of sexual orientation (sexual identity, sexual attraction, and sexual behavior). Those with a score of 0 and 1 were classified as heterosexual men, those with a score between 2 and 4 were classified as non-exclusively homosexual men, and those with a score of 5 and 6 were classified as exclusively homosexual men. When sexual orientation was measured via sexual behavior, individuals without any sexual experiences were excluded from this analysis. A 4 (Sexual orientation: heterosexual men, non-exclusively homosexual men, exclusively homosexual men, and heterosexual women) 9 2 (Hand) repeated measuresanalysisofvariance(ANOVA)wasconductedseparately by sexual orientation components. The ANOVA revealed a significant sexual orientationbyhand interactionforall threesexual orientation components, F(3, 415) = 3.53, p = .015, partial g2 = .03, F(3, 409) = 3.17, p = .048, partial g2 = .02, and F(3, 375) = 3.38, p = .019, partial g2 = .03 for sexual identity, sexual attraction, and sexual behavior, respectively. The interaction was examined further through a one-way ANOVA with these four levels comparing 2D:4D separately by hand and sexual orientation components. Table 2 shows the results of a one-way ANOVA. For left 2D:4D, the ANOVA revealed a significant main effect of sexual orientation for two sexual orientation components, F(3, 409) = 2.66, p = .048, partial g2 = .02, and F(3, 375) = 3.09, p = .027, partial g2 = .02 for sexual attraction and sexual behavior, respectively, and a marginally significant effect of sexual orientation for sexual identity, F(3, 415) = 2.59, p = .052, partial g2 = .02. Post-hoc analyses (LSD) showed that heterosexual women had a significantly higher left 2D:4D than heterosexual men (p = .016, p = .047, and p = .006 for sexual identity, Table 1 Correlations between age, latitude, and sexual orientation components with 2D:4D by hand Left 2D:4D Age (n = 309) Latitudea (n = 289) Sexual identity (n = 309)

Right 2D:4D

.09

.10

-.02

-.03

.14*

.11

Sexual attraction (n = 309)

.15**

.12*

Sexual behaviorb (n = 275)

.15*

.09

* p\.05; ** p\.01 a

Only the Han populations are included

b

Participants who did not have any sexual experiences were excluded from this analysis

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sexual attraction, and sexual behavior, respectively) and exclusively homosexual men had a significantly higher left 2D:4D than heterosexual men (p = .018, p = .006, and p = .01 for sexual identity, sexual attraction, and sexual behavior, respectively). Non-exclusively homosexual men had a significantly higher left 2D:4D than heterosexual men for sexual identity (p = .041) but there were no significant differences between non-exclusively homosexual men and heterosexual men for sexual attraction and sexual behavior (p = .19 and p = .20, respectively), between non-exclusively homosexual men and exclusively homosexual men (p = .87, p = .28, and, p = .75 for sexual identity, sexual attraction, and sexual behavior, respectively), between heterosexual women and exclusively homosexual men (p = .90, p = .53, and, p = .65 for sexual identity, sexual attraction, and sexual behavior, respectively), and between heterosexual women and non-exclusively homosexual men (p = .79, p = .61, and, p = .57 for sexual identity, sexual attraction, and sexual behavior, respectively) in left 2D:4D. For right 2D:4D, a one-way ANOVA revealed a significant effect of sexual orientation for all three sexual orientation components, F(3, 415) = 2.76, p = .042, partial g2 = .02, F(3, 409) = 2.76, p = .042, partial g2 = .02, and F(3, 375) = 3.35, p = .019, partial g2 = .03 for sexual identity, sexual attraction, and sexual behavior, respectively. Post-hoc analyses (LSD) showed that heterosexual women had a significantly higher right 2D:4D than heterosexual men (p = .006, p = .02, and p = .002 for sexual identity, sexual attraction, and sexual behavior, respectively) and exclusively homosexual men had a significantly higher right 2D:4D than heterosexual men for sexual attraction (p = .037). There were no significant differences between exclusively homosexual men and heterosexual men for sexual identity and sexual behavior (p = .101 and p = .14, respectively), between non-exclusively homosexual men and heterosexual men (p = .42, p = .85, and, p = .76 for sexual identity, sexual attraction, and sexual behavior, respectively), between non-exclusively homosexual men and exclusively homosexual men (p = .44, p = .096, and, p = .53 for sexual identity, sexual attraction, and sexual behavior, respectively), between heterosexual women and exclusively homosexual men (p = .21, p = .67, and, p = .056 for sexual identity, sexual attraction, and sexual behavior, respectively), and between heterosexual women and non-exclusively homosexual men (p = .061, p = .055, and, p = .083 for sexual identity, sexual attraction, and sexual behavior, respectively) in right 2D:4D. Table 3 shows the effect sizes for differences among homosexual men (exclusively and non-exclusively) and heterosexual men by sexual orientation components and hands. Table 3 shows that the effect sizes differed across sexual orientation components. The largest effect size was found in sexual attraction. Table 3 also shows that the effect sizes differed across homosexual men. The effect sizes found in exclusively homosexual

Arch Sex Behav Table 2 Mean 2D:4D for sexual orientation by sexual orientation components and hand F(3, 415)a

Heterosexual men

Heterosexual women

Non-exclusively Homosexual men

Exclusively Homosexual men

Sexual identity

n = 95

n = 110

n = 89

n = 125

Left 2D:4D

0.945 (.060)

0.963 (.049)

0.961 (.061)

0.962 (.050)

2.59

Right 2D:4D

0.950 (.059)

0.971 (.054)

0.956 (.057)

0.962 (.055)

2.76*

Sexual attraction

n = 98

n = 104

n = 69

n = 142

Left 2D:4D

0.945 (.058)

0.960 (.046)

0.956 (.056)

0.965 (.055)

2.66*

Right 2D:4D

0.949 (.058)

0.967 (.051)

0.951 (.053)

0.964 (.057)

2.76*

Sexual behavior Left 2D:4D

n = 95 0.944 (.061)

n = 104 0.966 (.049)

n = 28 0.959 (.049)

n = 152 0.963 (.053)

3.09*

Right 2D:4D

0.950 (.059)

0.974 (.054)

0.953 (.048)

0.960 (.056)

3.35*

* p\.05 a

For sexual behavior, participants who did not have any sexual experiences were excluded from this analysis. For sexual attraction, only women with a score of 0 and 1 were included. Thus, df is 409 and 375, respectively

Table 3 Effect sizes for differences between homosexual and heterosexual men by sexual orientation components and hand Non-exclusively homosexual men vs. Heterosexual men

Exclusively homosexual men vs. Heterosexual men

Left 2D:4D

0.27*

0.31*

Right 2D:4D

0.10

0.21

Left 2D:4D

0.20

0.36**

Right 2D:4D

0.04

0.26*

Left 2D:4D

0.26

0.34*

Right 2D:4D

0.05

0.18

Sexual identity

Sexual attraction

Sexual behavior

* p\.05; ** p\.01

men was larger than that in non-exclusively homosexual men for all three sexual orientation components.

Discussion The current research used direct self-digit measurement to explore the relationship between 2D:4D and male sexual orientationina large Chinese sample. Studies on2D:4D haveused eitherdirectmeasurement(directly measuredfromthe hand) or indirect measurement (i.e., photocopies, scans, X-rays) to measuredigitratio.Althoughhigher2D:4Dandsmallerbutsignificant sex differences in 2D:4D in samples using direct digit measurement have been reported compared to samples using indirect digit measurement(Caswell&Manning,2009;Manning,Fink,Neave, & Caswell, 2005), Caswell and Manning suggested that the

drawbacksof direct digit measurement can be countered if large numbers of participants are recruited and outliers of 2D:4D are removed.In addition, the finding of the current research showed that heterosexual men had a significantly lower 2D:4D than heterosexual women, which was consistent with previous studies (e.g., Grimbos et al., 2010; Hampson, Ellis, & Tenk, 2008). Moreover,themean2D:4Dinheterosexualmenandwomenfoundinthis studyweresimilartostudiesusingdirectmeasurementasreportedin ameta-analysisofChinese2D:4D (Xu &Zheng,2015).Theselines of evidence justify our use of self-measurement of 2D:4D. Our results suggested that 2D:4D of homosexual men was significantly higher compared to that of heterosexual men. This result supports the findings of some previous work on the relationship between 2D:4D and male sexual orientation (e.g., Hall & Schaeff, 2008; Lippa, 2003; Manning et al., 2007) suggesting that low prenatal androgen exposure in particular may be associated with homosexuality in men (Collaer & Hines, 1995; Ellis & Ames, 1987; Rahman & Wilson, 2003a). Ourresultsalsodemonstratedthatleft2D:4Dwassignificantly higher in homosexual men compared to heterosexual men, whereas right 2D:4D was the same for both homosexual and heterosexual men. This result supports the findings of some previous studies (Hall & Schaeff, 2008; Hiraishi et al., 2012; McFadden & Shubel, 2002), but conflicts with other work (Lippa, 2003; Manning et al., 2007). Manning et al. (1998) suggested that the right hand 2D:4D is likely to reflect prenatal androgen exposure more strongly than the left hand. Thus, we speculate that the magnitude of the difference in 2D:4D between homosexual and heterosexual men should be greater for the right hand than for the left hand, which is the opposite of the pattern we found. We suggest that ethnic differences may be one of the reasons our results conflict with some previous findings. Several studies have shown that ethnicity may affect 2D:4D (e.g., Manning et al., 2007; Manning & Robinson, 2003), although these studies largely

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focused on Western populations. The ethnic differences between Chinese and Western populations may explain the conflicting results we found here. Moreover, our results were consistent with onestudythatexploredtherelationshipbetween2D:4D andmale sexual orientation in Japan (Hiraishi et al., 2012). The ethnic difference between Chinese and Japanese participants is smaller than that between Chinese and Western populations, which supports the view that ethnic differences may be an important influence on the 2D:4D digit ratio. We also found significant positive correlations between sexual identity, sexual attraction, and sexual behavior with left 2D:4D, and a significant positive correlation between sexual attraction and right 2D:4D. Moreover, the largest effect size for differences in 2D:4D between homosexual and heterosexual men was found when sexual orientation was measured via sexual attraction. These results indicate that the components used to assess sexual orientation can affect the relationship between 2D:4D and male sexual orientation in China, and that sexual attraction may be the most sensitive measure of Chinese sexual orientation. Many factors, such as motivation and the opportunities to find desired sexual partners, can affect sexual behavior patterns. Moreover, if sexual behavior is used to assess sexual orientation, homosexual people without any sexual experience are excluded (Savin-Williams, 2006).Additionally, Chinese people show a relatively low recognition of lesbian and, especially gay, orientations (Gai, Wang, Gai, & Xun, 2013; Yu, Xiao, Wang, & Shun, 2010) and some Chinese homosexual people would not characterize themselves as homosexual.Thus, sexual attraction may be the most pragmatic way to assess Chinese sexual orientation. Ourresults demonstratedthat thecriteria used toclassifyindividuals as homosexual affected the relationship between 2D:4D and male sexual orientation. Exclusively homosexual men had a significantly higher left 2D:4D than heterosexual men, while only non-exclusively homosexual men had a significantly higher left 2D:4D than heterosexual men when sexual orientation was assessed via sexual identity. Additionally, the effect sizes for differences in 2D:4D between homosexual and heterosexual men varied according to the criteria used to classify individuals as homosexual: the more strict the criteria (scores closer to the homosexual category), the larger the effect sizes. These results suggest the importance of understanding how sexual orientation and homosexuality are measured, since measurement can affect the perceived prevalence of homosexuality, as suggested by Savin-Williams (2006). Thus, we suggest that the differences in the components used to assess sexual orientation, and the criteria used to classify individuals as homosexual in studies on the relationship between 2D:4D and male sexual orientation, may lead to the heterogeneity of the homosexual sample among studies and may be one of the reasons why there are conflicting research findings in this area. This study also demonstrated that latitude did not affect the 2D:4D in China, which is consistent with the results of Loehlin

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et al. (2006). Thus, it is also possible that latitude-related environmental variables do not affect 2D:4D. However, we directly explored the effect of latitude on the 2D:4D in China in the same ethnic group, which provides for a relatively robust test. The latitude range analyzed in this study was between 22720 N and 48290 N. Although this latitude range is close to the latitude range of China, it is limited by the fact that it lacked samples conducted in relatively low (near the equator) and high (near the ArcticCircle)latitudes,whichmayhavecontributedtothelackof observed significant effects of latitude on 2D:4D in China. Finally,theagerangeofparticipantsofthisstudywasbetween 15 and 58 years, and no significant correlation between age and 2D:4D was found, which is consistent with the notion that the 2D:4D is formed prenatally and remains stable after birth (McIntyre, Ellison, Lieberman, Demerath, & Towne, 2005). Studies on the relationship between 2D:4D and male sexual orientation have often produced contradictory results. Sinceethnicity may affect the 2D:4D (e.g., Lippa, 2003; Manning et al., 2007), we believe that the current study exploring the relationship between 2D:4D and male sexual orientation in China is an important contribution to this field of research.

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