Dermatoglyphics, Handedness, Sex, and Sexual Orientation

Both handedness and dermatoglyphic asymmetry reflect early, prenatal influences and both have been reported to be associated with male sexual orientation; handedness has been related to female sexual orientation as well. Neurohormonal and developmental perturbation are two competing hypothesis that attempt to explain these connections. We attempted to replicate these associations and to extend dermatoglyphic asymmetry findings to women. Dermatoglyphic directional asymmetry and fluctuating asymmetry were unrelated to sexual orientation. Homosexual women, but not homosexual men, had highly significant increases in non–right-handedness compared with same-sex heterosexual controls. Although this pattern of results does not allow resolution of the two competing models, it does lend additional support to a biological basis of sexual orientation.     

Birth Order,Sibling Sex Ratio,Handedness, and Sexual Orientation of Male and Female Participants in a BBC Internet Research Project

This study investigated the relations among sexual orientation, fraternal birth order (number of older brothers), and hand-preference. The participants were 87,798 men and 71,981 women who took part in a Web-based research project sponsored by the British Broadcasting Corporation (BBC). The results yielded some evidence confirming prior findings that non-right-handedness is associated with homosexuality in men and women, that older brothers increase the odds of homosexuality in men, and that the effect of older brothers on sexual orientation is limited to right-handed men. The evidence was weaker than in previous studies, however, probably because the usual relations among the variables of interest were partially obscured by the effects of other factors. Thus, the homosexual men and women had higher rates of non-right-handedness than their heterosexual counterparts, but the strongest handedness finding for both sexes was a marked tendency for participants who described themselves as ambidextrous also to describe themselves as bisexual. The birth order data were strongly affected by a tendency for the male participants to report an excess of older sisters, and the female participants to report an excess of older brothers. Statistical analyses confirmed that this was an artifact of the parental stopping rule, “Continue having children until you have offspring of both sexes.” In subsequent analyses, participants were divided into those who did and did not have younger siblings, on the grounds that the data of the former would be less contaminated by the stopping rule. In the former subsample, the right-handed homo/bisexual males showed the typical high ratio of older brothers to older sisters, whereas the non-right-handed homo/bisexual males did not.     

Gender-Related Traits of Heterosexual and Homosexual Men and Women

Two studies investigated the relation between sexual orientation and gender-related traits. Analyzing data from an Internet survey, Study 1 found that gay men and lesbians differed from same-sex heterosexuals most strongly on gender diagnosticity (GD) measures, which assess male- versus female-typicality of occupational preferences (effect sizes were 1.14 for men and 0.53 for women) and least strongly on instrumentality (I) and expressiveness (E). Study 2 found that GD measures showed large differences between 289 gay and 200 heterosexual men (d = 0.95) and between 296 lesbian and 435 heterosexual women (d = 1.32), whereas I and E showed much smaller differences. In Study 2 homosexual–heterosexual diagnosticity measures, computed from men's and women's occupational preferences, correlated very strongly with GD measures (r = 0.88 for men and 0.89 for women), indicating that occupational preference items that distinguished men from women also tended to distinguish heterosexual from homosexual individuals. LISREL 8 analyses showed that self-ascribed masculinity–femininity did not mediate the strong relation between sexual orientation and GD for men or for women.     

Correlates of sexual orientation in the German Democratic Republic

From 5469 participants of a sexual inquiry in the German Democratic Republic, 90 homosexual and 107 heterosexual women and men were selected, aged 16–30. A comparison was made concerning aspects of leisure time and sexual life. Some differences appear with regard to leisure time between homosexual and heterosexual women and men. The importance of love and sexuality is as great for young homosexuals as it is for young heterosexuals, but the mode and quantity of their specific sexual activities differ. Homosexual women appear to be more sexually active than heterosexual women on some study parameters.     

Same-sex sexuality and quality of life: findings from the Netherlands Mental Health Survey and Incidence Study

This study assessed differences in quality of life (QL) between homosexual and heterosexual people and attempted to identify factors accounting for observed differences. Data were collected in a representative sample of the Dutch population aged 18–64 (N = 7,076). Classification as heterosexual or homosexual was based upon reported sexual behavior in the preceding year; 84.8% of the total sample (N = 5,998) could be classified: 2.8% of 2,878 sexually active men and 1.4% of 3,120 sexually active women had had same-sex partners. Differences in QL were tested by analysis of variance. Factors accounting for observed differences in QL were identified by selecting determinants of QL on which homosexual and heterosexual people differed and including them with same-sex sexuality in multiple regression analyses. Homosexual men, but not women, differed from their heterosexual counterparts on various dimensions of QL. Lesser QL in homosexual men was predominantly explained by self-esteem and mastery. Same-sex sexuality contributed independently to some of the observed differences. Although same-sex sexuality is related to QL in men, the lack of association in women suggests that the link is mediated by other factors, indicating the need to explore in what respect the situation of homosexual men and women differs. This study also suggests the importance of finding out how lower sense of self-esteem and of mastery come about in homosexual men.     

Body Image Satisfaction in Heterosexual,Gay, and Lesbian Adults

Does the prevalence and degree of body dissatisfaction differ among heterosexual and homosexual men and women? Some theorists have suggested that, compared to their heterosexual peers, gay men are at greater risk for body dissatisfaction and lesbians at lower risk. Past studies examining this issue have generally relied on small samples recruited from gay or lesbian groups. Further, these studies have sometimes produced conflicting results, particularly for comparisons of lesbian and heterosexual women. In the present research, we compared body satisfaction and comfort with one’s body during sexual activity among lesbian women, gay men, heterosexual women, and heterosexual men through two large online studies (Ns = 2,512 and 54,865). Compared to all other groups, heterosexual men reported more positive evaluations of their appearance, less preoccupation with their weight, more positive effects of their body image on their quality of life and the quality of their sex life, more comfort wearing a swimsuit in public, and greater willingness to reveal aspects of their body to their partner during sexual activity. Few significant differences were found among gay men, lesbian women, and heterosexual women. Many gay men (42%) reported that their feelings about their body had negative effects on the quality of their sex life, as did some lesbian women (27%), heterosexual women (30%), and heterosexual men (22%). Overall, the findings supported the hypothesis that gay men are at greater risk than heterosexual men for experiencing body dissatisfaction. There was little evidence that lesbian women experience greater body satisfaction than heterosexual women.     

Comparative data of childhood and adolescence molestation in heterosexual and homosexual persons

In research with 942 nonclinical adult participants, gay men and lesbian women reported a significantly higher rate of childhood molestation than did heterosexual men and women. Forty-six percent of the homosexual men in contrast to 7% of the heterosexual men reported homosexual molestation. Twenty-two percent of lesbian women in contrast to 1% of heterosexual women reported homosexual molestation. This research is apparently the first survey that has reported substantial homosexual molestation of girls. Suggestions for future research were offered.     

Sex and Sexual Orientation Differences in Personality in China

Using data from an Internet survey, we assessed masculinity-femininity (self-ascribed masculinity-femininity [Self-MF], gender-related interests, instrumentality, expressiveness) and Big Five personality traits in a Chinese sample of 201 heterosexual men, 220 homosexual men, 353 heterosexual women, and 215 homosexual women. Sex differences and sexual orientation differences were largest for gender-related interests and Self-MF. Homosexual-heterosexual differences in emotional stability were opposite for men and women, supporting the “gender shift” over the “social stress” hypothesis. Sex and sexual orientation differences in gender-related interests, Self-MF, and emotional stability observed in China were consistent with those found in other countries, suggesting possible biological influences. In contrast, group differences in other traits were more variable, suggesting possible cultural influences.     

Sexual Orientation Differences in Cerebral Asymmetry and in the Performance of Sexually Dimorphic Cognitive and Motor Tasks

With each of the tasks in the present studies we expected to find the reported sex difference between heterosexual women and heterosexual men and we predicted a sexual orientation effect with the performance of homosexual men being similar to that of heterosexual women and different from that of heterosexual men. Study I aimed to replicate earlier findings by recording the performance of a group of homosexual men on a visuospatial task, the Vincent Mechanical Diagrams Test (VMDT), a dot detection divided visual field measure of functional cerebral asymmetry, and on five subtests of the Wechsler Adult Intelligence Scale (WAIS). For each task the profile of scores obtained for the homosexual men was similar to that of heterosexual women in that they scored lower than heterosexual men on the VMDT, they showed less asymmetry, and they recorded a higher Verbal than Performance IQ on the WAIS. In Study 2, a male-biased targeted throwing task favored heterosexual men while, in contrast, on the female-biased Purdue Pegboard single peg condition heterosexual men were outperformed by heterosexual women and homosexual men. On neither of these two tasks did the performances of homosexual men and heterosexual women differ. One task, manual speed, yielded neither sex nor sexual orientation differences. Another, the Purdue Pegboard assemblies condition, revealed a sex difference but no sexual orientation difference. Failure to obtain a sexual orientation difference in the presence of a sex difference suggests that the sexual orientation effect may be restricted to a subset of sexually dimorphic tasks.     

A Comparative Analysis of Functional Cerebral Asymmetry in Lesbian Women, Heterosexual Women, and Heterosexual Men

This study tested dichotic listening performance, a measure of functional cerebral asymmetry previously shown to be sexually dimorphic, in homosexual women (n=23), heterosexual women (n=27), and heterosexual men (n=24). All participants completed a verbal consonant-vowel dichotic listening task. On three laterality indices, heterosexual men displayed a significantly greater right-ear advantage compared to heterosexual women only. Homosexual women did not differ significantly from heterosexual men or from heterosexual women. Post-hoc comparisons (with a statistical correction) for each ear separately showed that heterosexual men displayed significantly greater right-ear scores compared to heterosexual women only. These data suggest that lesbian women are somewhat masculinized in their functional cerebral asymmetry. The results were interpreted in the context of sexual variation in models of linguistic hemispheric processing.     

Corpus Callosum Anatomy in Right-Handed Homosexual and Heterosexual Men

The results of several studies have shown that homosexual men have an increased prevalence of non-right-handedness and atypical patterns of hemispheric functional asymmetry. Non-right-handedness in men has been associated with increased size of the corpus callosum (CC), particularly of the isthmus, which is the posterior region of the callosal body connecting parietotemporal cortical regions. We hypothesized that isthmal area would be greater in homosexual men, even among right handers. Twelve homosexual and ten heterosexual healthy young men, all consistently right-handed, underwent a research-designed magnetic resonance imaging scan. We found that the isthmal area was larger in the homosexual group, adding to the body of findings of structural brain differences between homosexual and heterosexual men. This result suggests that right-handed homosexual men have less marked functional asymmetry compared to right-handed heterosexual men. The results also indicate that callosal anatomy and laterality for motoric functions are dissociated in homosexual men. A logistic regression analysis to predict sexual orientation category correctly classified 21 of the 22 men (96% correct classification) based on area of the callosal isthmus, a left-hand performance measure, water level test score, and a measure of abstraction ability. Our findings indicate that neuroanatomical structure and cognition are associated with sexual orientation in men and support the hypothesis of a neurobiological basis in the origin of sexual orientation.     

Biodemographic and Physical Correlates of Sexual Orientation in Men

To better understand sexual orientation from an evolutionary perspective, we investigated whether, compared to heterosexual men, the fewer direct descendants of homosexual men could be counterbalanced by a larger number of other close biological relatives. We also investigated the extent to which three patterns generally studied separately––handedness, number of biological older brothers, and hair-whorl rotation pattern––correlated with each other, and for evidence of replication of previous findings on how each pattern related to sexual orientation. We surveyed at Gay Pride and general community festivals, analyzing data for 894 heterosexual men and 694 homosexual men, both groups predominantly (~80%) white/non-Hispanic. The Kinsey distribution of sexual orientation for men recruited from the general community festivals approximated previous population-based surveys. Compared to heterosexual men, homosexual men had both more relatives, especially paternal relatives, and more homosexual male relatives. We found that the familiality for male sexual orientation decreased with relatedness, i.e., when moving from first-degree to second-degree relatives. We also replicated the fraternal birth order effect. However, we found no significant correlations among handedness, hair whorl rotation pattern, and sexual orientation, and, contrary to some previous research, no evidence that male sexual orientation is transmitted predominantly through the maternal line.     

The Subtlety of Sex-Atypicality

Memories of sex-atypical behavior and interests in childhood usually differ between homosexual and heterosexual people. However, variation within these broad groups has not previously been explored in detail, especially among women. We utilized data from a postal survey of a nationwide sample of Australian adult twins (n = 4,901, age range: 19–52 years). Among men, 15.2% reported homosexual behavior (ever), 11.5% said they had been sexually attracted to the same sex, and 6.4% said they were not heterosexual; the corresponding figures for women were 7.9, 10.6, and 3.5%. A continuous measure of childhood gender nonconformity (CGN) was sensitive to slight variations in homosexual attraction and behavior. In particular, among both men and women who identified as heterosexual, there were significant differences between complete heterosexuals and those who admitted to only one or a few same-sex behaviors but no homosexual attraction. Among men, CGN scores distinguished between heterosexuals who admitted to same-sex behavior only and those who admitted to some homosexual attraction. The sexual subgroups also differed on a measure of gender atypicality in adulthood. Implications for developmental theories of sexuality are discussed.     

The Relationship Between Digit Ratio (2D:4D) and Sexual Orientation in Men from China

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 and the criteria used to classify individuals as homosexual 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 in 2D:4D between homosexual and 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 latitude on Chinese 2D:4D. This study contributes to the current understanding of the relationship between 2D:4D and male sexual orientation.     

Handedness in homosexual and heterosexual men in the Kinsey interview data

The relationship between sexual orientation and handedness in a large sample of men was examined. Subjects were 6544 nondelinquent men interviewed by the Kinsey Institute for Research in Sex, Gender, and Reproduction from 1938 to 1963. Subjects were classified as either homosexual (n=1004) or heterosexual (n=4579). Results failed to demonstrate a difference in handedness, with both groups having rates of non-right-handedness (i.e., 11–12%) approximately equal to establish norms. These findings do not replicate some recent studies indicating an increased level of non-right-handedness in homosexual men.     

The Effects of Sex,Sexual Orientation,and Digit Ratio (2D:4D) on Mental Rotation Performance

In spite of the reduced level of experimental control, this large scale study brought some clarity into the relation between mental rotation task (MRT) performance and a number of variables where contradictory associations had previously been reported in the literature. Clear sex differences in MRT were observed for a sample of 134,317 men and 120,783 women, with men outperforming women. There were also MRT differences as a function of sexual orientation: heterosexual men performed better than homosexual men and homosexual women performed better than heterosexual women. Although bisexual men performed better than homosexual men but less well than heterosexual men, no significant differences were observed between bisexual and homosexual women. MRT performance in both men and women peaked in the 20-30 year range, and declined significantly and markedly thereafter. Both men and women showed a significant negative correlation between left and right digit finger ratio and MRT scores, such that individuals with smaller digit ratios (relatively longer ring finger than index finger) performed better than individuals with larger digit ratios.     

Sex Ratio of Older Siblings in Heterosexual and Homosexual,Right-Handed and Non-Right-Handed Men

This study investigated why older brothers, which increase the odds of homosexuality in later-born males who are right-handed, have no effect or the opposite effect on later-born males who are non-right-handed. The specific question was whether the different results for the non-right-handed men have to do with the heterosexual non-right-handers or the homosexual non-right-handers. The human sex ratio at birth (106 males per 100 females) was used as a gold standard for determining which groups differ from the general population and in which direction. All usable data from previous studies were combined to obtain the largest possible sample (N = 8,201). The observed ratio of older brothers to older sisters was 105 for the heterosexual right-handers, 128 for the homosexual right-handers, 127 for the heterosexual non-right-handers, and 96 for the homosexual non-right-handers. The ratios for the homosexual right-handers and the heterosexual non-right-handers differed significantly from the expected value. These results suggest that both heterosexual and homosexual non-right-handers contribute to the older brothers × handedness × sexual orientation interaction.     

Upset Over Sexual versus Emotional Infidelity Among Gay,Lesbian, Bisexual,and Heterosexual Adults

One hypothesis derived from evolutionary perspectives is that men are more upset than women by sexual infidelity and women are more upset than men by emotional infidelity. The proposed explanation is that men, in contrast to women, face the risk of unwittingly investing in genetically unrelated offspring. Most studies, however, have relied on small college or community samples of heterosexual participants. We examined upset over sexual versus emotional jealousy among 63,894 gay, lesbian, bisexual, and heterosexual participants. Participants imagined which would upset them more: their partners having sex with someone else (but not falling in love with them) or their partners falling in love with someone else (but not having sex with them). Consistent with this evolutionary perspective, heterosexual men were more likely than heterosexual women to be upset by sexual infidelity (54 vs. 35 %) and less likely than heterosexual women to be upset by emotional infidelity (46 vs. 65 %). This gender difference emerged across age groups, income levels, history of being cheated on, history of being unfaithful, relationship type, and length. The gender difference, however, was limited to heterosexual participants. Bisexual men and women did not differ significantly from each other in upset over sexual infidelity (30 vs. 27 %), regardless of whether they were currently dating a man (35 vs. 29 %) or woman (28 vs. 20 %). Gay men and lesbian women also did not differ (32 vs. 34 %). The findings present strong evidence that a gender difference exists in a broad sample of U.S. adults, but only among heterosexuals.     

Suicidality and Sexual Orientation: Differences Between Men and Women in a General Population-Based Sample From The Netherlands

Homosexuality has been shown to be associated with suicidality and mental disorders. It is unclear whether homosexuality is related to suicidality, independently of mental disorders. This study assessed differences in lifetime symptoms of suicidality (death ideation, death wishes, suicide contemplation, and deliberate self-harm) between homosexual and heterosexual men and women, controlling for lifetime psychiatric morbidity. Interaction effects of age and the role of perceived discrimination were also examined. Data were collected on a representative sample of the Dutch population aged 18–64 years. Classification as heterosexual or homosexual was based upon reported sexual behavior in the preceding year. Of those sexually active, 2.8% of 2,878 men and 1.4% of 3,120 women had had same-sex partners. Homosexual men differed from their heterosexual counterparts on all four suicide symptoms (OR ranging from 2.58 to 10.23, with higher ORs for more severe symptoms), and on the sum total of the four symptoms; homosexual women only differed from heterosexual women on suicide contemplation (OR=2.12). Controlling for psychiatric morbidity decreased the ORs, but among men all associations were still significant; the significance for suicide contemplation among women disappeared. Younger homosexuals were not at lower risk for suicidality than older homosexuals in comparison with their heterosexual counterparts. Among homosexual men, perceived discrimination was associated with suicidality. This study suggests that even in a country with a comparatively tolerant climate regarding homosexuality, homosexual men were at much higher risk for suicidality than heterosexual men. This relationship could not only be attributed to their higher psychiatric morbidity. In women, there was no such clear relationship.     

Heterosexual experience,marital status,and orientation of homosexual males

The penile volume responses of homosexual males to pictures of nude women and men were measured and related to the subjects' marital status and experience of heterosexual intercourse. Single subjects with no experience of heterosexual intercourse and married subjects with a history of intercourse with only their wives showed significantly greater response to pictures of men compared to pictures of women than did single subjects with experience of heterosexual intercourse and married subjects with experience of intercourse with women additional to their wives. It was concluded that extensive experience of heterosexual intercourse with one partner did not reduce homosexual responsiveness as measured by subjects' penile response to pictures of nude men and women. It was further concluded that some homosexual males showed physiological evidence of a degree of bisexuality in addition to the behavioral evidence that they sought heterosexual physical relationships.This investigation was supported in part by the National Health and Medical Research Council of Australia.