Stability and Change in Sexual Orientation and Genital Arousal over Time.

Longitudinal work suggests that sexual orientation can change over time in men and women. These studies, however, may be susceptible to the bias of self-report. The current study therefore examined self-reported sexual orientation in addition to an objective correlate: genital arousal to erotic videos showing males or females. For 52 men (19 heterosexual, 19 bisexual, 14 homosexual) and 67 women (31 heterosexual, 18 bisexual, 18 homosexual), these measures were taken twice, with approximately 1 year between sessions. For self-reported sexual orientation, women reported lower relative stability (weaker correlation) than men over time, even though women did not change more overall (no stronger mean difference) than men between sessions. Bisexual individuals reported lower relative stability and more mean change than heterosexual and homosexual individuals. For genital arousal, across all groups, response patterns were correlated over time to a similar extent and showed little difference between sessions. Moreover, change in self-reported sexual orientation did not correspond with the change in genital arousal, regardless of sex. Perhaps self-reports overestimate changes in sexual orientation, since these changes were not reflected in physiological sexual response.

Examining Visual Attention Patterns among Asexual and Heterosexual Individuals.

Asexuality has garnered much attention, and empirical data support its classification as a sexual orientation. Asexuality is defined as a lack of sexual attraction to others, with approximately 1% of the population falling in this category. As theoretical models situate attention as a central component of sexual response, the current study examined attentional processing of erotic stimuli in asexuals and heterosexuals. We hypothesized that heterosexual participants would have initial and controlled visual attention patterns favoring erotic images over non-erotic images. We predicted that asexual participants would have significantly smaller or non-existent differences in attention to erotic versus non-erotic images. Ninety-five adults completed an eye-tracking task viewing erotic and non-erotic images. Eye-tracking data showed no group differences in initial attention to erotic images. For controlled attention, there was a large effect size in the hypothesized direction. Heterosexual participants exhibited more and longer fixations on erotic images, whereas asexuals exhibited a more even distribution of attention across image types. Exploratory analysis of group differences in the association between visual attention and ratings of sexual attractiveness revealed a complex pattern of differences, with some indication of a stronger association between total fixation and sexual attraction for heterosexual participants. These findings suggest that differences in attention to sexual stimuli may represent key underlying differences between asexual and allosexual orientation. Findings also contribute to the larger literature on visual attention and attraction.

The relationship between finger length ratio, masculinity, and sexual orientation in women: A correlational study.

Homosexual women are, on average, more masculine in their appearance and behavior than heterosexual women. We hypothesized that their masculinity was influenced by exposure to elevated levels of prenatal androgen during early development. We recruited 199 women (including 67 homosexual women) and measured their masculinity via self-report and observer ratings. Our measure of prenatal androgen exposure was the ratio of the index to ring finger (2D:4D), which is hypothesized to be lower in women exposed to elevated levels of androgens during prenatal development. Homosexual women were substantially more masculine than heterosexual women in both self-report and observer ratings. However, homosexual women neither had more male-typical finger length ratios, nor did their finger length ratios relate to their masculinity in any predicted direction. Thus, we found no evidence that increased prenatal androgen exposure influenced masculinity in homosexual women.

Sex Differences in Sexual Arousal and Finger Length Ratio.

Most men show sexual arousal to one, preferred sex, whereas most women respond to both sexes, regardless of their sexual orientation. A different research program indicates that men have lower second-to-fourth finger length ratios (2D:4D) than women, possibly because men are exposed to higher levels of androgens during prenatal development. We hypothesized that sex differences in sexual arousal patterns are influenced by prenatal androgen exposure and would thus be explained by sex differences in 2D:4D. We measured the sexual response patterns of 139 men and 179 women via genital arousal and pupil dilation to erotic videos, in addition to their 2D:4D. Compared to women, men showed stronger responses to one sex over the other, although this pattern was clearer in genital arousal than pupil dilation. Men also had lower 2D:4D than women. However, there was no evidence that sex differences in sexual arousal related to sex differences in 2D:4D. Thus, whichever factor explains sex differences in sexual arousal patterns may not be reflected in 2D:4D.

Genome-Wide Linkage and Association Study of Childhood Gender Nonconformity in Males.

Male sexual orientation is influenced by environmental and complex genetic factors. Childhood gender nonconformity (CGN) is one of the strongest correlates of homosexuality with substantial familiality. We studied brothers in families with two or more homosexual brothers (409 concordant sibling pairs in 384 families, as well as their heterosexual brothers), who self-recalled their CGN. To map loci for CGN, we conducted a genome-wide linkage scan (GWLS) using SNP genotypes. The strongest linkage peaks, each with significant or suggestive two-point LOD scores and multipoint LOD score support, were on chromosomes 5q31 (maximum two-point LOD = 4.45), 6q12 (maximum two-point LOD = 3.64), 7q33 (maximum two-point LOD = 3.09), and 8q24 (maximum two-point LOD = 3.67), with the latter not overlapping with previously reported strongest linkage region for male sexual orientation on pericentromeric chromosome 8. Family-based association analyses were used to identify associated variants in the linkage regions, with a cluster of SNPs (minimum association p = 1.3 × 10-8) found at the 5q31 linkage peak. Genome-wide, clusters of multiple SNPs in the 10-6 to 10-8 p-value range were found at chromosomes 5p13, 5q31, 7q32, 8p22, and 10q23, highlighting glutamate-related genes. This is the first reported GWLS and genome-wide association study on CGN. Further increasing genetic knowledge about CGN and its relationships to male sexual orientation should help advance our understanding of the biology of these associated traits.

Sexual Orientation, Sexual Arousal, and Finger Length Ratios in Women.

In general, women show physiological sexual arousal to both sexes. However, compared with heterosexual women, homosexual women are more aroused to their preferred sex, a pattern typically found in men. We hypothesized that homosexual women's male-typical arousal is due to their sex-atypical masculinization during prenatal development. We measured the sexual responses of 199 women (including 67 homosexual women) via their genital arousal and pupil dilation to female and male sexual stimuli. Our main marker of masculinization was the ratio of the index to ring finger, which we expected to be lower (a masculine pattern) in homosexual women due to increased levels of prenatal androgens. We further measured observer- and self-ratings of psychological masculinity-femininity as possible proxies of prenatal androgenization. Homosexual women responded more strongly to female stimuli than male stimuli and therefore had more male-typical sexual responses than heterosexual women. However, they did not have more male-typical digit ratios, even though this difference became stronger if analyses were restricted to white participants. Still, variation in women's digit ratios did not account for the link between their sexual orientation and their male-typical sexual responses. Furthermore, homosexual women reported and displayed more masculinity than heterosexual women, but their masculinity was not associated with their male-typical sexual arousal. Thus, women's sexual and behavioral traits, and potential anatomical traits, are possibly masculinized at different stages of gestation.

Patterns of Genital Sexual Arousal in Transgender Men.

Most men show genital sexual arousal to one preferred gender. Most women show genital arousal to both genders, regardless of their sexual preferences. There is limited knowledge of whether this difference is driven by biological sex or gender identity. Transgender individuals, whose birth sex and gender identity are incongruent, provide a unique opportunity to address this question. We tested whether the genital responses of 25 (female-to-male) transgender men followed their female birth sex or male gender identity. Depending on their surgical status, arousal was assessed with penile gauges or vaginal plethysmographs. Transgender men's sexual arousal showed both male-typical and female-typical patterns. Across measures, they responded more strongly to their preferred gender than to the other gender, similar to (but not entirely like) 145 cisgender (nontransgender) men. However, they still responded to both genders, similar to 178 cisgender women. In birth-assigned women, both gender identity and biological sex may influence sexual-arousal patterns.

Robust evidence for bisexual orientation among men.

The question whether some men have a bisexual orientation-that is, whether they are substantially sexually aroused and attracted to both sexes-has remained controversial among both scientists and laypersons. Skeptics believe that male sexual orientation can only be homosexual or heterosexual, and that bisexual identification reflects nonsexual concerns, such as a desire to deemphasize homosexuality. Although most bisexual-identified men report that they are attracted to both men and women, self-report data cannot refute these claims. Patterns of physiological (genital) arousal to male and female erotic stimuli can provide compelling evidence for male sexual orientation. (In contrast, most women provide similar physiological responses to male and female stimuli.) We investigated whether men who self-report bisexual feelings tend to produce bisexual arousal patterns. Prior studies of this issue have been small, used potentially invalid statistical tests, and produced inconsistent findings. We combined nearly all previously published data (from eight previous studies in the United States, United Kingdom, and Canada), yielding a sample of 474 to 588 men (depending on analysis). All participants were cisgender males. Highly robust results showed that bisexual-identified men's genital and subjective arousal patterns were more bisexual than were those who identified as exclusively heterosexual or homosexual. These findings support the view that male sexual orientation contains a range, from heterosexuality, to bisexuality, to homosexuality.

Gender Nonconformity of Bisexual Men and Women.

The degree to which bisexual-identified individuals are distinct from either heterosexual or homosexual individuals in their sexual orientation is an ongoing debate. We examined potential differences between these groups with respect to a strong correlate of sexual orientation, gender nonconformity (femininity in males, masculinity in females). Across pooled data, we compared self-reports of childhood gender nonconformity (n = 919) and adulthood gender nonconformity (n = 1265) and observer ratings of adulthood gender nonconformity (n = 915) between sexual orientations. Most analyses suggested a steady increase in gender nonconformity from exclusively heterosexual to exclusively homosexual. However, in some analyses, bisexual men were closer to homosexual men than to heterosexual men in their gender nonconformity. The intermediate status of bisexual people in gender nonconformity was not due to the sample having a mixture of very gender-conforming and very gender-nonconforming individuals. In total, men and women with bisexual orientations appeared neither like heterosexual nor homosexual individuals, at least with respect to their gender-related traits.

Gender Nonconformity of Identical Twins with Discordant Sexual Orientations: Evidence from Video Recordings.

Gender nonconformity (femininity in males, masculinity in females) is more common in non-heterosexual (bisexual and homosexual) than heterosexual individuals. In the past research (Watts, Holmes, Raines, Orbell, & Rieger, 2018b), identical twins discordant for sexual orientation were perceived more similar in their gender nonconformity than unrelated heterosexual and non-heterosexual people. Yet, these perceptions were based on photographs, which do not contain all aspects of gender nonconformity, such as movement and sound. This could have led to an underestimation of observable difference within twin pairs. We examined evaluations of video recordings from adult identical twins with discordant sexual orientations (eight male pairs, 11 female pairs). These twins were a small subset of those who participated in Watts et al. (2018b). Non-heterosexual twins were rated as significantly more gender nonconforming than their heterosexual co-twins, but only when males and females were combined. Their difference was smaller than the analogous difference between identical twins who were concordant heterosexual (three male pairs, three female pairs) and, unrelated to them, identical twins who were concordant non-heterosexual (six male pairs, two female pairs). These patterns were partially confirmed with twins' self-reported gender nonconformity. Shared influences possibly made twins from discordant pairs somewhat similar in their gender nonconformity, even if non-shared factors differentiated their sexual orientations.

Familiality of Gender Nonconformity Among Homosexual Men.

We examined whether recalled childhood gender nonconformity and self-reported adult gender nonconformity is familial, using data from 1154 families selected for having at least two homosexual brothers. Specifically, we examined the extent to which homosexual men's variation in gender nonconformity runs in families by examining pairs of genetic brothers who were both homosexual (N = 672-697 full sibling concordant pairs). We also examined similarity between homosexual and heterosexual brothers (N = 79-82 full sibling discordant pairs). Consistent with past studies, concordant pairs yielded modest positive correlations consistent with moderate genetic and/or familial environmental effects on gender nonconformity. Unlike results of smaller past studies, discordant pairs also yielded modest positive, though nonsignificant, correlations. Our results support the feasibility of supplementing genetic studies of male sexual orientation with analyses of gender nonconformity variation.

Bisexual men with bisexual and monosexual genital arousal patterns.

Some research suggests that bisexual-identified men show bisexual genital arousal, whereas other research indicates monosexual arousal: they are aroused to one sex only. These seemingly contradictory findings may be due to the type of men identifying as bisexual and the performed analyses. We examined whether both bisexual and monosexual arousal patterns could co-occur within the same sample. 114 men of different sexual orientations viewed erotic videos of males or females while their penile circumference was measured. On average, bisexual-identified men were more aroused to males than females, and especially if they identified as "bisexual leaning gay." However, also on average, bisexual men showed bisexual arousal, and especially if they were "bisexual leaning straight". Furthermore, there was more variability in the arousal patterns of bisexual-identified men, compared with other men. Based on their physiological sexual arousal, bisexual men appear to be a more diverse group than men who identified as heterosexual or homosexual.

Correction to: Finger Length Ratios of Identical Twins with Discordant Sexual Orientations.

Readers should note that the confidence intervals for the effect of sexual orientation on 2D:4D in the left hand of female twins are incorrectly reported in Table 1 of this article. In particular, the upper limit of the confidence intervals is missing a minus sign.

Sexual Arousal Patterns of Identical Twins with Discordant Sexual Orientations.

Genetically identical twins can differ in their self-reported sexual orientations. However, whether the twins' subjective reports reflect valid differences in their sexual orientations is unknown. Measures of sexual orientation, which are free of the limitations of self-report, include genital arousal and pupil dilation while viewing sexual stimuli depicting men or women. We examined these responses in 6 male twin pairs and 9 female twin pairs who reported discordant sexual orientations. Across measures, heterosexual male twins responded more strongly to women than to men. Their homosexual co-twins showed an opposite pattern. Heterosexual female twins responded equally to both sexes, whereas their homosexual co-twins responded somewhat more to women than men. These differences within pairs were similar to differences between unrelated heterosexual and homosexual males and females. Our study provides physiological evidence confirming twins' discordant sexual orientations, thereby supporting the importance of the non-shared environment for the development of sexual orientation and sexual arousal.

Finger Length Ratios of Identical Twins with Discordant Sexual Orientations.

A proposed marker of prenatal androgen exposure is the ratio of the index finger to ring finger (2D:4D). Within each sex, this ratio may be lower for those who were exposed to higher levels of androgens and become attracted to women, as compared to those who were exposed to lower levels of androgens and become attracted to men. We examined these patterns in identical twins with discordant sexual orientations. Because these twins are genetically identical, differences in prenatal androgen exposure, as reflected in their different finger length ratios, might contribute to their discordance. For 18 female twin pairs, non-straight (bisexual or lesbian) twins had significantly lower, or more masculinized, 2D:4D ratios than their straight co-twins, but only in the left hand. For 14 male pairs, non-straight twins had, contrary to our prediction, more masculinized finger length ratios than straight co-twins, but this difference was not significant. A reanalysis of present and previous data (Hall & Love, 2003; Hiraishi, Sasaki, Shikishima, & Ando, 2012) suggested that these patterns were robust. Furthermore, males had more masculinized 2D:4D ratios than females. This sex difference did not vary by sexual orientation.

Gender nonconformity of identical twins with discordant sexual orientations: Evidence from childhood photographs.

Childhood gender nonconformity (femininity in males, masculinity in females) predicts a nonstraight (gay, lesbian, or bisexual) sexual orientation in adulthood. In previous work, nonstraight twins reported more childhood gender nonconformity than their genetically identical, but straight, cotwins. However, self-reports could be biased. We therefore assessed gender nonconformity via ratings of photographs from childhood and adulthood. These ratings came from independent observers naïve to study hypotheses. Identical twins with discordant sexual orientations (24 male pairs, 32 female pairs) visibly differed in their gender nonconformity from mid-childhood, with higher levels of gender nonconformity observed in the nonstraight twins. This difference was smaller than the analogous difference between identical twins who were concordant straight (4 male pairs, 11 female pairs) and identical twins unrelated to them who were concordant nonstraight (19 male pairs, 8 female pairs). Further, twins in discordant pairs correlated in their observer-rated gender nonconformity. Nongenetic factors likely differentiated the discordant twins' gender-related characteristics in childhood, but shared influences made them similar in some respects. We further tested how recall of past rejection from others related to gender nonconformity. Rejection generally increased with gender nonconformity, but this effect varied by the twins' sexual orientation. (PsycINFO Database Record

Genome-Wide Association Study of Male Sexual Orientation.

Family and twin studies suggest that genes play a role in male sexual orientation. We conducted a genome-wide association study (GWAS) of male sexual orientation on a primarily European ancestry sample of 1,077 homosexual men and 1,231 heterosexual men using Affymetrix single nucleotide polymorphism (SNP) arrays. We identified several SNPs with p < 10-5, including regions of multiple supporting SNPs on chromosomes 13 (minimum p = 7.5 × 10-7) and 14 (p = 4.7 × 10-7). The genes nearest to these peaks have functions plausibly relevant to the development of sexual orientation. On chromosome 13, SLITRK6 is a neurodevelopmental gene mostly expressed in the diencephalon, which contains a region previously reported as differing in size in men by sexual orientation. On chromosome 14, TSHR genetic variants in intron 1 could conceivably help explain past findings relating familial atypical thyroid function and male homosexuality. Furthermore, skewed X chromosome inactivation has been found in the thyroid condition, Graves' disease, as well as in mothers of homosexual men. On pericentromeric chromosome 8 within our previously reported linkage peak, we found support (p = 4.1 × 10-3) for a SNP association previously reported (rs77013977, p = 7.1 × 10-8), with the combined analysis yielding p = 6.7 × 10-9, i.e., a genome-wide significant association.

Sexual orientation health inequality: Evidence from Understanding Society, the UK Longitudinal Household Study.

Few studies from the United Kingdom have fully investigated inequalities between members of different sexual minority groups and heterosexuals over range of health outcomes. Using data from over 40,000 individuals, this study explores the health inequalities of sexual minority UK adults. We include respondents who identify as other and those who prefer not to say (PNS). Data come from wave three (2011-2012) of the nationally-representative Understanding Society, the UK Household Longitudinal Study. Sexual orientation was asked in the self-completion portion of the study. Markers of health include physical and mental functioning, minor psychological distress, self-rated health, substance use and disability. Multiple linear and logistic regression analyses tested for differences in markers of health between sexual orientation groups. Overall, heterosexual respondents had the best health while bisexual respondents had the worst. Gay and lesbian respondents reported poorer health than heterosexuals, specifically with regards to mental functioning, distress and illness status. The other and PNS respondents were most similar to each other and generally experienced fewer health inequalities than gay and lesbian respondents; they were less likely to use tobacco or alcohol. In sum, sexual minorities experience health inequality. The inclusion of other and PNS respondents has not been done in other studies and shows that while they may be healthier than gay/lesbian and bisexual respondents they still experiences poorer health than heterosexuals. Health promotion interventions are needed for these other and PNS individuals, who might not participate in interventions targeted toward known sexual minority groups.

Pupil Dilation to Explicit and Non-Explicit Sexual Stimuli.

Pupil dilation to explicit sexual stimuli (footage of naked and aroused men or women) can elicit sex and sexual orientation differences in sexual response. If similar patterns were replicated with non-explicit sexual stimuli (footage of dressed men and women), then pupil dilation could be indicative of automatic sexual response in fully noninvasive designs. We examined this in 325 men and women with varied sexual orientations to determine whether dilation patterns to non-explicit sexual stimuli resembled those to explicit sexual stimuli depicting the same sex or other sex. Sexual orientation differences in pupil dilation to non-explicit sexual stimuli mirrored those to explicit sexual stimuli. However, the relationship of dilation to non-explicit sexual stimuli with dilation to corresponding explicit sexual stimuli was modest, and effect magnitudes were smaller with non-explicit sexual stimuli than explicit sexual stimuli. The prediction that sexual orientation differences in pupil dilation are larger in men than in women was confirmed with explicit sexual stimuli but not with non-explicit sexual stimuli.

Gay, Mostly Gay, or Bisexual Leaning Gay? An Exploratory Study Distinguishing Gay Sexual Orientations Among Young Men.

This exploratory study assessed physiological, behavioral, and self-report measures of sexual and romantic indicators of sexual orientation identities among young men (mean age = 21.9 years) with predominant same-sex sexual and romantic interests: those who described themselves as bisexual leaning gay (n = 11), mostly gay (n = 17), and gay (n = 47). Although they were not significantly distinguishable based on physiological (pupil dilation) responses to nude stimuli, on behavioral and self-report measures a descending linear trend toward the less preferred sex (female) was significant regarding sexual attraction, fantasy, genital contact, infatuation, romantic relationship, sex appeal, and gazing time to the porn stimuli. Results supported a continuum of sexuality with distinct subgroups only for the self-report measure of sexual attraction. The other behavioral and self-report measures followed the same trend but did not significantly differ between the bisexual leaning gay and mostly gay groups, likely the result of small sample size. Results suggest that romantic indicators are as good as sexual measures in assessing sexual orientation and that a succession of logically following groups from bisexual leaning gay, mostly gay, to gay. Whether these three groups are discrete or overlapping needs further research.