Development and familiality of sexual orientation in females

Carving the Biodevelopment of Same-Sex Sexual Orientation at Its Joints

Sexual orientation is a core aspect of human experience and understanding its development is fundamental to psychology as a scientific discipline. Biological perspectives have played an important role in uncovering the processes that contribute to sexual orientation development. Research in this field has relied on a variety of populations, including community, clinical, and cross-cultural samples, and has commonly focused on female gynephilia (i.e., female sexual attraction to adult females) and male androphilia (i.e., male sexual attraction to adult males). Genetic, hormonal, and immunological processes all appear to influence sexual orientation. Consistent with biological perspectives, there are sexual orientation differences in brain development and evidence indicates that similar biological influences apply across cultures. An outstanding question in the field is whether the hypothesized biological influences are all part of the same process or represent different developmental pathways leading to same-sex sexual orientation. Some studies indicate that same-sex sexually oriented people can be divided into subgroups who likely experienced different biological influences. Consideration of gender expression in addition to sexual orientation might help delineate such subgroups. Thus, future research on the possible existence of such subgroups could prove to be valuable for uncovering the biological development of sexual orientation. Recommendations for such future research are discussed.

LGBTQ+ Perspectives on Conducting Genomic Research on Sexual Orientation and Gender Identity

We conducted in-depth, semi-structured interviews with LGBTQ+-identified individuals (n = 31) to explore the range of LGBTQ+ perspectives on genomic research using either sexual orientation or gender identity (SOGI) data. Most interviewees presumed that research would confirm genetic contributions to sexual orientation and gender identity. Primary hopes for such confirmation included validating LGBTQ+ identities, improved access to and quality of healthcare and other resources, and increased acceptance in familial, socio-cultural, and political environments. Areas of concern included threats of pathologizing and medicalizing LGBTQ+ identities and experiences, undermining reproductive rights, gatekeeping of health or social systems, and malicious testing or misuse of genetic results, particularly for LGBTQ+ youth. Overall, interviewees were divided on the acceptability of genomic research investigating genetic contributions to sexual orientation and gender identity. Participants emphasized researchers' ethical obligations to LGBTQ+ individuals and endorsed engagement with LGBTQ+ communities throughout all aspects of genomic research using SOGI data.

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.

Direct Reproduction and Sexual Orientation and Gender Diversity in Thailand

Human same-sex sexual attraction is considered to be an evolutionary paradox. This paradox rests on same-sex attracted individuals having lowered direct reproduction, indicating reduced direct fitness of genes that influence same-sex attraction. Yet, relatively few empirical studies have examined the relation between same-sex sexual attraction and direct reproduction. The present study examined direct reproduction (i.e., number of children produced) in a diverse Thai sample (N = 1623) of heterosexual men and women, gay and bisexual men, and lesbian and bisexual women, as well as unique Thai gender categories: sao praphet song (i.e., feminine androphilic third-gender males), toms (i.e., masculine gynephilic third-gender females), and dees (i.e., feminine females who are sexually attracted to toms). In males, heterosexual men were more likely to have produced children than other groups, especially as they aged, and none of the gay men or sao praphet song reported having children. In females, there was some degree of reproduction in each of the groups considered. On average, heterosexual and bisexual women had similar numbers of children, whereas heterosexual women had significantly more children than lesbian women, toms, and dees. Number of children was significantly positively associated with age among heterosexual women, bisexual women, toms, and dees. With age, the discrepancies in average number of children produced between heterosexual women and each of lesbian women and toms became significantly more pronounced. Discussion focuses on how these findings, in conjunction with those of prior studies, inform our understanding of evolutionary selection pressures related to human same-sex sexuality.

Age of Onset and Its Correlates in Men with Sexual Interest in Children

INTRODUCTION

Current discussions in the field of sex research concern the age at which sexual interest in children occurred or awareness emerged.

AIM

To investigate the age of onset (AOO) and its correlates in men with sexual interest in children.

METHODS

Using 2 samples (study 1, patients from an outpatient treatment center, n = 26; study 2, an online survey using 3 recruitment paths, n = 94), we assessed self-reported AOO of sexual interest in children, its flexibility, its exclusiveness, and individuals' motivation to change it. We further examined the interrelation between these variables.

MAIN OUTCOME MEASURE

AOO as the self-reported age at which participants retrospectively felt sexually attracted to children for the first time.

RESULTS

We found broad ranges in AOO (study 1: mean 20.0 ± 10.7; study 2: mean 17.0 ± 8.7), flexibility, and exclusiveness (in studies 1 and 2, 7.7% and 22.3%, respectively, reported that their sexual interest is exclusively in children). The earlier participants felt sexually attracted to children for the first time, the more they were attracted exclusively in children and the less they perceived it to be flexible. Participants who reported rather exclusive sexual interest in children were less likely to perceive it as flexible. The more participants reported on flexibility, the more they were motivated to change it. The earlier participants of study 2 felt sexually attracted to children for the first time, the less they were motivated to change.

CLINICAL IMPLICATIONS

The variety of our results indicates the contradiction of overall rules for individuals with sexual interest in children.

STRENGTH & LIMITATIONS

We included individuals with sexual interest in children from different contexts (eg, forensic vs non-forensic). Our results are in line with previous findings. However, both studies included rather small samples, limiting generalizability. There is not yet consent about how to operationalize AOO.

CONCLUSION

We recommend a differentiated perspective on individuals with sexual interest in children and on different forms of pedophilia in the diagnostic construct. Tozdan S, Briken P. Age of Onset and Its Correlates in Men with Sexual Interest in Children.Sex Med 2019;7:61-71.

The Diversity and Prevalence of Sexual Orientation Self-Labels in a New Zealand National Sample

In this study, we asked participants to "describe their sexual orientation" in an open-ended measure of self-generated sexual orientation. The question was included as part of the New Zealand Attitudes and Values Study (N = 18,261) 2013/2014 wave, a national probability survey conducted shortly after the first legal same-sex marriages in New Zealand. We present a two-level classification scheme to address questions about the prevalence of, and demographic differences between, sexual orientations. At the most detailed level of the coding scheme, 49 unique categories were generated by participant responses. Of those who responded with the following, significantly more were women: bisexual (2.1 % of women, compared to 1.5 % of men), bicurious (0.7 % of women, 0.4 % of men), and asexual (0.4 % of women and less than 0.1 % of men). However, significantly fewer women than men reported being lesbian or gay (1.8 % of women, compared to 3.5 % of men). Those openly identifying as bicurious, bisexual, or lesbian/gay were significantly younger than those with a heterosexual orientation. This study shows diversity in the terms used in self-generated sexual orientations, and provides up-to-date gender, age, and prevalence estimates for the New Zealand population. Finally, results reveal that a substantial minority of participants may not have understood the question about sexual orientation.

A Dynamical Systems Approach to the Development and Expression of Female Same-Sex Sexuality

Researchers have documented substantial variability in the development and expression of same-sex sexuality, especially among women, posing challenges to traditional linear developmental models. In this article, I argue for a new approach to conceptualizing the development and expression of female same-sex sexuality over the life course, based in dynamical systems theory. Dynamical systems models seek to explain how complex patterns emerge, stabilize, change, and restabilize over time. Although originally developed by mathematicians and physicists to model complex physical phenomena in the natural world, they have increasingly been applied to social-behavioral phenomena, ranging from motor development to cognition to language. I demonstrate the utility of this approach for modeling change over time in female same-sex sexuality, reviewing extant published research and also introducing data collected from an ongoing, 10-year longitudinal study of young nonheterosexual women. I provide evidence that female same-sex sexuality demonstrates the emblematic features of a dynamical system: nonlinear change over time, spontaneous emergence of novel forms, and periodic reorganizations and phase transitions within the overall system. I highlight the specific contribution of a dynamical systems perspective for understanding such phenomena and suggest directions for future study.

Genome-wide scan demonstrates significant linkage for male sexual orientation

BACKGROUND

Findings from family and twin studies support a genetic contribution to the development of sexual orientation in men. However, previous studies have yielded conflicting evidence for linkage to chromosome Xq28.

METHOD

We conducted a genome-wide linkage scan on 409 independent pairs of homosexual brothers (908 analyzed individuals in 384 families), by far the largest study of its kind to date.

RESULTS

We identified two regions of linkage: the pericentromeric region on chromosome 8 (maximum two-point LOD = 4.08, maximum multipoint LOD = 2.59), which overlaps with the second strongest region from a previous separate linkage scan of 155 brother pairs; and Xq28 (maximum two-point LOD = 2.99, maximum multipoint LOD = 2.76), which was also implicated in prior research.

CONCLUSIONS

Results, especially in the context of past studies, support the existence of genes on pericentromeric chromosome 8 and chromosome Xq28 influencing development of male sexual orientation.

Human homosexuality: a paradigmatic arena for sexually antagonistic selection?

Sexual conflict likely plays a crucial role in the origin and maintenance of homosexuality in our species. Although environmental factors are known to affect human homosexual (HS) preference, sibling concordances and population patterns related to HS indicate that genetic components are also influencing this trait in humans. We argue that multilocus, partially X-linked genetic factors undergoing sexually antagonistic selection that promote maternal female fecundity at the cost of occasional male offspring homosexuality are the best candidates capable of explaining the frequency, familial clustering, and pedigree asymmetries observed in HS male proband families. This establishes male HS as a paradigmatic example of sexual conflict in human biology. HS in females, on the other hand, is currently a more elusive phenomenon from both the empirical and theoretical standpoints because of its fluidity and marked environmental influence. Genetic and epigenetic mechanisms, the latter involving sexually antagonistic components, have been hypothesized for the propagation and maintenance of female HS in the population. However, further data are needed to truly clarify the evolutionary dynamics of this trait.

Same-sex sexual attraction does not spread in adolescent social networks

Peers have a powerful effect on adolescents' beliefs, attitudes, and behaviors. Here, we examine the role of social networks in the spread of attitudes towards sexuality using data from the National Longitudinal Study of Adolescent Health (Add Health). Although we found evidence that both sexual activity (OR = 1.79) and desire to have a romantic relationship (OR = 2.69) may spread from person to person, attraction to same sex partners did not spread (OR = 0.96). Analyses of comparable power to those that suggest positive and significant peer-to-peer influence in sexual behavior fail to demonstrate a significant relationship on sexual attraction between friends or siblings. These results suggest that peer influence has little or no effect on the tendency toward heterosexual or homosexual attraction in teens, and that sexual orientation is not transmitted via social networks.

The biological basis of human sexual orientation: is there a role for epigenetics?

Sexual orientation is one of the largest sex differences in humans. The vast majority of the population is heterosexual, that is, they are attracted to members of the opposite sex. However, a small but significant proportion of people are bisexual or homosexual and experience attraction to members of the same sex. The origins of the phenomenon have long been the subject of scientific study. In this chapter, we will review the evidence that sexual orientation has biological underpinnings and consider the involvement of epigenetic mechanisms. We will first discuss studies that show that sexual orientation has a genetic component. These studies show that sexual orientation is more concordant in monozygotic twins than in dizygotic ones and that male sexual orientation is linked to several regions of the genome. We will then highlight findings that suggest a link between sexual orientation and epigenetic mechanisms. In particular, we will consider the case of women with congenital adrenal hyperplasia (CAH). These women were exposed to high levels of testosterone in utero and have much higher rates of nonheterosexual orientation compared to non-CAH women. Studies in animal models strongly suggest that the long-term effects of hormonal exposure (such as those experienced by CAH women) are mediated by epigenetic mechanisms. We conclude by describing a hypothetical framework that unifies genetic and epigenetic explanations of sexual orientation and the continued challenges facing sexual orientation research.

Implicit sexual associations in heterosexual and homosexual women and men

Patterns of genital arousal to sexual stimuli are somewhat different between men and women. Heterosexual males and homosexual males show clear category specific arousal that is consistent with their self-reported sexual preference. However, heterosexual women do not show this category specificity. In the present study, we attempted to measure a person's automatic appraisals of stimuli with respect to the concept of sex via the use of implicit measures (the Implicit Association Test and the priming task). In three experiments, we showed that heterosexual females did not show a sex-related category specific response in favor of male versus female stimuli. However, this lack of specificity was not due to a lack of sex-related appraisals, but by equal appraisals of both male and female stimuli. On the other hand, heterosexual men, homosexual men, and homosexual women all showed automatic sex-related appraisals of stimuli that were category specific and in line with their self-reported sexual preference. The study shows difference in the pattern of sexual interest between genders at the earliest stages of the evaluation of a stimulus.

Stability and change in sexual orientation identity over a 10-year period in adulthood

We examined reports of sexual orientation identity stability and change over a 10-year period drawing on data from the National Survey of Midlife Development in the United States (MIDUS I and II) and tested for three patterns: (1) heterosexual stability, (2) female sexual fluidity, and (3) bisexual fluidity. Fifty-four percent of the 2,560 participants were female and the average age was approximately 47 years. At Wave 1, 2,494 (97.42%) reported a heterosexual identity, 32 (1.25%) a homosexual identity, and 34 (1.33%) a bisexual identity and somewhat more than 2% reported a different sexual orientation identity at Wave 2. Although some support for each hypothesis was found, initial sexual orientation identity interacted with gender to predict a more complex pattern. For the sample as a whole, heterosexuality was the most stable identity. For women, bisexuality and homosexuality were equally unstable and significantly less stable than heterosexuality, suggesting that sexual orientation identity fluidity is a pattern that applies more to sexual minority women than heterosexual women. For men, heterosexuality and homosexuality were both relatively stable compared to bisexuality, which stood out as a particularly unstable identity. This pattern of results was consistent with previous findings and helps to address methodological limitations of earlier research by showing the characteristics of a population-based sample of heterosexual, homosexual, and bisexual identified men and women over time.

The desire disorder in research on sexual orientation in women: contributions of dynamical systems theory

Over the past decade, numerous studies have documented fundamental differences between the phenomenology of male and female sexual orientation, largely centering on women's capacity for fluidity in their sexual attractions. The past decade has also witnessed fundamental changes in clinical perspectives on "normal" versus "dysfunctional" patterns of female sexual desire, largely centering on women's greater capacity for responsive and context-dependent sexual desires. In both cases, traditional male-based models of sexuality have been found inadequate to describe women's experiences. I argue that this inadequacy stems from a failure of traditional models to appropriately account for the phenomenon of variability over time, which may constitute a fundamental feature of female sexual phenomenology. I maintain that dynamical systems theory provides a useful and generative approach for reconceptualizing female sexual orientation, because dynamical systems models focus specifically on describing and explaining complex patterns of change over time. I review the key properties of dynamical systems models and provide an illustrative model of how this approach might yield new perspectives on female sexual orientation.

Differential processing of social chemosignals obtained from potential partners in regards to gender and sexual orientation

On an individual level, human body odors carry information about whether a person is an eligible mate. The current studies investigate if body odors also transmit information about individuals being potential partners in more general terms, namely in regards to gender and sexual orientation. In study 1, 14 gay and 14 heterosexual men were presented with body odors obtained from potential partners (gay male and heterosexual female body odors, respectively) and heterosexual male body odor as a control. In study 2, 14 lesbian and 14 heterosexual women were presented with lesbian female and heterosexual male body odors representing body odors of potential partners, and heterosexual female body odor as a control. Central nervous processing was analyzed using chemosensory event-related potentials and current source density analysis (64-channel EEG recording). Gay and heterosexual men responded with shorter P2 latencies to the body odors of their preferred sexual partners, and lesbian women responded with shorter P2 latencies to body odors of their preferred gender. In response to heterosexual male body odors, lesbian women displayed the most pronounced P3 amplitude, and distinct neuronal activation in medial frontal and parietal neocortical areas. A similar pattern of neuronal activation was observed in gay men when presented with heterosexual male body odor. Both the early processing advantage (P2) for desirable partners' body odors as well as the enhanced evaluative processing (P3, CSD) of undesirable partners' body odors suggest that human body odors indeed carry information about individuals being potential partners in terms of gender and sexual orientation.

Genetic and environmental influences on female sexual orientation, childhood gender typicality and adult gender identity

Background

Human sexual orientation is influenced by genetic and non-shared environmental factors as are two important psychological correlates – childhood gender typicality (CGT) and adult gender identity (AGI). However, researchers have been unable to resolve the genetic and non-genetic components that contribute to the covariation between these traits, particularly in women.

Methodology/Principal Findings

Here we performed a multivariate genetic analysis in a large sample of British female twins (N = 4,426) who completed a questionnaire assessing sexual attraction, CGT and AGI. Univariate genetic models indicated modest genetic influences on sexual attraction (25%), AGI (11%) and CGT (31%). For the multivariate analyses, a common pathway model best fitted the data.

Conclusions/Significance

This indicated that a single latent variable influenced by a genetic component and common non-shared environmental component explained the association between the three traits but there was substantial measurement error. These findings highlight common developmental factors affecting differences in sexual orientation.

The genetics of sex differences in brain and behavior

Biological differences between men and women contribute to many sex-specific illnesses and disorders. Historically, it was argued that such differences were largely, if not exclusively, due to gonadal hormone secretions. However, emerging research has shown that some differences are mediated by mechanisms other than the action of these hormone secretions and in particular by products of genes located on the X and Y chromosomes, which we refer to as direct genetic effects. This paper reviews the evidence for direct genetic effects in behavioral and brain sex differences. We highlight the 'four core genotypes' model and sex differences in the midbrain dopaminergic system, specifically focusing on the role of Sry. We also discuss novel research being done on unique populations including people attracted to the same sex and people with a cross-gender identity. As science continues to advance our understanding of biological sex differences, a new field is emerging that is aimed at better addressing the needs of both sexes: gender-based biology and medicine. Ultimately, the study of the biological basis for sex differences will improve healthcare for both men and women.

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.

Sexually antagonistic "zygotic drive" of the sex chromosomes

Genomic conflict is perplexing because it causes the fitness of a species to decline rather than improve. Many diverse forms of genomic conflict have been identified, but this extant tally may be incomplete. Here, we show that the unusual characteristics of the sex chromosomes can, in principle, lead to a previously unappreciated form of sexual genomic conflict. The phenomenon occurs because there is selection in the heterogametic sex for sex-linked mutations that harm the sex of offspring that does not carry them, whenever there is competition among siblings. This harmful phenotype can be expressed as an antagonistic green-beard effect that is mediated by epigenetic parental effects, parental investment, and/or interactions among siblings. We call this form of genomic conflict sexually antagonistic “zygotic drive”, because it is functionally equivalent to meiotic drive, except that it operates during the zygotic and postzygotic stages of the life cycle rather than the meiotic and gametic stages. A combination of mathematical modeling and a survey of empirical studies is used to show that sexually antagonistic zygotic drive is feasible, likely to be widespread in nature, and that it can promote a genetic “arms race” between the homo- and heteromorphic sex chromosomes. This new category of genomic conflict has the potential to strongly influence other fundamental evolutionary processes, such as speciation and the degeneration of the Y and W sex chromosomes. It also fosters a new genetic hypothesis for the evolution of enigmatic fitness-reducing traits like the high frequency of spontaneous abortion, sterility, and homosexuality observed in humans.

Our study describes a new form of sexual genomic conflict that operates through the process of antagonistic green-beard effects. Although past theoretical and empirical work indicated that green-beard effects rarely operate in nature, our new theory shows why this conclusion may have to be reevaluated. We integrate modeling analysis with extant empirical work to show that the unique properties of sex chromosomes can lead to a previously unappreciated form of sexual conflict (sexually antagonistic zygotic drive) that may be widespread in nature. It operates through harmful epigenetic parental effects, asymmetrical allocation of parental investment to sons and daughters, and asymmetrical interactions between brothers and sisters. Sexually antagonistic zygotic drive is functionally analogous to meiotic drive except that it operates due to competition among opposite-sex siblings rather than between competing gametes.

Re-evaluation of the "no differences" hypothesis concerning gay and lesbian parenting as assessed in eight early (1979-1986) and four later (1997-1998) dissertations

Academic and policy effects of eight early dissertations on gay and lesbian parenting are discussed with a focus on their having been cited at least 234 times in over 50 literature reviews, beginning with Gottman in 1989 and 1990. Most literature reviews, referencing these eight early dissertations and agreeing with Gottman's early conclusions, have reiterated the theme that parenting by gay men or lesbians has outcomes no different than parenting by heterosexual parents. Here it is proposed that certain potential adverse findings may have been obscured by suppressor effects which could have been evaluated had multivariate analyses been implemented. Further, several adverse findings were detected by reanalyzing data where sufficient information was yet available. Some of the dissertations' results (absent controls for social desirability and other differences between homosexual and heterosexual parents) supported the 2001 "no differences" hypothesis discussed by Stacey and Biblarz. Yet, differences were also observed, including some evidence in more recent dissertations, suggesting that parental sexual orientation might be associated with children's later sexual orientation and adult attachment style, among other outcomes. Odds ratios associated with some of the apparent effects were substantial in magnitude as well as statistically significant. Also, more recent research on gay and lesbian parenting continues to be flawed by many of the same limitations as previous research in this area of study, including overlooked suppressor effects.

Sex Differences in Brain and Behavior: Hormones Versus Genes

Sex determination is the commitment of an organism toward male or female development. Traditionally, in mammals, sex determination is considered equivalent to gonadal determination. Since the presence or the absence of the testes ultimately determines the phenotype of the external genitalia, sex determination is typically seen as equivalent to testis determination. But what exactly does sex determine? The endpoint of sex determination is almost invariably seen as the reproductive structures, which represent the most obvious phenotypic difference between the sexes. One could argue that the most striking differences between males and females are not the anatomy of the genitals, but the size of the gametes-considerably larger in females than males. In fact, there could be many different endpoints to sex determination, leading to differences between the sexes: brain sexual differences, behavioral differences, and susceptibility to disease. The central dogma of sexual differentiation, stemming initially from the gonad-transfer experiments of Alfred Jost, is that sexual dimorphisms of all somatic tissues are dependent on the testicular secretion of the developing fetus. In this chapter, we will take the example of sex differences in brain and behavior as an endpoint of sex determination. We will argue that genetic factors play a role in sexually dimorphic traits such as the number of dopaminergic cells in the mesencephalon, aggression, and sexual orientation, independently from gonadal hormones.

Pubertal onset and sexual orientation in an adolescent national probability sample

Using 6-year longitudinal data from the National Longitudinal Survey of Adolescent Health (Add Health) and multiple measures of puberty as it occurs and of sexual orientation (romantic attraction, sexual identity), the present study attempted to replicate previous research which reported that homosexuals and heterosexuals differed in their age of pubertal onset. The study hypotheses were not confirmed for either males or females: on most pubertal measures, same-sex oriented groupings did not differ from heterosexuals. The only significant findings regarding homosexual males indicated that they were more likely to report having a later rather than an earlier onset of puberty, and the significant findings regarding homosexual females were contradictory--they tended to have an earlier onset of puberty. These findings are attributed to methodological improvements in the present study that reduced retrospective bias, used multiple indicators of sexual orientation and puberty timing, and assessed less eroticized measures of puberty.

Immutability, science, and legislative debate over gay, lesbian and bisexual rights

Many gay rights advocates argued in the 1990s that scientific research claiming that sexual orientation is immutable should contribute to gaining civil rights for gays, lesbians and bisexuals. This paper analyzes ten legislative debates that took place at the local, state and federal levels over whether to adopt antidiscrimination laws, before and after the research was published. We hypothesize that if the research has had the impacts hoped for by gay rights supporters, then debates over gay rights should reflect certain changes consistent with such impacts. Although discussion of the origins of sexual orientation among legislators rose in the aftermath of the studies, we fail to find that the science had a major impact on the debate strategies pursued by either pro- or antigay rights legislators. Whether sexual orientation is immutable or a choice has not been a central claim of the two sides in the debate. Gay rights opponents even appear somewhat more willing to assert that sexual orientation is a choice after the studies than before. Furthermore, when the proponents of gay rights assert the immutability argument, they are as likely as not to invoke the cultural authority of science. We explain these outcomes by showing why the immutability issue is not of central relevance to most legislators or necessary for either side's key arguments. We also show that the scientific evidence merely supplemented a large amount of anecdotal information that legislators already possessed that spoke to the origins of sexual orientation.

Same-sex attraction in a birth cohort: prevalence and persistence in early adulthood

There is a continuing debate about the importance of social versus biological factors in the expression of same-sex attraction. Investigation of prevalence, continuities, and changes over time among young adults growing up in a country with a relatively accepting climate to homosexuality is likely to illuminate this debate. Analyses were therefore undertaken of self-reported same-sex attraction at age 21 and 26, in a cohort of about 1000 people born in 1972/3 in one New Zealand city. Participants were also asked about same-sex behaviour and attitudes to same-sex relationships. By age 26, 10.7% of men and 24.5% of women reported being attracted to their own sex at some time. This dropped to 5.6% of men and 16.4% of women who reported some current same-sex attraction. Current attraction predominantly to their own sex or equally to both sexes (major attraction) was reported by 1.6% of men and 2.1% of women. Occasional same-sex attraction, but not major attraction, was more common among the most educated. Between age 21 and 26, slightly more men moved away from an exclusive heterosexual attraction (1.9% of all men) than moved towards it (1.0%), while for women, many more moved away (9.5%) than towards (1.3%) exclusive heterosexual attraction. These findings show that much same-sex attraction is not exclusive and is unstable in early adulthood, especially among women. The proportion of women reporting some same-sex attraction in New Zealand is high compared both to men, and to women in the UK and US. These observations, along with the variation with education, are consistent with a large role for the social environment in the acknowledgement of same-sex attraction. The smaller group with major same-sex attraction, which changed less over time, and did not differ by education, is consistent with a basic biological dimension to sexual attraction. Overall these findings argue against any single explanation for homosexual attraction.

What does sexual orientation orient? A biobehavioral model distinguishing romantic love and sexual desire

Although it is typically presumed that heterosexual individuals only fall in love with other-gender partners and gay-lesbian individuals only fall in love with same-gender partners, this is not always so. The author develops a biobehavioral model of love and desire to explain why. The model specifies that (a) the evolved processes underlying sexual desire and affectional bonding are functionally independent; (b) the processes underlying affectional bonding are not intrinsically oriented toward other-gender or same-gender partners: (c) the biobehavioral links between love and desire are bidirectional, particularly among women. These claims are supported by social-psychological, historical, and cross-cultural research on human love and sexuality as well as by evidence regarding the evolved biobehavioral mechanisms underlying mammalian mating and social bonding.

Sexual identity, attractions, and behavior among young sexual-minority women over a 2-year period

Previous research suggests that the sexual identities, attractions, and behaviors of sexual-minority (i.e., nonheterosexual) women change over time, yet there have been few longitudinal studies addressing this question, and no longitudinal studies of sexual-minority youths. The results of 2-year follow-up interviews with 80 lesbian, bisexual, and "unlabeled" women who were first interviewed at 16-23 years of age are reported. Half of the participants changed sexual-minority identities more than once, and one third changed identities since the first interview. Changes in sexual attractions were generally small but were larger among bisexuals and unlabeled women. Most women pursued sexual behavior consistent with their attractions, but one fourth of lesbians had sexual contact with men between the two interviews. These findings suggest that there is more fluidity in women's sexual identities and behaviors than in their attractions. This fluidity may stem from the prevalence of nonexclusive attractions among sexual-minority women.

Spontaneous otoacoustic emissions in heterosexuals, homosexuals, and bisexuals

Click-evoked otoacoustic emissions (CEOAEs) were previously shown to be significantly less strong in homosexual and bisexual females than in heterosexual females. Here it is reported that the spontaneous otoacoustic emissions (SOAEs) of those same 60 homosexual and bisexual females were less numerous and weaker than those in 57 heterosexual females. That is, the SOAEs of the homosexual and bisexual females were intermediate to those of heterosexual females and heterosexual males. The SOAE and CEOAE data both suggest that the cochleas of homosexual and bisexual females have been partially masculinized, possibly as part of some prenatal processes that also masculinized whatever brain structures are responsible for sexual orientation. For males of all sexual orientation, the SOAEs were less numerous and weaker than for the females, and there were no significant differences among the 56 heterosexual, 51 homosexual, and 11 bisexual males. All subjects passed a hearing screening test. When all SOAEs above 3000 Hz were excluded (as a control against incipient, undetected hearing loss) the same results were obtained as with the full range of data (550-9000 Hz). The differential use of oral contraceptives by the heterosexual and nonheterosexual females also could not explain the differences in their OAEs.

A Crossover Interaction Between Sex, Sexual Orientation, and Handedness

The distribution of handedness scores was analysed in 1414 heterosexual, bisexual, and homosexual men and women. Hand preference was assessed by a questionnaire that distinguishes consistently right-handed from partially or completely left-handed individuals, and sexual orientation was measured by the Kinsey scales. As expected from population-based studies, heterosexual men were, on average, more left-handed than heterosexual women. By contrast, gay men were more right-handed than lesbians or heterosexual men, and lesbians were more left-handed than gay men or heterosexual women. This crossover interaction suggests that a common variable influences sex, sexual orientation, and hand preference.

Linkage between sexual orientation and chromosome Xq28 in males but not in females

We have extended our analysis of the role of the long arm of the X chromosome (Xq28) in sexual orientation by DNA linkage analyses of two newly ascertained series of families that contained either two gay brothers or two lesbian sisters as well as heterosexual siblings. Linkage between the Xq28 markers and sexual orientation was detected for the gay male families but not for the lesbian families or for families that failed to meet defined inclusion criteria for the study of sex-linked sexual orientation. Our results corroborate the previously reported linkage between Xq28 and male homosexuality in selected kinships and suggest that this region contains a locus that influences individual variations in sexual orientation in men but not in women.