Fraternal birth order and the maternal immune hypothesis of male homosexuality

The fraternal birth-order effect as a statistical artefact: convergent evidence from probability calculus, simulated data, and multiverse meta-analysis

The fraternal-birth order effect (FBOE) is a research claim which states that each older brother increases the odds of homosexual orientation in men via an immunoreactivity process known as the maternal immune hypothesis. Importantly, older sisters supposedly either do not affect these odds, or affect them to a lesser extent. Consequently, the fraternal birth-order effect predicts that the association between the number of older brothers and homosexual orientation in men is greater in magnitude than any association between the number of older sisters and homosexual orientation. This difference in magnitude represents the main theoretical estimand of the FBOE. In addition, no comparable effects should be observable among homosexual vs heterosexual women. Here, we triangulate the empirical foundations of the FBOE from three distinct, informative perspectives, complementing each other: first, drawing on basic probability calculus, we deduce mathematically that the body of statistical evidence used to make inferences about the main theoretical estimand of the FBOE rests on incorrect statistical reasoning. In particular, we show that throughout the literature researchers ascribe to the false assumptions that effects of family size should be adjusted for and that this could be achieved through the use of ratio variables. Second, using a data-simulation approach, we demonstrate that by using currently recommended statistical practices, researchers are bound to frequently draw incorrect conclusions. And third, we re-examine the empirical evidence of the fraternal birth-order effect in men and women by using a novel specification-curve and multiverse approach to meta-analysis (64 male and 17 female samples, N = 2,778,998). When analyzed correctly, the specific association between the number of older brothers and homosexual orientation is small, heterogenous in magnitude, and apparently not specific to men. In addition, existing research evidence seems to be exaggerated by small-study effects.

Alternative Sexual Orientation in Humans: What Is Known and What Needs to Be Known Further

Since the 20th century, multiple studies have linked the variations in human sexual orientation, from heterosexuality to bisexuality or homosexuality, to a wide range of biological factors. However, a clear mechanism that leads to the development of these variations has not been established yet. This review consolidates various comprehensive studies on the possible biological factors in the fields of genetics, epigenetics, uterine environment, hormones, neuroanatomy, and neurobiology that lead to these variations. One intriguing question that 'homosexuality phenotype' faces is its ability to avoid elimination by Darwinian selection. This review tries to explain why natural selection is not eliminating the genetic factors associated with homosexuality even at the cost of the evolutionary fitness of homosexual individuals. Studies supporting certain strong candidates for alternative sexual orientation (ASO) are highlighted, which can become new research avenues for investigators in this field. Further, a novel speculation is proposed that might be contributing to the development of variation in human sexuality.

Effect of birth order on stereoacuity in Chinese preschool children: a cross-sectional study

OBJECTIVE

This study aimed to investigate the relationship between birth order and stereoacuity among Chinese children aged 60-72 months.

DESIGN

Cross-sectional.

PARTICIPANTS

1342 children with complete data on the questionnaire, stereoacuity and refraction were included.

RESULTS

The mean stereoacuity was 53.2±1.7, 56.9±1.9 and 60.9±1.5 s of arc in the first-born group, second-born group and third-born group, respectively. Lower birth order was significantly correlated with better stereoacuity (p=0.036). Third-borns (OR=3.02, p=0.027) were at higher risk of having subnormal stereoacuity compared with first-borns in the multivariate analysis.

CONCLUSION

Later-borns had poorer stereoacuity than first-borns.

Sexual Orientation in Individuals With Congenital Adrenal Hyperplasia: A Systematic Review

Congenital adrenal hyperplasia (CAH) is a genetic condition of the steroidogenic enzymes in the adrenal cortex normally leading to variable degrees of cortisol and aldosterone deficiency as well as androgen excess. Exposure to androgens prenatally might lead to ambiguous genitalia. The fetal brain develops in traditional male direction through a direct action of androgens on the developing nerve cells, or in the traditional female direction in the absence of androgens. This may indicate that sexual development, including sexual orientation, are programmed into our brain structures prenatally. The objective of this study was to perform a systematic review of the literature, investigating sexual orientation in individuals with CAH. The study also aimed at identifying which measures are used to define sexual orientation across studies. The review is based on articles identified through a comprehensive search of the OVIDMedline, PsycINFO, CINAHL, and Web of Science databases published up to May 2019. All peer-reviewed articles investigating sexual orientation in people with CAH were included. Quantitative, qualitative, and mixed methods were considered, as well as self-, parent-, and third-party reports, and no age or language restrictions were enforced on publications. The present review included 30 studies investigating sexual orientation in patients with CAH assigned female at birth (46, XX) (n = 927) or assigned male at birth (46, XY and 46, XX) (n = 274). Results indicate that assigned females at birth (46, XX) with CAH had a greater likelihood to not have an exclusively heterosexual orientation than females from the general population, whereas no assigned males at birth (46, XY or 46, XX) with CAH identified themselves as non-heterosexual. There was a wide diversity in measures used and a preference for unvalidated and self-constructed interviews. Hence, the results need to be interpreted with caution. Methodological weaknesses might have led to non-heterosexual orientation being overestimated or underestimated. The methodological challenges identified by this review should be further investigated in future studies.

Interest, Personality, and Sexual Traits That Distinguish Heterosexual, Bisexual, and Homosexual Individuals: Are There Two Dimensions That Underlie Variations in Sexual Orientation?

A diverse U.S. sample comprising 1437 men and 1474 women was assessed on sexual orientation, masculinity-femininity of occupational preferences (MF-Occ), self-ascribed masculinity-femininity (Self-MF), Big Five personality traits, sex drive, and sociosexuality (positive attitudes toward uncommitted sex). Discriminant analyses explored which traits best distinguished self-identified heterosexual, bisexual, and homosexual individuals within each sex. These analyses correctly classified the sexual orientation of 55% of men and 60% of women, which was substantially better than a chance rate (33%) of assigning participants to one of three groups. For men, MF-Occ and Self-MF distinguished heterosexual, bisexual, and gay men, with heterosexual men most gender typical, gay men most gender atypical, and bisexual men intermediate. Independently, higher sex drive, sociosexuality, and neuroticism and lower conscientiousness distinguished bisexual men from other groups. For women, gender-related interests and Self-MF distinguished lesbians from other groups, with lesbians most gender atypical. Independently, higher sociosexuality, sex drive, and Self-MF distinguished non-heterosexual from heterosexual women. These findings suggest that variations in self-reported sexual orientation may be conceptualized in terms of two broad underlying individual difference dimensions, which differ somewhat for men and women: one linked to gender typicality versus gender atypicality and the other linked to sex drive, sociosexuality, and various personality traits.

Does Fraternal Birth Order Predict Male Homosexuality, Bisexuality, and Heterosexual Orientation with Same-Sex Attraction? Evidence from a Greek-Speaking Sample from Greece

Studies have established that having older brothers is associated with an increased incidence of male homosexuality. This so-called fraternal birth order effect has been found in different times and cultural settings. The current study attempted to examine whether this effect was present in the Greek cultural context and whether it could also predict bisexuality or heterosexuality with occasional same-sex attractions. On the basis of an online sample of 1617 Greek-speaking participants, it was found that, for men, a higher number of older brothers were associated with an increased probability to be homosexual, but it had no effect on the probability to be bisexual or heterosexual with same-sex attractions. In women, the number of older brothers had not any effect on sexual orientation.

Sex differences in neuroimmunity as an inherent risk factor

Identifying and understanding the sources of inherent risk to neurodevelopmental disorders is a fundamental goal of neuroscience. Being male or being exposed to inflammation early in life are two known risk factors, but they are only infrequently associated with each other. Cellular and molecular mechanisms mediating the masculinization of the brain in animal models reveal a consistent role for inflammatory signaling molecules and immune cells in the healthy male brain. Why this is so remains in the realm of speculation but may have its origins in the maternal immune system. Masculinization of the brain occurs during a restricted critical period that begins in utero and overlaps with the sensitive period during which maternal immune activation negatively impacts the developing brain. The convergence of maleness and early life inflammation as risk factors for neuropsychiatric disorders compels us to consider whether sexual differentiation of the brain in males creates an inherent and greater risk than that experienced by females.

The molecular mechanisms of sexual orientation and gender identity

Differences between males and females are widely represented in nature. There are gender differences in phenotypes, personality traits, behaviors and interests, cognitive performance, and proneness to specific diseases. The most marked difference in humans is represented by sexual orientation and core gender identity, the origins of which are still controversial and far from being understood. Debates continue on whether sexual behavior and gender identity are a result of biological (nature) or cultural (nurture) factors, with biology possibly playing a major role. The main goal of this review is to summarize the studies available to date on the biological factors involved in the development of both sexual orientation and gender identity. A systematic search of published evidence was performed using Medline (from January 1948 to June 2017). Review of the relevant literature was based on authors' expertise. Indeed, different studies have documented the possible role and interaction of neuroanatomic, hormonal and genetic factors. The sexual dimorphic brain is considered the anatomical substrate of psychosexual development, on which genes and gonadal hormones may have a shaping effect. In particular, growing evidence shows that prenatal and pubertal sex hormones permanently affect human behavior. In addition, heritability studies have demonstrated a role of genetic components. However, a convincing candidate gene has not been identified. Future studies (e.i. genome wide studies) are needed to better clarify the complex interaction between genes, anatomy and hormonal influences on psychosexual development.

Intragenomic Conflict and Immune Tolerance: Do Selfish X-Linked Alleles Drive Skewed X Chromosome Inactivation?

In mammalian females, diploid somatic cells contain two X chromosomes, one of which is transcriptionally silenced, in a process termed X chromosome inactivation (XCI). Whereas XCI is largely random in placental females, many women exhibit skewed XCI (SXCI), in which the vast majority cells have the same X chromosome inactivated. SXCI has serious health consequences, associated with conditions ranging from Alzheimer’s to various autoimmune disorders. SXCI is also associated with outcomes of pregnancies, with higher rates of recurrent spontaneous abortion in women with SXCI. Here, I suggest that SXCI could be driven by selfish X-linked alleles. Consistent with the association of SXCI with autoimmunity, I first note the possibility that recurrent spontaneous abortion could reflect immune rejection of fetuses inheriting alleles from the largely silenced maternal X chromosome. Preferential abortion of fetuses carrying silenced X-linked alleles implies a transmission advantage for X-linked alleles on the largely expressed chromosome, which could drive the emergence of X-linked alleles that make the chromosome resistant to XCI. I discuss the evolutionary dynamics, fitness tradeoffs and implications of this hypothesis, and suggest future directions.

Finger Length Ratio (2D:4D) in Central India and an Attempt to Verify Fraternal Birth Order Effect: A Population Based Cross-Sectional Study

INTRODUCTION

A normal physiology of a human being is not mere a series of functions occurring with specific intensities and timing. There are lot of factors that may change the normal physiological activity within normal limits. Finger length ratio is one of the markers of intrauterine androgen exposure and it is debated and contradicted by many authors. Digit ratio varies among the ethnicities. Many Indian studies show that there is considerable difference in finger length ratio in different population. Data regarding Central India was not found on extensive search.

AIM

To find out the finger length ratio and explore the birth order effect on finger length ratio among the first two successive born in the said population.

MATERIALS AND METHODS

We conducted a survey on 1500 volunteer persons (800 male and 700 female) over two years of time. We measured the length of the index finger (2D) and ring finger (4D) of both the hands and asked about their birth order history to find out the digit ratio for Central India population and any existing correlation of the same with birth order. T Test and Analysis of Variance (ANOVA) were used for the measure of significance and difference among the groups. The p< 0.05 was considered to be significant.

RESULTS

Our study reports that, study population mean for right hand 2D:4D ratio was 0.976 (SD±0.031) and for left hand it was found to be 0.969 (SD±0.035). For males, mean finger length ratio for right hand was 0.967 (SD±0.033) and 0.963 (SD±0.037) for left hand. In females the mean Finger length ratio was 0.982 (SD±0.027) for right hand and 0.974 (SD±0.034) for the left hand respectively. Finger length ratio was found to be significantly less (p=0.03) in males for right hand. No significant (p=0.24) difference was observed for left hand. When assessed fraternal birth order effect among the eldest, second born with elder brother and second born with elder sister groups, no significant (p>0.05) variation for finger length ratio of right and left hands observed in both male and female population.

CONCLUSION

Our study reports that the finger length ratio (2D:4D) for Central India population did not show significant association between finger length ratio and fraternal birth order among the first two successive born.

Sexual Orientation, Controversy, and Science

Summary

Ongoing political controversies around the world exemplify a long-standing and widespread preoccupation with the acceptability of homosexuality. Nonheterosexual people have seen dramatic surges both in their rights and in positive public opinion in many Western countries. In contrast, in much of Africa, the Middle East, the Caribbean, Oceania, and parts of Asia, homosexual behavior remains illegal and severely punishable, with some countries retaining the death penalty for it. Political controversies about sexual orientation have often overlapped with scientific controversies. That is, participants on both sides of the sociopolitical debates have tended to believe that scientific findings—and scientific truths—about sexual orientation matter a great deal in making political decisions. The most contentious scientific issues have concerned the causes of sexual orientation—that is, why are some people heterosexual, others bisexual, and others homosexual? The actual relevance of these issues to social, political, and ethical decisions is often poorly justified, however.

High Rates of Same-Sex Attraction/Gender Nonconformity in the Offspring of Mothers with Thyroid Dysfunction During Pregnancy: Proposal of Prenatal Thyroid Model

Both youngsters and adults with same-sex attraction are at greater risk for negative health outcomes. Despite mounting efforts to determine the biological background, a satisfactory conclusion has not been reached and there is a need to explore alternate factors like functioning of thyroid system during pregnancy. A retrospective chart review was undertaken of 790 eligible children and adolescents who had been admitted to child psychiatry between 2005 and 2013. This population consisted of 520 (65%) males and 270 (35%) females, aged 8 to 17 years. Fifteen mothers (1.8%) were found to have a history of thyroid dysfunction during pregnancy. Sixteen youngsters (2%) had a history of same-sex attraction. Twelve overlapping cases with both same-sex attraction and maternal thyroid dysfunction during pregnancy were identified, which was extremely significant (P<0.0001, by Fisher’s exact test). The association was also significant for each sex (P<0.0001, by Fisher’s exact test). There is evidence that thyroid gland plays a crucial and decisive role in determining sexual orientation in people. Maternal thyroid dysfunctions during pregnancy may result in homosexual orientation in the offspring.

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.

The price of pulchritude, the cost of concupiscence: how to have sex in late modernity

Research and scholarship on sexuality has grown exponentially over the last 60 years; but what is this 'sexuality' that so fascinates us. During those 60 years, three academic traditions or paradigms have emerged and evolved to provide that main ways we understand sexuality. These are: (1) sexology; (2) sex research; and (3) critical sexuality studies. These paradigms do not always agree; at times, they are incommensurable in the picture of sexuality they paint. However, they each affect how sexuality is researched and written about, and how it is understood in the popular imagination. After discussing these paradigms, attention is focused on the contemporary challenges facing the third paradigm: critical sexuality studies. The contribution of sexology and sex research to these challenges is noted. Three key issues are discussed: the body; how we commonly understand sexuality; and the commodification of sexuality in late modernity.

Fecundity of paternal and maternal non-parental female relatives of homosexual and heterosexual men

A variety of social, developmental, biological and genetic factors influence sexual orientation in males. Thus, several hypotheses have attempted to explain the sustenance of genetic factors that influence male homosexuality, despite decreased fecundity within the homosexuals. Kin selection, the existence of maternal effects and two forms of balancing selection, sexually antagonistic selection and overdominance, have been proposed as compensatory mechanisms for reduced homosexual fecundity. Here, we suggest that the empirical support for kin selection and maternal effects cannot account for the low universal frequency and stability of the distribution of homosexuals. To identify the responsible compensatory mechanism, we analyzed fecundity in 2,100 European female relatives, i.e., aunts and grandmothers, of either homosexual or heterosexual probands who were matched in terms of age, culture and sampling strategy. Female relatives were chosen to avoid the sampling bias of the fraternal birth order effect, which occurs when indirectly sampling mothers though their homosexual sons. We observed that the maternal aunts and grandmothers of homosexual probands were significantly more fecund compared with the maternal aunts and maternal grandmothers of the heterosexual probands. No difference in fecundity was observed in the paternal female lines (grandmothers or aunts) from either of the two proband groups. Moreover, due to the selective increase in maternal female fecundity, the total female fecundity was significantly higher in homosexual than heterosexual probands, thus compensating for the reduced fecundity of homosexuals. Altogether, these data support an X-linked multi-locus sexually antagonistic hypothesis rather than an autosomal multi-locus overdominance hypothesis.

Interbirth spacing and offspring mental health outcomes

BACKGROUND

The perinatal or early life environment may influence the development of mental illness in adulthood. It is not clear how, or when, any such influences might be mediated. Foetal exposure to maternal stress in the intrauterine environment has been suggested as a possible mediator of foetal origins of mental illness but the postnatal environment may also be of importance. This study aimed to test the foetal origins hypothesis by using retrograde and antegrade interbirth intervals (time to mother's most recent and next deliveries respectively) as proxy measures of antenatal and postnatal maternal stress.

METHOD

Linked datasets of the Scottish Morbidity Record (SMR) were used to identify a birth cohort. Where applicable, the dates of each mother's most recent previous and/or next subsequent delivery were noted, allowing birth intervals to be calculated. The cohort was followed up into young adulthood, using self-harm, substance misuse, psychotic disorder and affective disorder as outcome measures. Data were analysed using Cox regression.

RESULTS

No significant relationship was observed between affective disorders and interbirth interval, neither retrograde nor antegrade. Short (<18-month) antegrade birth intervals were independently associated with increased risk of psychotic disorder and self-harm. Long (>72-month) retrograde intervals were associated with increased risk of self-harm and substance misuse.

CONCLUSIONS

The data do not provide evidence for the foetal origins of mental disorders but, in the cases of psychotic disorders, and of self-harm, suggest that the early postnatal rather than the antenatal environment may be of greater importance.

The Project TALENT Twin and Sibling Study

Project TALENT is a US national longitudinal study of about 377,000 individuals born in 1942-1946, first assessed in 1960. Students in about 1,200 schools participated in a 2-day battery covering aptitudes, abilities, interests, and individual and family characteristics (Flanagan, 1962; www.projectTALENT.org). Follow-up assessments 1, 5, and 11 years later assessed educational and occupational outcomes. The sample includes approximately 92,000 siblings from 40,000 families, including 2,500 twin pairs and 1,200 other siblings of twins. Until recently, almost no behavior genetic research has been conducted with the sample. In the original data collection information was not collected with the intent to link family members. Recently, we developed algorithms using names, addresses, birthdates, and information about family structure to link siblings and identify twins. We are testing several methods to determine zygosity, including use of yearbook photographs. In this paper, we summarize the design and measures in Project TALENT, describe the Twin and Sibling sample, and present our twin-sib-classmate model. In most twin and family designs, the 'shared environment' includes factors specific to the family combined with between-family differences associated with macro-level variables such as socioeconomic status. The school-based sampling design used in Project TALENT provides a unique opportunity to partition the shared environment into variation shared by siblings, specific to twins, and associated with school- and community-level factors. The availability of many measured characteristics on the family, schools, and neighborhoods enhances the ability to study the impact of specific factors on behavioral variation.

Sibling sex ratio and birth order in early-onset gender dysphoric adolescents

Several sibship-related variables have been studied extensively in sexual orientation research, especially in men. Sibling sex ratio refers to the ratio of brothers to sisters in the aggregate sibships of a group of probands. Birth order refers to the probands' position (e.g., first-born, middle-born, last-born) within their sibships. Fraternal birth order refers to their position among male siblings only. Such research was extended in this study to a large group of early-onset gender dysphoric adolescents. The probands comprised 94 male-to-female and 95 female-to-male gender dysphoric adolescents. The overwhelming majority of these were homosexual or probably prehomosexual. The control group consisted of 875 boys and 914 girls from the TRAILS study. The sibling sex ratio of the gender dysphoric boys was very high (241 brothers per 100 sisters) compared with the expected ratio (106:100). The excess of brothers was more extreme among the probands' older siblings (300:100) than among their younger siblings (195:100). Between-groups comparisons showed that the gender dysphoric boys had significantly more older brothers, and significantly fewer older sisters and younger sisters, than did the control boys. In contrast, the only notable finding for the female groups was that the gender dysphoric girls had significantly fewer total siblings than did the control girls. The results for the male probands were consistent with prior speculations that a high fraternal birth order (i.e., an excess of older brothers) is found in all homosexual male groups, but an elevated sibling sex ratio (usually caused by an additional, smaller excess of younger brothers) is characteristic of gender dysphoric homosexual males. The mechanisms underlying these phenomena remain unknown.

The second to fourth digit ratio (2D:4D) in a Japanese twin sample: heritability, prenatal hormone transfer, and association with sexual orientation

The second to fourth digit ratio has been argued to reflect prenatal hormonal influences and is reportedly associated with various psychological and behavioral traits, such as sexual orientation, cognitive abilities, and personality. We examined genetic and environmental influences on the second to fourth digit ratio (2D:4D) using a Japanese twin sample (N=300). The genetic analysis showed substantial additive genetic influences for both right and left hand 2D:4D. The rest of the variance was explained mainly by environmental influences not shared within twin pairs. These findings were, in general, in accordance with preceding studies with primarily Caucasian twin samples. The bivariate genetic analysis revealed that the additive genetic influences were largely shared between the right and left hand, while the non-shared environmental influences were largely unique to each hand. Results from a comparison of opposite-sex and same-sex twins were not significant, although they were in the predicted direction according to the prenatal hormone transfer hypothesis. Female monozygotic twin pairs discordant in sexual orientation showed significant within-pair differences in left hand 2D:4D, where non-heterosexual twins had lower (more masculinized) 2D:4D. In addition, we found that non-heterosexual male MZ twins had larger (more feminized) 2D:4D than their heterosexual co-twins. These results suggest the existence of non-shared environmental influences that affect both 2D:4D and sexual orientation.

Adolescents who have sexually offended: is phallometry valid?

It is unclear whether deviant sexual preferences distinguish adolescents who commit sex offenses in the same way that such deviance characterizes adult sex offenders. We compared male adolescents (mean age = 15 at the time of a referral sex offense), matched adult sex offenders, and normal men (adult nonoffenders or nonsex offenders). We hypothesized the following: phallometric responses of the adolescents would be similar to those of adult sex offenders and would differ from normals; adolescents with male child victims would exhibit greater evidence of sexual deviance than those whose only victims were female children; among adolescents who had molested children, those with a history of sexual abuse would exhibit more evidence of sexual deviance than those with no such history; and phallometric measures would predict recidivism. With some notable exceptions or qualifications, results confirmed the hypotheses. Phallometry has valid clinical and research uses with adolescent males who commit serious sex offenses.

Is homosexuality a paraphilia? The evidence for and against

Whether homosexuality should be described as one among many paraphilic sexual interests or an altogether different dimension of sexual interest has long been discussed in terms of its political and social implications. The present article examined the question instead by comparing the major correlates and other features of homosexuality and of the paraphilias, including prevalence, sex ratio, onset and course, fraternal birth order, physical height, handedness, IQ and cognitive neuropsychological profile, and neuroanatomy. Although those literatures remain underdeveloped, the existing findings thus far suggest that homosexuality has a pattern of correlates largely, but not entirely, distinct from that identified among the paraphilias. At least, if homosexuality were deemed a paraphilia, it would be relatively unique among them, taxonometrically speaking.

Perinatal and psychosocial circumstances associated with risk of attempted suicide, non-suicidal self-injury and psychiatric service use. A longitudinal study of young people

BACKGROUND

Past studies using large population based datasets link certain perinatal circumstances (birth weight, parity, etc) with mental health outcomes such as suicide, self-harm and psychiatric problems. Problematically, population datasets omit a number of social confounds. The aim of this study is to replicate past research linking perinatal circumstances and mental health (suicidality and use of psychiatric services) and to determine if such associations remain after adjusting for social circumstances.

METHODS

A longitudinal school-based survey of 2157 young people (surveyed at age 11, 13, 15) followed up in early adulthood (age 19). At age 11 parents of participants provided information about perinatal circumstances (birth weight, birth complications, etc.) and psychiatric service use. Participants provided data about their mental health at age 15 (attempted suicide, suicidal thoughts) and at ages 19 (self-harm, psychiatric service use). In addition, data were collected about their social and psychosocial circumstances (gender, deprivation, religion, sexual behaviour, etc.).

RESULTS

Predictably, social factors were linked to mental health outcomes. For example, those with same sex partners were more likely (OR 4.84) to self-harm than those without a same sex partner. With a single exception, in both unadjusted and adjusted models, perinatal circumstances were not or only marginally associated with mental health outcomes. The exception was the number of birth complications; young people with two or more complications were approximately 2-3 times more likely than those without complications to use psychiatric services.

CONCLUSIONS

While we failed to replicate results found using large population based datasets, some of our results are compatible with prior research findings. Further, evidence from this study supports the influence of perinatal circumstances (birth complications) on later psychiatric problems, or at least higher than expected contact with psychiatric service.

Prenatal Influences on Sexual Orientation: Digit Ratio (2D:4D) and Number of Older Siblings

Prenatal androgen levels are suggested to influence sexual orientation in both sexes. The 2D:4D digit ratio has been found to associate with sexual orientation, but published findings have often been contradictory, which may partly be due to the large ethnic diversity between and within studied populations. In men, number of older brothers has been found to correlate positively with homosexuality. This phenomenon has been explained with a maternal immune reaction, which is provoked only by male fetuses and which gets stronger after each pregnancy. Here we assessed the relationship of sexual orientation to 2D:4D ratios and number of older siblings in Finland, where the population is found to be genetically relatively homogeneous. As in many previous studies, heterosexual men had lower 2D:4D than non-heterosexual men, which supports the notion that non-heterosexual men experience higher androgen levels in utero than population norms. Contrary to previous reports, non-heterosexual women had higher 2D:4D than heterosexual women. Non-heterosexual men had more older brothers and older sisters than heterosexual men. The greater number of older sisters in non-heterosexual men indicates that there are other factors that contribute to the higher birth order of homosexual men than the maternal immunization.

Sexual differentiation of the human brain: relation to gender identity, sexual orientation and neuropsychiatric disorders

During the intrauterine period a testosterone surge masculinizes the fetal brain, whereas the absence of such a surge results in a feminine brain. As sexual differentiation of the brain takes place at a much later stage in development than sexual differentiation of the genitals, these two processes can be influenced independently of each other. Sex differences in cognition, gender identity (an individual's perception of their own sexual identity), sexual orientation (heterosexuality, homosexuality or bisexuality), and the risks of developing neuropsychiatric disorders are programmed into our brain during early development. There is no evidence that one's postnatal social environment plays a crucial role in gender identity or sexual orientation. We discuss the relationships between structural and functional sex differences of various brain areas and the way they change along with any changes in the supply of sex hormones on the one hand and sex differences in behavior in health and disease on the other.

Exploring the causal machinery behind sex ratios at birth: does hepatitis B play a role?

The causal machinery underlying sex determination is directly relevant to many questions relating gender and family composition to social and economic outcomes. In recent work, Oster highlighted a correlation between parental hepatitis B carrier status and sex of the child. One of her analyses went further, speaking directly to causality. That analysis appeared to have answered an important question that had remained unresolved in medical and biological literatures—namely, does chronic infection with hepatitis B cause male‐skewed sex ratios at birth? Oster’s creative empirical analysis appeared to suggest that it does; however, in this article I reassess the result and present evidence that, at the very least, the question remains open. Further investigation into questions around the causal machinery of sex determination is warranted in the social science literature, as well as in that of biology and medicine. However, my results suggest that it is extremely unlikely that chronic hepatitis B infection plays a biologically significant role.

Effects of gestational length, gender, postnatal age, and birth order on visual contrast sensitivity in infants

To investigate effects of visual experience versus preprogrammed mechanisms on visual development, we used multiple regression analysis to determine the extent to which a variety of variables (that differ in the extent to which they are tied to visual experience) predict luminance and chromatic (red/green) contrast sensitivity (CS), which are mediated by the magnocellular (M) and parvocellular (P) subcortical pathways, respectively. Our variables included gestational length (GL), birth weight (BW), gender, postnatal age (PNA), and birth order (BO). Two-month-olds (n = 60) and 6-month-olds (n = 122) were tested. Results revealed that (1) at 2 months, infants with longer GL have higher luminance CS; (2) at both ages, CS significantly increases over a approximately 21-day range of PNA, but this effect is stronger in 2- than 6-month-olds and stronger for chromatic than luminance CS; (3) at 2 months, boys have higher luminance CS than girls; and (4) at 2 months, firstborn infants have higher CS, while at 6 months, non-firstborn infants have higher CS. The results for PNA/GL are consistent with the possibility that P pathway development is more influenced by variables tied to visual experience (PNA), while M pathway development is more influenced by variables unrelated to visual experience (GL). Other variables, including prenatal environment, are also discussed.

Endocrine treatment of transsexual persons: an Endocrine Society clinical practice guideline

OBJECTIVE

The aim was to formulate practice guidelines for endocrine treatment of transsexual persons.

EVIDENCE

This evidence-based guideline was developed using the Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) system to describe the strength of recommendations and the quality of evidence, which was low or very low.

CONSENSUS PROCESS

Committees and members of The Endocrine Society, European Society of Endocrinology, European Society for Paediatric Endocrinology, Lawson Wilkins Pediatric Endocrine Society, and World Professional Association for Transgender Health commented on preliminary drafts of these guidelines.

CONCLUSIONS

Transsexual persons seeking to develop the physical characteristics of the desired gender require a safe, effective hormone regimen that will 1) suppress endogenous hormone secretion determined by the person's genetic/biologic sex and 2) maintain sex hormone levels within the normal range for the person's desired gender. A mental health professional (MHP) must recommend endocrine treatment and participate in ongoing care throughout the endocrine transition and decision for surgical sex reassignment. The endocrinologist must confirm the diagnostic criteria the MHP used to make these recommendations. Because a diagnosis of transsexualism in a prepubertal child cannot be made with certainty, we do not recommend endocrine treatment of prepubertal children. We recommend treating transsexual adolescents (Tanner stage 2) by suppressing puberty with GnRH analogues until age 16 years old, after which cross-sex hormones may be given. We suggest suppressing endogenous sex hormones, maintaining physiologic levels of gender-appropriate sex hormones and monitoring for known risks in adult transsexual persons.

Prenatal sex hormones (maternal and amniotic fluid) and gender-related play behavior in 13-month-old Infants

Testosterone, estradiol, and progesterone levels were measured in the second trimester of pregnancy in maternal serum and amniotic fluid, and related to direct observations of gender-related play behavior in 63 male and 63 female offspring at age 13 months. During a structured play session, sex differences in toy preference were found: boys played more with masculine toys than girls (d = .53) and girls played more with feminine toys than boys (d = .35). Normal within-sex variation in prenatal testosterone and estradiol levels was not significantly related to preference for masculine or feminine toys. For progesterone, an unexpected significant positive relationship was found in boys between the level in amniotic fluid and masculine toy preference. The mechanism explaining this relationship is presently not clear, and the finding may be a spurious one. The results of this study may indicate that a hormonal basis for the development of sex-typed toy preferences may manifest itself only after toddlerhood. It may also be that the effect size of this relationship is so small that it should be investigated with more sensitive measures or in larger populations.

Family and sexual orientation: the family-demographic correlates of homosexuality in men and women

Using a nationally representative sample of young adults, I identify the family-demographic correlates of sexual orientation in men and women. Hence, I test the maternal immune hypothesis, which posits that the only biodemographic correlate of male homosexuality is the number of older brothers, and there are no biodemographic correlates of female homosexuality. For men, I find that having one older brother does not raise the likelihood of homosexuality. Although having multiple older brothers has a positive coefficient, it is not significant. Moreover, having any older sisters lowers the likelihood of homosexual or bisexual identity. For women, I find that having an older brother or having any sisters decreases the likelihood of homosexuality. Family structure, ethnicity, and education are also significantly correlated with male and female sexual orientation. Therefore, the maternal immune hypothesis cannot explain the entire pattern of family-demographic correlates. The findings are consistent with either biological or social theories of sexual orientation.

Genetic factors increase fecundity in female maternal relatives of bisexual men as in homosexuals

INTRODUCTION

Recent studies on male homosexuals showed increased fecundity of maternal female relatives of homosexual probands, compared to those of heterosexual controls. We have suggested that these data could be explained by the transmission, in the maternal line, of an X-linked genetic factor that promotes androphilic behavior in females and homosexuality in males.

AIM

Our original studies were on relatives of male subjects who declared themselves to be exclusively homosexual. However, the relationship between homosexuality and bisexuality, including the possibility of shared genetic factors, is complex and largely unexplored. To cast light on this issue, in the present study we examined whether relatives of bisexuals show the same indirect fitness advantage as previously demonstrated for homosexuals.

MAIN OUTCOME MEASURES

Subjects completed a questionnaire on their sexual orientation, sexual behavior, and their own and their relatives' fecundity.

METHODS

We studied 239 male subjects, comprising 88 who were exclusively or almost exclusively heterosexual (pooled to comprise our "heterosexual" group), 86 who were bisexual, and 65 exclusively or almost exclusively homosexual individuals (pooled in our "homosexual" group). Bisexuals were here defined on the basis of self-identification, lifetime sexual behavior, marital status, and fecundity.

RESULTS

We show that fecundity of female relatives of the maternal line does not differ between bisexuals and homosexuals. As in the previous study on homosexuals, mothers of bisexuals show significantly higher fecundity, as do females in the maternal line (cumulated fecundity of mothers, maternal grandparents, and maternal aunts), compared to the corresponding relatives of heterosexual controls.This study also shows that both bisexuals and homosexuals were more frequently second and third born. However, only homosexuals had an excess of older male siblings, compared to heterosexuals.

CONCLUSIONS

We present evidence of an X-chromosomal genetic factor that is associated with bisexuality in men and promotes fecundity in female carriers.

Masculinized finger-length ratios of boys, but not girls, are associated with attention-deficit/hyperactivity disorder

Gonadal hormones may exert permanent organizational effects on sexually dimorphic finger-length ratios and sexually dimorphic behavior expressed in childhood attention deficit-hyperactivity disorder (ADHD). This study extended recent work examining associations between finger-length ratios (specifically, 2D:4D) and ADHD in a well-characterized, clinically diagnosed, community-recruited sample of boys and girls. A multistage, diagnostic procedure was utilized to identify 113 children with ADHD and 137 non-ADHD comparison children. Right-hand digit ratios showed significant mean differences by gender, as well as associations with ADHD diagnosis. Boys with ADHD had more masculinized digit ratios than control-group boys. More masculine right 2D:4D and 3D:4D ratios were correlated with parent- and teacher-rated inattentive and hyperactive-impulsive symptoms in boys but not in girls. Masculinized finger-length ratios were associated with hyperactive-impulsive and oppositional- defiant symptoms, but associations were largest with symptoms of inattention. It is concluded that prenatal, organizational effects of gonadal hormones may play a role in the development of ADHD and contribute to explaining sex differences in the prevalence rates of this childhood disorder.

Sexual orientation and fluctuating asymmetry in men and women

Previous research suggests that individuals' sexual orientation may be affected by developmental instability (DI) induced by exposure to prenatal stresses. We tested this relationship using fluctuating asymmetry (FA), the small random deviations from symmetry that arise in otherwise bilaterally symmetrical traits as a consequence of developmental noise and developmental instability. Differences among individuals reflect variation in their exposure to and ability to accommodate for stresses experienced during development as well as to developmental noise that arises due to cellular stocasticity. FA measurements for 156 heterosexual and 132 homosexual men and women participants provided strong support for the developmental instability hypothesis: FA was significantly higher in both male and female homosexuals (men: four of seven bilateral traits and composite FA values (cFA); women: five of seven bilateral traits and composite FA values). Although finger-length ratios (FLRs), an indirect marker for prenatal hormones, were sex-atypical (e.g., feminized) for homosexual men, we failed to detect any relationship between FA levels and 2D:4D finger-length ratios (FLRs). Hence, although elevated levels of developmental stress appear to be linked to shifts in sexual orientation, the underlying mechanism does not seem to be connected to sex-atypical prenatal hormones. Additional analyses with sex atypical individuals are needed to confirm this.

Fluctuating asymmetry and sexual orientation in men and women

The present study measured handedness and bodily fluctuating asymmetry (FA), two markers of developmental instability, in 89 heterosexual and 78 gay men and women. Asymmetry in ear breadth, ear length, ankle breadth, second digit length, fourth digit length, and two composite indices were calculated for each participant and a modified Edinburgh Inventory was used to assess handedness. Results showed that, for men, there was a significant positive correlation between three measures of FA and sexual orientation scores (SOS). As ear breadth FA and two composite FA scores increased so did SOS on a modified Kinsey scale (where 0 indicated exclusive heterosexuality and 6 indicated exclusive homosexuality). No significant relationships were found between SOS and FA for women. Similarly, sexual orientation was not related to handedness for either sex. The theoretical implications of the present results are discussed.

Sexual differentiation of the brain and behavior

During the intrauterine period the human brain develops in the male direction via direct action of a boy's testosterone, and in the female direction through the absence of this hormone in a girl. During this time, gender identity (the feeling of being a man or a woman), sexual orientation, and other behaviors are programmed. As sexual differentiation of the genitals takes places in the first 2 months of pregnancy, and sexual differentiation of the brain starts during the second half of pregnancy, these two processes may be influenced independently of each other, resulting in transsexuality. This also means that in the case of an ambiguous gender at birth, the degree of masculinization of the genitals may not reflect the same degree of masculinization of the brain. Differences in brain structures and brain functions have been found that are related to sexual orientation and gender.

Beliefs about the etiology of homosexuality and about the ramifications of discovering its possible genetic origin

Homosexuality is viewed by many as a social problem. As such, there is a keen interest in elucidating the origins of homosexuality among many scholars, from anthropologists to zoologists, from psychologists to theologians. Research has shown that those who believe sexual orientation is inborn are more likely to have tolerant attitudes toward gay men and lesbians, whereas those who believe it is a choice have less tolerant attitudes. The current qualitative study used in-depth, open-ended telephone interviews with 42 White and 44 Black Americans to gain insight into the public's beliefs about the possible genetic origins of homosexuality. Along with etiological beliefs (and the sources of information used to develop these beliefs), we asked respondents to describe the benefits and dangers of scientists discovering the possible genetic basis for homosexuality. We found that although limited understanding and biased perspectives likely led to simplistic reasoning concerning the origins and genetic basis of homosexuality, many individuals appreciated the complex and interactive etiological perspectives. These interactive perspectives often included recognition of some type of inherent aspect, such as a genetic factor(s), that served as an underlying predisposition that would be manifested after being influenced by other factors such as choice or environmental exposures. We also found that beliefs in a genetic basis for homosexuality could be used to support very diverse opinions including those in accordance with negative eugenic agendas.

Biological versus nonbiological older brothers and men's sexual orientation

The most consistent biodemographic correlate of sexual orientation in men is the number of older brothers (fraternal birth order). The mechanism underlying this effect remains unknown. In this article, I provide a direct test pitting prenatal against postnatal (e.g., social/rearing) mechanisms. Four samples of homosexual and heterosexual men (total n = 944), including one sample of men raised in nonbiological and blended families (e.g., raised with half- or step-siblings or as adoptees) were studied. Only biological older brothers, and not any other sibling characteristic, including nonbiological older brothers, predicted men's sexual orientation, regardless of the amount of time reared with these siblings. These results strongly suggest a prenatal origin to the fraternal birth-order effect.