Human Sexual Orientation: The Importance of Evidentiary Convergence

To What Extent are Prenatal Androgens Involved in the Development of Male Homosexuality in Humans?

Endocrine variations, including possibly reduced exposure to androgens, may contribute to the development of male homosexuality, with animal models demonstrating same-sex mate preference with altered exposure during prenatal or early postnatal development. As similar studies in humans are impossible, indirect physical and cognitive measures of androgen exposure are used. Some studies suggest that physical measures affected by prenatal androgens, including the index-to-ring finger ratio, growth indices, and facial structure, are more "feminine" in gay men. Gay men also exhibit significant childhood gender non-conformity and a "feminized" anatomical and functional brain pattern in sexual arousal, as well as domains such as language, visuospatial skills and hemispheric relationships. However, many of these results are equivocal and may be confounded by other factors. Research has also been hampered by inconsistencies in the reporting of sexual orientation and the potentially unrepresentative populations of gay men studied, while additional complexities pertaining to gender conformity and sexual role may also influence results.

Effects of Sexual Function, Social Media Use, and Self-Efficacy on Quality of Life Among Home Parenteral Nutrition Patients

BACKGROUND

Quality of life (QOL) of home parenteral nutrition (HPN) patients is a critical issue for functioning and survival. This study evaluates the roles of sexual function (SF), self-efficacy (SE), and the use of social media (USM) in the QOL of HPN patients.

MATERIALS AND METHODS

The study model investigates the independent variables USM and SF and the dependent variable QOL, and SE is a mediator variable between SF and USM.

RESULTS

We included 203 participants with HPN who completed self-administered, validated questionnaires for QOL, SF, SE, and USM. Statistical analysis included a t-test, Sobel test, bootstrapping method, and Pearson correlations between variances. The mean HPN duration was 10.5 ± 8 years. Results show a significant correlation between QOL scores and SF (P = .001). USM was positively correlated with SE (P = .001). SE as a mediator between USM and SF was supported by significant results in the Sobel test. Patients with a stoma were significantly less sexually active and had lower SE ratings than those without a stoma.

CONCLUSION

Physical changes that affect SE and boost social relationships by allowing emotional support through social networks are important factors for QOL improvement. These findings may guide health professionals in the management of HPN patients.

Sexual partner preference in animals and humans

Sex differences in brain and behavior of animals including humans result from an interaction between biological and environmental influences. This is also true for the differences between men and women concerning sexual orientation. Sexual differentiation is mediated by three groups of biological mechanisms: early actions of sex steroids, more direct actions of sex-specific genes not mediated by gonadal sex steroids and epigenetic mechanisms. Differential interactions with parents and conspecifics have additionally long-term influences on behavior. This presentation reviews available evidence indicating that these different mechanisms play a significant role in the control of sexual partner preference in animals and humans, in other words the homosexual versus heterosexual orientation. Clinical and epidemiological studies of phenotypically selected populations indicate that early actions of hormones and genetic factors clearly contribute to the determination of sexual orientation. The maternal embryonic environment also modifies the incidence of male homosexuality via immunological mechanisms. The relative contribution of each of these mechanisms remains however to be determined.

Programmed for Preference: The Biology of Same-Sex Attraction in Rams

The sheep is a valuable model to test whether hormone mechanisms that sexually differentiate the brain underlie the expression of sexual partner preferences because as many as 8% of rams prefer same-sex partners. This review presents an overview and update of the experimental evidence that supports this hypothesis. New evidence is presented that demonstrates a critical role for kisspeptin-GnRH signaling for regulating stable fetal testosterone levels necessary for masculinization of brain and behavior. Although these studies provide substantial support for the idea that prenatal hormones program sexual preferences, further experimentation is needed to establish causality.

Associations of Bisexuality and Homosexuality with Handedness and Footedness: A Latent Variable Analysis Approach

Non-right-handedness appears to be more common among bisexuals and homosexuals than among heterosexuals, which might be indirect evidence of effects of prenatal androgen exposure. Current data suggest higher prenatal testosterone levels among bisexual and homosexual women, but are inconclusive for men. This study examined the association between sexual orientation and non-right-handedness for sex differences and whether higher rates of mixed-handedness, rather than left-handedness, might be the driving factor. This allowed for more specific tests regarding the predictions of two competing theories of prenatal androgen exposure, the Geschwind-Galaburda theory and the callosal hypothesis, than in previous research. Being a potentially better indicator of cerebral lateralization than handedness, associations with footedness were also explored. To counter inconsistencies and shortcomings of previous research, we utilized two large discovery and replication datasets (ns = 2368 and 1565) and applied latent variable analysis to reliably classify lateral preferences (i.e., handedness, footedness). This maximized the statistical conclusion validity and allowed for direct tests of replicability. Sexual orientation was differentially associated with lateral preferences among men and women. Associations among women were consistent with predictions of the Geschwind-Galaburda theory, whereas among men they were consistent with predictions of the callosal hypothesis. The results were further consistent with models of homosexuality that suggest a role of parental epigenetic marks on sexually dimorphic fetal development. Research efforts should be increased with regard to footedness and epigenetic theories of homosexuality.

A Life History Approach to the Female Sexual Orientation Spectrum: Evolution, Development, Causal Mechanisms, and Health

Women's capacity for sexual fluidity is at least as interesting a phenomenon from the point of view of evolutionary biology and behavioral endocrinology as exclusively homosexual orientation. Evolutionary hypotheses for female nonheterosexuality have failed to fully account for the existence of these different categories of nonheterosexual women, while also overlooking broader data on the causal mechanisms, physiology, ontogeny, and phylogeny of female nonheterosexuality. We review the evolutionary-developmental origins of various phenotypes in the female sexual orientation spectrum using the synergistic approach of Tinbergen's four questions. We also present femme-specific and butch-specific hypotheses at proximate and ultimate levels of analysis. This review article indicates that various nonheterosexual female phenotypes emerge from and contribute to hormonally mediated fast life history strategies. Life history theory provides a biobehavioral explanatory framework for nonheterosexual women's masculinized body morphology, psychological dispositions, and their elevated likelihood of experiencing violence, substance use, obesity, teenage pregnancy, and lower general health. This pattern of life outcomes can create a feedback loop of environmental unpredictability and harshness which destabilizes intrauterine hormonal conditions in mothers, leading to a greater likelihood of fast life history strategies, global health problems, and nonheterosexual preferences in female offspring. We further explore the potential of female nonheterosexuality to function as an alloparental buffer that enables masculinizing alleles to execute their characteristic fast life history strategies as they appear in the female and the male phenotype. Synthesizing life history theory with the female sexual orientation spectrum enriches existing scientific knowledge on the evolutionary-developmental mechanisms of human sex differences.

Psychosexual Aspects, Effects of Prenatal Androgen Exposure, and Gender Change in 46,XY Disorders of Sex Development

CONTEXT

In 46,XY disorders of sexual development (DSD) patients, several factors may affect psychosexual development, leading to gender identity discrepancy and gender change later in life. Prenatal sexual steroid exposure and external genital virilization are considered to influence human psychosexual development, but their roles not completely understood yet.

DESIGN

A total of 144 individuals (18 to 60 years of age) with a clinical/molecular diagnosis of 46,XY DSD from a single tertiary center were enrolled. Psychosexual outcomes (gender role, gender identity, and sexual orientation) were assessed using questionnaires and psychological test. The Sinnecker score was used for genital virilization measurement. Prenatal androgen exposure was estimated according to 46,XY DSD etiology.

RESULTS

We found a positive association between prenatal androgen exposure and male psychosexual outcomes. Alternatively, prenatal estrogen exposure, age of gonadectomy, and the degree of external genital virilization did not influence any psychosexual outcome. There were 19% (n = 27) with gender change, which was associated with prenatal androgen exposure (P < 0.001) but not with the external genital virilization. The median age of gender change was 15 years, but most of the patients reported the desire for gender change earlier.

CONCLUSIONS

Prenatal androgen exposure influenced psychosexual development in 46,XY DSD favoring male psychosexuality in all psychosexual outcomes, whereas the degree of external genital virilization did not influence these outcomes. The organizational effect of sexual steroids on psychosexuality at puberty appears to be weak in comparison with the prenatal effects. Prenatal androgen exposure also influenced female-to-male gender change frequency. All 46,XY DSD conditions with prenatal androgen exposure must be followed for gender issues in their management.

Neurobiology of gender identity and sexual orientation

Sexual identity and sexual orientation are independent components of a person's sexual identity. These dimensions are most often in harmony with each other and with an individual's genital sex, although not always. The present review discusses the relationship of sexual identity and sexual orientation to prenatal factors that act to shape the development of the brain and the expression of sexual behaviours in animals and humans. One major influence discussed relates to organisational effects that the early hormone environment exerts on both gender identity and sexual orientation. Evidence that gender identity and sexual orientation are masculinised by prenatal exposure to testosterone and feminised in it absence is drawn from basic research in animals, correlations of biometric indices of androgen exposure and studies of clinical conditions associated with disorders in sexual development. There are, however, important exceptions to this theory that have yet to be resolved. Family and twin studies indicate that genes play a role, although no specific candidate genes have been identified. Evidence that relates to the number of older brothers implicates maternal immune responses as a contributing factor for male sexual orientation. It remains speculative how these influences might relate to each other and interact with postnatal socialisation. Nonetheless, despite the many challenges to research in this area, existing empirical evidence makes it clear that there is a significant biological contribution to the development of an individual's sexual identity and sexual orientation.