Handedness and Birth Order Among Heterosexual Men, Gay Men, and Sao Praphet Song in Northern Thailand

Recalled Childhood Separation Anxiety in Relation to Sex, Sexual Orientation, and Gender Identity in Thailand

Same-sex sexual attraction is an evolutionary paradox. It is influenced by genes but also associated with reduced reproduction. An altruistic disposition toward kin could increase relatives' reproduction, thus addressing this paradox. Developmentally, such a disposition may manifest as anxiety during separation from kin. This hypothesis has been supported among androphilic (i.e. sexually attracted to males) males, but few similar studies of gynephilic (i.e. sexually attracted to females) females exist. We examined recalled childhood separation anxiety in Thailand and employed the largest and most sexually and gender-diverse sample to date (N = 1403). Among heterosexuals, men recalled less concern for parents' and siblings' well-being during separation than women. Androphilic males evidenced elevated concern for parents' and siblings' well-being during separation, and transfeminine androphilic males known as sao praphet song reported heightened anxiety when separated from parents. Among females, transmasculine gynephilic females known as toms recalled less concern about parents' well-being during separation than feminine females who are attracted to toms and known as dees. Bisexual women recalled less anxiety when separated from parents than dees and lesbian and heterosexual women. These findings suggest a disposition toward heightened kin-directed altruism is evident in childhood among androphilic males, but not gynephilic 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.

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.

New Data on Birth Order in Homosexual Men and Women and a Reply to Vilsmeier et al. (2021a, 2021b)

The fraternal birth order effect (FBOE) is the repeated finding that older brothers increase the odds of homosexuality in later-born males. It has been our working assumption, based on the majority of previous studies, that a similar FBOE does not occur in females. In an elaborate quantitative review posted last year to a preprint server, Vilsmeier et al. (2021a) concluded that there is no valid evidence for an FBOE in men or women. Ablaza et al. (2022) subsequently published a study of population-level data from the Netherlands with conclusions completely opposite to those of Vilsmeier et al., namely, that there is robust evidence of an FBOE in both men and women. The present research was initially undertaken to refute the assertion of Vilsmeier et al. that there is no proof of an FBOE in men and to investigate how they obtained such a discrepant conclusion. We found evidence that the discrepancy may relate to Vilsmeier et al.'s use of the large and demonstrably unreliable sample published by Frisch and Hviid (2006). After the publication by Ablaza et al., we expanded our article to address their finding of an FBOE in women. We argue that our preferred explanation of the FBOE in men-that it reflects the progressive immunization of some mothers to Y-linked antigen by each succeeding male fetus and the concomitantly increasing effects of anti-male antibody on sexual differentiation in the brain in each succeeding male fetus-could plausibly be extended to female homosexuality.

A Novel Method for Studying the Effect of Older Brothers on Sexual Orientation and Its Robustness to Stopping Rule Distortions

In a recent article, Ablaza, Kabátek, and Perales describe a novel statistical methodology for studying the relation between sibship composition and sexual orientation, and they report the results of applying that methodology to a fresh sample. Research conducted for this commentary investigated whether Ablaza et al.'s method would be robust to the distorting effect of stopping rules, that is, quasi-rules that parents follow in deciding whether to have another child. Results obtained with an archived sample in which stopping rule distortion was known to be present indicated that their method probably is not robust to this particular problem. On another topic, it is argued that Ablaza et al.'s finding that older brothers increased the odds of homosexuality in women needs to be confirmed with further research, because past studies have been inconsistent in this regard. It is further argued that, even if an effect of older brothers on women's sexual orientation is confirmed, this would not necessarily falsify the hypothesis that maternal immunization underlies the effect of older brothers on men's sexual orientation. That hypothesis would need to be extended but not necessarily abandoned.

Culture influences the development of children's gender-related peer preferences: Evidence from China and Thailand

Current understanding of how culture relates to the development of children's gender-related peer preferences is limited. To investigate the role of societal acceptance of gender nonconformity, this study compared children from China and Thailand. Unlike China and other cultures where the conceptualization of gender as binary is broadly accepted, individuals who identify as a nonbinary "third" sex/gender have been highly visible and tolerated in Thai society for at least several decades. Chinese and Thai 4- to 9-year-olds (N = 458) viewed vignettes of four hypothetical peers who varied on gender (i.e., boy vs. girl) and gender-typed toy play behavior (i.e., masculine vs. feminine), and were asked to give a friendship preference rating for each peer. Chinese, compared with Thai, children evidenced gender-related peer preferences that emerged earlier, remained more stable across age groups, and were relatively more biased against gender-nonconforming behavior. The only cultural similarity was in children's preference for peers who were of the same gender and/or displayed same-gender-typed behavior. Thus, while preference for peers who are of the same gender and/or display same-gender-typed behavior is common among children across cultures, the developmental onset and course of these preferences vary by culture. Moreover, societal acceptance of gender nonconformity might be key to limiting children's bias against gender-nonconforming peers.

Testing Women's Trust in Other Women and Same-Sex Attracted Males in Three Cultures

Heterosexual women trust mating-relevant advice received from gay men more than that received from heterosexual women. This trust is predicated on women's perception that gay men lack ulterior sexual motives and romantically pursue other gay men. However, this trust may not hold in all cultures. For example, in both Samoa and the Istmo Zapotec of Southern Mexico, women take part in mate competition against feminine same-sex attracted males-referred to as fa'afafine and muxe, respectively-who regularly engage in sexual activity with masculine men. The present studies sought to replicate and extend research on women's trust in males who are same-sex attracted. Experiments were conducted in Canada, Samoa, and the Istmo Zapotec, with women randomly assigned to consider the likelihood of various mate-poaching behaviors performed by either a rival woman or a same-sex attracted male. In Canada, women were more trusting of cisgender gay men than other women. Similarly, Samoan women were more trusting of fa'afafine than other women. In the Istmo Zapotec, women were equally distrustful of women and feminine muxe gunaa, whereas more masculine muxe nguiiu were rated as more trustworthy than women and muxe gunaa. These results illustrate that women's trust in same-sex attracted males varies both between and within cultural contexts, perhaps impacted by the relative femininity of the male in question.

No country for old gay men: Age and sexuality category intersection renders older gay men invisible

Four studies analyzed how sexual orientation (heterosexual vs. gay) and age categories (young vs. elderly) referring to men are cognitively combined. In Study 1, young gay men were judged as more prototypical of gay men than adult or elderly gay men, while young, adult, and elderly heterosexual men were perceived as equally prototypical of heterosexual men. In Study 2, gay men were stereotyped more by young rather than elderly stereotypical traits, while heterosexual men were not stereotyped in terms of age. In Study 3, elderly men were stereotyped more by heterosexual than gay-stereotypical traits, while young men were not stereotyped in terms of sexual orientation. In Study 4, gay men were judged to be young rather than elderly, while elderly men were judged to be heterosexual rather than gay. Overall, elderly gay men were overlooked when processing their constituent categories, “gay” and “elderly” men. Implications for models of intersectionality are discussed.