1
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Fořt J, Flegr J, Kuba R, Kaňková Š. Fertility of Czech Gay and Straight Men, Women, and Their Relatives: Testing the Sexually Antagonistic Gene Hypothesis. ARCHIVES OF SEXUAL BEHAVIOR 2024; 53:1747-1761. [PMID: 38472605 PMCID: PMC11106150 DOI: 10.1007/s10508-024-02827-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/10/2023] [Revised: 02/02/2024] [Accepted: 02/05/2024] [Indexed: 03/14/2024]
Abstract
One proposal for the persistence of homosexuality in the human population is the sexually antagonistic gene hypothesis, which suggests that the lower fertility of homosexual individuals, especially men, may be compensated by higher fertility of their relatives of the opposite sex. To test this hypothesis, we have collected data from 7,312 heterosexual men, 459 gay men, 3,352 heterosexual women, and 79 lesbian women mainly from Czechia. In an online survey, participants answered questions regarding their own as well as their parents' and grandparents' fertility. For men, we obtained no significant results except for higher fertility of gay men's paternal grandmothers, but the magnitude of this effect was very small. For the female sample, we recorded lower fertility of lesbian women's mothers and fathers. In line with our expectations, both gay men and lesbian women had lower fertility rates than their heterosexual counterparts. Our results are consistent with recent studies which likewise do not support the sexually antagonistic gene hypothesis.
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Affiliation(s)
- Jakub Fořt
- Department of Zoology, Faculty of Science, Charles University, Viničná 7, 128 00, Prague, Czechia.
| | - Jaroslav Flegr
- Department of Philosophy and History of Science, Faculty of Science, Charles University, Prague, Czechia
| | - Radim Kuba
- Department of Philosophy and History of Science, Faculty of Science, Charles University, Prague, Czechia
- Department of Biology Education, Faculty of Science, Charles University, Prague, Czechia
| | - Šárka Kaňková
- Department of Philosophy and History of Science, Faculty of Science, Charles University, Prague, Czechia
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2
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Raymond M, Turek D, Crochet PA. Testing Fraternal Birth Order Effects and Antagonistic Effects for Homosexual Men: Power Comparison of Various Methods. ARCHIVES OF SEXUAL BEHAVIOR 2024:10.1007/s10508-024-02820-w. [PMID: 38438815 DOI: 10.1007/s10508-024-02820-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/23/2023] [Revised: 01/19/2024] [Accepted: 01/20/2024] [Indexed: 03/06/2024]
Abstract
Research on the biological determinants of male homosexual preference has long realized that the older brother effect (FBOE, i.e., a higher fraternal birth rank of homosexuals) and the antagonist effect (AE, i.e., more fertile women have a higher chance of having a homosexual son) can both generate family data where homosexual men have more siblings and more older siblings than heterosexual men. Various statistical approaches were proposed in the recent literature to evaluate whether the action of FBOE or AE could be discriminated from empirical data, by controlling for the other effect. Here, we used simulated data to formally compare all the approaches that we could find in the relevant literature for their ability to reject the null hypothesis in the presence of a specified alternative hypothesis (tests based on regression, Bayesian modeling, or contingency tables). When testing for the FBOE, the relative performance of the different tests was different depending on the specific function generating the older brother effect. Even if no tests were found to always perform better than the others, some tests performed systematically poorly, and some tests displayed a systematic high rate of type-I error. For testing the AE, the relative performance of the tests was generally not changed across all parameter values assayed, providing a clear ranking of the various proposed approaches. Pros and cons for each candidate test are discussed, taking into consideration power and the rate of type-I error but also practicability, the possibility to control for confounding variables, and to consider alternative hypotheses.
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Affiliation(s)
- Michel Raymond
- Institut des Sciences de l'Evolution, University of Montpellier, CNRS, EPHE, IRD, place E. Bataillon, 34095, Montpellier, France.
| | - Daniel Turek
- Department of Mathematics, Lafayette College, Easton, PA, USA
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3
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Bartlett NT, Morin JR, Hurd PL. Does the Fraternal Birth Order Effect Influence Handedness? ARCHIVES OF SEXUAL BEHAVIOR 2024; 53:205-211. [PMID: 37415027 DOI: 10.1007/s10508-023-02649-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/08/2022] [Revised: 06/11/2023] [Accepted: 06/12/2023] [Indexed: 07/08/2023]
Abstract
The fraternal birth order effect (FBOE) is the phenomenon whereby the probability that a man has a same-sex sexual orientation in adulthood increases with each biological older brother. Several studies have found evidence that the FBOE is limited to right-handed men, and left-handed men do not show an FBOE. Recent debates about the appropriate methods for quantifying the FBOE center on distinguishing the FBOE from other effects, such as the female fecundity effect (FFE), whereby mothers more prone to bearing gay sons are also more fecund. The FBOE and FFE are confounded in that a real FFE will result in data consistent with the FBOE under some analyses. Here, we applied some recent proposed analytic methods for the FBOE to the property of handedness. A straightforward application of Khovanova's technique to the binary trait of handedness yielded support for a fraternal birth order effect consistent with the maternal immune hypothesis, in that the ratios of handedness differed between men with one older brother only, and men with one younger brother only, while no such effect was seen in women. This effect was not seen, however, when the confounding effects of parental age were controlled for. Models including factors to simultaneously test multiple posited effects find significant female fecundity effects, as well as paternal age and birth order effects on handedness in men, but no FBOE. The effects seen in women were different, with no fecundity or parental age effects, but birth order and sex of older siblings had effects. We conclude, based on this evidence, that many of the factors thought to contribute to sexual orientation in men may also have an influence on handedness, and further note that parental age is a potential confound which may be overlooked by some analyses of the FBOE.
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Affiliation(s)
- Nathan T Bartlett
- Department of Psychology, University of Alberta, Edmonton, AB, T6G 2E9, Canada
| | - Janessa R Morin
- Department of Psychology, University of Alberta, Edmonton, AB, T6G 2E9, Canada
| | - Peter L Hurd
- Department of Psychology, University of Alberta, Edmonton, AB, T6G 2E9, Canada.
- Neuroscience and Mental Health Institute, University of Alberta, Edmonton, AB, Canada.
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4
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Semenyna SW, Gómez Jiménez FR, VanderLaan DP, Vasey PL. Male androphilia, fraternal birth order, and female fecundity in Samoa: A 10-y retrospective. Proc Natl Acad Sci U S A 2023; 120:e2313284120. [PMID: 38048455 PMCID: PMC10723044 DOI: 10.1073/pnas.2313284120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2023] [Accepted: 10/25/2023] [Indexed: 12/06/2023] Open
Abstract
Two separate but related literatures have examined familial correlates of male androphilia (i.e., sexual attraction and arousal to masculine adult males). The fraternal birth order effect (FBOE) is a widely established finding that each biological older brother a male has increased the probability of androphilia 20-35% above baseline rates. Other family demographic variables, such as reproduction by mothers, maternal aunts, and grandmothers, have been used to test evolutionary hypotheses that sexually antagonistic genes lead to androphilia among males, lowering or eliminating reproduction, which is offset by greater reproductive output among their female relatives. These proposed female fecundity effects (FFEs), and the FBOE, have historically been treated as separate yet complementary ways to understand the development and evolution of male androphilia. However, this approach ignores a vital confound within the data. The high overall reproductive output indicative of an FFE results in similar statistical patterns as the FBOE, wherein women with high reproductive output subsequently produce later-born androphilic sons. Thus, examination of the FBOE requires analytic approaches capable of controlling for the FFE, and vice-versa. Here, we present data simultaneously examining the FBOE and FFE for male androphilia in a large dataset collected in Samoa across 10 y of fieldwork, which only shows evidence of the FBOE.
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Affiliation(s)
| | - Francisco R. Gómez Jiménez
- Centre for Culture and Evolution, Department of Life Sciences, Brunel University London, LondonUB8 3PH, United Kingdom
| | - Doug P. VanderLaan
- Department of Psychology, University of Toronto, Mississauga, ONL5L 1C6, Canada
| | - Paul L. Vasey
- Department of Neuroscience, University of Lethbridge, Lethbridge, ABT1K 3M4, Canada
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5
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Raymond M, Crochet PA. Carving Non-Proximal Explanations for Same-Sex Sexual Orientation. ARCHIVES OF SEXUAL BEHAVIOR 2023; 52:3007-3012. [PMID: 36469147 DOI: 10.1007/s10508-022-02497-z] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/14/2022] [Revised: 11/19/2022] [Accepted: 11/21/2022] [Indexed: 06/17/2023]
Affiliation(s)
- Michel Raymond
- CNRS, EPHE, IRD, Institut des Sciences de l'Evolution, Univ Montpellier, Place E. Bataillon, 34095, Montpellier Cedex 05, France.
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6
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VanderLaan DP, Skorska MN, Peragine DE, Coome LA. Carving the Biodevelopment of Same-Sex Sexual Orientation at Its Joints. ARCHIVES OF SEXUAL BEHAVIOR 2023; 52:2939-2962. [PMID: 35960401 DOI: 10.1007/s10508-022-02360-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/31/2022] [Revised: 05/30/2022] [Accepted: 06/04/2022] [Indexed: 06/15/2023]
Abstract
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.
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Affiliation(s)
- Doug P VanderLaan
- Department of Psychology, University of Toronto Mississauga, 3359 Mississauga Road, Mississauga, ON, L5L 1C6, Canada.
- Child and Youth Psychiatry, Centre for Addiction and Mental Health, Toronto, ON, Canada.
| | - Malvina N Skorska
- Child and Youth Psychiatry, Centre for Addiction and Mental Health, Toronto, ON, Canada
| | - Diana E Peragine
- Department of Psychology, University of Toronto Mississauga, 3359 Mississauga Road, Mississauga, ON, L5L 1C6, Canada
| | - Lindsay A Coome
- Department of Psychology, University of Toronto Mississauga, 3359 Mississauga Road, Mississauga, ON, L5L 1C6, Canada
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7
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Luoto S. Understanding the Biodevelopment of Sexual Orientation Requires a Multilevel Evolutionary Analysis. ARCHIVES OF SEXUAL BEHAVIOR 2023; 52:3001-3006. [PMID: 36575266 DOI: 10.1007/s10508-022-02515-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/27/2022] [Revised: 12/19/2022] [Accepted: 12/20/2022] [Indexed: 06/17/2023]
Affiliation(s)
- Severi Luoto
- School of Population Health, University of Auckland, 1023, Auckland, New Zealand.
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8
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Vilsmeier JK, Kossmeier M, Voracek M, Tran US. The fraternal birth-order effect as a statistical artefact: convergent evidence from probability calculus, simulated data, and multiverse meta-analysis. PeerJ 2023; 11:e15623. [PMID: 37609443 PMCID: PMC10441532 DOI: 10.7717/peerj.15623] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2021] [Accepted: 06/01/2023] [Indexed: 08/24/2023] Open
Abstract
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.
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Affiliation(s)
- Johannes K. Vilsmeier
- Department of Cognition, Emotion, and Methods in Psychology, Faculty of Psychology, University of Vienna, Vienna, Austria
| | - Michael Kossmeier
- Department of Cognition, Emotion, and Methods in Psychology, Faculty of Psychology, University of Vienna, Vienna, Austria
| | - Martin Voracek
- Department of Cognition, Emotion, and Methods in Psychology, Faculty of Psychology, University of Vienna, Vienna, Austria
| | - Ulrich S. Tran
- Department of Cognition, Emotion, and Methods in Psychology, Faculty of Psychology, University of Vienna, Vienna, Austria
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9
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Blanchard R, Skorska MN. New Data on Birth Order in Homosexual Men and Women and a Reply to Vilsmeier et al. (2021a, 2021b). ARCHIVES OF SEXUAL BEHAVIOR 2022; 51:3319-3349. [PMID: 35713755 DOI: 10.1007/s10508-022-02362-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/18/2022] [Revised: 05/28/2022] [Accepted: 06/06/2022] [Indexed: 06/15/2023]
Abstract
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.
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Affiliation(s)
- Ray Blanchard
- Department of Psychiatry, University of Toronto, Toronto, ON, M5T 1R8, Canada.
| | - Malvina N Skorska
- Child and Youth Psychiatry, Centre for Addiction and Mental Health, Toronto, ON, Canada
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10
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Semenyna SW, Gómez Jiménez FR, Vasey PL. Confounds, Causality, and Sexual Orientation: The Implications of a Population-Level Study of Sibling Characteristics and Same-Sex Attraction. JOURNAL OF SEX RESEARCH 2022; 59:690-696. [PMID: 35040379 DOI: 10.1080/00224499.2021.1990199] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Representative samples, and especially population samples, are coveted sources of high-quality data in psychological science. In their recent article, Ablaza et al. (2021) used a population sample of marriages and registered partnerships in the Netherlands to examine the relationships between sibling characteristics and sexual orientation. We discuss the implications of this work for understanding the fraternal and sororal birth order effects on male and female same-sex attraction, and how both relate to maternal reproduction. The causal assumptions of these findings are explored, as well as the necessity of population-level data, and whether the data presented by Ablaza et al. are truly representative of the Dutch population.
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Affiliation(s)
| | | | - Paul L Vasey
- Department of Psychology, University of Lethbridge
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11
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Ablaza C, Kabátek J, Perales F. Are Sibship Characteristics Predictive of Same Sex Marriage? An Examination of Fraternal Birth Order and Female Fecundity Effects in Population-level Administrative Data from the Netherlands. JOURNAL OF SEX RESEARCH 2022; 59:671-683. [PMID: 35040387 DOI: 10.1080/00224499.2021.1974330] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Despite historical increases in the number of individuals engaging in same-sex relations and entering same-sex unions, the causes of sexual orientation remain an open question. Two biological processes that have received some degree of empirical validation are the fraternal birth-order effect (FBOE) and the female-fecundity effect (FFE). Respectively, these processes posit that having a greater number of older brothers and being part of larger sibships independently increase the odds of male homosexuality. Nevertheless, previous studies have relied on suboptimal data and methods, including underpowered and selected samples, and models that fail to fully disentangle the two processes. In addition, they have rarely analyzed samples of women. We address these limitations using high-quality, population-level linked register data from the Netherlands (n = 9,073,496). Applying a novel multivariable approach, we jointly examine the FBOE and FFE by comparing the sibship characteristics of men (n = 26,542) and women (n = 33,534) who entered a same-sex union against those who did not (n = 4,607,785 men and 4,405,635 women). Our analyses yield robust evidence of an FBOE on both male and female homosexuality, but no support for the FFE. Additionally, we find that individuals' birth order affects the probability of entering a same-sex union, regardless of the sex of older siblings.
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Affiliation(s)
- Christine Ablaza
- School of Social Science, Faculty of Humanities and Social Sciences, The University of Queensland, St Lucia
- , ARC Centre of Excellence for Children and Families over the Life Course
| | - Jan Kabátek
- , ARC Centre of Excellence for Children and Families over the Life Course
- Melbourne Institute of Applied Economic and Social Research, The University of Melbourne
- Institute of Labor Economics (IZA)
- CentER, Tilburg University
| | - Francisco Perales
- School of Social Science, Faculty of Humanities and Social Sciences, The University of Queensland, St Lucia
- , ARC Centre of Excellence for Children and Families over the Life Course
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12
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Blanchard R. A Novel Method for Studying the Effect of Older Brothers on Sexual Orientation and Its Robustness to Stopping Rule Distortions. JOURNAL OF SEX RESEARCH 2022; 59:684-689. [PMID: 35040381 DOI: 10.1080/00224499.2021.1984379] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
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.
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13
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Blanchard R. Estimation of the Fraternal Birth Order Effect in the UK Biobank Data Reported by Abé et al. (2021). ARCHIVES OF SEXUAL BEHAVIOR 2021; 50:1853-1858. [PMID: 34014431 DOI: 10.1007/s10508-021-02041-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/08/2021] [Revised: 04/26/2021] [Accepted: 05/06/2021] [Indexed: 06/12/2023]
Affiliation(s)
- Ray Blanchard
- Department of Psychiatry, University of Toronto, Toronto, ON, M5T 1R8, Canada.
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14
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Blanchard R, Beier KM, Gómez Jiménez FR, Grundmann D, Krupp J, Semenyna SW, Vasey PL. Meta-Analyses of Fraternal and Sororal Birth Order Effects in Homosexual Pedophiles, Hebephiles, and Teleiophiles. ARCHIVES OF SEXUAL BEHAVIOR 2021; 50:779-796. [PMID: 32895872 DOI: 10.1007/s10508-020-01819-3] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/09/2020] [Revised: 07/19/2020] [Accepted: 08/05/2020] [Indexed: 06/11/2023]
Abstract
This study investigated the relations between numbers of older brothers, numbers of older sisters, and the odds of homosexuality in later-born males, including males who are most attracted sexually to prepubescent or early pubescent children (pedohebephiles) and males who are most attracted sexually to adults (teleiophiles). The authors meta-analyzed data from 24 samples of homosexual and heterosexual men, originally reported in 18 studies, and totaling 18,213 subjects. The results confirmed that older brothers increase the odds of same-sex preference in pedohebephiles as they do in teleiophiles. They also replicated the recent finding that older sisters have a similar but weaker statistical association with the odds of homosexuality. These findings have two theoretical implications. First, the findings for older brothers and older sisters indicate some commonality in the factors that influence sexual preference in teleiophiles and those that influence sexual preference in pedohebephiles. Second, the finding for older sisters confirms a prediction stemming from the hypothesis that male fetuses stimulate maternal antibodies that increase the odds of homosexuality in later-born males. Such immunization could result from miscarried as well as full-term fetuses, and number of older sisters should correlate with number of male fetuses miscarried before gestation of the subject.
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Affiliation(s)
- Ray Blanchard
- Department of Psychiatry, University of Toronto, Toronto, ON, M5T 1R8, Canada.
| | - Klaus M Beier
- Department of Health and Human Sciences, Institute of Sexology and Sexual Medicine, Charité-Universitätsmedizin Berlin, Berlin, Germany
| | | | - Dorit Grundmann
- Department of Health and Human Sciences, Institute of Sexology and Sexual Medicine, Charité-Universitätsmedizin Berlin, Berlin, Germany
| | - Jurian Krupp
- Department of Health and Human Sciences, Institute of Sexology and Sexual Medicine, Charité-Universitätsmedizin Berlin, Berlin, Germany
| | - Scott W Semenyna
- Department of Psychology, University of Lethbridge, Lethbridge, AB, Canada
| | - Paul L Vasey
- Department of Psychology, University of Lethbridge, Lethbridge, AB, Canada
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15
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Blanchard R, Lippa RA. Reassessing the Effect of Older Sisters on Sexual Orientation in Men. ARCHIVES OF SEXUAL BEHAVIOR 2021; 50:797-805. [PMID: 33025292 DOI: 10.1007/s10508-020-01840-6] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/09/2020] [Revised: 09/10/2020] [Accepted: 09/11/2020] [Indexed: 06/11/2023]
Abstract
This research reanalyzed questionnaire data from 8279 homosexual and 79,519 heterosexual men who participated in 2005 in an internet-based research project sponsored by the British Broadcasting Corporation. It focused on parameters of sibship composition (older brothers, older sisters, younger siblings) previously shown or hypothesized to influence sexual orientation in males. The results included the usual finding that older brothers increase the odds of homosexuality in later-born males. As predicted, older sisters also increase those odds, although by a lesser amount than older brothers. Other results confirmed that the odds of homosexuality are increased in only-children, the amount of increase being equal to that produced by one older brother and greater than that produced by one older sister. Finally, the results indicated that younger siblings have no effect on the odds of homosexuality in males. These results might be explained by the hypothesis that two different types of immune responses in pregnant women can affect the future sexual orientation of their male fetuses. One type of response affects fetuses in first pregnancies and reduces subsequent fertility. The other type affects fetuses in later pregnancies and has little or no effect on fertility. Finally, we conducted an estimate of combined sibship effects. Men who were exposed to any of the influences that we identified (being an only-child or having an older sibling) had 27% greater odds of homosexuality than did subjects who were exposed to none of these influences (i.e., the first-born of two or more children).
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Affiliation(s)
- Ray Blanchard
- Department of Psychiatry, University of Toronto, Toronto, ON, M5T 1R8, Canada.
| | - Richard A Lippa
- Department of Psychology, California State University, Fullerton, CA, USA
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16
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Skorska MN, Coome LA, Saokhieo P, Kaewthip O, Chariyalertsak S, VanderLaan DP. Handedness and Birth Order Among Heterosexual Men, Gay Men, and Sao Praphet Song in Northern Thailand. ARCHIVES OF SEXUAL BEHAVIOR 2020; 49:2431-2448. [PMID: 32623540 DOI: 10.1007/s10508-020-01774-z] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/07/2019] [Revised: 06/10/2020] [Accepted: 06/12/2020] [Indexed: 06/11/2023]
Abstract
Previous research has examined handedness and birth order to inform sexual orientation and gender identity/role expression development; however, sexual orientation and gender identity/role expression have rarely been disentangled to provide a more nuanced perspective. In Thailand, we investigated sexual orientation and gender identity simultaneously via comparison of 282 heterosexual men, 201 gay men, and 178 sao praphet song-i.e., androphilic, markedly feminine males recognized as a "third" gender. Handedness was examined as: extremely left-handed, moderately left-handed, ambidextrous, moderately right-handed, or extremely right-handed. Birth order was examined as numbers of older and younger brothers and sisters, by using Berglin's, fraternal, and sororal indices, and by examining the older brother odds ratio and sibling sex ratio. Compared with heterosexual men, gay men and sao praphet song were more likely to be extremely right-handed. Sao praphet song were also more likely to be extremely left-handed than heterosexual and gay men. Heterosexual men and sao praphet song had later sororal birth order compared with the expected Thai population value, suggesting stopping rules influenced when probands' mothers ceased having children. These findings provide new insights and replicate previous findings in a non-Western sample. Regarding handedness, in males, mechanisms related to extreme right-handedness likely influence the development of androphilia, whereas mechanisms related to both extreme right- and extreme left-handedness likely explain the combination of androphilia and feminine gender identity/role expression. Regarding birth order, similar to the conclusions of some prior research, stopping rules pose a challenge for testing the fraternal birth order effect.
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Affiliation(s)
- Malvina N Skorska
- Department of Psychology, University of Toronto Mississauga, 3359 Mississauga Road North, Mississauga, ON, L5L 1C6, Canada
| | - Lindsay A Coome
- Department of Psychology, University of Toronto Mississauga, 3359 Mississauga Road North, Mississauga, ON, L5L 1C6, Canada
| | - Pongpun Saokhieo
- Research Institute of Health Sciences, Chiang Mai University, Chiang Mai, Thailand
| | - Oranitcha Kaewthip
- Research Institute of Health Sciences, Chiang Mai University, Chiang Mai, Thailand
| | - Suwat Chariyalertsak
- Research Institute of Health Sciences, Chiang Mai University, Chiang Mai, Thailand
- Faculty of Public Health, Chiang Mai University, Chiang Mai, Thailand
| | - Doug P VanderLaan
- Department of Psychology, University of Toronto Mississauga, 3359 Mississauga Road North, Mississauga, ON, L5L 1C6, Canada.
- Child and Youth Psychiatry, Centre for Addiction and Mental Health, Toronto, ON, Canada.
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