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Fořt J, Kunc B, Valentova JV, Bártová K, Hudáčová K. Examining the Fraternal Birth Order Effect and Sexual Orientation: Insights from an East European Population. ARCHIVES OF SEXUAL BEHAVIOR 2024; 53:2905-2922. [PMID: 38869747 PMCID: PMC11335834 DOI: 10.1007/s10508-024-02892-8] [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: 03/20/2023] [Revised: 05/05/2024] [Accepted: 05/07/2024] [Indexed: 06/14/2024]
Abstract
The development of human sexual orientation remains a complex and multifaceted subject. It is often studied but its origins continue to elude us. In this preregistered study, our primary objective was to demonstrate the fraternal birth order effect (FBOE), which assumes a higher prevalence of older brothers in gay men than in their straight counterparts and which has also been recently recorded in lesbian women. Our second aim was to explore any potential impact of the FBOE on anal-erotic role orientation (AERO), both in gay and straight men. Our study sample included 693 gay men, 843 straight men, 265 lesbian women, and 331 straight women from Czechia and Slovakia. Employing a conventionally parameterized logistic regression model, we substantiated the FBOE among both gay men (OR = 1.35 for maternal older brothers) and lesbian women (OR = 1.71). These outcomes were confirmed by a more nuanced parameterization recently proposed by Blanchard (2022). Nonmaternal older brothers did not exhibit a significant influence on their younger brothers' sexual orientation. Contrary to some earlier reports, however, our data did not establish the FBOE as exclusive to gay men with the receptive AERO. Furthermore, our observations indicated a lower offspring count for mothers of gay men compared to mothers of straight men. Emphasizing the positive FBOE outcomes, we acknowledge the need for caution regarding the various options that can be used to estimate the familial influences on sexual orientation.
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Affiliation(s)
- Jakub Fořt
- Department of Zoology, Faculty of Science, Charles University, Viničná 7, 128 00, Prague, Czechia.
- Department of Psychology, Faculty of Arts, Charles University, Prague, Czechia.
| | - Benjamin Kunc
- Department of Neurosciences, Faculty of Medicine, KU Leuven, Leuven, Belgium
| | | | - Klára Bártová
- Department of Psychology and Life Sciences, Faculty of Humanities, Charles University, Prague, Czechia
- National Institute of Mental Health, Klecany, Czechia
| | - Kateřina Hudáčová
- Department of Psychology, Faculty of Arts, Charles University, Prague, Czechia
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2
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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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3
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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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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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5
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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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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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Lerch BA, Servedio MR. Indiscriminate Mating and the Coevolution of Sex Discrimination and Sexual Signals. Am Nat 2023; 201:E56-E69. [PMID: 36957998 DOI: 10.1086/723213] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
AbstractThe presence of same-sex sexual behavior across the animal kingdom is often viewed as unexpected. One explanation for its prevalence in some taxa is indiscriminate mating-a strategy wherein an individual does not attempt to determine the sex of its potential partner before attempting copulation. Indiscriminate mating has been argued to be the ancestral mode of sexual reproduction and can also be an optimal strategy given search costs of choosiness. Less attention has been paid to the fact that sex discrimination requires not just the attempt to differentiate between the sexes but also some discernible difference (a signal or cue) that can be detected. To address this, we extend models of mating behavior to consider the coevolution of sex discrimination and sexual signals. We find that under a wide range of parameters, including some with relatively minor costs, indiscriminate mating and the absence of sexual signals will be an evolutionary end point. Furthermore, the absence of both sex discrimination and sexual signals is always evolutionarily stable. These results suggest that an observable difference between the sexes likely arose as a by-product of the evolution of different sexes, allowing discrimination to evolve.
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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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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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Jain S, Rana M. Alternative Sexual Orientation in Humans: What Is Known and What Needs to Be Known Further. JOURNAL OF HOMOSEXUALITY 2022; 69:1004-1029. [PMID: 33788667 DOI: 10.1080/00918369.2021.1898805] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
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.
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Affiliation(s)
- Sidhant Jain
- Department of Zoology, University of Delhi, Delhi, India
| | - Meenakshi Rana
- Department of Zoology, University of Delhi, Delhi, India
- Dyal Singh College, University of Delhi, Delhi, India
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Apostolou M. The Direct Reproductive Cost of Same-Sex Attraction: Evidence from Two Nationally Representative U.S. Samples. ARCHIVES OF SEXUAL BEHAVIOR 2022; 51:1857-1864. [PMID: 35377112 DOI: 10.1007/s10508-021-02199-y] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/15/2019] [Revised: 10/16/2021] [Accepted: 10/16/2021] [Indexed: 06/14/2023]
Abstract
Same-sex attraction is associated with a direct reproductive cost, i.e., a reduced number of biological children. The current study aimed to assess this cost for different forms of sexual attraction (i.e., only attracted to opposite sex, mostly attracted to opposite sex, equally attracted to both sexes, mostly attracted to same-sex, only attracted to same-sex), using two large nationally representative datasets (N = 15,208) from the USA. The results indicated that same-sex attraction was associated with substantial loss in direct reproductive output. More specifically, significant differences between the different types of same-sex attraction were found: Exclusive and mostly homosexual orientation identities were associated with the highest direct reproductive cost, while mostly attracted to opposite sex orientation and bisexuality identities were associated with lower direct reproductive costs. In addition, bisexual women did not differ significantly from exclusively heterosexual women in terms of their reproductive output. The implications of these findings for the evolutionary origins of same-sex attraction are further discussed.
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Affiliation(s)
- Menelaos Apostolou
- Department of Social Sciences, University of Nicosia, 46 Makedonitissas Ave., 1700, Nicosia, Cyprus.
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12
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Gómez Jiménez FR, Vasey PL. Facial Attractiveness of the Sisters of Istmo Zapotec Men and Muxes: Implications for the Evolution of Male Androphilia. JOURNAL OF SEX RESEARCH 2022; 59:354-359. [PMID: 34213985 DOI: 10.1080/00224499.2021.1943737] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Research shows that the female relatives of androphilic (i.e., sexually attracted to adult males) males have more children than the female relatives of gynephilic (i.e., sexually attracted to adult females) males. The mechanisms by which this occurs are unclear. The hypergyny hypothesis suggests that the female relatives of androphilic males have elevated attractiveness which allows them to obtain male partners with higher socioeconomic status, which in turn, provide them with more resources to produce and sustain multiple offspring. We tested whether the female kin of male androphiles are characterized by elevated attractiveness compared to the female kin of male gynephiles. The research was conducted among the Istmo Zapotec from Oaxaca, Mexico, where androphilic males are recognized as a third gender, muxes. We recruited 115 gynephilic men who rated the facial attractiveness of 27 women with at least one muxe sibling and 27 women with only gynephilic male siblings (i.e., control sisters). The results showed that gynephilic men found the faces of control sisters more attractive than the faces of muxe sisters. This finding is inconsistent with the hypergyny hypothesis and suggests that elevated facial attractiveness is not the mechanism by which the female relatives of androphilic males achieve elevated reproduction.
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Affiliation(s)
| | - Paul L Vasey
- Department of Psychology, University of Lethbridge
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13
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Bai FY, Han DY, Duan SF, Wang QM. The Ecology and Evolution of the Baker's Yeast Saccharomyces cerevisiae. Genes (Basel) 2022; 13:230. [PMID: 35205274 PMCID: PMC8871604 DOI: 10.3390/genes13020230] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2021] [Revised: 01/24/2022] [Accepted: 01/25/2022] [Indexed: 01/01/2023] Open
Abstract
The baker's yeast Saccharomyces cerevisiae has become a powerful model in ecology and evolutionary biology. A global effort on field survey and population genetics and genomics of S. cerevisiae in past decades has shown that the yeast distributes ubiquitously in nature with clearly structured populations. The global genetic diversity of S. cerevisiae is mainly contributed by strains from Far East Asia, and the ancient basal lineages of the species have been found only in China, supporting an 'out-of-China' origin hypothesis. The wild and domesticated populations are clearly separated in phylogeny and exhibit hallmark differences in sexuality, heterozygosity, gene copy number variation (CNV), horizontal gene transfer (HGT) and introgression events, and maltose utilization ability. The domesticated strains from different niches generally form distinct lineages and harbor lineage-specific CNVs, HGTs and introgressions, which contribute to their adaptations to specific fermentation environments. However, whether the domesticated lineages originated from a single, or multiple domestication events is still hotly debated and the mechanism causing the diversification of the wild lineages remains to be illuminated. Further worldwide investigations on both wild and domesticated S. cerevisiae, especially in Africa and West Asia, will be helpful for a better understanding of the natural and domestication histories and evolution of S. cerevisiae.
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Affiliation(s)
- Feng-Yan Bai
- State Key Laboratory of Mycology, Institute of Microbiology, Chinese Academy of Sciences, Chaoyang District, Beijing 100101, China; (D.-Y.H.); (S.-F.D.)
- College of Life Sciences, University of Chinese Academy of Sciences, Shijingshan District, Beijing 100049, China
| | - Da-Yong Han
- State Key Laboratory of Mycology, Institute of Microbiology, Chinese Academy of Sciences, Chaoyang District, Beijing 100101, China; (D.-Y.H.); (S.-F.D.)
| | - Shou-Fu Duan
- State Key Laboratory of Mycology, Institute of Microbiology, Chinese Academy of Sciences, Chaoyang District, Beijing 100101, China; (D.-Y.H.); (S.-F.D.)
| | - Qi-Ming Wang
- School of Life Sciences, Institute of Life Sciences and Green Development, Hebei University, Baoding 071002, China;
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Cezar L, Pisaneschi F, Valentova JV, Delval I. Interações sexuais entre indivíduos do mesmo sexo: um olhar evolucionista. PSICOLOGIA USP 2022. [DOI: 10.1590/0103-6564e210068] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Resumo Sob uma perspectiva evolutiva, as interações sexuais entre indivíduos do mesmo sexo foram por muito tempo consideradas um grande paradoxo. Isso por terem persistido no decorrer das gerações apesar de supostamente não oferecerem benefícios reprodutivos diretos, reduzindo, aparentemente, a aptidão individual. Apesar disso, são comuns em muitas espécies animais. Neste artigo, revisaremos algumas das hipóteses funcionais que tentam resolver esse quebra-cabeça evolutivo. Algumas dessas hipóteses consideram essas interações adaptativas, o que significa que trariam benefícios para os indivíduos. Outras as consideram neutras, derivadas de características realmente vantajosas. Por fim, existem as que consideram essas interações como não-adaptativas e potencialmente prejudiciais aos indivíduos. Ao final, abordaremos uma hipótese revolucionária que, de forma inédita, questiona se as interações sexuais envolvendo exclusivamente indivíduos de sexos diferentes seriam realmente o estado basal do comportamento sexual.
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15
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Harper JA, Janicke T, Morrow EH. Systematic review reveals multiple sexually antagonistic polymorphisms affecting human disease and complex traits. Evolution 2021; 75:3087-3097. [PMID: 34723381 PMCID: PMC9299215 DOI: 10.1111/evo.14394] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2021] [Revised: 08/30/2021] [Accepted: 10/10/2021] [Indexed: 01/17/2023]
Abstract
An evolutionary model for sex differences in disease risk posits that alleles conferring higher risk in one sex may be protective in the other. These sexually antagonistic (SA) alleles are predicted to be maintained at frequencies higher than expected under purifying selection against unconditionally deleterious alleles, but there are apparently no examples in humans. Discipline-specific terminology, rather than a genuine lack of such alleles, could explain this disparity. We undertook a two-stage review of evidence for SA polymorphisms in humans using search terms from (i) evolutionary biology and (ii) biomedicine. Although the first stage returned no eligible studies, the second revealed 51 genes with sex-opposite effects; 22 increased disease risk or severity in one sex but protected the other. Those with net positive effects occurred at higher frequencies. None were referred to as SA. Our review reveals significant communication barriers to fields as a result of discipline-specific terminology.
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Affiliation(s)
- Jon Alexander Harper
- Evolution, Behaviour and Environment Group, School of Life SciencesUniversity of SussexBrightonBN1 9QGUnited Kingdom
| | - Tim Janicke
- Centre d’Écologie Fonctionnelle et Évolutive, UMR 5175, CNRSUniversité de Montpellier, École Pratique des Hautes ÉtudesMontpellier34293France
- Applied ZoologyTechnical University DresdenDresden01062Germany
| | - Edward H. Morrow
- Department of Environmental and Life SciencesKarlstad UniversityKarlstadSE‐65188Sweden
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Kanazawa S, Larere A. Infertility and same-sex attraction in women. Int J Gynaecol Obstet 2021; 158:528-543. [PMID: 34796501 DOI: 10.1002/ijgo.14035] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2021] [Accepted: 11/17/2021] [Indexed: 11/07/2022]
Abstract
A polygyny hypothesis of female sexual fluidity proposes that women may have been evolutionarily selected to be sexually fluid, in order to have occasional sex with their cowives in polygynous marriage to reduce tension and conflict inherent in such marriage, while at the same time reproducing children with their husbands. Among others, the hypothesis predicts that women who are biologically (but not surgically) infertile would experience greater same-sex attraction. Biological infertility stems from natural, evolutionarily familiar causes such as menopause, whereas surgical infertility stems from artificial, evolutionarily novel causes such as tubal ligation or hysterectomy. Consistent with the prediction, the analyses of the National Survey of Family Growth data showed that biological infertility, but not surgical infertility, was significantly associated with same-sex self-identified labels, behavior and sexual attraction in women. Biological infertility nearly doubled the odds of women having engaged in same-sex behavior and the number of same-sex partners in the last 12 months and nearly tripled the number of same-sex partners in life. In sharp contrast, biological infertility was not associated (and surgical infertility was significantly negatively associated) with same-sex attraction in men.
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Affiliation(s)
- Satoshi Kanazawa
- Department of Management, London School of Economics and Political Science, London, UK
| | - Adrien Larere
- Department of Management, London School of Economics and Political Science, London, UK
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17
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Zietsch BP, Sidari MJ, Abdellaoui A, Maier R, Långström N, Guo S, Beecham GW, Martin ER, Sanders AR, Verweij KJH. Genomic evidence consistent with antagonistic pleiotropy may help explain the evolutionary maintenance of same-sex sexual behaviour in humans. Nat Hum Behav 2021; 5:1251-1258. [PMID: 34426668 DOI: 10.1038/s41562-021-01168-8] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2019] [Accepted: 06/18/2021] [Indexed: 01/31/2023]
Abstract
Human same-sex sexual behaviour (SSB) is heritable, confers no immediately obvious direct reproductive or survival benefit and can divert mating effort from reproductive opportunities. This presents a Darwinian paradox: why has SSB been maintained despite apparent selection against it? We show that genetic effects associated with SSB may, in individuals who only engage in opposite-sex sexual behaviour (OSB individuals), confer a mating advantage. Using results from a recent genome-wide association study of SSB and a new genome-wide association study on number of opposite-sex sexual partners in 358,426 individuals, we show that, among OSB individuals, genetic effects associated with SSB are associated with having more opposite-sex sexual partners. Computer simulations suggest that such a mating advantage for alleles associated with SSB could help explain how it has been evolutionarily maintained. Caveats include the cultural specificity of our UK and US samples, the societal regulation of sexual behaviour in these populations, the difficulty of measuring mating success and the fact that measured variants capture a minority of the total genetic variation in the traits.
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Affiliation(s)
- Brendan P Zietsch
- Centre for Psychology and Evolution, School of Psychology, University of Queensland, Brisbane, Queensland, Australia.
| | - Morgan J Sidari
- Centre for Psychology and Evolution, School of Psychology, University of Queensland, Brisbane, Queensland, Australia
| | - Abdel Abdellaoui
- Department of Psychiatry, Amsterdam UMC location AMC, University of Amsterdam, Amsterdam, the Netherlands
| | - Robert Maier
- Department of Genetics, Harvard Medical School, Boston, MA, USA
| | - Niklas Långström
- Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden
| | - Shengru Guo
- Department of Human Genetics, University of Miami, Miami, FL, USA
| | - Gary W Beecham
- Department of Human Genetics, University of Miami, Miami, FL, USA
| | - Eden R Martin
- Department of Human Genetics, University of Miami, Miami, FL, USA
| | - Alan R Sanders
- Department of Psychiatry and Behavioral Sciences, NorthShore University HealthSystem Research Institute, Evanston, IL, USA.,Department of Psychiatry and Behavioral Neuroscience, University of Chicago, Chicago, IL, USA
| | - Karin J H Verweij
- Department of Psychiatry, Amsterdam UMC location AMC, University of Amsterdam, Amsterdam, the Netherlands
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18
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Zietsch BP. More Evidence and Context Are Needed to Evaluate the Possibility That Scent Perception Is Part of the Same-Sex Sexual Behavior Story. ARCHIVES OF SEXUAL BEHAVIOR 2021; 50:2313-2315. [PMID: 31646403 DOI: 10.1007/s10508-019-01562-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/25/2019] [Revised: 10/03/2019] [Accepted: 10/09/2019] [Indexed: 06/10/2023]
Affiliation(s)
- Brendan P Zietsch
- Centre for Psychology and Evolution, School of Psychology, University of Queensland, Brisbane, 4072, Australia.
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19
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Parental Investment Is Biased toward Children Named for Their Fathers. HUMAN NATURE-AN INTERDISCIPLINARY BIOSOCIAL PERSPECTIVE 2021; 32:387-405. [PMID: 34228304 DOI: 10.1007/s12110-021-09396-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 04/05/2021] [Indexed: 10/20/2022]
Abstract
Namesaking (naming a child after a parent or other relative) can be viewed as a mechanism to increase perceived parent-child similarity and, consequently, parental investment. Male and, to a lesser extent, firstborn children are more frequently namesakes than female and later-born children, respectively. However, a direct link between namesaking and parental investment has not been examined. In the present study, 632 participants (98 men and 534 women) from Central Europe indicated their first name, sex, birth order, number of siblings, sexual orientation, socioeconomic status, paternal and maternal first names, as well as relationship quality with, and time and financial investment they received from, both parents during childhood. Mixed-effects models revealed associations between namesaking and parental investment. However, the effect of namesaking often appeared significant only in interaction with specific predictors, such as sex and primogeniture. It suggests instead that namesaking has an additive effect-it enhances the effect of biological factors on parental investment. In general, we found evidence for the bias in parental investment linked to name similarity among both parents, and support for the hypothesis that namesaking serves as a mechanism to increase paternity confidence and, thus, paternal investment. The effect of namesaking influences only certain types of parental investment-namely, those at the level of relationship quality. In addition, nonheterosexual orientation was the strongest negative predictor of paternal investment. Our study extends the research on parental investment by showing that cultural mechanisms, such as namesaking, can also exert some influence on parental rearing behavior.
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20
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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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21
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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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22
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Han DY, Han PJ, Rumbold K, Koricha AD, Duan SF, Song L, Shi JY, Li K, Wang QM, Bai FY. Adaptive Gene Content and Allele Distribution Variations in the Wild and Domesticated Populations of Saccharomyces cerevisiae. Front Microbiol 2021; 12:631250. [PMID: 33679656 PMCID: PMC7925643 DOI: 10.3389/fmicb.2021.631250] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2020] [Accepted: 01/26/2021] [Indexed: 11/29/2022] Open
Abstract
Recent studies on population genomics of Saccharomyces cerevisiae have substantially improved our understanding of the genetic diversity and domestication history of the yeast. However, the origin of the domesticated population of S. cerevisiae and the genomic changes responsible for ecological adaption of different populations and lineages remain to be fully revealed. Here we sequenced 64 African strains from various indigenous fermented foods and forests in different African countries and performed a population genomic analysis on them combined with a set of previously sequenced worldwide S. cerevisiae strains representing the maximum genetic diversity of the species documented so far. The result supports the previous observations that the wild and domesticated populations of S. cerevisiae are clearly separated and that the domesticated population diverges into two distinct groups associated with solid- and liquid-state fermentations from a single ancestor. African strains are mostly located in basal lineages of the two domesticated groups, implying a long domestication history of yeast in Africa. We identified genes that mainly or exclusively occur in specific groups or lineages and genes that exhibit evident group or lineage specific allele distribution patterns. Notably, we show that the homing endonuclease VDE is generally absent in the wild but commonly present in the domesticated lineages of S. cerevisiae. The genes with group specific allele distribution patterns are mostly enriched in functionally similar or related fundamental metabolism processes, including the evolutionary conserved TOR signaling pathway.
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Affiliation(s)
- Da-Yong Han
- State Key Laboratory of Mycology, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China.,College of Life Sciences, University of Chinese Academy of Sciences, Beijing, China
| | - Pei-Jie Han
- State Key Laboratory of Mycology, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China
| | - Karl Rumbold
- School of Molecular and Cell Biology, University of the Witwatersrand, Johannesburg, South Africa
| | - Anbessa Dabassa Koricha
- State Key Laboratory of Mycology, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China.,College of Life Sciences, University of Chinese Academy of Sciences, Beijing, China.,Department of Biology, College of Natural Sciences, Jimma University, Jimma, Ethiopia
| | - Shou-Fu Duan
- State Key Laboratory of Mycology, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China.,College of Life Sciences, University of Chinese Academy of Sciences, Beijing, China
| | - Liang Song
- State Key Laboratory of Mycology, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China.,College of Life Sciences, University of Chinese Academy of Sciences, Beijing, China
| | - Jun-Yan Shi
- State Key Laboratory of Mycology, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China.,College of Life Sciences, University of Chinese Academy of Sciences, Beijing, China
| | - Kuan Li
- State Key Laboratory of Mycology, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China
| | - Qi-Ming Wang
- State Key Laboratory of Mycology, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China
| | - Feng-Yan Bai
- State Key Laboratory of Mycology, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China.,College of Life Sciences, University of Chinese Academy of Sciences, Beijing, China
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23
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Swaab DF, Wolff SEC, Bao AM. Sexual differentiation of the human hypothalamus: Relationship to gender identity and sexual orientation. HANDBOOK OF CLINICAL NEUROLOGY 2021; 181:427-443. [PMID: 34238476 DOI: 10.1016/b978-0-12-820683-6.00031-2] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Gender identity (an individual's perception of being male or female) and sexual orientation (heterosexuality, homosexuality, or bisexuality) are programmed into our brain during early development. During the intrauterine period in the second half of pregnancy, a testosterone surge masculinizes the fetal male brain. If such a testosterone surge does not occur, this will result 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 and can result in gender dysphoria. Nature produces a great variability for all aspects of sexual differentiation of the brain. Mechanisms involved in sexual differentiation of the brain include hormones, genetics, epigenetics, endocrine disruptors, immune response, and self-organization. Furthermore, structural and functional differences in the hypothalamus relating to gender dysphoria and sexual orientation are described in this review. All the genetic, postmortem, and in vivo scanning observations support the neurobiological theory about the origin of gender dysphoria, i.e., it is the sizes of brain structures, the neuron numbers, the molecular composition, functions, and connectivity of brain structures that determine our gender identity or sexual orientation. There is no evidence that one's postnatal social environment plays a crucial role in the development of gender identity or sexual orientation.
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Affiliation(s)
- Dick F Swaab
- Department Neuropsychiatric Disorders, Netherlands Institute for Neuroscience, An Institute of the Royal Netherlands Academy of Arts and Sciences, Amsterdam, The Netherlands
| | - Samantha E C Wolff
- Department Neuropsychiatric Disorders, Netherlands Institute for Neuroscience, An Institute of the Royal Netherlands Academy of Arts and Sciences, Amsterdam, The Netherlands
| | - Ai-Min Bao
- Department of Neurobiology and Department of Neurology of the Second Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, China; NHC and CAMS Key Laboratory of Medical Neurobiology, School of Brain Science and Brain Medicine, Zhejiang University, Hangzhou, China.
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24
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Skorska MN, Coome LA, Zahran A, Peragine DE, VanderLaan DP. Facial Attractiveness of Sisters of Thai Gay Men and Sao Praphet Song. JOURNAL OF SEX RESEARCH 2021; 58:116-121. [PMID: 32239969 DOI: 10.1080/00224499.2020.1742858] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Androphilia refers to sexual attraction toward adult males. Androphilic males' female genetic relatives might offset the fitness cost of androphilia by having elevated numbers of offspring. Increased attractiveness relative to other women may enable these females to marry up the social hierarchy, providing greater access to resources to support more offspring. In Thailand, there is a marked status hierarchy and male androphiles are highly visible - identifying as gay men or as a third gender known as sao praphet song. Thus, a field experiment was conducted in which 208 heterosexual men rated the facial attractiveness of 25 sisters of Thai gay men or sao praphet song and 25 comparison women with no known same-sex attracted relatives. Contrary to the prediction, the comparison group was rated as more attractive than the sisters, casting doubt on hypotheses that posit greater attractiveness of female relatives of male androphiles as a proximate mechanism facilitating the evolutionary maintenance of genes influencing male androphilia. Also, men from rural areas rated the women, regardless of group, as more attractive than men from urban areas, consistent with some prior studies showing rural-urban differences in perceptions of attractiveness.
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Affiliation(s)
| | | | - Adhm Zahran
- Department of Psychology, University of Toronto Mississauga
| | | | - Doug P VanderLaan
- Department of Psychology, University of Toronto Mississauga
- Child and Youth Psychiatry, Centre for Addiction and Mental Health
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25
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Ciani AC, Capiluppi C. Gene Flow by Selective Emigration as a Possible Cause for Personality Differences between Small Islands and Mainland Populations. EUROPEAN JOURNAL OF PERSONALITY 2020. [DOI: 10.1002/per.774] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Whether personality differences exist between populations is a controversial question. Even though such differences can be measured, it is still not clear whether they are due to individual phenotypic responses to the environment or whether they have a genetic influence. In a population survey we compared the personality traits of inhabitants of an Italian archipelago (the three Egadi islands; N = 622) with those of the closest mainland population (Trapani area; N = 106) and we found that personality differences between small populations can be detected. Islanders scored significantly lower on the personality traits of openness to experience and extraversion and higher on conscientiousness. We suggest that these personality trait differences could be an adaptive response to a confined socio–environmental niche, genetically produced by a strong, non–random gene flow in the last 20–25 generations, rather than the flexible response of islanders to environmental variables. To test this hypothesis, we compared subsets of the islander population classified by ancestry, birthplace, immigration and emigration and found that differences in extraversion can be accounted for by gene flow, while openness to experience and conscientiousness can also be accounted for by some gene–environment interactions. We propose a Personality Gene Flow hypothesis suggesting that, in small isolated communities, whenever there is strong, non–random emigration, paired with weak and random immigration, we can expect rapid genetic personality change within the population. Copyright © 2010 John Wiley & Sons, Ltd.
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26
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Camperio Ciani AS, Capiluppi C, Veronese A, Sartori G. The adaptive value of personality differences revealed by small island population dynamics. EUROPEAN JOURNAL OF PERSONALITY 2020. [DOI: 10.1002/per.595] [Citation(s) in RCA: 92] [Impact Index Per Article: 23.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Whether differences in personality among populations really exist and, if so, whether they are only due to cultural and linguistic differences or have a genetically selected adaptive value, is a controversial issue. In this research, we compared three Italian populations living on three small archipelagos in the Tyrrhenian Sea (n = 993), with their corresponding neighbouring mainlanders (n = 598), i.e. sharing the same geographical origin, culture and language. We used an adjective‐based Big Five questionnaire in order to measure personality traits in four categories of individuals for each archipelago/mainland population: (1) original islanders; (2) non‐original islanders; (3) mainlanders and (4) immigrants to the islands. We further analysed original and non‐original islanders who had or had not emigrated from the islands. We found that islanders had different personality traits from mainlanders, the former being more conscientious and emotionally stable and less extraverted and open to experience. We also found that the subgroup of islanders whose ancestors had inhabited their island for about 20 generations in isolation (original islanders, n = 624) were less extraverted and open to experience than immigrants (n = 193). In contrast, immigrants retained the typical personality profile of the mainland populations. Lastly, emigrants from the islands (n = 209) were significantly more extraverted and open to experience than original and non‐original islanders who had never left their island (n = 741). We hypothesise that population differences in extraversion and openness to experience are more probably related to genetic differences which evolved rapidly, presumably through an active gene flow produced by selective emigration from the islands. Copyright © 2006 John Wiley & Sons, Ltd.
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Affiliation(s)
| | - Claudio Capiluppi
- Department of Psychology and Cultural Anthropology, University of Verona, Lungadige Porta Vittoria 17, 37129 Verona, Italy
| | - Antonio Veronese
- Department of Medicine and Public Health, University of Verona, Piazzale Scuro 10, 37134 Verona, Italy
| | - Giuseppe Sartori
- Department of General Psychology, University of Padova, Via Venezia 8, 35131 Padova, Italy
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27
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Colledani D, Camperio Ciani A. A Worldwide Internet Study Based on Implicit Association Test Revealed a Higher Prevalence of Adult Males' Androphilia than Ever Reported Before. J Sex Med 2020; 18:4-16. [PMID: 33250358 DOI: 10.1016/j.jsxm.2020.09.011] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2019] [Revised: 07/18/2020] [Accepted: 09/28/2020] [Indexed: 11/15/2022]
Abstract
BACKGROUND Social constrictions or the lack of a clear awareness about one's sexual orientation may influence the ability of individuals to explicitly declare their sexual preferences. Thus, the actual prevalence of males' sexual attraction toward adult males, which is estimated by studies relying only on explicit questionnaires, may be biased. Conversely, the implicit measurement of androphilia may be a promising method to obtain more reliable data. AIM In the present work, explicit and implicit methods have been used to investigate the rates of explicit nonheterosexuality and implicit androphilia in a large sample of adult males from all around the world. For implicit androphilia, a rate consistent across the continents and close to that predicted by recent genetic models (about 15%) was expected. In contrast, for self-declared homosexuality, a lower and more variable rate was expected. METHODS A sample of 1,050 participants was recruited through an online platform. All participants completed a short biographical questionnaire, an Autobiographical-Implicit Association Test, the Sexual Preference-Implicit Association Test, and an explicit measure of sexual orientation. The answers to these measures were used to explore explicit sexual orientation and implicit androphilia across six main geographical areas (Middle East and Africa, South America, North America, Asia, Europe, and Oceania). OUTCOMES The main outcome measures were the D score at the Sexual Preference-Implicit Association Test and the scores at the explicit measure of sexual orientation. RESULTS The rate of nonheterosexuality, which can be found using explicit measures, is rather low, variable (from 6.3% to 11.4%), and influenced by cultural factors. In contrast, the prevalence of androphilia resulting from implicit methods is higher and consistent across geographical areas (from 14.4% to 17.6%). CLINICAL IMPLICATIONS Studying the diffusion of adult males' androphilia may be useful to better understand sexual behaviors and preferences and to develop effective health promotion programs among males who have sex with males. STRENGTHS & LIMITATIONS The large and cross-cultural sample and the use of both implicit and explicit measures allowed for obtaining a detailed picture of adult males' sexual orientation and androphilia. The main limitations were the Web-based characteristics of the protocol and the lack of an investigation of actual sexual behaviors. CONCLUSION Compared with the explicit measurement of nonheterosexuality, the implicit measurement of sexual preferences showed a prevalence of androphilia among adult males that is higher, more stable across continents, and more consistent with the predictions of recent genetic models. Colledani D,A. Camperio Ciani Worldwide Internet Study Based on Implicit Association Test Revealed a Higher Prevalence of Adult Males' Androphilia than Ever Reported Before. J Sex Med 2021;18:4-16.
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Affiliation(s)
- Daiana Colledani
- Department of Philosophy, Sociology, Education and Applied Psychology - School of Psychology, University of Padua, Padua, Italy
| | - Andrea Camperio Ciani
- Department of Philosophy, Sociology, Education and Applied Psychology - School of Psychology, University of Padua, Padua, Italy.
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28
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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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29
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Gómez Jiménez FR, Semenyna SW, Vasey PL. The relationship between fraternal birth order and childhood sex‐atypical behavior among the Istmo Zapotec
muxes. Dev Psychobiol 2020; 62:792-803. [DOI: 10.1002/dev.21987] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2020] [Revised: 04/14/2020] [Accepted: 04/15/2020] [Indexed: 12/22/2022]
Affiliation(s)
| | - Scott W. Semenyna
- Department of Psychology University of Lethbridge Lethbridge Alberta Canada
| | - Paul L. Vasey
- Department of Psychology University of Lethbridge Lethbridge Alberta Canada
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Blanchard R, Krupp J, VanderLaan DP, Vasey PL, Zucker KJ. A method yielding comparable estimates of the fraternal birth order and female fecundity effects in male homosexuality. Proc Biol Sci 2020; 287:20192907. [PMID: 32183625 PMCID: PMC7126035 DOI: 10.1098/rspb.2019.2907] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2019] [Accepted: 02/26/2020] [Indexed: 12/16/2022] Open
Abstract
The fraternal birth order effect (FBOE) is the finding that older brothers increase the probability of homosexuality in later-born males, and the female fecundity effect (FFE) is the finding that the mothers of homosexual males produce more offspring than the mothers of heterosexual males. In a recent paper, Khovanova proposed a novel method for computing independent estimates of these effects on the same samples and expressing the magnitude and direction of the effects in the same metric. In her procedure, only families with one or two sons are examined, and daughters are ignored. The present study investigated the performance of Khovanova's method using archived data from 10 studies, comprising 14 samples totalling 5390 homosexual and heterosexual subjects. The effect estimate for the FBOE showed that an increase from zero older brothers to one older brother is associated with a 38% increase in the odds of homosexuality. By contrast, the effect estimate for the FFE showed that the increase from zero younger brothers to one younger brother is not associated with any increase in the odds of homosexuality. The former result supports the maternal immune hypothesis of male homosexuality; the latter result does not support the balancing selection hypothesis.
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Affiliation(s)
- Ray Blanchard
- Department of Psychiatry, University of Toronto, Toronto, Ontario, Canada
| | - Jurian Krupp
- Department of Health and Human Sciences, Institute of Sexology and Sexual Medicine, Charité-Universitätsmedizin Berlin, Berlin, Germany
| | - Doug P. VanderLaan
- Department of Psychology, University of Toronto Mississauga, Mississauga, Ontario, Canada
| | - Paul L. Vasey
- Department of Psychology, University of Lethbridge, Lethbridge, Alberta, Canada
| | - Kenneth J. Zucker
- Department of Psychiatry, University of Toronto, Toronto, Ontario, Canada
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Gómez Jiménez FR, Semenyna SW, Vasey PL. Offspring Production Among the Relatives of Istmo Zapotec Men and Muxes. ARCHIVES OF SEXUAL BEHAVIOR 2020; 49:581-594. [PMID: 31897830 DOI: 10.1007/s10508-019-01611-y] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/17/2018] [Revised: 12/12/2019] [Accepted: 12/14/2019] [Indexed: 06/10/2023]
Abstract
Male androphilia (i.e., sexual attraction toward adult males) is influenced by biological factors, reliably occurs across diverse cultures, and has persisted over evolutionary time despite the fact that it reduces reproduction. One possible solution to this evolutionary paradox is the sexually antagonistic gene hypothesis (SAGH), which states that genes associated with male androphilia reduce reproduction when present in males but increase reproduction when present in their female relatives. The present study tested the SAGH among the Istmo Zapotec-a non-Euro-American culture in Oaxaca, Mexico, where transgender and cisgender androphilic males are known as muxe gunaa and muxe nguiiu, respectively. To test the SAGH, we compared offspring production by the biological relatives of muxe gunaa (n = 115), muxe nguiiu (n = 112), and gynephilic men (i.e., cisgender males who are sexually attracted to adult females; n = 171). The mothers and paternal aunts of muxe gunaa had higher offspring production than those of muxe nguiiu. Additionally, the relatives of muxe gunaa had more offspring than those of gynephilic men, whereas no such differences were found between the families of gynephilic men and muxe nguiiu. Elevated reproduction by the mothers and, particularly the aunts, of muxe gunaa is consistent with the SAGH. However, the absence of group differences between gynephilic men and muxe nguiiu, and the group differences between the two types of muxes are not predicted by the SAGH. This is the first study to demonstrate reproductive differences between kin of transgender and cisgender androphilic males within the same non-Euro-American culture.
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Affiliation(s)
- Francisco R Gómez Jiménez
- Department of Psychology, University of Lethbridge, 4401 University Drive, Lethbridge, AB, T1K 3M4, Canada.
| | - Scott W Semenyna
- Department of Psychology, University of Lethbridge, 4401 University Drive, Lethbridge, AB, T1K 3M4, Canada
| | - Paul L Vasey
- Department of Psychology, University of Lethbridge, 4401 University Drive, Lethbridge, AB, T1K 3M4, Canada
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Apostolou M. Does Fraternal Birth Order Predict Male Homosexuality, Bisexuality, and Heterosexual Orientation with Same-Sex Attraction? Evidence from a Greek-Speaking Sample from Greece. ARCHIVES OF SEXUAL BEHAVIOR 2020; 49:575-579. [PMID: 31119421 DOI: 10.1007/s10508-019-01466-3] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/29/2018] [Revised: 05/08/2019] [Accepted: 05/10/2019] [Indexed: 06/09/2023]
Abstract
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.
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Affiliation(s)
- Menelaos Apostolou
- Department of Social Sciences, University of Nicosia, 46 Makedonitissas Ave., 1700, Nicosia, Cyprus.
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Nila S, Crochet PA, Barthes J, Rianti P, Juliandi B, Suryobroto B, Raymond M. Male Homosexual Preference: Femininity and the Older Brother Effect in Indonesia. EVOLUTIONARY PSYCHOLOGY 2019; 17:1474704919880701. [PMID: 31742436 PMCID: PMC10358421 DOI: 10.1177/1474704919880701] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2019] [Accepted: 09/13/2019] [Indexed: 09/09/2023] Open
Abstract
Male homosexual preference (MHP) is an evolutionary enigma because it is partially heritable and imposes a fertility cost. In occidental societies, homosexual men are feminized at various levels and they have more older brothers than heterosexual men. To evaluate whether femininity and the fraternal birth order (FBO) effect are universal features of MHP or not, we collected original data from homosexual men, heterosexual men, and heterosexual women from Java (Indonesia). Facial photographs were used to test whether homosexual faces are feminized when compared with heterosexual ones. We found that faces manipulated to resemble the average face of homosexual men are perceived as facially feminized, suggesting that homosexual men are facially feminized compared to heterosexual men, although a higher facial femininity was not captured by morphological analyses. Then, family data were used to detect differences in siblings' composition between homosexuals and heterosexuals. Homosexual men displayed a higher number of older brothers than heterosexual men, even when sibship size was controlled for, suggesting that the FBO effect exists in Indonesian populations. Independent of sexual orientation, men with older brothers seem more feminized than those without older brothers, consistent with the immune origin of the FBO effect. In conclusion, MHP in Indonesia is partially feminized and they have more older brothers. Such features are also associated with MHP in other cultural contexts, suggesting a cross-cultural effect of men homosexual preference. An evolutionary explanation is available for the feminizing effect, although the FBO effect remains unexplained even if proximal mechanisms start to be identified.
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Affiliation(s)
- Sarah Nila
- Department of Biology, Faculty of Mathematics and Natural Sciences, IPB University (Bogor Agricultural University), Indonesia
| | - Pierre-Andre Crochet
- CEFE, CNRS, Université de Montpellier, Université Paul-Valéry Montpellier, EPHE, France
| | - Julien Barthes
- ISEM, Université de Montpellier, CNRS, IRD, EPHE, France
| | - Puji Rianti
- Department of Biology, Faculty of Mathematics and Natural Sciences, IPB University (Bogor Agricultural University), Indonesia
| | - Berry Juliandi
- Department of Biology, Faculty of Mathematics and Natural Sciences, IPB University (Bogor Agricultural University), Indonesia
| | - Bambang Suryobroto
- Department of Biology, Faculty of Mathematics and Natural Sciences, IPB University (Bogor Agricultural University), Indonesia
| | - Michel Raymond
- ISEM, Université de Montpellier, CNRS, IRD, EPHE, France
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Luoto S, Krams I, Rantala MJ. A Life History Approach to the Female Sexual Orientation Spectrum: Evolution, Development, Causal Mechanisms, and Health. ARCHIVES OF SEXUAL BEHAVIOR 2019; 48:1273-1308. [PMID: 30229521 DOI: 10.1007/s10508-018-1261-0] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/15/2017] [Revised: 05/29/2018] [Accepted: 06/14/2018] [Indexed: 05/12/2023]
Abstract
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.
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Affiliation(s)
- Severi Luoto
- English, Drama and Writing Studies, University of Auckland, Arts 1, Building 206, Room 616, 14A Symonds St., Auckland, 1010, New Zealand.
- School of Psychology, University of Auckland, Auckland, New Zealand.
| | - Indrikis Krams
- Department of Zoology and Animal Ecology, University of Latvia, Riga, Latvia
- Institute of Ecology and Earth Sciences, University of Tartu, Tartu, Estonia
| | - Markus J Rantala
- Department of Biology & Turku Brain and Mind Center, University of Turku, Turku, Finland
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Swift-Gallant A, Coome LA, Aitken M, Monks DA, VanderLaan DP. Evidence for distinct biodevelopmental influences on male sexual orientation. Proc Natl Acad Sci U S A 2019; 116:12787-12792. [PMID: 31182568 PMCID: PMC6600923 DOI: 10.1073/pnas.1809920116] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Several biological mechanisms have been proposed to influence male sexual orientation, but the extent to which these mechanisms cooccur is unclear. Putative markers of biological processes are often used to evaluate the biological basis of male sexual orientation, including fraternal birth order, handedness, and familiality of same-sex sexual orientation; these biomarkers are proxies for immunological, endocrine, and genetic mechanisms. Here, we used latent profile analysis (LPA) to assess whether these biomarkers cluster within the same individuals or are present in different subgroups of nonheterosexual men. LPA defined four profiles of men based on these biomarkers: 1) A subgroup who did not have these biomarkers, 2) fraternal birth order, 3) handedness, and 4) familiality. While the majority of both heterosexual and nonheterosexual men were grouped in the profile that did not have any biomarker, the three profiles associated with a biomarker were composed primarily of nonheterosexual men. We then evaluated whether these subgroups differed on measures of gender nonconformity and personality that reliably show male sexual orientation differences. The subgroup without biomarkers was the most gender-conforming whereas the fraternal birth order subgroup was the most female-typical and agreeable, compared with the other profiles. Together, these findings suggest there are multiple distinct biodevelopmental pathways influencing same-sex sexual orientation in men.
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Affiliation(s)
- Ashlyn Swift-Gallant
- Department of Psychology, Memorial University of Newfoundland, St. John's, NL A1B 3X9, Canada;
| | - Lindsay A Coome
- Department of Psychology, University of Toronto Mississauga, Mississauga, ON L5L 1C6, Canada
| | - Madison Aitken
- Department of Psychiatry, University of Toronto, Toronto, ON M5T 1R8, Canada
- Child, Youth, and Emerging Adult Program, Centre for Addiction and Mental Health, Toronto, ON M6J 1H4, Canada
| | - D Ashley Monks
- Department of Psychology, University of Toronto Mississauga, Mississauga, ON L5L 1C6, Canada
| | - Doug P VanderLaan
- Department of Psychology, University of Toronto Mississauga, Mississauga, ON L5L 1C6, Canada;
- Child and Youth Psychiatry, Centre for Addiction and Mental Health, Toronto, ON M6J 1H4, Canada
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Kanazawa S. Father absence, sociosexual orientation, and same-sex sexuality in women and men. INTERNATIONAL JOURNAL OF PSYCHOLOGY 2019; 55:234-244. [PMID: 30706463 DOI: 10.1002/ijop.12569] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2017] [Accepted: 12/25/2018] [Indexed: 11/09/2022]
Abstract
A recent evolutionary theory of female sexual fluidity suggests that women may not have sexual orientations in the same sense that men do, and that women's apparent sexual orientation may instead be a byproduct of their sociosexual orientation. One developmental factor that has consistently been shown to influence sociosexual orientation is father absence in childhood. Consistent with the prediction of the theory, the analyses of the National Longitudinal Study of Adolescent to Adult Health (Add Health) data show that father absence significantly increases women's, but not men's, same-sex sexuality in adulthood, whether it is measured by self identity, sexual behaviour, or romantic attraction. Further consistent with the theory, the association between father absence and same-sex sexuality in women is entirely mediated by their sociosexual orientation.
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Affiliation(s)
- Satoshi Kanazawa
- Department of Management, London School of Economics and Political Science, London, UK
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37
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Nila S, Barthes J, Crochet PA, Suryobroto B, Raymond M. Kin Selection and Male Homosexual Preference in Indonesia. ARCHIVES OF SEXUAL BEHAVIOR 2018; 47:2455-2465. [PMID: 29797146 DOI: 10.1007/s10508-018-1202-y] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/24/2015] [Revised: 03/14/2018] [Accepted: 03/20/2018] [Indexed: 06/08/2023]
Abstract
Male homosexual preference (MHP) challenges evolutionary thinking because the preference for male-male relationships is heritable, implies a fertility cost (lower offspring number), and is relatively frequent in some societies (2-6% in Western countries) for a costly trait. It has been proposed that individuals with a MHP counterbalance reproductive costs through the transfer of resources to kin, thereby improving their indirect reproduction through kin's reproductive success. This kin selection hypothesis is not supported in Western countries and Japan, although consistent evidence has been obtained in Samoa. In this study, data from Java (Indonesia) were obtained to assess the avuncular tendencies of men with contrasting sexual orientation to measure possible resource transfer. Consistent with the kin selection hypothesis, males with a homosexual orientation reported an increased willingness to transfer resources toward nephews and nieces and declared having transferred more money to nephews and nieces. We developed a method to quantitatively estimate the contribution of kin selection on inclusive reproduction associated to sexual orientation, taking into account various possible biases. Kin selection reduced the direct reproductive cost of homosexual men by 20%, so suggesting that kin selection alone is insufficient to explain the maintenance of male homosexuality. Other potential factors are discussed, as well as the limitations of the study and the social determinant operating for the expression of increased avuncular tendencies of homosexual men.
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Affiliation(s)
- Sarah Nila
- Department of Biology, Faculty of Mathematics and Natural Sciences, Bogor Agricultural University, Bogor, Indonesia
| | - Julien Barthes
- Institute of Evolutionary Sciences, CC065 Université de Montpellier, CNRS, IRD, EPHE, Place Eugène Bataillon, 34095, Montpellier Cedex 05, France
| | - Pierre-Andre Crochet
- CEFE, CNRS, Université de Montpellier - Université Paul-Valéry Montpellier-EPHE, Montpellier Cedex 05, France
| | - Bambang Suryobroto
- Department of Biology, Faculty of Mathematics and Natural Sciences, Bogor Agricultural University, Bogor, Indonesia
| | - Michel Raymond
- Institute of Evolutionary Sciences, CC065 Université de Montpellier, CNRS, IRD, EPHE, Place Eugène Bataillon, 34095, Montpellier Cedex 05, France.
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Fisher AD, Ristori J, Morelli G, Maggi M. The molecular mechanisms of sexual orientation and gender identity. Mol Cell Endocrinol 2018; 467:3-13. [PMID: 28847741 DOI: 10.1016/j.mce.2017.08.008] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/28/2017] [Revised: 08/02/2017] [Accepted: 08/15/2017] [Indexed: 12/21/2022]
Abstract
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.
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Affiliation(s)
- Alessandra D Fisher
- Department of Experimental, Clinical and Biomedical Sciences, Careggi University Hospital, Florence, Italy
| | - Jiska Ristori
- Department of Experimental, Clinical and Biomedical Sciences, Careggi University Hospital, Florence, Italy
| | - Girolamo Morelli
- Department of Surgical, Medical, Molecular and of the Critical Area Pathology, University of Pisa, Pisa, Italy
| | - Mario Maggi
- Department of Experimental, Clinical and Biomedical Sciences, Careggi University Hospital, Florence, Italy.
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Gómez FR, Semenyna SW, Court L, Vasey PL. Familial patterning and prevalence of male androphilia among Istmo Zapotec men and muxes. PLoS One 2018; 13:e0192683. [PMID: 29466410 PMCID: PMC5821324 DOI: 10.1371/journal.pone.0192683] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2017] [Accepted: 11/08/2017] [Indexed: 11/18/2022] Open
Abstract
Male androphilia (i.e., male sexual attraction to other adult males) is known to cluster within families. Some studies demonstrate that male androphilia clusters in both the paternal and maternal familial lines, whereas other studies demonstrated that it clusters only in the latter. Most of these studies were conducted in Euro-American populations where fertility is low and the sexual orientation of male relatives can sometimes be difficult to ascertain. These two factors can potentially confound the results of such studies. To address these limitations, we examined the familial patterning of male androphilia among the Istmo Zapotec of Oaxaca, Mexico--a high fertility, non-Euro-American population where androphilic males are known locally as muxes, a third gender category. The Istmo Zapotec recognize two types of muxes--muxe gunaa and muxe nguiiu--who typify the transgender and cisgender forms of male androphilia, respectively. We compared the familial patterning of male androphilia between muxe gunaa and muxe nguiiu, as well as between gynephilic men and muxes (both cisgender and transgender forms combined). Istmo Zapotec muxe gunaa and muxe nguiiu exhibit similar familial patterning of male androphilia. Overall, muxes were characterized by significantly more muxe relatives than gynephilic men. This familial patterning was equivalent in both the paternal and maternal lines of muxes. The population prevalence rate of male androphilia was estimated to fall between 3.37-6.02% in the Istmo Zapotec. This is the first study that has compared cisgender and transgender androphilic males from the same high fertility population and demonstrated that the two do not differ with respect to the familial patterning of male androphilia.
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Affiliation(s)
- Francisco R. Gómez
- Department of Psychology, University of Lethbridge, Lethbridge, Alberta, Canada
| | - Scott W. Semenyna
- Department of Psychology, University of Lethbridge, Lethbridge, Alberta, Canada
| | - Lucas Court
- Department of Psychology, University of Lethbridge, Lethbridge, Alberta, Canada
| | - Paul L. Vasey
- Department of Psychology, University of Lethbridge, Lethbridge, Alberta, Canada
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Gavrilets S, Friberg U, Rice WR. Understanding Homosexuality: Moving on from Patterns to Mechanisms. ARCHIVES OF SEXUAL BEHAVIOR 2018; 47:27-31. [PMID: 28986707 DOI: 10.1007/s10508-017-1092-4] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/20/2017] [Accepted: 09/26/2017] [Indexed: 06/07/2023]
Affiliation(s)
- Sergey Gavrilets
- Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, TN, 37996, USA.
- Department of Mathematics, University of Tennessee, Knoxville, TN, USA.
- National Institute for Mathematical and Biological Synthesis, University of Tennessee, Knoxville, TN, USA.
| | - Urban Friberg
- IFM Biology, Linkoping University, Linkoping, Sweden
| | - William R Rice
- Department of Ecology, Evolution and Marine Biology, University of California Santa Barbara, Santa Barbara, CA, USA
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Blanchard R. Fraternal Birth Order, Family Size, and Male Homosexuality: Meta-Analysis of Studies Spanning 25 Years. ARCHIVES OF SEXUAL BEHAVIOR 2018; 47:1-15. [PMID: 28608293 DOI: 10.1007/s10508-017-1007-4] [Citation(s) in RCA: 63] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/09/2017] [Revised: 05/15/2017] [Accepted: 05/22/2017] [Indexed: 06/07/2023]
Abstract
The fraternal birth order effect is the tendency for older brothers to increase the odds of homosexuality in later-born males. This study compared the strength of the effect in subjects from small versus large families and in homosexual subjects with masculine versus feminine gender identities. Meta-analyses were conducted on 30 homosexual and 30 heterosexual groups from 26 studies, totaling 7140 homosexual and 12,837 heterosexual males. The magnitude of the fraternal birth order effect was measured with a novel variable, the Older Brothers Odds Ratio, computed as (homosexuals' older brothers ÷ homosexuals' other siblings) ÷ (heterosexuals' older brothers ÷ heterosexuals' other siblings), where other siblings = older sisters + younger brothers + younger sisters. An Older Brothers Odds Ratio of 1.00 represents no effect of sexual orientation; values over 1.00 are positive evidence for the fraternal birth order effect. Evidence for the reliability of the effect was consistent. The Older Brothers Odds Ratio was significantly >1.00 in 20 instances, >1.00 although not significantly in nine instances, and nonsignificantly <1.00 in 1 instance. The pooled Older Brothers Odds Ratio for all samples was 1.47, p < .00001. Subgroups analyses showed that the magnitude of the effect was significantly greater in the 12 feminine or transgender homosexual groups than in the other 18 homosexual groups. There was no evidence that the magnitude of the effect differs according to family size.
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Affiliation(s)
- Ray Blanchard
- Department of Psychiatry, University of Toronto, Toronto, ON, M5T 1R8, Canada.
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Camperio Ciani A, Battaglia U, Cesare L, Camperio Ciani G, Capiluppi C. Possible Balancing Selection in Human Female Homosexuality. HUMAN NATURE-AN INTERDISCIPLINARY BIOSOCIAL PERSPECTIVE 2017; 29:14-32. [DOI: 10.1007/s12110-017-9309-8] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
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Semenyna SW, VanderLaan DP, Petterson LJ, Vasey PL. Familial Patterning and Prevalence of Male Androphilia in Samoa. JOURNAL OF SEX RESEARCH 2017; 54:1077-1084. [PMID: 27593894 DOI: 10.1080/00224499.2016.1218416] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Previous research established that male androphilia (i.e., sexual arousal and attraction to adult males) clusters in families. Some studies find that male androphilia clusters in both the paternal and maternal lines, while others find that it clusters only in the latter. Most of the research investigating the familial nature of male androphilia has taken place in Western cultural contexts that are problematic for such research because they are characterized by low fertility. To address this, our previous work has examined familial patterning of male androphilia in Samoa, a high-fertility population in which androphilic males are readily identified due to their public status as fa'afafine (a third gender category). Building on this work, the present study replicated the familial nature of male androphilia in Samoa using a sample size that was ~122% larger than the one we previously employed (N = 382, M ±SD age: 29.72 years ±10.16). Samoan fa'afafine had significantly more fa'afafine relatives in their maternal and paternal lines compared to Samoan gynephilic males (p < .001). The prevalence of male androphilia was equivalent across both the paternal and maternal lines (all p > .15). The revised prevalence estimate of male androphilia in Samoa falls between 0.61% and 3.51%.
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Affiliation(s)
| | - Doug P VanderLaan
- b Department of Psychology, University of Toronto Mississauga; Underserved Populations Research Program, Child, Youth and Family Division , Centre for Addiction and Mental Health
| | | | - Paul L Vasey
- a Department of Psychology , University of Lethbridge
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Howard RM, Perilloux C. Is mating psychology most closely tied to biological sex or preferred partner's sex? PERSONALITY AND INDIVIDUAL DIFFERENCES 2017. [DOI: 10.1016/j.paid.2016.05.009] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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Semenyna SW, VanderLaan DP, Vasey PL. Birth order and recalled childhood gender nonconformity in Samoan men and fa'afafine. Dev Psychobiol 2017; 59:338-347. [PMID: 28261795 DOI: 10.1002/dev.21498] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2016] [Accepted: 12/10/2016] [Indexed: 11/12/2022]
Abstract
Having a greater than average number of older biological brothers is a robust correlate of male androphilia (i.e., sexual attraction and arousal to adult males). Previous investigations have sought to understand whether this fraternal birth order (FBO) effect is also systematically related to recalled indicators of childhood gender nonconformity (CGN). However, these investigations have relied on data from low-fertility Western populations in which expressions of femininity in male children are routinely stigmatized and consequently, suppressed. The present study examined the FBO effect (among other sibship characteristics) and recalled indicators of CGN in Samoa, a high-fertility population, whose members are relatively tolerant of male femininity. Indeed, Samoans identify feminine androphilic males as belonging to an alternative gender category, known locally as fa'afafine. The present study compared the sibship characteristics of 231 fa'afafine and 231 opposite-sex attracted men from Samoa, as well as how these characteristics related to recalled CGN. Results replicated the well-established FBO effect for predicting male sexual orientation, with each older brother increasing the odds of being androphilic by 21%. However, no relationship was found between the number of older brothers (or other siblings) a participant had and their recalled CGN. Although fa'afafine reported significantly more CGN than Samoan men, CGN did not mediate the FBO effect, nor did the FBO effect and CGN interact to predict male sexual orientation. These findings are consistent with previous studies suggesting that the FBO effect is associated with male sexual orientation, but not childhood female-typical gender expression among androphilic males.
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Affiliation(s)
- Scott W Semenyna
- Department of Psychology, University of Lethbridge, Lethbridge, Alberta, Canada
| | - Doug P VanderLaan
- Department of Psychology, University of Toronto Mississauga, Toronto, Ontario, Canada.,Underserved Populations Research Program, Child, Youth, and Family Division, Center for Addiction and Mental Health, Toronto, Ontario, Canada
| | - Paul L Vasey
- Department of Psychology, University of Lethbridge, Lethbridge, Alberta, Canada
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Semenyna SW, Petterson LJ, VanderLaan DP, Vasey PL. A Comparison of the Reproductive Output Among the Relatives of Samoan Androphilic Fa'afafine and Gynephilic Men. ARCHIVES OF SEXUAL BEHAVIOR 2017; 46:87-93. [PMID: 27785648 DOI: 10.1007/s10508-016-0765-8] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/04/2015] [Revised: 04/22/2016] [Accepted: 04/26/2016] [Indexed: 06/06/2023]
Abstract
The sexually antagonistic gene hypothesis (SAGH) for male androphilia posits that genes associated with androphilia (i.e., sexual attraction to adult males) will result in lowered reproduction when present in males, but increased reproduction when present in females. Findings derived from some Western European samples furnish support for the SAGH; however, results from studies conducted in other regions of the world have been more equivocal. Our previous research in Samoa indicated that the mothers as well as the maternal and paternal grandmothers of androphilic males (known locally as fa'afafine) exhibit elevated reproductive output when compared to the relatives of gynephilic men (i.e., males that are sexually attracted to adult females). The present replication study tested the SAGH in Samoa using a sample that was 122 % larger than the one previously studied by our group (VanderLaan, Forrester, Petterson, & Vasey, 2012). In line with the predictions of the SAGH, we hypothesized that the grandmothers, aunts, and mothers of fa'afafine would show elevated reproductive output compared to those of Samoan gynephilic men. Data were collected from 191 fa'afafine and 191 gynephilic men on the reproductive output of their paternal and maternal biological relatives (i.e., mothers, grandmothers, aunts, uncles). The mothers and maternal grandmothers of fa'afafine showed elevated reproductive output compared to those of gynephilic men. The paternal grandmother effect was not replicated. Although these results are consistent with the SAGH, a lack of difference in the reproductive output of aunts renders support for the SAGH in Samoa equivocal.
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Affiliation(s)
- Scott W Semenyna
- Department of Psychology, University of Lethbridge, C866 University Hall, 4401 University Drive, Lethbridge, AB, T1K 3M4, Canada.
| | - Lanna J Petterson
- Department of Psychology, University of Lethbridge, C866 University Hall, 4401 University Drive, Lethbridge, AB, T1K 3M4, Canada
| | - Doug P VanderLaan
- Department of Psychology, University of Toronto Mississauga, Mississauga, ON, Canada
- Underserved Populations Research Program, Child, Youth and Family Division, Centre for Addiction and Mental Health, Toronto, ON, Canada
| | - Paul L Vasey
- Department of Psychology, University of Lethbridge, C866 University Hall, 4401 University Drive, Lethbridge, AB, T1K 3M4, Canada
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Abstract
Previous research has indicated that biological older brothers increase the odds of androphilia in males. This finding has been termed the fraternal birth order effect. The maternal immune hypothesis suggests that this effect reflects the progressive immunization of some mothers to male-specific antigens involved in fetal male brain masculinization. Exposure to these antigens, as a result of carrying earlier-born sons, is hypothesized to produce maternal immune responses towards later-born sons, thus leading to female-typical neural development of brain regions underlying sexual orientation. Because this hypothesis posits mechanisms that have the potential to be active in any situation where a mother gestates repeated male fetuses, a key prediction is that the fraternal birth order effect should be observable in diverse populations. The present study assessed the association between sexual orientation and birth order in androphilic male-to-female transsexuals in Brazil, a previously unexamined population. Male-to-female transsexuals who reported attraction to males were recruited from a specialty gender identity service in southern Brazil (n=118) and a comparison group of gynephilic non-transsexual men (n=143) was recruited at the same hospital. Logistic regression showed that the transsexual group had significantly more older brothers and other siblings. These effects were independent of one another and consistent with previous studies of birth order and male sexual orientation. The presence of the fraternal birth order effect in the present sample provides further evidence of the ubiquity of this effect and, therefore, lends support to the maternal immune hypothesis as an explanation of androphilic sexual orientation in some male-to-female transsexuals.
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Chaladze G. Heterosexual Male Carriers Could Explain Persistence of Homosexuality in Men: Individual-Based Simulations of an X-Linked Inheritance Model. ARCHIVES OF SEXUAL BEHAVIOR 2016; 45:1705-1711. [PMID: 27067240 DOI: 10.1007/s10508-016-0742-2] [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: 03/23/2015] [Revised: 09/30/2015] [Accepted: 03/15/2016] [Indexed: 06/05/2023]
Abstract
Homosexuality has been documented throughout history and is found in almost all human cultures. Twin studies suggest that homosexuality is to some extent heritable. However, from an evolutionary perspective, this poses a problem: Male homosexuals tend to have on average five times fewer children than heterosexual males, so how can a phenomenon associated with low reproductive success be maintained at relatively stable frequencies? Recent findings of increased maternal fecundity of male homosexuals suggest that the genes responsible for homosexuality in males increase fecundity in the females who carry them. Can an increase in maternal fecundity compensate for the fecundity reduction in homosexual men and produce a stable polymorphism? In the current study, this problem was addressed with an individual-based modeling (IBM) approach. IBM suggests that male homosexuality can be maintained in a population at low and stable frequencies if roughly more than half of the females and half of the males are carriers of genes that predispose the male to homosexuality.
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Affiliation(s)
- Giorgi Chaladze
- Institute of Ecology, Ilia State University, 3/5 Cholokashvili Ave, 0162, Tbilisi, Georgia.
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Kanazawa S. Possible evolutionary origins of human female sexual fluidity. Biol Rev Camb Philos Soc 2016; 92:1251-1274. [PMID: 27196099 DOI: 10.1111/brv.12278] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2015] [Revised: 03/15/2016] [Accepted: 03/17/2016] [Indexed: 11/30/2022]
Abstract
I propose an evolutionary theory of human female sexual fluidity and argue that women may have been evolutionarily designed to be sexually fluid in order to allow them to have sex with their cowives in polygynous marriage and thus reduce conflict and tension inherent in such marriage. In addition to providing an extensive definition and operationalization of the concept of sexual fluidity and specifying its ultimate function for women, the proposed theory can potentially solve several theoretical and empirical puzzles in evolutionary psychology and sex research. Analyses of the National Longitudinal Study of Adolescent Health (Add Health) confirm the theory's predictions that: (i) women (but not men) who experience increased levels of sexual fluidity have a larger number of children (suggesting that female sexual fluidity, if heritable, may be evolutionarily selected); (ii) women (but not men) who experience marriage or parenthood early in adult life subsequently experience increased levels of sexual fluidity; and (iii) sexual fluidity is significantly positively correlated with known markers of unrestricted sexual orientation among women whereas it is significantly negatively correlated with such markers among men.
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Affiliation(s)
- Satoshi Kanazawa
- Managerial Economics and Strategy Group, Department of Management, London School of Economics and Political Science, Houghton Street, London, WC2A 2AE, UK
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