Fertility of Czech Gay and Straight Men, Women, and Their Relatives: Testing the Sexually Antagonistic Gene Hypothesis

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.

Biogenetic ties and parent-child relationships: The misplaced critique

According to an almost axiomatic standard in bioethics, moral commitment should ground parents' relationship with their children, rather than biogenetic relatedness. This standard has been used lately to express skepticism about extending existing assisted reproductive treatments (ARTs) to same-sex couples and to research into novel fertility interventions for those couples, but this skepticism is misplaced on several grounds. As a matter of access and equity, same-sex couples seem presumptively entitled to genetic relatedness to their children as far as possible both in regard to existing ARTs and to novel ARTs under investigation. For those worried about the effects of trying to secure biogenetic relatedness for same-sex couples, it may be noted that same-sex couples will only ever be a fraction of the parents implicated in propping up "biologism," as the expectation of biogenetic relatedness it is sometimes called. The cultural force of biologism would survive almost intact even if no same-sex couples were ever to have genetically related children. It is therefore hard to see why same-sex couples should forfeit aspirations to biogenetic relationships with their children or enjoy less subsidy for ARTs than the subsidy given to different-sex couples. As matter of moral consistency, the full implications of the biologism critique have yet to be evaluated relative to different-sex couples.

Large-scale GWAS reveals insights into the genetic architecture of same-sex sexual behavior

Twin and family studies have shown that same-sex sexual behavior is partly genetically influenced, but previous searches for specific genes involved have been underpowered. We performed a genome-wide association study (GWAS) on 477,522 individuals, revealing five loci significantly associated with same-sex sexual behavior. In aggregate, all tested genetic variants accounted for 8 to 25% of variation in same-sex sexual behavior, only partially overlapped between males and females, and do not allow meaningful prediction of an individual's sexual behavior. Comparing these GWAS results with those for the proportion of same-sex to total number of sexual partners among nonheterosexuals suggests that there is no single continuum from opposite-sex to same-sex sexual behavior. Overall, our findings provide insights into the genetics underlying same-sex sexual behavior and underscore the complexity of sexuality.

Lesbian motherhood and mitochondrial replacement techniques: reproductive freedom and genetic kinship

In this paper, we argue that lesbian couples who wish to have children who are genetically related to both of them should be allowed access to mitochondrial replacement techniques (MRTs). First, we provide a brief explanation of mitochondrial diseases and MRTs. We then present the reasons why MRTs are not, by nature, therapeutic. The upshot of the view that MRTs are non-therapeutic techniques is that their therapeutic potential cannot be invoked for restricting their use only to those cases where a mitochondrial DNA disease could be 'cured'. We then argue that a positive case for MRTs is justified by an appeal to reproductive freedom, and that the criteria to access these techniques should hence be extended to include lesbian couples who wish to share genetic parenthood. Finally, we consider a potential objection to our argument: that the desire to have genetically related kin is not a morally sufficient reason to allow lesbian couples to access MRTs.

An Exploratory Study of Differences in Views of Factors Affecting Sexual Orientation for a Sample of Lesbians and Gay Men

An exploratory study of lesbians (70) and gay men (118) from a rural state in the mid-South was conducted using a self-administered, mail-out survey. The nonrandom sample was drawn from organizational mailing lists, snowball sampling, and a convenience sample at a community event. Respondents were asked to indicate the extent to which each of the following affected sexual orientation: genetics, relationship between parents, relationship with parents, birth order, peers, growing up in a dysfunctional family, growing up in a single-parent family, negative experiences with the opposite sex, and positive experiences with the same sex. Similar to studies of heterosexual men and women, these gay men were more likely to view sexual orientation as a result of genetics than the lesbian respondents. Further, the lesbian group were more likely to view positive relationships with the same sex to have a great influence on sexual orientation. These data indicate there are sex differences in views on factors that affect sexual orientation.

Human homosexuality: a paradigmatic arena for sexually antagonistic selection?

Sexual conflict likely plays a crucial role in the origin and maintenance of homosexuality in our species. Although environmental factors are known to affect human homosexual (HS) preference, sibling concordances and population patterns related to HS indicate that genetic components are also influencing this trait in humans. We argue that multilocus, partially X-linked genetic factors undergoing sexually antagonistic selection that promote maternal female fecundity at the cost of occasional male offspring homosexuality are the best candidates capable of explaining the frequency, familial clustering, and pedigree asymmetries observed in HS male proband families. This establishes male HS as a paradigmatic example of sexual conflict in human biology. HS in females, on the other hand, is currently a more elusive phenomenon from both the empirical and theoretical standpoints because of its fluidity and marked environmental influence. Genetic and epigenetic mechanisms, the latter involving sexually antagonistic components, have been hypothesized for the propagation and maintenance of female HS in the population. However, further data are needed to truly clarify the evolutionary dynamics of this trait.

The biogeography and evolution of female homosexual behavior in Japanese macaques

In certain Japanese macaque (Macaca fuscata) populations, females routinely engage in same-sex courtship, mounting, and consortship activity. Drawing on behavioral, biogeographic, and genetic research, we suggest that female homosexual behavior may be associated with genetically distinct free-ranging populations of Japanese macaques. In addition, we briefly discuss the implications of this research for the evolution of female homosexual behavior in this species.

Genetic and environmental effects on same-sex sexual behavior: a population study of twins in Sweden

There is still uncertainty about the relative importance of genes and environments on human sexual orientation. One reason is that previous studies employed self-selected, opportunistic, or small population-based samples. We used data from a truly population-based 2005-2006 survey of all adult twins (20-47 years) in Sweden to conduct the largest twin study of same-sex sexual behavior attempted so far. We performed biometric modeling with data on any and total number of lifetime same-sex sexual partners, respectively. The analyses were conducted separately by sex. Twin resemblance was moderate for the 3,826 studied monozygotic and dizygotic same-sex twin pairs. Biometric modeling revealed that, in men, genetic effects explained .34-.39 of the variance, the shared environment .00, and the individual-specific environment .61-.66 of the variance. Corresponding estimates among women were .18-.19 for genetic factors, .16-.17 for shared environmental, and 64-.66 for unique environmental factors. Although wide confidence intervals suggest cautious interpretation, the results are consistent with moderate, primarily genetic, familial effects, and moderate to large effects of the nonshared environment (social and biological) on same-sex sexual behavior.

[Prenatal maternal mnemonic effects on the human neuro-psychic sex: a new proposition from fetus-maternal tolerance-rejection]

In approximately 15% of homosexual men, their phenotype is associated to the fraternal birth order. Older biological brothers induce in their mothers anti-male factors (antibodies) that interfere the brain maleness development of younger fetuses. This effect is seldom seen in non-right-handed men and is not seen in women. The influence of older siblings is seen in their sex ratio (SR). In contradiction with previous hypothesis, significant heterogeneities of SR have been found among older siblings of males or females, right or non-right-handed and homo or heterosexual individuals. This can only be understood as if the findings among homosexuals were part of a general mechanism of fetus-maternal tolerance-rejection processes of placental mammals. We found, in relation to ABO and Rh systems and sex, that embryos with genes different from those of their mothers, induced better pregnancies and maternal tolerance than embryos similar to their mothers. Assuming that homo or heterosexuality and right or non-right-handedness behave similar to ABO or Rh alleles, the author provides a speculative interpretation of these results. Homosexual women and especially if they are non-right-handed, are preceded by siblings with a high SR (maternal environment with anti-female or pro-male factors); then lesbianism or non-right-handedness may induce tolerance to be a woman in such anti-female environment. Non-right-handedness could induce tolerance for anti-male factors of mothers, thus preventing the production of gays in a pro-male maternal environment, but leading to the production of non-right-handed gays in anti-male maternal environments. Several new hypotheses and interpretations merge from this new proposition. Also, complete sexual orientation could be acquired after birth.

Religion, genetics, and sexual orientation: the Jewish tradition

This paper probes the implications of a genetic basis for sexual orientation for traditional branches of Judaism, which are struggling with how accepting to be of noncelibate gays and lesbians in their communities. The paper looks at the current attitudes toward homosexuality across the different branches of Judaism; social and cultural factors that work against acceptance; attitudes toward science in Jewish culture; and the likelihood that scientific evidence that sexual orientation is at least partly genetically determined will influence Jewish scholars' and leaders' thinking on this issue.

Sexual orientation in women with classical or non-classical congenital adrenal hyperplasia as a function of degree of prenatal androgen excess

46,XX individuals with classical congenital adrenal hyperplasia (CAH) due to deficiency of the enzyme, 21-hydroxylase, show variable degrees of masculinization of body and behavior due to excess adrenal androgen production. Increased bisexuality and homosexuality have also been reported. This article provides a review of existing reports of the latter and presents a new study aimed at replicating the previous findings with detailed assessments of sexual orientation on relatively large samples, and at extending the investigation to the mildest form, non-classical (NC) CAH. Also, this is the first study to relate sexual orientation to the specific molecular genotypes of CAH. In the present study, 40 salt-wasters (SW), 21 SV (simple-virilizing), 82 NC, and 24 non-CAH control women (sisters and female cousins of CAH women) were blindly administered the Sexual Behavior Assessment Schedule (SEBAS-A, 1983 ed.; H. F. L. Meyer-Bahlburg & A. A. Ehrhardt, Privately printed). Most women were heterosexual, but the rates of bisexual and homosexual orientation were increased above controls not only in women with classical CAH, but also in NC women, and correlated with the degree of prenatal androgenization. Classifying women by molecular genotypes did not further increase the correlation. Diverse aspects of sexual orientation were highly intercorrelated, and principal components analysis yielded one general factor. Bisexual/homosexual orientation was (modestly) correlated with global measures of masculinization of non-sexual behavior and predicted independently by the degree of both prenatal androgenization and masculinization of childhood behavior. We conclude that the findings support a sexual-differentiation perspective involving prenatal androgens on the development of sexual orientation.

Eye color, hair color, blood type, and the rhesus factor: exploring possible genetic links to sexual orientation

The present study sought to expand the limited evidence that sexual orientation is influenced by genetic factors. This was accomplished by seeking statistical differences between heterosexuals and homosexuals for four traits that are known to be genetically determined: eye color, natural hair color, blood type, and the Rhesus factor. Using a sample of over 7,000 U.S. and Canadian college students supplemented with additional homosexual subjects obtained through internet contacts, we found no significant differences between heterosexuals and homosexuals regarding eye color or hair color. In the case of blood type and the Rh factor, however, interesting patterns emerged. Heterosexual males and females exhibited statistically identical frequencies of the A blood type, while gay men exhibited a relatively low incidence and lesbians had a relatively high incidence (p < .05). In the case of the Rh factor, unusually high proportions of homosexuals of both sexes were Rh- when compared to heterosexuals (p < .06). The findings suggest that a connection may exist between sexual orientation and genes both on chromosome 9 (where blood type is determined) and on chromosome 1 (where the Rh factor is regulated).

Reproductive cloning combined with genetic modification

Although there is widespread opposition to reproductive cloning, some have argued that its use by infertile couples to have genetically related children would be ethically justifiable. Others have suggested that lesbian or gay couples might wish to use cloning to have genetically related children. Most of the main objections to human reproductive cloning are based on the child's lack of unique nuclear DNA. In the future, it may be possible safely to create children using cloning combined with genetic modifications, so that they have unique nuclear DNA. The genetic modifications could be aimed at giving such children genetic characteristics of both members of the couple concerned. Thus, cloning combined with genetic modification could be appealing to infertile, lesbian, or gay couples who seek genetically related children who have genetic characteristics of both members. In such scenarios, the various objections to human reproductive cloning that are based on the lack of genetic uniqueness would no longer be applicable. The author argues that it would be ethically justifiable for such couples to create children in this manner, assuming these techniques could be used safely.

The neurodevelopment of human sexual orientation

One of the most enduring and controversial questions in the neuroscience of sexual behaviour surrounds the mechanisms which produce sexual attraction to either males or females. Here, evidence is reviewed which supports the proposal that sexual orientation in humans may be laid down in neural circuitry during early foetal development. Behaviour genetic investigations provide strong evidence for a heritable component to male and female sexual orientation. Linkage studies are partly suggestive of X-linked loci although candidate gene studies have produced null findings. Further evidence demonstrates a role for prenatal sex hormones which may influence the development of a putative network of sexual-orientation-related neural substrates. However, hormonal effects are often inconsistent and investigations rely heavily on 'proxy markers'. A consistent fraternal birth order effect in male sexual orientation also provides support for a model of maternal immunization processes affecting prenatal sexual differentiation. The notion that non-heterosexual preferences may reflect generalized neurodevelopmental perturbations is not supported by available data. These current theories have left little room for learning models of sexual orientation. Future investigations, across the neurosciences, should focus to elucidate the fundamental neural architecture underlying the target-specific direction of human sexual orientation, and their antecedents in developmental neurobiology.

A critical review of recent biological research on human sexual orientation

This article provides a comprehensive review and critique of biological research on sexual orientation published over the last decade. We cover research investigating (a) the neurohormonal theory of sexual orientation (psychoneuroendocrinology, prenatal stress, cerebral asymmetry, neuroanatomy, otoacoustic emissions, anthropometrics), (b) genetic influences, (c) fraternal birth-order effects, and (d) a putative role for developmental instability. Despite inconsistent results across both studies and traits, some support for the neurohormonal theory is garnered, but mostly in men. Genetic research using family and twin methodologies has produced consistent evidence that genes influence sexual orientation, but molecular research has not yet produced compelling evidence for specific genes. Although it has been well established that older brothers increase the odds of homosexuality in men, the route by which this occurs has not been resolved. We conclude with an examination of the limitations of biological research on sexual orientation, including measurement issues (paper and pencil, cognitive, and psychophysiological), and lack of research on women.

The heritability of gender identity disorder in a child and adolescent twin sample

The heritability and prevalence of the gender identity disorder (GID) was examined, as well as its comorbidity with separation anxiety and depression, in a nonretrospective study of child and adolescent twins. The parents of 314 twins (ages 4-17 years; 96 monozygotic pairs [MZ] and 61 dizygotic [DZ] pairs) completed the Coolidge Personality and Neuropsychological Inventory (CPNI) containing a six-item DSM-IV-based GID scale. Prevalence of clinically significant GID symptomatology in the twin sample was estimated to be 2.3%. Univariate model fitting analyses were conducted using an ordinal transformation of the GID scale. The model that best described the data included a significant additive genetic component accounting for 62% of the variance and a nonshared environmental component accounting for the remaining 38% of the variance. Results suggested no heterogeneity in the parameter estimates resulting from age. The correlation between GID and depression was modest, but significant (r = .20; P < .05), whereas the correlation between GID and separation anxiety was nonsignificant (P > .05). Overall, the results support the hypothesis that there is a strong heritable component to GID. The findings may also imply that gender identity may be much less a matter of choice and much more a matter of biology.

Female-to-male transsexual with 47,XXX karyotype

BACKGROUND

There are few reports describing chromosomal abnormalities in transsexuals. In rare cases, transsexualism and sexual chromosomal multiplicity coexist. Six cases of male-to-female transsexuals with 47,XYY chromosomal pattern have been previously reported. We have not encountered any female transsexual cases with 47,XXX karyotype in the literature.

METHODS

A 21-year-old female patient came to our outpatient department with depressive symptoms and suicidal thoughts. On psychiatric interview, she reported that she had feelings of discomfort with her gender identity and had desired to be male since her childhood. Then, we performed cytogenetic investigation using blood culture and G chromosome banding.

RESULTS

Histology and DNA histograms of the patient revealed a chromosomal pattern of 47,XXX.

CONCLUSIONS

We conclude that sexual chromosomal abnormalities in some transsexuals may cause a vulnerability to development of a gender identity disorder.

Birth order and ratio of brothers to sisters in transsexuals

BACKGROUND

As previous studies with homosexual males have revealed a later birth order, more older brothers and more brothers than sisters, this research was extended to a large series of transsexual males and females, some of whom are homosexual.

METHODS

The male sample comprised 442 male-to-female transsexuals, subdivided by sexual partner preference: 106 homosexual, 135 heterosexual, 155 bisexual and 46 asexual. One hundred female-to-male transsexuals were also studied: 75 homosexual, 16 bisexual, seven heterosexual and five asexual. Birth order was computed by both Slater's Index and Berglin's Index.

RESULTS

Homosexual male-to-female transsexuals have a later than expected birth order and more older brothers than other subgroups of male-to-female transsexuals. Each older brother increases the odds that a male transsexual is homosexual by 40 %.

CONCLUSIONS

Hypotheses explaining the extension of prior findings to this large sample of transsexual males include a progressive maternal immunization to the male foetus either through the H-Y antigen or protein-bound testosterone or alterations in foetal androgen levels in successive pregnancies, all modifying male psychosexual development. Data on the sexual orientation of younger brothers of homosexual male transsexuals in this study are not consistent with the progressive immunization hypothesis.

Genetic and environmental influences on sexual orientation and its correlates in an Australian twin sample

We recruited twins systematically from the Australian Twin Registry and assessed their sexual orientation and 2 related traits: childhood gender nonconformity and continuous gender identity. Men and women differed in their distributions of sexual orientation, with women more likely to have slight-to-moderate degrees of homosexual attraction, and men more likely to have high degrees of homosexual attraction. Twin concordances for nonheterosexual orientation were lower than in prior studies. Univariate analyses showed that familial factors were important for all traits, but were less successful in distinguishing genetic from shared environmental influences. Only childhood gender nonconformity was significantly heritable for both men and women. Multivariate analyses suggested that the causal architecture differed between men and women, and, for women, provided significant evidence for the importance of genetic factors to the traits' covariation.

Ethical implications of scientific research on the causes of sexual orientation

In this article, we evaluate the status of current biological research into sexual orientation and examine the relevance of such research on the legal and social status of gay men and lesbians. We begin with a review of hormonal neuroanatomical and genetic studies of sexual orientation. We argue that the scientific study of sexual orientation is, at best, still in its infancy. We turn then to the ethical and social implications of this research. We argue that even if scientists could explain how sexual orientation develops, no significant ethical conclusions would follow. Further, we suggest that the current emphasis on finding a biological basis for sexual orientation is potentially harmful to lesbians, gay men and other sexual minorities in various ways (although perhaps it is in some ways potentially helpful as well).

Inheritance of randomness

The mouse mutant iv is characterized by "a random determination of a developmental process' in that 50 rather than 100% of the homozygotes have situs inversus. The same explanation is given to the inheritance of situs inversus in the human immotile-cilia syndrome. There are probably two alleles of the responsible gene, one for control of the proper asymmetry and one without control and hence resulting in equal numbers of situs solitus and situs inversus in the homozygote. Left-handedness may be similarly inherited; furthermore, because of its high prevalence (around 10-12%) it has been assumed that there is an advantage of carrying both alleles ("balanced polymorphism'). With these two assumptions, a prevalence of left-handedness of 12.5% is expected, a 50% chance of left-handedness in matings between two left-handed persons, and equal numbers of discordant and left-handed concordant monozygotic twins. These values are close to those actually found. As the values for (female) homosexuality are similar to those of left-handedness a similar inheritance is proposed.

Linkage between sexual orientation and chromosome Xq28 in males but not in females

We have extended our analysis of the role of the long arm of the X chromosome (Xq28) in sexual orientation by DNA linkage analyses of two newly ascertained series of families that contained either two gay brothers or two lesbian sisters as well as heterosexual siblings. Linkage between the Xq28 markers and sexual orientation was detected for the gay male families but not for the lesbian families or for families that failed to meet defined inclusion criteria for the study of sex-linked sexual orientation. Our results corroborate the previously reported linkage between Xq28 and male homosexuality in selected kinships and suggest that this region contains a locus that influences individual variations in sexual orientation in men but not in women.

Development and familiality of sexual orientation in females

The development and familial clustering of sexual orientation were studied in 358 heterosexual, bisexual, and homosexual women. Sexual orientation, as measured by the Kinsey scales, was diverse yet showed statistical congruity and stability over a 1- to 1.5-year time span. Developmental patterns, as measured by retrospective reports on the ages of first sexual or romantic attraction and of self-acknowledgement of sexual orientation were very similar in the heterosexual and lesbian subjects except for the difference in object choice. The bisexual subjects displayed intermediate patterns that were more similar to the heterosexuals' on most facets yet closer to the lesbian subjects' on other dimensions. Familial clustering of nonheterosexual orientation was significant. Using two criteria, elevated rates of nonheterosexuality were found in four classes of relatives: sisters, daughters, nieces, and female cousins through a paternal uncle. The current data are not sufficient to distinguish between genetic and shared environmental sources of this familial aggregation. We discuss the possibility of using developmental criteria to differentiate between inherited and cultural sources of variation in female sexual orientation.

Homosexuality, type 1: an Xq28 phenomenon

Despite the absence of phenotypic manifestations in alternating generations characteristic of X-linked disorders, a thesis is presented that a major type of Kinsey grades 5 and 6 male homosexuality is determined by a gene in the Xq28 region. A total of 133 families in 78 kinshps of male and female homosexual probands, in addition to 116 families (including those of 40 famous homosexuals) from the literature, revealed an unbalanced secondary sex ratio in the maternal generation of male, but not of female, homosexuals. On the maternal side, in this study, the ratio of all uncles to all aunts of 90 males homosexuals was 132/209, chi 2 = 8.52, p = 0.004. On the maternal side for the total of all sources, the ratio of uncles to aunts of male homosexuals was 241/367, chi 2 = 13.20; p < 0.0001. The male/female ratio of the total number of maternal sibships bearing homosexuals (310/628: 0.491) was a measure of fetal wastage of the mothers' male sibs; 49%. This ratio was very close to that of the total number of children born to fathers affected with any one of nine Xq28-linked male semilethal conditions (255/508: ratio 0.556); for the difference between the two populations chi 2 = 0.859, p = 0.354. The male/female ratio of the total number of children born to female carriers of any one of these same conditions (1,232/1,062: ratio 1.16), chi 2 = 13.8 p < or = 0.0001, is close to that of the total number of children in homosexual sibships: 511/413, chi 2 = 10.4, p = 0.005. Between the number of children born to Xq28 mothers and to those born of mothers of homosexuals chi 2 = 0.581, p = 0.446. One may readily surmise that the maternal influence so often related to homosexuality may lie in the mother being a genetic carrier, with traits thereto associated. In this study, 65% of the mothers of homosexuals had no or only one live-born brother. Additional support for a genetic hypothesis is found in the occurrence of multiple instances--almost exclusively among maternal relatives--of infertility, spontaneous abortions, miscarriages, stillbirths, remaining single past age 30, and suicide. Of 109 male and 43 female homosexual index cases in the present series there were 6 instances of brother/sister homosexual sibships.(ABSTRACT TRUNCATED AT 400 WORDS)

Handedness and sexual orientation

Surveys of handedness distribution (i.e., the distribution across handedness categories in large samples, typically based upon self-reported right-, mixed- and left-handed classification) indicate approximately 90% of the population is right-handed (Springer & Deutsch, 1989). This distribution toward right-handedness has been called right shift based on a genetic model (Annett, 1985). The present study examined possible handedness distribution differences between 141 gay, lesbian, and bisexuals and 260 heterosexuals who have a homosexual/bisexual first-degree (biological) relative. Based on a five-category self-assessment handedness questionnaire that was validated using Briggs and Nebes' (1975) reformulation of Annett's inventory (1970), non-heterosexuals showed a reduction of right shift compared to heterosexuals (i.e., a population shift toward mixed- and left-handedness), confirming the results of Lindesay (1987) and Becker et al., (1989). Sexual orientation also weakly predicted handedness. The findings indirectly support the hypothesis of Geschwind and Galaburda (1985a, 1985b) that sexual orientation and handedness may be linked, both possibly influenced prenatally by testosterone. The discussion emphasizes (a) the meaninglessness in distinguishing genetic from hormonal influences and (b) non-heterosexually biased assumptions about human sexuality.