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.

De la necesidad, de la posibilidad, de la autorrealización, de la orientación sexual y de ser padres y madres / No disponible

No disponible

Common genetic factors among sexual orientation, gender nonconformity, and number of sex partners in female twins: implications for the evolution of homosexuality.

INTRODUCTION: Homosexuality is a stable population-level trait in humans that lowers direct fitness and yet is substantially heritable, resulting in a so-called Darwinian "paradox." Evolutionary models have proposed that polymorphic genes influencing homosexuality confer a reproductive benefit to heterosexual carriers, thus offsetting the fitness costs associated with persistent homosexuality. This benefit may consist of a "sex typicality" intermediate phenotype. However, there are few empirical tests of this hypothesis using genetically informative data in humans. AIM: This study aimed to test the hypothesis that common genetic factors can explain the association between measures of sex typicality, mating success, and homosexuality in a Western (British) sample of female twins. METHODS: Here, we used data from 996 female twins (498 twin pairs) comprising 242 full dizygotic pairs and 256 full monozygotic pairs (mean age 56.8) and 1,555 individuals whose co-twin did not participate. Measures of sexual orientation, sex typicality (recalled childhood gender nonconformity), and mating success (number of lifetime sexual partners) were completed. MAIN OUTCOME MEASURE: Variables were subject to multivariate variance component analysis. RESULTS: We found that masculine women are more likely to be nonheterosexual, report more sexual partners, and, when heterosexual, also report more sexual partners. Multivariate twin modeling showed that common genetic factors explained the relationship between sexual orientation, sex typicality, and mating success through a shared latent factor. CONCLUSIONS: Our findings suggest that genetic factors responsible for nonheterosexuality are shared with genetic factors responsible for the number of lifetime sexual partners via a latent sex typicality phenotype in human females. These results may have implications for evolutionary models of homosexuality but are limited by potential mediating variables (such as personality traits) and measurement issues.

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.

Testing causal models of the relationship between childhood gender atypical behaviour and parent-child relationship.

An association between childhood gender atypical behaviour (GAB) and a negative parent-child relationship has been demonstrated in several studies, yet the causal relationship of this association is not fully understood. In the present study, different models of causation between childhood GAB and parent-child relationships were tested. Direction of causation modelling was applied to twin data from a population-based sample (n= 2,565) of Finnish 33- to 43-year-old twins. Participants completed retrospective self-report questionnaires. Five different models of causation were then fitted to the data: GAB → parent-child relationship, parent-child relationship → GAB, reciprocal causation, a bivariate genetic model, and a model assuming no correlation. It was found that a model in which GAB and quality of mother-child, and father-child relationship reciprocally affect each other best fitted the data. The findings are discussed in light of how we should understand, including causality, the association between GAB and parent-child relationship.

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.

Efectos mnemónicos maternos prenatales sobre el sexo psíquico humano: insuficiencia del mecanismo inmunitario: nueva propuesta desde la tolerancia-rechazo materno-fetal / Prenatal maternal mnemonic effects on the human neuro-psychic sex: a new proposition from fetus-maternal tolerance-rejection

In approximately 15 percent 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 ofyounger 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 individuáis. This can only be understood as if the ñndings found 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 alíeles, the author provides a speculative interpretation ofthese results. Homosexual women (¡esbians) 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 ofgays 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 newproposition. Also, complete sexual orientation could be acquired after birth.

[Overview of the biological etiology of transsexualism]. / A transzszexualizmus biológiai kóroktanának áttekintése.

Gender identity disorder, or transsexualism as it is more commonly known, is a highly complex clinical entity. The general belief among behavioural scientists and physicians is that transsexualism is an identifiable and incapacitating disease which can be diagnosed and successfully treated by reassignment surgery. Although the exact etiology of gender identity disorder is unknown, several environmental, genetic and anatomical theories have been described. The reviewers draw attention to the possible genetic, hormonal, immunological and anatomical causes. An attempt is made to point out the future trends in research, highlighting their progressive features.

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).

[Prenatal maternal mnemonic effects on the human neuro-psychic sex: a new proposition from fetus-maternal tolerance-rejection]. / Efectos mnemónicos maternos prenatales sobre el sexo psíquico humano. Insuficiencia del mecanismo inmunitario: Nueva propuesta desde la tolerancia-rechazo materno-fetal.

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.

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.

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.

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.

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.