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In recent years, a number of researchers have advocated extending the modern synthesis in evolutionary biology. One of the core arguments made in favour of an extension comes from work on soft inheritance systems, including transgenerational epigenetic effects, cultural transmission and niche construction. In this study, we outline this claim and then take issue with it. We argue that the focus on soft inheritance has led to a conflation of proximate and ultimate causation, which has in turn obscured key questions about biological organization and calibration across the life span to maximize average lifetime inclusive fitness. We illustrate this by presenting hypotheses that we believe incorporate the core phenomena of soft inheritance and will aid in understanding them.

This study tested direct and indirect associations between minority stressors and psychological distress a large, geographically diverse sample of transgender individuals (N = 1,207). Transgender individuals were recruited for an online, cross-sectional survey using targeted sampling. Structural equation modelling was used to test the hypothesized model, which was based on Hatzenbuehler's (2009) integrative mediation framework. Expectations of rejection, self-stigma and prejudice events were all associated with psychological distress, and these relationships were partially accounted for by rumination. This model had good fit (TLI = .96, CFI = .98, RMSEA = .05 (90% CI [.05, .06]) and explained 54.5% of the variance in psychological distress and 29.3% in rumination. This is the first study to examine a model of minority stress and psychological distress that includes rumination and all four minority stressors from Meyer's (2003) framework in a large sample of transgender individuals. Results indicate a strong relationship between minority stressors and psychological distress among transgender people, and that these relationships are partially explained by rumination. Results need to be considered in relation to the cross-sectional nature of the design and the possible role for additional variables. Future research should investigate these findings using designs that provide tests of causality.

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.

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This study tested the mechanisms by which social stigma contributes to psychological distress in lesbian, gay, and bisexual individuals. A large community sample (N = 4248, M age = 29.9 years, 42.9% female, 57.1% male, 35.7% bisexual, 64.3% lesbian/gay, 9.9% non-white) was recruited using targeted and general advertisements for an online cross-sectional survey. Participants completed measures of childhood gender nonconformity, prejudice events, victimization, microaggressions, sexual orientation concealment, sexual orientation disclosure, expectations of rejection, self-stigma, rumination, and distress. Structural equation modeling was used to test the relationships between these variables in a model based upon minority stress theory and the integrative mediation framework with childhood gender nonconformity as the initial independent variable and distress (depression, anxiety, and well-being) as the final dependent variable. The results broadly support the hypothesized model. The final model had good fit χ 2 (37) = 440.99, p < .001, TLI = .96, CFI = .98, RMSEA = .05 [.05, .06] and explained 50.2% of the variance in psychological distress and 24.8% in rumination. Sexual orientation and gender had moderating effects on some individual paths. Results should be considered in the context of the cross-sectional nature of the data, which prevented tests of causality, and self-report measures used, which are vulnerable to bias. Findings indicate strong relationships between minority stressors and psychological distress in lesbian, gay, and bisexual individuals, which are partially accounted for by rumination. These results may inform the development of interventions that address the added burden of minority stress among lesbian, gay, and bisexual individuals.

Background. Increased psychiatric morbidity has been widely reported among non-heterosexual individuals (defined as reporting a homosexual/bisexual identity and/or same-sex sexual partners). However, the causes of this psychiatric ill-health are mostly unknown.Method. We attempted to estimate the influence of minority stress and familial factors on psychiatric disorder among adults with same-sex sexual partners. Self-report data from a 2005 survey of adults (age 20-47 years, n=17 379) in the population-based Swedish Twin Registry were analysed with regression modelling and co-twin control methodology.Results. Rates of depression, generalized anxiety disorder (GAD), eating disorders, alcohol dependence and attention deficit hyperactivity disorder (ADHD) were increased among men and women with same-sex sexual experiences. Adjusting for perceived discrimination and hate crime victimization lowered this risk whereas controlling for familial (genetic or environmental) factors in within-twin pair comparisons further reduced or eliminated it.Conclusions. Components of minority stress influence the risk of psychiatric ill-health among individuals with any same-sex sexual partner. However, substantial confounding by familial factors suggests a common genetic and/or environmental liability for same-sex sexual behaviour and psychiatric morbidity.

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