Qazi Rahman

Sexual orientation and the 2nd to 4th finger length ratio: evidence for organising effects of sex hormones or developmental instability?

It has been proposed that human sexual orientation is influenced by prenatal sex hormones. Some evidence examining putative somatic markers of prenatal sex hormones supports this assumption. An alternative suggestion has been that homosexuality may be due to general developmental disruptions independent of hormonal effects. This study investigated the ratio of the 2nd to 4th finger digits (the 2D:4D ratio), a measure often ascribed to the organisational actions of prenatal androgens, and the fluctuating asymmetry (FA-a measure of general developmental disruption) of these features, in a sample of 240 healthy, right handed and exclusively heterosexual and homosexual males and females (N=60 per group). Homosexual males and females showed significantly lower 2D:4D ratios in comparison to heterosexuals, but sexual orientation did not relate to any measures of FA. The evidence may suggest that homosexual males and females have been exposed to non-disruptive, but elevated levels of androgens in utero. However, these data also draw attention to difficulties in the interpretation of results when somatic features are employed as biological markers of prenatal hormonal influences.

Born gay? The psychobiology of human sexual orientation

Sexual orientation is fundamental to evolution and shifts from the species-typical pattern of heterosexuality may represent biological variations. The growth of scientific knowledge concerning the biology of sexual orientation during the past decade has been considerable. Sexual orientation is characterised by a bipolar distribution and is related to fraternal birth order in males. In females, its distribution is more variable; females being less prone towards exclusive homosexuality. In both sexes homosexuality is strongly associated with childhood gender nonconformity. Genetic evidence suggests a heritable component and putative gene loci on the X chromosome. Homosexuality may have evolved to promote same sex affiliation through a conserved neurodevelopmental mechanism. Recent findings suggest this mechanism involves atypical neurohormonal differentiation of the brain. Key areas for future research include the neurobiological basis of preferred sexual targets and correlates of female homosexuality.

The extended evolutionary synthesis and the role of soft inheritance in evolution

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.

Psychiatric morbidity associated with same-sex sexual behaviour: influence of minority stress and familial factors

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.

Large sexual-orientation-related differences in performance on mental rotation and judgment of line orientation tasks.

This study examined the performance of heterosexual and homosexual men and women on 2 tests of spatial processing, mental rotation (MR) and Benton Judgment of Line Orientation (JLO). The sample comprised 60 heterosexual men, 60 heterosexual women, 60 homosexual men, and 60 homosexual women. There were significant main effects of gender (men achieving higher scores overall) and Gender x Sexual Orientation interactions. Decomposing these interactions revealed large differences between the male groups in favor of heterosexual men on JLO and MR performance. There was a modest difference between the female groups on MR total correct scores in favor of homosexual women but no differences in MR percentage correct. The evidence suggests possible variations in the parietal cortex between homosexual and heterosexual persons.

Sex, sexual orientation, and identification of positive and negative facial affect

Sex and sexual orientation related differences in processing of happy and sad facial emotions were examined using an experimental facial emotion recognition paradigm with a large sample (N = 240). Analysis of covariance (controlling for age and IQ) revealed that women (irrespective of sexual orientation) had faster reaction times than men for accurate identification of facial emotion and were more accurate in identifying male faces than female ones, whereas men performed the same regardless of the sex of the face. However, there were no overall sex differences in accuracy. These findings suggest a limited role for sex in the perception of facial affect.

Fluctuating asymmetry, second to fourth finger length ratios and human sexual orientation.

Sexual orientation in humans may be influenced by levels of prenatal sex steroids which canalise neurodevelopment along sex-typical (heterosexual) or sex-atypical (homosexual) lines. Some evidence for sexual-orientation-related differences in putative somatic markers of prenatal sex hormones supports this view. A competing theory asserts that human homosexuality is due to developmental instability (DI) because it represents a shift from the species-typical pattern of heterosexual orientation. Evidence for elevated rates of non-right handedness among homosexuals provides limited support for this account. The current study tested both theories by examining nine bilateral somatic traits in 120 healthy heterosexual and homosexual men and women in order to compute second to fourth finger length ratios (2D:4D), a measure ascribed to levels of prenatal sex steroids, and fluctuating asymmetry (FA), a measure of DI. Homosexual men and women had significantly lower right hand 2D:4D ratios (even after controlling for handedness, height and weight differences) in comparison to heterosexuals, but sexual orientation did not relate to composite FA scores. The findings constrain the number of possible neurodevelopmental pathways responsible for sexual orientation in humans.

Which behaviors constitute "having sex" among university students in the UK?

The aim of this study was to establish which behaviors were considered to constitute sexual relations and to compare a group of undergraduates in the UK with a group in the US. An opportunistic sample of 190 female and 124 male UK undergraduate university students was surveyed by questionnaire. The main outcome measure was percentage of responses to 11 different behaviors believed to constitute “having sex.” The majority of respondents regarded having sex as involving penile–vaginal and penile–anal intercourse. One-third of respondents regarded oral–genital contact as having sex, around 17% regarded touching genitals, whilst 6% regarded oral or other touching of breasts and nipples as constituting having sex. There were significant gender- and age-related differences in responses. These findings broadly support the findings of an earlier US study. It is clear that British students hold divergent opinions about which behaviors do and do not constitute having sex. The age-related trends merit further exploration. Any studies of sex-related behaviors need to specify precisely which are encompassed by the terms used.

Sexual orientation related differences in spatial memory

The purpose of this study was to investigate and extend previously reported sex differences in object location memory by comparing the performance of heterosexual and homosexual males and females. Subjects were 240 healthy, right-handed heterosexual and homosexual males and females. They were instructed to study 16 common, gender-neutral objects arranged randomly in an array and subsequently tested for object recall, object recognition and spatial location memory. Females recalled significantly more objects than males, although there were no group differences in object recognition. Decomposition of significant interactions between sex and sexual orientation on spatial location memory (controlling for differences in object recall, age and IQ) revealed that heterosexual females and homosexual males scored better than heterosexual males, and no different from each other. There were no differences between homosexual and heterosexual females. The findings suggest that homosexual males and heterosexual females encode, store and retrieve positional and relational information about spatial layouts similarly, pointing to within-sex variations in the neural architecture underlying spatial memory.

Sexual-orientation-related differences in verbal fluency

This study examined the performance of 60 heterosexual men, 60 gay men, 60 heterosexual women, and 60 lesbians on 3 tests of verbal fluency known to show gender differences: letter, category, and synonym fluency. Gay men and lesbians showed opposite-sex shifts in their profile of scores. For letter fluency, gay men outperformed all other groups; lesbians showed the lowest scores. For category fluency, gay men and heterosexual women jointly outperformed lesbians and heterosexual men. Finally, gay men outperformed all other groups on synonym fluency, whereas lesbians and heterosexual men performed similarly. A difference between heterosexual men and women was demonstrated on category and synonym fluency only. The findings implicate within-sex differences in the functioning of the prefrontal and temporal cortices.