Studiensammlung 2: Homosexualität, Geschlechterunterschiede und Sex


Facial Structure Predicts Sexual Orientation in Both Men and Women.

Biological models have typically framed sexual orientation in terms of effects of variation in fetal androgen signaling on sexual differentiation, although other biological models exist. Despite marked sex differences in facial structure, the relationship between sexual orientation and facial structure is understudied. A total of 52 lesbian women, 134 heterosexual women, 77 gay men, and 127 heterosexual men were recruited at a Canadian campus and various Canadian Pride and sexuality events. We found that facial structure differed depending on sexual orientation; substantial variation in sexual orientation was predicted using facial metrics computed by a facial modelling program from photographs of White faces. At the univariate level, lesbian and heterosexual women differed in 17 facial features (out of 63) and four were unique multivariate predictors in logistic regression. Gay and heterosexual men differed in 11 facial features at the univariate level, of which three were unique multivariate predictors. Some, but not all, of the facial metrics differed between the sexes. Lesbian women had noses that were more turned up (also more turned up in heterosexual men), mouths that were more puckered, smaller foreheads, and marginally more masculine face shapes (also in heterosexual men) than heterosexual women. Gay men had more convex cheeks, shorter noses (also in heterosexual women), and foreheads that were more tilted back relative to heterosexual men. Principal components analysis and discriminant functions analysis generally corroborated these results. The mechanisms underlying variation in craniofacial structure–both related and unrelated to sexual differentiation–may thus be important in understanding the development of sexual orientation.


Pubertal Stress and Nutrition and their Association with Sexual Orientation and Height in the Add Health Data

A number of studies have indicated that gay men tend to be shorter, on average, than heterosexual men. Less evidence exists that lesbian women are taller, on average, than heterosexual women. The most popular explanation of the association between sexual orientation and height involves prenatal factors, such that, for example, gay men may have been exposed to lower than typical androgens during fetal development, which impacts their height and sexual orientation as adults. An alternative explanation involves stress, given that stress has been associated with sexual minority identification and with lower height. Another alternative explanation involves nutrition, although its relationship is less clear with sexual minority identification. Using the Add Health data, which is a large, nationally representative and longitudinal sample of American adolescents (n = 14,786), we tested a mediation model, such that sexual orientation → pubertal stress/nutrition → height. Within men, we found that gay men (n = 126) were shorter, on average, than heterosexual men (n = 6412). None of the 24 pubertal stress-related and 15 pubertal nutrition-related variables assessed in the Add Health data mediated the relationship between sexual orientation and height in men. Within women, lesbians (n = 75) did not differ significantly in stature compared to heterosexual women (n = 6267). Thus, prenatal mechanisms (e.g., hormones, maternal immune response) are likely better candidates for explaining the height difference between gay men and heterosexual men.


Common Genetic Factors among Sexual Orientation, Gender Nonconformity, and Number of Sex Partners in Female Twins: Implications for the Evolution of Homosexuality

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.

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.

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.

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.

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.

Und ein paar Tweets mit interessanten Grafiken:

Leider fehlt die Quellenangabe, aber es wäre ein interessanter Beleg dafür, dass mit höherem Wohlstand und mehr Freiheiten für den einzelnen auch die Leute ihre Geschlechterunterschiede eher ausleben

Die Kurve oben zeigt das Abschneiden bei mentalen Rotationstest für Männer und Frauen. Wie man sieht gibt es in den allermeisten Gegenden einen deutlichen Unterschied zwischen Männern und Frauen.

Das müsste aus dieser Studie sein:

Gender Differences in Personality and Interests: When, Where, and Why?

How big are gender differences in personality and interests, and how stable are these differences across cultures and over time? To answer these questions, I summarize data from two meta-analyses and three cross-cultural studies on gender differences in personality and interests. Results show that gender differences in Big Five personality traits are ‘small’ to ‘moderate,’ with the largest differences occurring for agreeableness and neuroticism (respective ds = 0.40 and 0.34; women higher than men). In contrast, gender differences on the people–things dimension of interests are ‘very large’ (d = 1.18), with women more people-oriented and less thing-oriented than men. Gender differences in personality tend to be larger in gender-egalitarian societies than in gender-inegalitarian societies, a finding that contradicts social role theory but is consistent with evolutionary, attributional, and social comparison theories. In contrast, gender differences in interests appear to be consistent across cultures and over time, a finding that suggests possible biologic influences.

Da geht es darum, wie viele Studenten in einem bestimmten Studiengang noch keinen Sex hatten.

Die Grafik kommt von dieser Seite:

Last December I passed a paper along to Razib showing that high-school age adolescents with higher IQs and extremely low IQs were less likely to have had first intercourse than those with average to below average intelligence. (i.e. for males with IQs under 70, 63.3% were still virgins, for those with IQs between 70-90 only 50.2% were virgin, 58.6% were virgins with IQs between 90-110, and 70.3% with IQs over 110 were virgins)

In fact, a more detailed study from 2000 is devoted strictly to this topic, and finds the same thing: Smart Teens Don’t Have Sex (or Kiss Much Either).
The team looked at 1000s of representative teens grades 7-12 in the National Longitudinal Study of Adolescent Health and The Biosocial Factors in Adolescent Development datasets, both of which include an IQ test, and include detailed sexual experience questions ranging from hand-holding to intercourse. As with the other study there was a curvilinear relationship: students with IQs above 100 and below 70 were significantly less likely to have had intercourse than those in between. Also like the other study, they found teens with IQs ranging from 75 to 90 had the lowest probability of virginity (the authors note this is also the same IQ range where propensity towards crime peaks).

Depending on the specific age and gender, an adolescent with an IQ of 100 was 1.5 to 5 times more likely to have had intercourse than a teen with a score of 120 or 130. Each additional point of IQ increased the odds of virginity by 2.7% for males and 1.7% for females. But higher IQ had a similar relationship across the entire range of romantic/sexual interactions, decreasing the odds that teens had ever kissed or even held hands with a member of the opposite sex at each age.

While these authors leave off at grade 12th, it would seem plausible to expect that this relationship extends beyond high school. To explore this, plenty of interesting facts come from a 2001 campus sex survey by the joint MIT/Wellesley college magazine Counterpoint (PDF). Looking within and between colleges, IQ appears to delay sexual activity on into young adulthood.

By the age of 19, 80% of US males and 75% of women have lost their virginity, and 87% of college students have had sex. But this number appears to be much lower at elite (i.e. more intelligent) colleges. According to the article, only 56% of Princeton undergraduates have had intercourse. At Harvard 59% of the undergraduates are non-virgins, and at MIT, only a slight majority, 51%, have had intercourse. Further, only 65% of MIT graduate students have had sex.

The student surveys at MIT and Wellesley also compared virginity by academic major. The chart for Wellesley displayed below shows that 0% of studio art majors were virgins, but 72% of biology majors were virgins, and 83% of biochem and math majors were virgins! Similarly, at MIT 20% of ‚humanities‘ majors were virgins, but 73% of biology majors. (Apparently those most likely to read Darwin are also the least Darwinian!)

Looking at this chart it would strongly appear that higher complexity majors contain more virgins than majors with lower cognitive demand. This paper provides me with GRE scores by academic discipline, and, in fact, the correlation between the percentage of virgins in each Wellesley major and the average ‚Analytical‘ GRE score associated with the discipline is 0.60.

One reason we might guess that smarter people in high school, or in more challenging colleges or majors, delay their sexual debuts is because they are delaying gratification in expectation of future reward. Sexual behavior (or at least the investment needed to procure a partner or sustain one) may compete with time/resources required for other goals, and intelligent people may have more demanding goals.

Interessant wäre da natürlich eine Aufschlüsselung nach Geschlecht: Kunst dürften auch wesentlich mehr Frauen studieren als die Naturwissenschaften. Und in Fächern mit einer hohen Frauenquote gibt es auch mehr Kandidatinnen zum Sex haben.