Man... I knew I should have written them down, but, I looked at so much stuff. Going through my history links, some where:
Bailey and Pillard (1991)
Bearman and Bruckner (2002)
Hershberger (2001)
Niklas Långström, Qazi Rahman, Eva Carlström, Paul Lichtenstein, 7 June 2008, doi 10.1007/s10508-008-9386-1
But my conclusion was based on a recent summary doc that took into account all the above, plus several more, and drew a conclusion or summary, and it is not in my history links... so give me a little bit to try and find it. I think it was a Chicago Journal pdf file.
Bailey and Pillard (1991)
A Genetic Study of Male Sexual Orientation
Abstract:
[FONT=verdana, arial, helvetica, sans-serif]
Homosexual male probands with monozygotic cotwins, dizygotic cotwins, or adoptive brothers were recruited using homophile publications. Sexual orientation of relatives was assessed either by asking relatives directly, or when this was impossible, asking the probands. Of the relatives whose sexual orientation could be rated, 52% (29/56) of monozygotic cotwins, 22% (12/54) of dizygotic cotwins, and 11% (6/57) of adoptive brothers were homosexual. Heritabilities were substantial under a wide range of assumptions about the population base rate of homosexuality and ascertainment bias. However, the rate of homosexuality among nontwin biological siblings, as reported by probands, 9.2% (13/142), was significantly lower than would be predicted by a simple genetic hypothesis and other published reports. A proband's self-reported history of childhood gender non-conformity did not predict homosexuality in relatives in any of the three subsamples. Thus, childhood gender nonconformity does not appear to be an indicator of genetic loading for homosexuality. Cotwins from concordant monozygotic pairs were very similar for childhood gender nonconformity. [/FONT]
Source:
http://archpsyc.ama-assn.org/cgi/content/abstract/48/12/1089
Bearman and Bruckner (2002)
Opposite Sex Twins and Adolescent Same Sex Attraction
Abstract:
The etiology of human same-sex romantic attraction is generally
framed in terms of (1) social influences, (2) genetic influences, or (3)
hormonal influences. In this article, we show that adolescent males
who are opposite-sex twins are twice as likely as expected to report
same-sex attraction; and that the pattern of concordance (similarity
across pairs) of same-sex preference for sibling pairs does not suggest
genetic influence independent of social context. Our data falsify the
hormone transfer hypothesis by isolating a single condition that
eliminates the opposite-sex twin effect we observethe presence of
an older same-sex sibling. We also consider and reject a speculative
evolutionary theory that rests on observing birth-order effects on
same-sex orientation. In contrast, our results support the hypothesis
that less gendered socialization in early childhood and preadoles-
cence shapes subsequent same-sex romantic preferences.
Source:
http://0-search.ebscohost.com.libra...rue&db=psyh&AN=2002-15745-002&site=ehost-live
Critique:
The problem with this study (Bearman and Bruckner (2002)) is that when reviewing their methods they didn't actually state what scales they used. In valid research the researchers will either tell what scales they used or give the validity of scales they have made themselves, since neither of these exist in the article it is impossible to know how they got their information. One very important fact that many people don't know is that in psychology we cannot just ask one question to determine one characteristic. Using multiple questions to determine a characteristic reduces the chance of answers based on social desireability.
Hershberger (2001)
??? Couldn't find that one ???
Niklas Långström, Qazi Rahman, Eva Carlström, Paul Lichtenstein, 7 June 2008
Genetic and Environmental Effects on Same-sex Sexual Behavior: A Population Study of Twins in Sweden
Abstract:
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.