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| quote: | Originally posted by CyberneticAngel
Its time someone injected some science into this argument
There is little evidence to support the genetic view of inherited sexual preference. There have only been three studies (although several are ongoing) that found a link and none of them have been repeatable with the exact same results at this time. The three studies in question are Hamer/Hu in 1993, Hall/Kimura in 1994, and McGue/Bailey in 1998 and 1999
Hamer/Hu - This study found a correlation between homosexual orientation and the presence of polymorphic markers on the X chromosome. One of the interesting points of this particular study was the lack of correlation in females, the study's findings relate to males only.
This study was rebutted by Faust-Sterling/Balaban in 1995 (not sure about that date, but I think that's it) Faust-Sterling/Balaban did not attempt to recreate the Hamer/Hu study, rather they focused on the methodology of the study arguing that the results were invalid due to an inadequate control group, various statistical assumptions, and a low number of significant cases. They called for a more scientific repeat of this study. To my knowledge this study has not yet been repeated.
Hall/Kimura - This study showed that a particular type of fingerprint pattern was statistically more prevalent in homosexual men then in heterosexual men. Because the formation of fingerprints occurs early in fetus development Hall and Kimura hoped that this pointed to a link between this gene and homosexual.
This study was repeated in 2002 by Forastieri. He could not reach the same results and concluded that there were no significant differences between heterosexual and homosexual males. Several other studies since have generally confirmed this lack of a link.
McGue/Bailey - In 1998 McGue used twin adoption studies to show that behavioral characteristics are heritable. In 1999 Bailey repeated McGue's twin adoption experiments. His results showed much less connection but came to the same conclusion. This is the only study that I am aware of (I did do all this research last year so there might have been some developments) that supports the genetic based theories of homosexuality. There have as of yet been no studies refuting it but several articles have been written questioning the differences in results between the two studies. Some questions have also been raised as to whether there were other related cause other than genetics which might have screwed the results in one study or the other.
If anyone cares I can find the sources for most of these articles with little trouble. |
Hi CA,
Thanks for your input. I’ll admit that sexual preference research is not my strong point, but I am familiar with these 3 studies you outlined. I think it’s been pretty apparent that the “single gay gene” theory was pretty weak at best, and that Hamer’s study was somewhat like searching for a needle in a haystack in the genome. I believe most researchers in that field had come to the conclusion that a polygenetic trait was likely here, but the evidence wasn’t very strong. The Bailey study is often the one that is most cited as the strongest evidence towards a genetic component involved, and as you mentioned McGue’s follow-up did give significant support, albeit not quite as strong. The most recent study by Mustanski, however, does give more credence to a genetics component here. I am surprised at their conclusions that possible environmental factors were involved, especially in lieu of these past studies that concluded very little to no environmental factors contributing:
| quote: | Bogaert AF.
Number of older brothers and sexual orientation: new tests and the attraction/behavior distinction in two national probability samples.
J Pers Soc Psychol. 2003 Mar;84(3):644-52.
Abstract: The extent to which number of older brothers or "fraternal birth order" predicted the 2 main components that researchers have traditionally used to conceptualize sexual orientation-that is, psychological attraction and sexual behavior-was examined in 2 recent national probability samples. In both studies, fraternal birth order predicted same-sex attraction in men, with each additional older brother increasing the odds of homosexual attraction by an average of 38%. Results also indicated that the fraternal birth order/same-sex attraction relationship in men was independent of sexual behavior, including early same-sex behavior. No sibling characteristics predicted sexual orientation in women. Results suggest experience-based theories (e.g., early same-sex play) of the fraternal birth order effect in men are unlikely to be correct.
http://www.ncbi.nlm.nih.gov/entrez/...t_uids=12635923 |
| quote: | Whitam FL, Diamond M, Martin J.
Homosexual orientation in twins: a report on 61 pairs and three triplet sets.
Arch Sex Behav. 1993 Jun;22(3):187-206.
Abstract: Twin pairs in which at least one twin is homosexual were solicited through announcements in the gay press and personal referrals from 1980 to the present. An 18-page questionnaire on the "sexuality of twins" was filled out by one or both twins. Thirty-eight pairs of monozygotic twins (34 male pairs and 4 female pairs) were found to have a concordance rate of 65.8% for homosexual orientation. Twenty-three pairs of dizygotic twins were found to have a concordance rate of 30.4% for homosexual orientation. In addition, three sets of triplets were obtained. Two sets contained a pair of monozygotic twins concordant for sexual orientation with the third triplet dizygotic and discordant for homosexual orientation. A third triplet set was monozygotic with all three concordant for homosexual orientation. These findings are interpreted as supporting the argument for a biological basis in sexual orientation.
http://www.ncbi.nlm.nih.gov/entrez/...st_uids=8494487 |
| quote: | Buhrich N, Bailey JM, Martin NG.
Sexual orientation, sexual identity, and sex-dimorphic behaviors in male twins.
Behav Genet. 1991 Jan;21(1):75-96.
Abstract: Sexual orientation, sexual identity, and sex-dimorphic behaviors were assessed concurrently and retrospectively, for childhood, in 95 pairs of male monozygotic (MZ) twins and 63 pairs of dizygotic (DZ) twins. There was a significantly higher rate of adult homosexuality among the MZ than among DZ twins. We employed a model-fitting approach using LISREL to test for genetic and environmental influences on variation for each trait singly and on the covariation among all six traits (three for childhood and three for adulthood). Univariate analyses confirmed the presence of familial factors for five of the six variables but were generally unable to distinguish shared environmental from genetic influences. Hierarchical tests of multivariate models supported the existence of an additive genetic factor contributing to the covariance among the variables. More restrictive multivariate models yielded a significant genetic influence on sexual orientation. Because of the different rates of orientation by zygosity and because of the restrictive nature of some of the multivariate models, our results are best considered tentative but do suggest that further biometrically oriented studies of sexual orientation and its correlates would be worthwhile.
http://www.ncbi.nlm.nih.gov/entrez/...st_uids=2018464 |
And as for studies that demonstrate actual biological differences between gay and straight individuals, i.e. possible hormonal influences:
| quote: | McFadden D, Pasanen EG.
Comparison of the auditory systems of heterosexuals and homosexuals: click-evoked otoacoustic emissions.
Proc Natl Acad Sci U S A. 1998 Mar 3;95(5):2709-13.
Abstract: Click-evoked otoacoustic emissions (CEOAEs) are echo-like waveforms emitted by normal-hearing cochleas in response to a brief transient. CEOAEs are known to be stronger in females than in males. In this experiment, the CEOAEs of homosexual and bisexual females were found to be intermediate to those of heterosexual females and heterosexual males. A parsimonious explanation is that the auditory systems of homosexual and bisexual females, and the brain structures responsible for their sexual orientation, have been partially masculinized by exposure to high levels of androgens prenatally. No difference in CEOAEs was observed between homosexual and heterosexual males.
http://www.ncbi.nlm.nih.gov/entrez/...st_uids=9482952 |
| quote: | Lippa RA.
Are 2D:4D finger-length ratios related to sexual orientation? Yes for men, no for women.
J Pers Soc Psychol. 2003 Jul;85(1):179-88.
Abstract: The ratio of index and ring finger lengths (2D:4D) is thought to be a marker of prenatal androgen exposure. In a sample of over 2,000 participants, men had significantly lower 2D:4D ratios than women (d = .36 and .23 for right and left hands, respectively), and these results were consistent across ethnic groups. Heterosexual men had significantly lower (more male typical) 2D:4D ratios than gay men (d = .32 and .31 for right and left hands, respectively), and these results tended to be consistent across ethnic groups. Heterosexual and lesbian women showed no significant differences in 2D:4D ratios, after ethnicity was taken into account. The current findings add to evidence that prenatal hormonal factors may be linked to men's sexual orientation.
http://www.ncbi.nlm.nih.gov/entrez/...t_uids=12872893 |
| quote: | Manning JT, Robinson SJ.
2nd to 4th digit ratio and a universal mean for prenatal testosterone in homosexual men.
Med Hypotheses. 2003 Aug;61(2):303-6. Review.
Abstract: Male homosexuals are said to have experienced high prenatal testosterone, and testosterone may have deleterious effects on the immune system. The question of the prenatal androgen status of male homosexuals is therefore of importance. There is evidence that the relative length of the 2nd and 4th digit (2D:4D) is negatively correlated with prenatal testosterone. We review the available literature, and provide further data on 2D:4D in male heterosexuals and homosexuals. Normative values of male mean 2D:4D ratio vary between 0.94 to 1.00 across populations. However, mean 2D:4D ratio is relatively constant among male homosexuals from different populations, with a mean of 0.96 to 0.97. Therefore homosexuals appear to be more androgenised (lower 2D:4D) than heterosexuals in some populations, while in others they appear to be less androgenised (higher 2D:4D) than heterosexuals. Speculations regarding the effect of early sex steroids on the health of male homosexuals should therefore focus on the effects of prenatal testosterone levels associated with 2D:4D ratios of between 0.96 and 0.97.
http://www.ncbi.nlm.nih.gov/entrez/...t_uids=12888323 |
| quote: | Rahman Q, Wilson GD.
Sexual orientation and the 2nd to 4th finger length ratio: evidence for organising effects of sex hormones or developmental instability?
Psychoneuroendocrinology. 2003 Apr;28(3):288-303.
Abstract: 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.
http://www.ncbi.nlm.nih.gov/entrez/...t_uids=12573297 |
So clearly there’s something biological going on here, and though it’s highly likely that a genetic component is involved, the details are still sketchy. I think that’s to be expected, however, given our current knowledge of the genome, though we have made some very significant progress in our current understanding of the genome. I’m getting pretty longwinded, and I didn’t touch much on the animal studies factor much, but the one I’m familiar with off the top of my head was the Zhang and Odenwald study on fruit flies:
| quote: | Zhang SD, Odenwald WF.
Misexpression of the white (w) gene triggers male-male courtship in Drosophila.
Proc Natl Acad Sci U S A. 1995 Jun 6;92(12):5525-9.
Abstract: We report here that the general ectopic expression of a tryptophan/guanine transmembrane transporter gene, white (w), induces male-male courtship in Drosophila. Activation of a hsp-70/miniwhite (mini-w) transgene in mature males results in a marked change in their sexual behavior such that they begin to vigorously court other mature males. In transformant populations containing equal numbers of both sexes, most males participate, thus forming male-male courtship chains, circles, and lariats. Mutations that ablate the w transgene function also abolish this inducible behavior. Female sexual behavior does not appear to be altered by ectopic w expression. By contrast, when exposed to an active homosexual courtship environment, non-transformant males alter their behavior and actively participate in the male-male chaining. These findings demonstrate that, in Drosophila, both genetic and environmental factors play a role in male sexual behavior.
http://www.ncbi.nlm.nih.gov/entrez/...st_uids=7777542 |
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Whence September dusk grows crisper still,
with leaves all crimson conquered,
I yearn to shout,
and dance about,
and stick pickles in my honker...
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