Prenatal hormones and sexual orientation 2651531 226114666 2008-07-16T21:50:46Z User0529 7280847 Ext Links to bottom {{Sexual orientation}} The hormonal theory of sexuality holds that, just as exposure to certain hormones plays a role in fetal [[sex differentiation]], such exposure also influences the [[sexual orientation]] that emerges later in the adult. Fetal hormones may be seen as the primary determiner of adult sexual orientation, or a co-factor with genes and/or environmental and social conditions. ==Prenatal hormones and sexuality-linked characteristics== ===Male homosexuality as hyper-masculine=== There is evidence of a correlation between sexual orientation and traits that are determined [[in utero]]<ref>Wilson, G.D. & Rahman, Q (2005) ''Born Gay: The Psychobiology of Sex Orientation'', Peter Owen, London</ref>. Williams ''et al.'' (2000) found that [[digit ratio|finger length ratio]], a characteristic controlled by prenatal hormones, is different in people of distinct sexual orientations.[http://mendel.ugr.es/genysoc/pdfs/sexorientation-finger.pdf] Another study by McFadden in 1998 found that auditory systems in the [[brain]], another physical trait influenced by prenatal hormones is different in those of differing orientations, likewise the suprachiasmatic nucleus of homosexual men was found by Swaab and Hopffman to be larger in homosexual men than in heterosexual men, [http://www.dafml.unito.it/anatomy/panzica/pubblicazioni/pdf/1995PanzicaJEI.pdf], the suprachiasmatic nucleus is also known to be larger in men than in women [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=7955323&dopt=Abstract]. Gay men have also been shown to have higher levels of circulating androgens <ref>Brodie, H. K. H. et al. Am. J. Psychiatry 131, 82-83 (1974).</ref> and larger penises <ref>Bogaert, A. F. and S. Hershberger (1999). "The relation between sexual orientation and penile size." Arch Sex Behav 28(3): 213-21.</ref>, on average, than straight men. Gay men have more older [[brothers]] on average, a phenomenon known as the [[Fraternal birth order and sexual orientation|fraternal birth order effect]]. It has been suggested that the greater the number of older male siblings the higher the level of [[androgen]] fetuses are exposed to <!--I think this is a reference to Williams et al Nature paper, but I don't think it says quite says what this last sentence says-->. ===Male homosexuality as feminine or hypo-masculine=== In a 1991 study, [[Simon LeVay]] demonstrated that a tiny clump <!--name that 'clump' (& call it a nucleus) --> of neurons of the anterior [[hypothalamus]]—which is believed to control sexual behavior and linked to prenatal hormones—was on average more than twice the size in heterosexual men when contrasted to homosexual men. Initially he could not rule out that this may be due to [[AIDS]] since all of his homosexual male subjects had died from it before the autopsies were performed. However in 2003 scientists at [[Oregon State University]] announced that it replicated his findings in sheep.<!-- I believe this has also been replicated in non-AIDS human subjects: Byne, W., S. Tobet, ''et al.'' (2001). "The interstitial nuclei of the human anterior hypothalamus: an investigation of variation with sex, sexual orientation, and hiv status." Horm Behav 40(2): 86-92. Dr. Simon LeVay, in his study of the hypothalamic differences between the brains of homosexual and heterosexual men, offered the following criticisms of his own research, "It's important to stress what I didn't find. I did not prove that homosexuality is genetic, or find a genetic cause for being gay. I didn't show that gay men are born that way, the most common mistake people make in interpreting my work. Nor did I locate a gay center in the brain."--> ===Female homosexuality=== Girls with [[congenital adrenal hyperplasia]] (an autosomal recessive condition which results in high androgen levels during fetal development) have more masculinized sex role identities and are more likely to have a homosexual sexual orientation as adults than controls (Dittmann ''et al.'' 1990ab, 1992; Zucker ''et al.'', 1996; Hines ''et al.'', 2004). An alternative explanation for this effect is that the fact that girls with this condition are born with masculinized external genitalia leads their parents to raise them in a more masculine manner which then influences their sexual orientation as adults. However, the degree to which the girls' genitals are masculinized does not correlate with their sexual orientation, suggesting that prenatal hormones are the causal factor, not parental influence. ==See also== * [[Biology and sexual orientation]] * [[Handedness and sexual orientation]] * [[Pathogenic hypothesis of homosexuality]] * [[David Reimer]] ==References== <references/> * Green, R. (1987). ''The "sissy boy syndrome" and the development of homosexuality.'' New Haven, CT: Yale University Press. * Dailey, T. and Sprigg , P. (2001). ''Getting It Straight — What the Research Shows about Homosexuality'', Family Research Council, Washington D.C. <!--is this cited in the article?--> * Dittmann ''et al.'' (1990) Congenital adrenal hyperplasia. I: Gender-related behavior and attitudes in female patients and sisters. ''Psychoneuroendocrinology'' 15:401-420. * Dittmann ''et al.'' (1990) Congenital adrenal hyperplasia. II: Gender-related behavior and attitudes in female salt-wasting and simple-virilizing patients. ''Psychoneuroendocrinology'' 15:421-434. * Dittmann ''et al.'' (1992) Sexual behavior in adolescent and adult females with congenital adrenal hyperplasia. ''Psychoneuroendocrinology'' 17:153-170. * Hines ''et al.'' (2004). Androgen and psychosexual development: core gender identity, sexual orientation, and recalled childhood gender role behavior in women and men with Congenital Adrenal Hyperplasia. ''[[Journal of Sex Research]]'' 41:75-81. * Rahman Q. (2005). The neurodevelopment of human sexual orientation. ''Neuroscience and Biobehavioral Reviews'' '''29 ''':1057–1066. * [http://msu.edu/~breedsm/pdf/breedlove2000.pdf Williams ''et al.'' (2000). Finger-lengths ratios and sexual orientation. ''Nature'' 404:455-456.] * Zucker ''et al.'' (1996) Psychosexual Development of Women with Congenital Adrenal Hyperplasia. Hormones and Behavior 30:300-318. ==External links== * [http://my.webmd.com/content/article/22/1728_56075?src=Inktomi&condition=Home%20&%20Top%20Stories WEBMD: Pointing the Finger at Androgen as a Cause of Homosexuality] * [http://www.boston.com/news/globe/magazine/articles/2005/08/14/what_makes_people_gay/?page=1 Boston Globe: "What makes people gay?"] [[Category:Sexual orientation and science]] [[Category:Sexual orientation and medicine]]