Sexual differentiation of the human brain

Relevance for gender identity, transsexualism and sexual orientation

2004 Study Abstracts

Male sexual differentiation of the brain and behavior are thought, on the basis of experiments in rodents, to be caused by androgens, following conversion to estrogens.

Sexual differentiation of the human brain: relevance for gender identity, transsexualism and sexual orientation, Gynecological endocrinology : the official journal of the International Society of Gynecological Endocrinology, US National Library of Medicine National Institutes of Health, NCBI PubMed PMID: 15724806, 2004 Dec.

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However, observations in human subjects with genetic and other disorders show that direct effects of testosterone on the developing fetal brain are of major importance for the development of male gender identity and male heterosexual orientation.

Solid evidence for the importance of postnatal social factors is lacking. In the human brain, structural diferences have been described that seem to be related to gender identity and sexual orientation.

… The importance of the fetal male testosterone surge for sexual differentiation of the brain following aromatization to estrogens agrees with the observations that girls whose mothers were exposed to diethylstilbestrol (DES) during pregnancy run a higher risk of developing bi- or homosexuality. …

… Sex hormones during development also have an influence on sexual orientation, as appears from the increased proportion of bi- and homosexual girls with congenital adrenal hyperplasia. Then there is DES, a compound related to estrogens that increases the occurrence of bi- or homosexuality in girls whose mothers received DES during pregnancy to prevent miscarriage (quod non). DES was given between 1939 and the 1960s to millions of pregnant women. However, these authors could not confirm an increase in the likelihood of homosexual behavior in DES-exposed girls or boys in adulthood. The ratio of the second to fourth finger digits, a measure ascribed to the organizational actions of prenatal androgens, was significantly lower in the homosexual males and females as compared with heterosexuals. This observation suggests that homosexual males and females have been exposed to elevated levels of androgens in utero. …

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