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Prenatal hormones and 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. Prenatal hormones may be seen as the primary determinant of adult sexual orientation, or a co-factor with genes, biological factors and/or environmental and social conditions.
==Sex-typed behavior==
The hormonal theory of sexuality and gender identity holds that, just as exposure to certain hormones plays a role in fetal sex differentiation, such exposure also influences the sexual orientation and or gender identity that emerges later in the adult. Differences in brain structure that come about from chemical messengers and genes interacting on developing brain cells are believed to be the basis of sex differences in countless behaviors, including sexual orientation.〔Garcia-Falgueras A, Swaab DF. Sexual hormones and the brain: an essential alliance for sexual identity and sexual orientation. Endocr Dev. 2010;17:22-35. PMID 19955753〕 Prenatal factors that affect or interfere with the interaction of these hormones on the developing brain can influence later sex-typed behavior in children.〔 This hypothesis is originated from countless experimental studies in non-human mammals, yet the argument that similar effects can be seen in human neurobehavioral development is a much debated topic among scholars.〔 Recent studies, however, have provided evidence in support of prenatal androgen exposure influencing childhood sex-typed behavior.
Fetal hormones may be seen as either the primary influence upon adult sexual orientation or as a co-factor interacting with genes and/or environmental and social conditions.〔Wilson, G., & Q. Rahman, ''Born Gay: The Psychobiology of Human Sex Orientation'', Peter Owen Publishers; 2nd edition (May 1, 2008) ISBN 9780720613094〕 However, Garcia-Falgueras and Dick Swaab disagree that social conditions influence sexual orientation to a large degree. As seen in young children as well as in vervet and rhesus monkeys, sexually differentiated behavior in toy preference is differing in males versus females, where females prefer dolls and males prefer toy balls and cars; these preferences can be seen as early as 3–8 months in humans.〔 Further, differences in viewing preference can be seen as early as the first day of life, where females prefer human faces and males prefer mechanical mobiles. Despite this, is it impossible to completely rule out the social environment or the child's cognitive understanding of gender when discussing sex typed play in androgen-exposed girls.〔 Conversely, environmental/social conditions may affect the presentation of sexually differentiated behavior in males more than females, as male-typical play behavior is much more encouraged and female behavior discouraged among male children. Children also tend towards objects which have been labelled for their own sex, or toys that they have seen members of their sex playing with previously.〔
An endocrinology study by Garcia-Falgueras and Swaab postulated that "In humans, the main mechanism responsible of sexual identity and orientation involves a direct effect of testosterone on the developing brain."〔 Further, their study puts forward that intrauterine exposure to hormones is largely determinative. Sketching the argument briefly here, the authors say that sexual organs are differentiated first, and then the brain is sexually differentiated "under the influence, mainly, of sex hormones such as testosterone, estrogen and progesterone on the developing brain cells and under the presence of different genes as well . . . . The changes brought about in this stage are permanent. . . . ()exual differentiation of the brain is not caused by hormones alone, even though they are very important for gender identity and sexual orientation."〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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