Prenatal hormones and sexual orientation
Encyclopedia
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.
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 either the primary influence upon adult sexual orientation or as a co-factor interacting with genes and/or environmental and social conditions.
A 2010 endocrinology study by Garcia-Falgueras and Swaab says that intrauterine exposure to hormones is largely determinative. Sketching the argument briefly here, it says that sexual organs are differentiated 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 [p. 24:] stage are permanent. . . . [S]exual differentiation of the brain is not caused by hormones alone, even though they are very important for gender identity and sexual orientation." ". . . . These fetal and neonatal peaks of testosterone, together with the functional steroid receptor activity, are thought to fix the development of structures and circuits in the brain for the rest of a boy's life (producing 'programming' or 'organizing' effects). Later, the rising hormonal levels that occur during puberty 'activate' circuits and behavioral patterns that were built during development, in a masculinized and de-feminized direction for male brains or in a feminized and de-masculinized direction for female brains." Because organ differentiation and brain differentiation occur at different times, in "rare" cases transsexualism can result (transsexualism resulting from having organs of one gender and feelings of the other). "The brain structure differences that result from the interaction between hormones, genes and developing brain cells are thought to be the basis of sex differences in a wide spectrum of behaviors, such as . . . sexual orientation (heterosexuality, homosexuality, or bisexuality) . . . . Factors that interfere with the interactions between hormones and the developing brain systems during development in the womb may permanently influence later behavior." "In humans, the main mechanism responsible of [sic] sexual identity and orientation involves a direct effect of testosterone on the developing brain." Drawing on some transsexualism cases, the authors say, "[f]rom these examples it appears that the direct action of testosterone on the developing brain in boys and the lack of such action on the developing brain in girls are crucial factors in the development of male and female gender identity and sexual orientation . . . ." "There are no indications that postnatal social factors could be responsible for the occurrence of transsexuality." "With regard to sexual orientation, the most likely outcome of childhood gender identity disorder is homosexuality or bisexuality." "The apparent impossibility of getting someone to change their sexual orientation . . . is a major argument against the importance of the social environment in the emergence of homosexuality, as well as against the idea that homosexuality is a lifestyle choice." "The presence of a genetic component of over 50% in the development of sexual orientation is apparent from family and twin studies." "Women with gay sons appeared to have an extreme skewing of X-inactivation [referring to the "X-chromosome"] . . . ." "[S]ome two million pregnant women . . . were prescribed diethylstilbestrol (DES)[,] . . . . an estrogen-like substance[,] . . . [and] it [was] . . . found . . . to increase the chance of bisexuality or homosexuality in girls." "The . . . . fraternal birth order effect . . . is putatively explained by an immunological response by the mother to a product of the Y chromosome of her sons. The chance of such an immune response to male factors would increase with every pregnancy resulting in the birth of a son." "Prenatal exposure to nicotine, amphetamine, or thyroid-gland hormones increases the chances of giving birth to lesbian daughters." Stress in pregnancy makes birth of a gay son likelier. "Although it has often been postulated that postnatal development is also important for the direction of sexual orientation, there is no solid proof for this."
. Williams et al. (2000) found that finger length ratio
, a characteristic controlled by prenatal hormones, is different in lesbians than in straight women. However, they found no difference between gay and straight men. 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
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. Gay men have also been shown to have higher levels of circulating androgens and larger penises, on average, than straight men.
Gay men have more older brothers
on average, a phenomenon known as the 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.
demonstrated that a tiny clump 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. In 2003 scientists at Oregon State University
announced that they had replicated his findings in sheep.
(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. An alternative explanation for this effect is the fact that girls with this condition are born with masculinized external genitalia, which 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.
Sexual orientation
Sexual orientation describes a pattern of emotional, romantic, or sexual attractions to the opposite sex, the same sex, both, or neither, and the genders that accompany them. By the convention of organized researchers, these attractions are subsumed under heterosexuality, homosexuality,...
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
The hormonal theory of sexuality holds that, just as exposure to certain hormonesBiology and sexual orientation
Biology and sexual orientation is the subject of research into the role of biology in the development of human sexual orientation. No simple, single cause for sexual orientation has been conclusively demonstrated, but research suggests that it is by a combination of genetic, hormonal, and...
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 either the primary influence upon adult sexual orientation or as a co-factor interacting with genes and/or environmental and social conditions.
A 2010 endocrinology study by Garcia-Falgueras and Swaab says that intrauterine exposure to hormones is largely determinative. Sketching the argument briefly here, it says that sexual organs are differentiated 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 [p. 24:] stage are permanent. . . . [S]exual differentiation of the brain is not caused by hormones alone, even though they are very important for gender identity and sexual orientation." ". . . . These fetal and neonatal peaks of testosterone, together with the functional steroid receptor activity, are thought to fix the development of structures and circuits in the brain for the rest of a boy's life (producing 'programming' or 'organizing' effects). Later, the rising hormonal levels that occur during puberty 'activate' circuits and behavioral patterns that were built during development, in a masculinized and de-feminized direction for male brains or in a feminized and de-masculinized direction for female brains." Because organ differentiation and brain differentiation occur at different times, in "rare" cases transsexualism can result (transsexualism resulting from having organs of one gender and feelings of the other). "The brain structure differences that result from the interaction between hormones, genes and developing brain cells are thought to be the basis of sex differences in a wide spectrum of behaviors, such as . . . sexual orientation (heterosexuality, homosexuality, or bisexuality) . . . . Factors that interfere with the interactions between hormones and the developing brain systems during development in the womb may permanently influence later behavior." "In humans, the main mechanism responsible of [sic] sexual identity and orientation involves a direct effect of testosterone on the developing brain." Drawing on some transsexualism cases, the authors say, "[f]rom these examples it appears that the direct action of testosterone on the developing brain in boys and the lack of such action on the developing brain in girls are crucial factors in the development of male and female gender identity and sexual orientation . . . ." "There are no indications that postnatal social factors could be responsible for the occurrence of transsexuality." "With regard to sexual orientation, the most likely outcome of childhood gender identity disorder is homosexuality or bisexuality." "The apparent impossibility of getting someone to change their sexual orientation . . . is a major argument against the importance of the social environment in the emergence of homosexuality, as well as against the idea that homosexuality is a lifestyle choice." "The presence of a genetic component of over 50% in the development of sexual orientation is apparent from family and twin studies." "Women with gay sons appeared to have an extreme skewing of X-inactivation [referring to the "X-chromosome"] . . . ." "[S]ome two million pregnant women . . . were prescribed diethylstilbestrol (DES)[,] . . . . an estrogen-like substance[,] . . . [and] it [was] . . . found . . . to increase the chance of bisexuality or homosexuality in girls." "The . . . . fraternal birth order effect . . . is putatively explained by an immunological response by the mother to a product of the Y chromosome of her sons. The chance of such an immune response to male factors would increase with every pregnancy resulting in the birth of a son." "Prenatal exposure to nicotine, amphetamine, or thyroid-gland hormones increases the chances of giving birth to lesbian daughters." Stress in pregnancy makes birth of a gay son likelier. "Although it has often been postulated that postnatal development is also important for the direction of sexual orientation, there is no solid proof for this."
Male homosexuality as hypermasculine
There is evidence of a correlation between sexual orientation and traits that are determined in uteroIn utero
In utero is a Latin term literally meaning "in the womb". In biology, the phrase describes the state of an embryo or fetus. In legal contexts, the phrase is used to refer to unborn children. Under common law, unborn children are still considered to exist for property transfer purposes.-See also:*...
. Williams et al. (2000) found that finger length ratio
Digit ratio
The digit ratio is the ratio of the lengths of different digits or fingers typically measured from the bottom crease where the finger joins the hand to the tip of the finger. It has been suggested by some scientists that the ratio of two digits in particular, the 2nd and 4th , is affected by...
, a characteristic controlled by prenatal hormones, is different in lesbians than in straight women. However, they found no difference between gay and straight men. http://mendel.ugr.es/genysoc/pdfs/sexorientation-finger.pdf Another study by McFadden in 1998 found that auditory systems in the brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
, another physical trait influenced by prenatal hormones is different in those of differing orientations, likewise the suprachiasmatic nucleus
Suprachiasmatic nucleus
The suprachiasmatic nucleus or nuclei, abbreviated SCN, is a tiny region on the brain's midline, situated directly above the optic chiasm. It is responsible for controlling circadian rhythms...
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. Gay men have also been shown to have higher levels of circulating androgens and larger penises, on average, than straight men.
Gay men have more older brothers
Brothers
Brothers are male siblings.Brothers may also refer to:- Film :* Brothers , an American silent film directed by D. W. Griffith* Brothers , an American film starring Vonetta McGee and Bernie Casey...
on average, a phenomenon known as the fraternal birth order effect. It has been suggested that the greater the number of older male siblings the higher the level of androgen
Androgen
Androgen, also called androgenic hormone or testoid, is the generic term for any natural or synthetic compound, usually a steroid hormone, that stimulates or controls the development and maintenance of male characteristics in vertebrates by binding to androgen receptors...
fetuses are exposed to.
Male homosexuality as hypomasculine
In a 1991 study, Simon LeVaySimon LeVay
Simon LeVay is a British-American neuroscientist. He is known for his studies about brain structures and sexual orientation.-Personal life:LeVay was born on August 28, 1943 in Oxford, England...
demonstrated that a tiny clump of neurons of the anterior hypothalamus
Hypothalamus
The Hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions...
—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. In 2003 scientists at Oregon State University
Oregon State University
Oregon State University is a coeducational, public research university located in Corvallis, Oregon, United States. The university offers undergraduate, graduate and doctoral degrees and a multitude of research opportunities. There are more than 200 academic degree programs offered through the...
announced that they had replicated his findings in sheep.
Female homosexuality
Girls with congenital adrenal hyperplasiaCongenital adrenal hyperplasia
Congenital adrenal hyperplasia refers to any of several autosomal recessive diseases resulting from mutations of genes for enzymes mediating the biochemical steps of production of cortisol from cholesterol by the adrenal glands ....
(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. An alternative explanation for this effect is the fact that girls with this condition are born with masculinized external genitalia, which 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 orientationBiology and sexual orientationBiology and sexual orientation is the subject of research into the role of biology in the development of human sexual orientation. No simple, single cause for sexual orientation has been conclusively demonstrated, but research suggests that it is by a combination of genetic, hormonal, and...
- Environment and sexual orientationEnvironment and sexual orientationEnvironment and sexual orientation is research into possible environmental influences on the development of human sexual orientation. Some researchers distinguish environmental influences from hormonal influences while others include biological influences such as prenatal hormones as part of...
- Handedness and sexual orientationHandedness and sexual orientationA relationship between handedness and sexual orientation has been suggested but not verified by a number of researchers, who report that heterosexual individuals are somewhat more likely to be right-handed than homosexual individuals...
- Genetics of gender
- Pathogenic hypothesis of homosexuality
- David ReimerDavid ReimerDavid Reimer was a Canadian man who was born as a healthy male, but was sexually reassigned and raised as female after his penis was accidentally destroyed during circumcision. Psychologist John Money oversaw the case and reported the reassignment as successful, and as evidence that gender...
- Mental roots of sexual orientationMental roots of sexual orientationA theory about the development of sexual orientation and sexual arousal suggests that these behavior patterns are learned unconsciously from asexual experiences during childhood. The learning begins when the child distinguishes between men and women by the pitch of their voice...