1. BRYAN CURRIE BRAIN DEVELOPMENT OF YOUTH HDFS 892 MICHIGAN STATE UNIVERSITY Biological Causes for the Homosexual Brain

2. Why Study Homosexual Brain Development? Puberty – the amazing time when adolescents realize their sexual attractions and abilities – is both exciting and terrifying. During puberty, heterosexual youth may be confused by their newfound attractions, but are assured by their culture that they are “normal.” Homosexual youth, however, are not as fortunate. From a very early age, lesbian, gay, bisexual, and transgender (LGBT) youth are often keenly aware that they are “different” (source). In addition to figuring out the “normal” struggles of sexual attraction, LGBT youth often question whether they are broken, strange, or immoral because their attractions aren’t like everyone else’s. Some of these youth even pursue dangerous therapies to try to “fix” their sexual orientation. It is important for youth development professionals to understand theories surrounding the development of the homosexual brain so that they can assure frightened LGBT youth that their newly discovered desires are simply a part of their beautiful design.

3. The Homosexual Brain: Premise and Thesis Premise: Various in-utero factors may affect the development of the homosexual brain so that both its form (i.e. physical structure) and function (i.e. sexual attraction) are slightly different from the heterosexual brain. Thesis: Although both nature (genetics and/or biology) and nurture (environment, etc.) may play a role in the development of sexual orientation, this presentation will focus on biological theories for homosexual brain development. Biological theories include the ways hormones affect the fetus in-utero and should not be confused with genetic theories, which include the search for the “gay gene.” In addition to discussing the formation of the homosexual brain, this presentation will also explore whether the brains of homosexual youth are physically different from those of their heterosexual peers. Disclaimer: It is important to understand that “masculine” and “male” are not synonyms. Gay men are neither inherently less “masculine” nor “male” simply because of their sexual orientation. Although many of the studies referenced in this report refer to the “masculine” or “feminine” brain, it should be understood that these words refer to biological differentiation of the brain (ie. whether it is structured more like a male brain or a female brain). These words are not intended to comment on the masculinity/femininity (i.e. culturally defined behavior) of homosexual people.

4. THE HOMOSEXUAL BRAIN Biological Theories of Development

5. Major Biological Theories There are two major theories for biological (in-utero) causes of homosexuality:  The mother may produce an immune reaction that prevents the male brain from developing in a typically “masculine” pattern.  The hormone wash which “defeminizes” the brain in-utero is disturbed due to maternal stress.

6. IT HAS BEEN SUGGESTED THAT THE MALE FETUS MAY SOMETIMES PRODUCE AN IMMUNE RESPONSE IN THE MOTHER WHICH TRIGGERS THE RELEASE OF ANTIBODIES. THESE ANTIBODIES CHANGE THE FETUS’S BRAIN DEVELOPMENT AND CAUSE A HOMOSEXUAL ORIENTATION. Maternal Immune Reaction

7. Maternal Immune Reaction: Antigens Because of a male child’s XY gene structure, HY antigens are present on the surface of his developing cells. Because the expectant mother is used to having only XX cells in her body, Blanchard and Bogaert (1996) propose that when the male fetus’s HY antigens are released into the mother’s bloodstream, her body may trigger the immune system to release HY antibodies. These antibodies cross the placenta and enter into the male fetus’s developing brain. HY antigens help the male fetus develop sex-typical traits. Exposure to HY antibodies (which attack and potentially weaken the HY antigens) may therefore affect subsequent sexual behavior in men, increasing the likelihood that the male child will be more attracted to men than women (Blanchard & Klassen, 1997). Antigen: any substance foreign to the body that evokes an immune response from the host.

8. Maternal Immune Reaction: Evidence In most cases, a mother’s immune system becomes stronger with every pregnancy. Therefore, each time a mother carries a male fetus, the chances increase that her body will develop an immune response to his HY Antigens. This may explain why male homosexuality correlates with birth order. Each additional older brother increases the likelihood a male child will be homosexual by 33% (Blanchard & Klassen, 1997; Cantor, Blanchard, Paterson, & Bogaert, 2002).

9. Maternal Immune Reaction: Evidence “the same genetic factors that induce gayness in males also promote fecundity (high reproductive success) in those males’ female maternal relatives” (Wolchover, 2012,). If there is a “gay gene” it likely resides on the X chromosome. Evolutionary biologists suggest that the presence of this gene in mothers may “increase androphilia, or attraction to men, thereby making the males who possess the gene homosexual and the females who possess it more promiscuous” (Wolchover, 2012). If this theory holds true, larger family sizes may not be the cause of homosexual male children, but rather an evolutionary result of the “gay gene” as it is carried by women on the X chromosome. New research has, however, begun to question whether having multiple male children is a cause of homosexuality (due to an immune reaction) or an evolutionary product of the “gay gene.” According to research that will be published in an upcoming issue of the Journal of Sexual Medicine:

10. ALL FETUSES BEGIN BIOLOGICALLY FEMALE. A WASH OF TESTOSTERONE DURING THE 12-14 TH WEEKS OF PREGNANCY PRODUCES A MASCULINE BRAIN. DISRUPTIONS IN THIS PROCESS MAY PREVENT THE BRAIN FROM BECOMING FULLY MASCULINE. Hormone Wash

11. Hormone Wash: Androgens If a fetus carries the XY chromosome, testosterone is needed to activate the newly forming hypothalamus into a male brain. This process is called “defeminization” (Kula & Sowikowska-Hilczer, 2000). Different levels of testosterone exposure during this process influence “the structure and function of brain regions that control the direction of sexual attraction” (Wilson & Rahman, 2005, p. 70). Because the genitals are developed during a different period of gestation and through a different process than the defeminization of the brain, the presence of a masculine body does not necessarily indicate the presence of a masculine brain. This may partially explain why the brain structure of homosexual males may more closely resemble that of heterosexual females. Androgen: A steroid, such as testosterone, that controls the development and maintenance of masculine characteristics.

12. Hormone Wash & Maternal Stress Because the stress hormone seems to mimic testosterone, the wash of testosterone is less effective, causing a disturbance in the "defeminization" of the hypothalamus (Swab, Chung, Kruijiver, Hofman, & Ishunia, 2002) and preventing “normal” sex differences in the brain to be acquired (Looy, 1995). If a mother is stressed during the early stages of pregnancy, she will release an adrenaline related hormone. This hormone (androstendione) is structurally similar to testosterone, but affects the fetus differently. During the 12th to 14th week of pregnancy, a developing male fetus will receive a wash of androgens (testosterone) over its brain. This hormone wash defeminizes it and differentiates it into the male form (Gooren & Kruijver, 2002).

13. Hormone Wash: Evidence Ingebog Ward (1972) tested this theory in studies of pregnant rats. Ward divided pregnant rats into three groups. She subjected the first group to stress during the first ten days of gestation by irritating the mothers with bright lights, noise and vibrations. Ten days in a rat's pregnancy corresponds to the first trimester (3 months) of human pregnancy. The second group was subjected to stress during the end of their pregnancy, just before birth. The third group was comprised of male offspring from both prenatal stressed mothers and unstressed mothers. Dr. Ward then allowed all the males to grow to adulthood without further interference. The sexually mature male rats were placed in cages with healthy females to observe their ability and desire to mate with normal adult females.

14. Hormone Wash: Evidence Instead of trying to “mount” female rats, the stressed males allowed themselves to be mounted. This was attributed to stress caused reactions during critical stages of sexual differentiation. “Specifically, it appears that stress causes an increase in the weak adrenal androgen, androstendione, from the maternal fetal adrenal cortices, or both, and a concurrent decrease in the potent gonadal androgen, testosterone” (Ward, 1972, p. 82). Ward concluded that “exposure of pregnant rats to environmental stressors modifies the normal process of sexual behavior differentiation in male fetuses by decreasing functional testosterone and elevating androstenedione levels during prenatal development” (Ward, 1975, p. 83). Stress during pregnancy seems to prevent testosterone from developing a brain that is sexually attracted to females.

15. THE HOMOSEXUAL BRAIN Neurological Differences

16. Brain Differences It has been shown that the brains of heterosexual males, homosexual males, heterosexual females, and homosexual females function differently and are differently structured. * It is not clear if the differences between the homosexual and heterosexual brain are due to biological factors, genetic factors, or conditioning.

17. Functional Differences: Cerebral Asymmetry Click box to play video. Video can also be viewed online here.here

18. Structural Differences Many of the structural differences between the homosexual and heterosexual brain are found in the hypothalamus, the region of the brain that controls how humans experience sexual attraction (Dorner, 1979). These differences may be contained in any of three regions:  Sexually Dimorphic Nucleus (SDN)  Suprachuiasmatic Nucleus (SCN)  Anterior Commissure (AC)

19. Structural Differences: SDN The sexually dimorphic nucleus (SDN) is a cluster of cells in the preoptic area of the hypothalamus. The SDN is believed to help regulate sexual behavior (Allen, Hines, Shyne, & Gorski, 1989; Anderson, Fleming, Rhees, & Kinghorn, 1986).  The SDN is commonly 2.5x larger in males than females, containing 2.2x more cells (Swaab & Fliers, 1985).  Researchers hypothesize that brains attracted to women (heterosexual men and homosexual women) should have a lager SDN.  Sections of the SDN, known as INAH 3, have been shown to be up to 3x larger in heterosexual men than heterosexual men (LeVay, 1991).*  These findings (that both heterosexual women and homosexual men have a smaller SDN) seem to indicate that male homosexual brain structure influences/causes a sexual attraction to men. *The study referenced (LeVay, 1991) was performed on post-mortem AIDS patents. Some researchers question the study’s findings, claiming that the enlarged INAH 3 region found in homosexual men may be a result of the AIDS virus.

20. Structural Differences: SCN The suprachiasmatic nucleus (SCN) is a small region in the brain’s midline. It is responsible for regulating circadian rhythms (i.e. body functions in a 24 hour cycle) and has been associated with reproductive processes (Swaab & Hofman, 1995).  The SCN has been shown to be 1.7x larger in homosexual males than in heterosexual males, containing 2.1x more cells (Swaab & Hoffman, 1990).  Swaab produced a similar difference in rats by disturbing the interaction between testosterone and the developing brain. The experiment yielded bisexual rats that had a significantly larger SCN.  Swaab (2008) suggests that his tests on rats indicate that the larger SCN in homosexual males is not caused by their behavior (nurture), but rather “by an atypical interaction between sex hormones and the developing brain” (p. 10273).

21. Structural Differences: Anterior Commissure The Anterior Commissure (AC) is a fiber tract that is responsible for transmitting sensory information between the brain’s temporal lobes (Harrison, 1994).  The AC is typically larger in women than in men (Allen & Gorski, 1991).  The AC of homosexual men has been shown to be 18% larger than heterosexual women and 34% larger than heterosexual men (Allen & Gorski, 1992).  While the AC is not associated with reproductive functions, it is related to cognitive abilities and language (Swaab, 2008). The presence of a larger AC may explain why homosexual men seem to display many “feminine” brain functions (see “functional differences” above).

22. Conclusion Click box to play video. Video can also be viewed online here.here

23. Bibliography Bibliographical references can be found in the notes section below.