THE NEUROBIOLOGY OF HOMOSEXUALITY
By Stanley M. Bierman, M.D., F.A.C.P. (C2005)
The choice of homosexuality as the subject of this newsletter is based on the frequency with which Acquired Immune Deficiency Syndrome has appeared as a main topic of this periodical. While a scholarly discussion of the subject has little practical application, the intellectual challenge of understanding the reason why individuals chose this particular life style is substantial. The litany of names of distinguished homosexual men and women of science, art, literature and sports include Hans Christian Anderson, Sir Francis Bacon, Truman Capote, Leonardo da Vinci, Amelia Earhart, Malcolm Forbes, and David Geffen....and I have only gotten to the "Gs" in the alphabet of gays whose lives have profoundly impacted on the straight world.
LABIA an acronym for Lesbians and Bisexuals in Association, a gay women's caucus group in San Francisco, have proposed the following "Heterosexual Questionnaire" as a challenge to their straight counterparts: (1) What do you think caused your heterosexuality? (2) When and how did you decide that you were heterosexual? (3) To who have you disclosed your heterosexuality? How did they react? (4) Is it possible that your heterosexuality stems from a neurotic fear of others of your same gender? (4) Heterosexuals have a history of failure in gay relationships. Do you think you may have turned heterosexual out of fear of rejection? (5) Why do you flaunt your lifestyle with wedding rings, photos of spouses, and talk of your sexual escapades? (6) Why do so many heterosexuals try to seduce others into their orientation? (7) Are cancer, earthquakes and floods God's way of punishing heterosexuals?
Well, anyway, there are additional disingenuous questions, but it is clear that these gay-advocates are using sarcasm in addressing the prejudice with which many in the straight community view homosexuals. Many in the gay community have put forward the thesis that homophobia, designating a decidedly disapproving antihomosexual attitude, can be equated to racism. This particular anti-gay attitude is fostered by many religious fundamentalists who view homosexuality with contempt from biblical injunctions, and depict gays in negative stereotypes.
The medical profession has taken a decidedly solicitous view of the matter. The deletion of homosexuality from the American Psychiatric Associations primer on Diagnostic and Statistic Manual in 1980 marked a dramatic reversal in the judgment that homosexuality was a psychiatric disorder that could be treated by traditional psychiatric approaches. Heretofore homosexuality was viewed in Freudian terminology with psycholinguistic flourishes equating homosexuality with gender identity, masochism, paranoia and narcissism. Alfred Kinsey was one of the earliest researchers to approach the subject of homosexuality in a dispassionate scientific mode. In his seminal study on Sexual Behavior in the Human Male (1948), Kinsey observed that 4 percent of men and 2 percent of women were exclusively homosexual, while 37 percent men and 13 percent of women reported at least one homosexual experience resulting in orgasm. Recent studies by Robert Michael et al in Sex in America (1994) claim the 1.4 percent of women consider themselves lesbian and 2.8 percent of men identify themselves as exclusively homosexual.
Why do some individuals chose to become homosexual given the decidedly negative sentiment by the public? Do gay men and lesbian women really have a choice in the matter? There is little question that homosexual behavior is impacted by genetic determinants. In recent studies by Hamer using DNA linkage analyses, a gene influencing homosexual orientation has been found on the X chromosome (Science 1993; 261:321-7). Bailey has reported increased concordance for homosexuality among male and female monozygotic (identical) twins (Arch Gen Psych 1993; 50:217-23). A genetic influence toward homosexual orientation is suggested by select cases where identical twins concordant for homosexuality were separated early in life and reared apart (Arch Sex Beh 1993; 22:187-206). Recently Canadian scientists have found that gays have more fingerprint ridges bolstering the theory that sexual orientation is determined before birth.
Neither plasma levels of androgens nor other endocrinologic studies in mature adults reliably distinguish groups with regard to sexual orientation. While administration of male hormones can influence sexual desire, homosexuality is certainly not produced by castration. However studies of sexual behavior in select laboratory animals have led to the belief that androgenic deficiency in the brain of guinea pig fetuses lead to male homosexual behavior, and that prenatal androgen excess resulted in female homosexuality (Endocrinology 1959; 65:369-82). Another reason for suggesting prenatal steroid hormones may influence sexual orientation is borne out by behavioral antecedents: during the childhood of gay men, aversion to play that involves fighting and rough-and-tumble team sports is common. Likewise, the opposite pattern of tom boyishness is common in women who become lesbians. In other studies, Dorner has speculated that inadequate prenatal androgenization of the central nervous system leads to a partially female differentiated brain during a critical period of sexual orientation (Endocrin 1980; 75:365-68).
Reports have appeared in the literature documenting statistical differences in anatomic structures within the brain and sexual orientation. It is claimed that there is an increase in size of the superchiasmatic nucleus of the hypothalamus (Brain Res 1990; 537:141-8), decrease in size of the anterior interstitial nucleus (Science 1991; 253:1034-7) and increased size of the anterior commissure in homosexual men (Proc Natl Acad Sci 1992; 89:7199-202).
Important insights of psychosexual development have been derived from studies of patients with so-called intersex disorders. As innocent participants of experiments in nature, newborn females exposed to male-like hormone arising from congenital tumors of the adrenal gland develop a masculinizing syndrome with hirsutism (excessive hair growth) and clitoral enlargement. As the child matures into adolescence, she has a high proclivity to engage in homosexual behavior. Lewis (1982) reported an increased incidence of homosexuality in young boys with idiopathic adolescent gynecomastia (breast enlargement).
Although there has been a rapid growth in an understanding of human sexual orientation, fundamental questions still remain in our understanding. While scientific data has been gathered to correct many misconceptions widely accepted about gay men and women, community laws and public policy are still influenced by views long discarded by behavioral scientists. Political activists in religious groups such as the Moral Majority have been unrelenting in their condemnation of gays, and homosexual acts are still considered as criminal in many states, and decisions regarding custody, visitation rights and adoption are frequently made on the basis of sexual orientation. Finally, gay men and women receive unequal treatment in the military.
Given these verities, why do some individuals become homosexual? While this essay has not proven a definitive neuroendrocrinologic basis, it is possible that the brain of gay men and women was indelibly imprinted at birth, and sexual orientation is not a simple matter of choice!