By Bruce L. Gerig
Recently, I was engaged in email correspondence that claimed in part that: "Sexual orientation is a myth and a philosophical category created by propagandists. The sad thing is that you believe it. Being 'gay' is a frame of mind not a state of being, like having black skin. You are gay because you want to be gay. … Even heterosexuality is learned … There is no definitive scientific evidence that homosexuality is biological…" Since this letter raises the very interesting – and now hotly debated – question of what causes homosexuality, it might be helpful to take a look at what science has recently discovered in this area.
In reply, I answered this man along these lines: "Homosexual orientation is a myth? All of the broad surveys on sexual-development studies that I have read recently conclude that there are clearly prenatal influences (cf. Balswick, Judith, & Jack Balswick, Authentic Human Sexuality: An Integrated Christian Approach, 1999; Gudorf, C., "The Bible and Science on Sexuality," in Balch, D., ed., Homosexuality, Science, and the ‘Plain Sense’ of Scripture, 2000; Friedman, R. & J. Downey, Sexual Orientation and Psychoanalysis, 2002; and Garnets, L. & D. Kimmel, eds., Psychological Perspectives on Lesbian, Gay, and Bisexual Experiences, 2nd ed., 2003). In surveying the scientific literature, the Balswicks at Fuller Theological Seminary (perhaps America's preeminent evangelical seminary) note that the five highest-ranking factors held by psychiatrists in one survey (Gallagher et al., 1993) were all biological, with genetic inheritance and prenatal hormones at the top of the list. Sixth and seventh on the list were a dominant mother and a weak father (p. 80-81). While they highly value heterosexual marriage, the Balswicks also recognize the reality of 'homosexual orientation,' that a gay person while having free will is still often limited in a variety of ways, that the Bible can be variously interpreted because its references to homosexuality are few and debated, and that the 'guilt and shame' that Christians heap on gay people are 'disheartening' (p. 86-96).
"If you want to know what it is like for a gay person to grow up in a conservative Christian world and suffer the torture there of realizing that he or she is gay (even leading to attempted suicide) and how God can then lead that person into a healing sense of self-acceptance and into a loving, committed relationship with another gay Christian, read Mel White's autobiography, Stranger at the Gate (1994). In all of my life, I can honestly say that I have never felt even one heterosexual desire, while from the earliest awakening of sexual awareness I found men in magazine swimsuit photos 'attractive.' I grew up in a Christian (evangelical) home, had wonderful, loving parents – and cannot tell you why I am gay. In my teenage and college years, I sought healing from the Lord through fasting and prayer, went to visit a faith healer, tried to date girls (a disaster), got treatment from a Christian psychiatrist (modification therapy), and in despair tried to kill myself. However, praise God, he spared my life, brought me back to study the Word in a more-in-depth way on the 'homosexuality' passages, gave me a miraculous assurance one day of his gracious love and full acceptance of me as a gay person (removing all of my self-hatred and guilt in a moment); and then eventually he led me to find a wonderful man with whom to share a Christian life and ministry. I can only bear witness of the great things Jesus has done for me!"
Surveying and evaluating the scientific literature on homosexuality is not easy. Caution is called for because of subconscious researcher biases, small samples often used, and the difficulty of finding valid random samples of gays and heterosexuals for study.1 Also, research is muddied, note Rahman and Wilson, by the nurture/nature debate, between social constructionists who argue that sexuality is fluid and can only be understood in socio-political contexts and biological scientists who feel that postmodern philosophy is a poor intellectual framework in which to understand the biology that underlies sexual development.2 Yet, the research keeps accumulating. In one search, for example, Daniel Olsen found more than 600 articles related to sexual orientation published within a two-and-a-half-year period (1/00-6/02), in biology, neuroscience, psychology and social science journals.3 Recently, psychiatrists Qazi Rahman and Glenn Wilson, in the department of psychology at the University of London, drew from 264 peer-reviewed articles to give an up-to-date summary of the biological findings in "Born Gay? The Psychobiology of Human Sexual Orientation," published in the journal Personality and Individual Differences (June, 2003).
Two other major reviews available are Edward Stein's The Mismeasure of Desire (1999), a social-constructionist attack on the biological research, and Joan Roughgarden's Evolution's Rainbow (2004), a review of biological evidence that focuses for the first time on transgender issues. Stein is a queer-studies philosophy lecturer at Yale University, while Roughgarden is a biology professor at Stanford University and also a person who transitioned from "Jonathan" to "Joan" in 1998. Dean Hamer, who spearheaded genetic linkage studies (1993, 1994, 1999) relating to sexual orientation is a gay senior scientist, who worked with Angela Pattatucci, a young out lesbian (along with other researchers).4 Some might complain that such gay and trans scholars are biased, but surely no more so or less capable as objective scientists than heterosexuals or nontransgenders. Roughgarden notes, for example, that gays and lesbians are highly underrepresented within the sciences, probably related to the "atmosphere of the laboratory." She explains, "It is a difficult environment for women and gays because of the sexually explicit humor." Also, "The party line according to Darwin and most sociobiologists is that females are looking for males with great genes. The proposition is clearly nonsense. … Scientists talk about the desire to test hypotheses, but there's enormous peer pressure for confirming existing dogma [heterosexual and otherwise]."5 Biologist Bruce Bagemihl, in Biological Exuberance: Animal Homosexuality and Natural Diversity (1999), not only presents the first systematic review on this subject but also discusses the homophobic bias that has often distorted scientific reporting on this.6 We should thank those scientists who are GLBT who push forward bravely to break new ground in important areas such as sexual orientation; and it's a healthy sign that they can disagree, as well.
Rahman and Wilson note that one area to look for biological influences on sexual orientation is heredity and genetics.7 Early research suggested that identical twins might share the same orientation, although Kallmann's 100% rate (1952) was rejected as extreme and his study suffered from numerous methodological problems, as well. More recently, with a larger sample, J.M. Bailey and colleagues (1991, 1993, 1993) reported that with identical twins (sharing all the same genes), 52% of the gay brothers had a gay twin and 48% of the lesbian sisters had a lesbian twin. With fraternal twins (from separately fertilized eggs, and typically sharing 50% of their genes) the figures were 22% and 16%, and with adoptive siblings the figures dropped to 11% and 6%.8 Edward Stein criticizes the Bailey study, suggesting (hypothetically) that some parents may treat identical twins more alike than fraternal twins and maybe the fraternal twins did not share "equal environments" to the extent that the identical twins did.9 Yet, while questions have been raised (e.g. later studies with twins showed varying figures), now at least seven studies support the conclusion that an identical twin of a gay person is about twice as likely to be gay as a fraternal twin would be, suggesting that genetics can play an important role in forming sexual orientation.10 Many would claim that the non-genetic variance here implies environmental influences (e.g. Stein11); however, K. Dawood and colleagues (2000) failed to find any shared social factors among the gay brothers such as paternal distance, material dominance, or fraternal incest. This study did confirm, however, that gay brothers often share a childhood gender nonconformity (CGN),12 although the question remains how much of this may derive from biological factors or social factors. Overall, these hereditary findings appear "robust."13
Dean Hamer's discovery of a genetic marker on the X (male) chromosome,
called Xq28, which might determine homosexuality (1993), has been
widely criticized; and indeed any claim of there being a simple “gay
gene" is unwarranted. In fact, Joan Roughgarden describes how genes cooperate
together, in a kind of "committee action," to fashion an individual's
gender and sexuality. Clearly the impact of the genes on sexual determination
is profound; and the ripple effect of this can makes for lots of biochemical
variation and produce normal people who are as "genetically diverse as
snowflakes."14 The powerful effect of genes (and
perhaps other prenatal factors) is revealed in Bouchard's study (1990, 1998)
of identical twins who were separated at birth, raised apart, and came to
know each other only as adults. Bouchard found many uncanny similarities,
e.g. one set of male twins, reunited at age 39, found that both of them had
a carpentry workshop installed in the home, hated baseball, drank the same
brand of beer and smoked the same brand of cigarettes, had suffered from migraine
headaches from teenage years, bit his fingernails, wrote love notes to his
wife which were then left around the house, and had a ten-pound weight gain
at the same age as the other twin, to name a few.15
It seems likely that the approximately 30,000 genes on the 46 human chromosomes
(usually XX pairs in the female and XY pairs in the male) in a fetus that
determine so many of an individual's traits (including physical gender and
appearance, as well as innate predispositions and talents), would play some
major role in sexual orientation formation, even in subtle and indirect ways
(such as predisposing a boy to prefer reading and music to rough-and-tumble
sports). Three studies by Hamer et al. (1993) and others (1995, 1999) have
suggested that gay men have more gay male relatives (uncles and cousins)
on their mother's side of the family than on their father's side,
consistent with the theory of an X-linkage.16
Because of the difficulty of tracing genetic and hormonal influences, scientists in the recent past have turned to studying neurogender differentiation in the brain using indirect research of what they call "correlates." This involves the study of (1) body features overall, (2) neuropsychological features, and (3) neuroanatomical features in the brain.17 The fundamental reasoning goes like this: If being right-handed or left-handed is not a matter of choice and the nature of one's fingerprints cannot be changed, then since homosexuality has been shown to relate to atypical characteristics in these areas, it probably also shares a biological basis.18 Relating to body features overall, for example, Lalumier and colleagues (2000) did a meta-analysis of 20 studies, confirming a relationship between homosexual orientation and greater left-handedness (higher in lesbians than in gay men). Wilson et al. (2000) found that lesbians typically have reduced 2D:4D finger ratios; that is, they display a lower ratio of lengths between the index (second) finger and the ring (fourth) finger on the right hand, compared with heterosexual women, showing a more male characteristic. Several other studies suggest that gay men may show an increased number of fingerprint ridges on their left hand, although this may not be true with male transsexuals (1994, 2000). Large contemporary studies, as well as the Kinsey data, show that gay men generally report an earlier onset of puberty than heterosexual males, as well as a lower height and weight – appearing to have moved in a feminine direction (1996, 1996). Not differing from their heterosexual counterparts in terms of the onset of menarche (the monthly cycle), lesbians do typically display greater height and weight (1997, 1998, 1999). McFadden and Pasanen (1989, 1999) reported that lesbian and bisexual women have fewer and weaker OAEs, especially in the right ear, than straight women, but higher levels than those observed in both straight and gay men. These otoacoustic emissions (OAEs) are clicking sounds generated by the cochlea, the snail-shaped part of the inner ear, which though not heard in a normal way can be picked up by a microphone. Also, when hearing a loud noise, lesbians blink more like straight men than straight women.19 In summary, then, gay men typically appear more female-like related to earlier pubertal onset and lower weight and height – but more "hyper-male" related to left-handedness, finger-length ratio, and perhaps genital size. Lesbians are consistently more masculinized, related frequently to left-handedness, finger-length ratio, OAE clicking, blinking, and height and weight.20
Relating to neuropsychological features, it has been documented that males excel in cognitive tasks involving spatial rotation and navigation (1999), whereas females excel in verbal fluency and memory, and facial emotional perception (1999, 2000). Independent studies have shown that gay men often perform worse on mental rotations and visual-motor targeting tasks but better on verbal fluency tasks than heterosexual men (1997, 1998, 1999), not related to differences in physical strength or sports history. (If this is present in childhood, it could explain why some boys do not like sports.) It has also been recently discovered that gay men are more female-like in their skill in object location memory. Thus, gay men tend to be more female-like in their spatial and visual-motor performance (lower) and in verbal performance (higher), compared to heterosexual men. Lesbians may show a male-like trend in visual-motor skill, but otherwise here are more female-typical. Also related to cognitive performance, Alexander & Sufka (1993), recording electroencephalographic (EEG) activity during the performance of verbal and spatial tasks, found patterns of alpha activity (rhythmic electrical oscillations) in gay men more like women than heterosexual men. Reite et al. (1995), using magnetoencephalographic (MEG) testing, found more symmetrical auditory source locations in gay men, again more like women than heterosexual men.21 How all of this relates specifically to homosexual orientation remains uncertain, yet the data suggest multiple biological atypical gender shifts.
Different neuroanatomic features in the brain have also be noted, that appear to relate to sexual orientation. Biologists who study the brain are used to looking for fine details.22 Allen and Gorski (1992) reported that the midsagittal plane of the anterior commissure (AC) is larger in gay men and more female sized. This refers to the front part of the AC nerve fibers that run between the brain's two hemispheres; and this increased size might indicate a greater transfer between the left and right hemispheres of the brain, generally associated with women's enhanced language fluency but reduced visual-spatial ability (1992). This greater interconnection of the right and left speech centers may also be related to the larger isthmus found in gay men, more like straight women than straight men (1994). The isthmus is a narrow structure that connects the two halves of the brain. Since another study (1997) connected a larger-sized isthmus with increased circulating testosterone, Rahman and Wilson conjecture that gay males may at some point during prenatal development have been exposed to greater amounts of testosterone than straight males (while at other times reduced amounts).23 Swaab and Hofman (1990) reported finding a larger, more elongated supra-chiasmatic nucleus (SCN) in gay males (a brain region associated with sleep rhythms and sexual behavior) and more female-like, than found in heterosexual men. In connection to this, Rahman and Silber (2000) documented that gay men and lesbians often rise earlier and retire later than heterosexuals, apparently requiring less sleep and possibly related to a larger SCN and its neural action. Simon LeVay (1991) reported that an area of the hypothalamus called INAH-3 was smaller in gay men and female sized.24 The hypothalamus is a small area located at the very bottom of the brain, above the roof of the mouth; and INAH-3 refers to the third interstitial nucleus of the anterior (front part of the) hypothalamus.25 Animal studies have shown that lesions (damages to tissue) in the front region of the hypothalamus can affect sexual behavior and gender preference. Rahman and Wilson conclude, therefore, that gay men appear to show a trend toward female-typicality in various neural regions of the brain, specifically in the isthmus, AC, SCN and INAH-3. There is insufficient data to say whether lesbians show any male-typicality here or not.26
Unrelated to gay people, two studies (1995, 2000) have reported that male-to-female transsexuals display a more female-sized bed nucleus of the stria terminalis, in the central area (BSTc) than gays or straight men. These findings are the first to identify a correlate (relationship) between neuroanatomy and gender identity.27 The BSTc (or BNST) is a rice-grain sized area located near the hypothalamus; and while the data supporting the idea that this may be a gender-identity locus (location) in the brain is thin, Roughgarden says that this possibility should be taken seriously.28 These studies (Zhou et al., 1995; Kruijver et al., 2000) analyzed 34 brains preserved in formaldehyde in the Netherlands Brain Bank, including brains from heterosexuals, homosexuals, 6 transgendered women, and 1 transgendered man. The heterosexual males and gay males showed a BSTc size about one-and-one-half the size of the heterosexual females, while the BSTc size of the 6 transgendered women matched that of the heterosexual women and the BSTc size of the 1 transgendered man fell into the male range. The investigators suggested that these neural differences between transgendered and nontransgendered people are "likely to have been established … during early brain development," just as testosterone organizes BST dimorphism (male or female gender) in rodents soon after birth. Roughgarden believes that the larger data point rather to a wide variety of brain features and combinations, not just a two-gender model. Still, as Stein notes, it is interesting that there appear to be "relatively few bisexuals and asexuals, at least among men."29 Roughgarden notes that these studies and some animal models suggest an organic counterpart to some of the variation in gender identity, revealing "something deep about ourselves."30 From all the data, she concludes that gender identity probably takes place sometime between the middle trimester (three-month period) of pregnancy, when genitals develop, and perhaps a year after birth, although why some babies focus on the same-gender parent and some on the opposite-gender parent remains unclear.31 Also, science has no good reason to explain the ratio of gays to straights (10% for the men and 5% for the women) nor why lesbians overall appear to be more bisexual.32 I would suggest that these point to something deep (biological), as well, relating to human nature and sexual development.
Sexual orientation is also affected by sex hormones, that play a critical role during fetal development in the womb. A large body of research shows that the male fetal brain is masculinized by male sex hormones during critical periods of development and that an absence of proper levels of male hormones results a feminization of the male fetal brain. Hormonal exposure at this time organizes the brain in a lasting manner and determines male-typical or female-typical patterns in both sexes, including sexual preference, gender identity, childhood interests, and later sexual behavior.33 G. Dorner as well as other researchers found in animal models (guinea pigs, rhesus monkeys and rats) that if testosterone is blocked from a male fetus during the early stages of development that animal at maturity will display sexual attraction and behavior toward the same sex rather than the opposite sex; and similar effects have been observed when elevated levels of testosterone are given to mothers carrying female fetuses.34 Evidence for this also comes from studies of "homosexual rams," the first report of "exclusive homosexual behavior" in animals without human intervention, where there was found to be a reduced conversion of testosterone into absorbed dihydrotestosterone, a form that masculinizes estrogen receptors in the male (2000).35
While manipulation of sex hormone levels in the human fetus cannot ethically be done, it is known that human males with complete androgen (male sex hormone) insensitivity syndrome (CAIS) report female-typical sexual behavior (2000). Conversely, girls with congenital adrenal hyperpasia (CAH) display a male shift. With this condition, the body is XX but synthesizes too much male hormone and so external genitalia are produced. CAH children typically display reduced interest in playing with dolls and wearing feminine clothes (with lace and frills); and when they become teenagers, despite social pressures, they prefer boy playmates, male-typical activities, and careers over marriage (Berenbaum 1999). A further observation is that the more extreme and prolonged exposure the prenatal brain has to male hormones, the more likely intersex children will display male-typical role behavior.36 While more research is needed, Rahman and Wilson note that hormonal action in the brain can provide an adequate framework for explaining both male and female homosexuality.37 While Stein notes that humans share 98% of our genetic code with both the common and the pigmy chimpanzee and that primates are far more promising than nonprimate models for related research, he concludes that no primates are suitable models for human comparison – because humans have more complex languages and cultures, most animals who engage in homosexual activity also engage in heterosexual activity, and human sexual orientation involves complex cognitive, emotional, and social properties that primates do not have.38 His arguments here (as often), are extreme.39 Granted, humans do not display mounting and copulating patterns like rats; yet still, as Bailey notes, such animal studies have immense informational value in suggesting various human models to study.40 Roughgarden notes that differing hormonal experiences are a major source of diversity in the sexual development narratives of people, including testosterone, estrogen and the other sex hormones, which are widespread throughout the vertebrates. This variation not only relates to how much of a hormone is present at various critical points in development, but whether and to what degree brain cells have receptors that respond to them.41 Freidman and Downey conclude that "it seems possible that many or even most males on a gay development track are not exposed to the prenatal organizational effects of androgen [male hormones] in the same way as those on a heterosexual tract."42
Turning from biologists to experiential theorists, Stein notes that most of
the latter believe that at birth we all have roughly the same (neutral) potential
relating to sexual desire; and that different experiences and environments
account for differences in sexual orientation. Theories fall generally into
three camps: (1) Sexual orientation is determined by a child's early
sexual experience, perhaps fixed by his or her first pleasurable
sexual experience, and directed homosexually if a child has pleasurable sex
with the someone of the same gender or unpleasant sex with someone of the
opposite gender, or is seduced by a homosexual. (2) Sexual orientation is
determined by family dynamics, growing out of Freud's view
that male homosexuality results from having a strong mother and a distant
father, or the opposite with lesbianism. (3) Sexual orientation is determined
by gender (a)typicality, which suggests that boys who play
physical sports and pretend to be soldiers will grow up heterosexual, while
boys who play with dolls and pretend to cook ("sissies") will grow
up to be gay.43
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