The Biology of Homosexuality Updated

Carl S. Keener

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The aim of this article is to provide an update concerning some significant research and commentary since Douglas Swartzendruber and I published an article in Booklet #5 of the Welcome to Dialogue Series (Keener and Swartzendruber 2001). However, before examining some of the recent research, I will point out several important problems that always seem to be in the background when Christians discuss gay and lesbian matters.

Use of the word “homosexual.” This word is better used as an adjective. Furthermore, the word is ambiguous, and can refer to one’s sexual orientation (“being”) or to one’s sexual practices (“doing”). Merely being gay or lesbian indicates nothing about one’s sexual practices, one’s sexual identity (whether a person whose sexual orientation is gay or lesbian actually thinks of himself or herself as gay or lesbian), or gender identity (a person’s perception as being either male or female) and we should be clear about this point. Still, there are those who believe that a person cannot be a celibate gay! Furthermore, one’s behavior does not necessarily indicate one’s sexual orientation.

Ascertainment bias. Determining a person’s sexual orientation isn’t simple, and this problem continues to plague investigators. At issue is what specific component is the best indicator that a person is indeed gay or lesbian, etc. With respect to sexual behavior, Kernberg (2002) lists four basic components: core gender identity (subjective sense of being male/female), gender role identity (enactment of male/female roles, such as rough and tumble play), object choice (which sex is the desired sexual object), and intensity of erotic desire. To be sure, these components may not always be in agreement, as, for example, a man may have sexual relations with his wife although his fantasies are that he desires sex with males.

Essentialism and social constructivism. At issue are two very different ways of viewing the world we live in. Sorting out the differences between essentialism and constructivism isn’t easy, and is certainly not reducible to pat formulas. Even the terms themselves have different meanings. As used here, according to social constructivism, “truth” is subjective, and one’s culture itself influences one’s perceptions of reality. Moreover, quantitative research with its well-defined categories is called into question (DeLamater and Hyde 1998, Robboy 2002). This means that the categories of sexual orientation are cultural constructs of human societies rather than naturally occurring universal categories, and thus they differ in various societies as well as different times throughout human history. Social forces, thus, shape human behavior, including human sexuality, and knowledge as such is a product of human discourse (Norton 1997, Stein 1998). As Caroline Robboy (2002) states, “social constructionism questions biological assumptions.” Moreover, some social constructionists question whether “sexual orientation” is a meaningful category. On the other hand, according to modern essentialism, certain observable phenomena are natural, classifiable, culturally independent, and overall imply “ … the presence of a fixed sexual quality in a person, a lack of choice about the existence of the quality, and an underlying and enduring core basis for categorical descriptions of persons based on the quality” (Stein 1998). To put my cards on the table, following Sir Karl Popper, John Searle, and many others, I am an external realist (= modern essentialist) in that I believe there is a world “out there” independent of any of our mental functions or anything we might think about that world. We did not construct oak trees, viruses, chromosomes, and DNA no matter what language we use or what our perception is of these natural phenomena. Nor did we construct human and animal sexuality. To be sure, we have given names to the structures and processes we have discovered: Krebs cycle, photosynthesis, interstitial nuclei of the anterior hypothalamus, egg and sperm, to name a few items at random. But the structures and processes were there all the time, and only with better investigative procedures has our knowledge of how the world works likewise increased. Moreover, there are objective criteria enabling us to judge the relative truth/falsity of our conjectures. For example, if we state that oak trees are more closely related phylogenetically to chestnuts than they are to huckleberries, we have objective criteria by which to judge this statement. This brings me then to state my belief that human nature as such is open to empirical investigation and this kind of investigation includes our sexuality. To be sure, social constructionism may help us to better understand the cultural contexts of human sexuality, but it has not helped us understand why certain persons become gay, lesbian, etc. (LeVay 2003b).

Some Recent Research Concerning the Biology of Same-sex Attraction

Simon LeVay recently published a comprehensive overview of the theories (non-biological and biological) and current research related to sexual orientation, and the reader is urged to consult LeVay for a more thorough review (see LeVay 2003b and references therein). Although not all of these studies will be reviewed further here, they include twin and pedigree (sibling) studies, molecular (gene) studies, possible function of “gay” genes within populations, various studies involving prenatal hormonal levels and their effects on brain structure and function, and various cognitive studies (see also Keener and Swartzendruber 2001 for additional information). As Simon LeVay (2003b) states, “the biological processes, especially the prenatal, hormonally-controlled sexual differentiation of the brain, are likely to influence a person’s ultimate sexual orientation.” For a fine readable overview of the biological nature of homosexuality with special emphasis on transsexuality, see Bailey (2003).

Brain Studies. The neuroanatomist Simon LeVay created quite a stir when he announced over a decade ago that in one region of the brain-the interstitial nuclei of the anterior hypothalamus (INAH3)-there were significant differences between the brains of gay and straight men, and that in this region the brains of gay men were similar to females (LeVay 1991). Incidentally, among other functions, the hypothalamus helps generate our sexual behavior. LeVay’s research had been criticized by a number of people, including William Byne. However, Byne has now repeated LeVay’s work and essentially agrees with LeVay in that there are size differences in the INAH3 region between gay/straight men and that the cause of death (AIDS, etc.) does not affect the relative size of the INAH3 region (Byne et al. 2000, 2001; see also Swaab et al. 2001, and Bailey 2003, 119ff.). Furthermore, Charles Roselli et al. (2004) have reported that, as compared to humans, there are similar structural differences between gay/straight rams. That said, however, we “know nothing about the ontogeny [developmental origins] of human INAH3” (Morris et al. 2004).

Fraternal birth order. There is some evidence that fraternal birth order is a critical variable in male homosexuality. With an increased number of older brothers, there is a greater chance a younger brother will become a homosexual adult such that “roughly 1 gay man in 7 owes his sexual orientation to the fraternal birth order effect” (Cantor et al. 2002). Moreover, neither older brothers nor older sisters affect the sexual orientation of later born females, nor, for that matter, do older sisters affect later born males. According to Cantor et al. (2002), the fraternal birth order effect exceeds “all other causes of homosexuality in groups of gay men with 3 or more older brothers.” Research increasingly points to the possibility that the birth order effect may be caused by certain critical prenatal hormonal influences affecting the pattern of brain development. It appears that some sort of antigen/antibody interaction may occur between a mother and her earlier male offspring such that in later males her antibodies may affect the developing structures of the brain during the time when the fetus is in utero (Blanchard and Klassen 1997, Blanchard 2001, Cantor 2002).

Gender nonconformity and gender identity disorder. Studies of young children suggest that young boys with highly feminine traits (“sissies”) frequently in later life become males with a same-sex attraction. As recent research shows, this childhood gender nonconformity (CGN) has a heritable component (Pillard and Bailey 1998, Bailey et al. 2000, Kirk et al. 2000, Bailey 2003). Moreover, gender identity disorder (GID), i.e., a persistent cross-gender identification and discomfort with one’s biological sex, is known to have a significant additive genetic component (Coolidge et al. 2002). These gender identity disorders resulting in nonconformed childhood gender differences typically show up in a child’s life long before any sexual awareness occurs. Moreover, these traits are associated with a neurohormonal theory of sexual orientation in that a sex-atypical hormonal profile affects neurodevelopment-too few androgens for males, too many for females, thus resulting in homosexual males and females (Gangestad et al. 2000).

Animal studies. In my opinion, the best evidence for a biological basis of same-sex orientation comes from animal studies, such as Bruce Bagemihl’s monumental compilation and Perkins and Fitzgerald’s sheep studies (see Keener and Swartzendruber 2001 for additional information). Recently, Charles Roselli and his colleagues (2004) have presented the first documented evidence that rams exhibiting same-sex preference have a cell group related to sexual preference that is significantly larger in female-oriented rams than in male-oriented rams. It is now clear on the basis of recent research that the “median preoptic anterior hypothalamic (MPOA-AH) continuum is the most critical brain structure for the control of masculine sexual behaviors in all vertebrate species that have been studied” (Roselli et al. 2002). One hypothesis is that “naturally occurring variations in sexual partner preference may be related to differences in brain anatomy and capacity for estrogen synthesis” (Roselli et al. 2004; see also Roselli et al. 2002). As Roselli et al. (2002) indicate, “MO [male-oriented] rams exhibited hormone profiles and responses distinctly different from their heterosexual counterparts.” Their data support the earlier study of Simon LeVay (1991) who found a similar correlation in the brain structures between homosexual and heterosexual men. To be sure, there is a lot more research yet to be done, especially with respect to the precise relationship of certain hormones and their impact on observed brain differences (Morris et al. 2004). But the fact that animals show the same sort of brain anatomical differences as do humans lends important support to the view that human sexual orientation has a biological-developmental basis, and cannot be relegated to simple choice or to bad parenting.

A Note on Transsexuality. Although there has been a considerable literature dealing with gay and lesbian sexuality, relatively little has been written for the lay public concerning transsexuality. In The Man Who Would be Queen, J. Michael Bailey, Professor of Psychology at Northwestern University, and a significant sex researcher, has redressed this gap. As Bailey (2003, x) states, “[s]cientifically, we have begun a renaissance period for taking femininity and masculinity seriously.” Bailey believes that “sexual orientation, gender identity, and gender role behavior” are not necessarily “separate, independent psychological traits,” and that moreover “femininity and homosexuality are closely bound together in men” (Bailey 2003, xi). Furthermore, “[o]ne cannot understand transsexualism without studying transsexuals’ identity” (Bailey 2003, xii). Now understanding transsexuality has not been easy for at least two reasons: there are relatively few subjects, and relatively few competent researchers. Space forbids a thorough review here, and thus the reader is urged to read Bailey’s book containing a fine overview of the biological aspects of homosexuality in conjunction with its analysis of two categories of male-to-female transsexuality (Bailey however discusses only feminine males-as he says, “masculine females deserve their own book.”). Briefly, here are some of the important points (pages refer to Bailey 2003):

  1. Clear-cut distinctions between females and males are simply not possible either biologically or behaviorally (39ff.; 50).
  2. Sexual orientation is not a recent invention by social constructionists-it’s an essential part of human nature (ch. 7).
  3. Gender identity disorder (GID) shows both behavioral criteria (e.g., preference for cross-dressing, etc.) and discomfort with one’s biological sex (23).
  4. Feminine boys often exhibit a variety of feminine behaviors (18).
  5. Transgender homosexuality occurs when one man takes on a feminine role, often dressing like a woman and taking a woman’s name, and has sex with masculine men” (134), whereas “[e]galitarian homosexuality occurs when two individuals of similar age and class form a homosexual relationship.” In the former type, only one of the partners is truly gay, whereas in the latter type both partners are gay (134-138).
  6. Transsexualism is the “desire to become a member of the opposite sex” (144), and is relatively rare (only about 1 in 20,000 persons is transsexual) (142).
  7. Following the research of Ray Blanchard, Bailey recognizes two types of transsexuals who began their life as males: homosexual transsexuals(extremely feminine gay men who early on behave like a female, and are strongly attracted to men but only by becoming a woman) and autogynephilic (or nonhomosexual) transsexuals (“men erotically obsessed with the image of themselves as women,” and are primarily attracted to the woman they might become) (146ff., 164). Autogynephiles are not especially feminine, and are not, Bailey insists, “women trapped in men’s bodies,” [but] are men who desperately want to become women.” Their cross-dressing is no fetish, but begins in late childhood or early adolescence (169). As adolescents, these persons often secretly wore women’s clothing, and would become sexually aroused when doing so (159). At present, we do not understand the deep biological causes of autogynephilia (172). As Bailey (175) states, “[s]omething about autogynephilia creates a need not only to erect a feminine self, but also to actually believe in her.” Although not everyone agrees with Bailey’s analysis of transsexuality, it should be clear that “[t]rue acceptance of the transgendered requires that we truly understand who they are” (176).
  8. Only a few gay men become transsexual, but “homosexual transsexuals are a type of gay man, [thus] a form of homosexuality” (178, 179). On the other hand, autogynephilia “is a very unusual sexual orientation (towards oneself as a woman)” (181). Sex reassignment surgery is “no longer a curiosity, but a business” (195) that involves fairly expensive procedures, and requires considerable social adjustments.
  9. Bailey believes that both “autogynephilic and homosexual gender dysphoria result from early and irreversible developmental processes in the brain” (207).

I should add that Bailey’s book has created a veritable firestorm of criticism. Whether Bailey’s research as well as that by Blanchard and others will hold up, is certainly an open question. It’s clear that doing research on transsexuality is neither easy nor cheap. My own view is that Bailey should be taken seriously, and only time will reveal to what extent his views are reflective of the origins of various types of transsexuals. Thus when we write GLBTI (gay, lesbian, bisexual, transsexual, intersexual) we are referring to categories of people, although the categories themselves are not always clear-cut.

A Note on “Reparative Therapy.” Despite the deletion of homosexuality as a pathological mental disorder from the second edition of *Diagnostic and Statistical Manual of Mental Disorders*by the American Psychiatric Association in 1968, some contemporary mental health professionals still regard homosexuality as a pathological state (Zucker 2003). Beginning around 1990, a movement arose to help gay and lesbian persons change their orientation. Known as “reparative therapy,” this movement has attracted a considerable following, including a report several years ago by Columbia University psychiatrist Robert Spitzer that indeed there is convincing evidence that human sexual orientation can be changed. At the invitation of Kenneth Zucker, editor of Archives of Sexual Behavior, Spitzer wrote an article based on his research which was included in the October 2003 issue of Archives of Sexual Behavior, together with 26 responses, some laudatory (Joseph Nicolosi: “I am grateful to Spitzer for giving a voice to ex-gays”) and others which were quite critical (Lawrence Hartman: “Spitzer’s article … is in essence irresponsible and unscientific”), and finally a response by Spitzer.

Anyone interested in understanding reparative therapy for gays and lesbians cannot overlook this important number (over 70 pages devoted to the subject). In brief, Spitzer’s study “tested the hypothesis that some individuals whose sexual orientation is predominately homosexual can, with some form of reparative therapy, become predominantly heterosexual” (Spitzer 2003a). Moreover, “[r]eparative therapists believe that same-sex attractions reflect a developmental disorder and can be significantly diminished through development of stronger and more confident gender identification” (Spitzer, 2003a). The study was based on 200 self-selected, mostly highly religious, white, Protestant, middle class individuals who were interviewed by telephone, and on the basis of a structured interview, produced evidence that many had indeed had a significant change in their sexual orientation. Spitzer (2003a) concluded that, for “some individuals, changing sexual orientation can be a rational, self-directed goal,” but he also suggested that “[c]hange in sexual orientation should be seen as complex and on a continuum.” Nevertheless, Spitzer (2003b) believes that in his survey sample of 200 ex-gays, the majority “reported changes in sexual attraction, fantasy, and desire that are consistent with what would be expected if true changes from predominantly homosexual to predominantly heterosexual orientation had occurred.”

The critics charged that Spitzer’s study has serious methodological limitations (e.g., sample biased and too small, use of unreliable self-reports), whether “reparative therapy” actually accomplished its aims, and if so, how, whether the ethical implications of sexual orientation modification have been sufficiently considered, whether Spitzer’s subjects were in fact bisexual (and not a 6 on the Kinsey scale), and finally what percentage of those wishing to change their sexual orientation actually in fact did so successfully. As Richard Friedman (2003) stated, “[p]atients who seek reparative therapy have a conflict between their erotic desires and [their] conscience/value systems.” If one’s erotic desires are for same-sex relationships, but if one’s religious beliefs sternly repress such desires by insisting that the only acceptable sexual outlet is through a heterosexual marriage, the resulting cognitive dissonance may well propel one to seek some sort of reorientation therapy. This, I think, is a critical component in the current debates. Well-meaning persons sometimes suggest to gays and lesbians that they can change their sexual orientation provided that one works hard enough, has sufficient faith, and consults a good Christian therapist. As Hill and DiClementi (2003) state, the “desire to change one’s lesbian or gay sexual orientation is typically based on deeply entrenched negative attitudes about one’s same-sex feelings, frequently called internalized homophobia,” and which, quoting Meyer and Dean, is “the most insidious of the minority stress processes…leading to a devaluation of the self and resultant internal conflicts and poor self-regard.” As Mark Yarhouse (2003) expressed it, there is a “disenfranchised group of persons who experience same-sex attraction but dis-identify with a gay identity.” Such persons, Yarhouse believes, will welcome Spitzer’s study. Indeed, as Spitzer (2003b) himself acknowledges, the term “reparative therapy” denotes derogatory assumptions, that one’s sexual orientation needs fixing. The preferred term is now “reorientation therapy” (Spitzer 2003b). Several of the peer commentators commented on the cognitive dissonance arising from a devaluation or even rejection of one’s core sexual orientation, an aspect Christian therapists need to consider. That is, to what extent is it crucial that one’s sexual orientation (what a person actually is) is identical to one’s sexual orientation identity (what a person would like to be)? Can a person opt for a heterosexual *identity*but still continue to have a predominantly homosexual sexual orientation? This question needs further exploration. To what extent would a religious belief that having a same-sex attraction is morally questionable have any effect on whether an individual actually became changed in one’s core sexual orientation?

Finally, neuroscientist Simon LeVay (2003a) suggested that “[a]nyone who respects personal autonomy must agree that people have the right to try to change their sexual orientation and to seek professional help in doing so. Yet gay people who wish to become heterosexual should be aware that the odds are stacked heavily against them, and that the effort to change may be marked by great hardship, expense and wasted years. They might do well, before they embark on the therapy, to read accounts by gay people who subjected themselves to all kinds of tortures in a futile effort to become straight.”

Concluding Comments

The late English philosopher G. E. Moore always insisted that we have a moral obligation to make the world a little bit better than when we found it. This calls for reasonableness, the “ … settled disposition to guide one’s belief and conduct by the evidence” (Blanshard 1984, 247). This obligation also calls for reflective judgment, of weighing values against each other, and constantly raising the question “why.” Truth itself has a moral component, and surely this includes following the evidence where it leads. Truth also requires that we do not give a false witness, that in our research we observe as scrupulously as possible the canons of good scholarship, and to the best of our knowledge our reportage is as accurate as we can make it. All this is set in a wider scope of what it means to follow Jesus in a complex world. How and whether we overcome our prejudices is surely a test of our love, that steady devotion to enrich the lives of our fellow humans.


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Roselli, C. E., K. Larkin, J. A. Resko, J. N. Stellflug, and F. Stormshak. 2004. The volume of a sexually dimorphic nucleus in the ovine medial preoptic area/anterior hypothalamus varies with sexual partner preference. Endocrinology 145: 478-483.

Roselli, C. E., J. A. Resko, and F. Stormshak. 2002. Hormonal influences on sexual partner preference in rams. Arch. Sexual Behav. 31: 43-49.

Spitzer, R. L. 2003a. Can some gay men and lesbians change their sexual orientation? 200 participants reporting a change from homosexual to heterosexual orientation. Arch. Sexual Behav. 32: 403-417.

Spitzer, R. L. 2003b. Reply: Study results should not be dismissed and justify further research on the efficacy of sexual reorientation therapy. Arch. Sexual Behav. 32: 469-472.

Stein, T. S. 1998. Social constructionism and essentialism: Theoretical and clinical considerations relevant to psychotherapy. J. Gay & Lesbian Psychotherapy 2: 29-49.

Swaab, D., W. C. J. Chung, F. P. M. Kruijver, M. A. Hoffman, and T. A. Ishunina. 2001. Structural and functional sex differences in the human hypothalamus. Hormones and Behavior 40: 93-98.

Yarhouse, M. A. 2003. How Spitzer’s study gives a voice to the disenfranchised within a minority group. Arch. Sexual Behav. 32: 462-463.

Zucker, K. J. 2003. The politics and science of “reparative therapy.” Arch. Sexual Behav. 32: 399-402.

23 February 2004

Carl Keener would welcome any suggestions of important new research, as well as any corrections to this article. He can be reached at [email protected]

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