The Biology of Homosexuality
by Jacques Balthazart
Oxford University Press
188 pages, $49.99
THE U.S. SUPREME COURT finally ruled on two historic same-sex marriage cases on June 27, effectively overturning California’s Proposition 8 along with the federal Defense of Marriage Act (DOMA). Given how polarized the Court is on social issues, the legal reasoning was, surprisingly, not all that cautious: Prop 8 was vacated on the grounds that the gay marriage opponents lacked standing, while DOMA was overturned as a federal infringement of states’ rights.
Although the decision pointed out that “DOMA singles out a class of persons deemed by a State entitled to recognition and protection to enhance their own liberty,” it did not support a national constitutional right to same-sex marriage.
Even histrionic Justice Scalia, never a friend of homosexuals, rightly chastised the majority ruling on the Prop. 8 case: “The Court has cheated both sides, robbing the winners of an honest victory, and the losers of the peace that comes from a fair defeat.” We can only hope that he is correct in predicting that the language of the decision nevertheless lays the groundwork for a national case for LGBT civil equality because, “By formally declaring anyone opposed to same-sex marriage an enemy of human decency, the majority arms well every challenger to a state law restricting marriage to its traditional definition.” Ironically, Scalia’s own dissents have tossed powerfully worded ammo to the LGBT rights side (the “homosexual agenda,” as he called it in Lawrence v. Texas [2003]).
Although these two cases did not rely on biological arguments, many other courts considering LGBT civil rights cases have given special attention to claims for and against the biological basis and, by extension, the congenital and unalterable characteristic of sexual orientation. The court of public opinion frequently does so as well. Republican Senator Rob Portman, long a staunch opponent of gay rights, stunned conservatives when he declared his support for gay marriage because his son had come out as gay, and “his sexual orientation wasn’t something he chose; it was simply a part of who he is” (Columbus Dispatch, Mar. 15, 2013). Many legal scholars have argued about the validity of biological arguments in propping up gay rights and, surprisingly, the general American public seems to find it less necessary. Gallup polling over the past three decades finds that belief in the congenital nature of homosexuality grew steadily from 1977 to 2001, and since then has been pretty much on a par with the belief that homosexuality is due to upbringing or the environment. Nevertheless, favorable opinion of gay relationships and the morality of homosexuality have mostly continued to grow even since 2001 such that they are now the majority view.
Smaller surveys find that a majority of lesbians and gay men (more men than women) believe their sexual orientation is innate and that it is already a scientifically resolved issue. It certainly is not. Many scientists and journalists have covered this territory over the past two decades, including Chandler Burr, Simon LeVay, and Dean Hamer; and I have probably reviewed all of them in these pages. However, Jacques Balthazart’s The Biology of Homosexuality is not only the most current; it also makes the strongest, the most detailed, and the most balanced argument in favor of the biological case.
Balthazart is an associate professor of behavioral neuroendocrinolgy in Liège, Belgium, where his lab studies a range of sex steroid effects on the brain of small vertebrates (primarily birds) and how these neurological and physiological effects relate to sex-differentiated behaviors (like bird song) and reproductive behaviors. Given his expertise, he naturally leans towards neuroendocrinological explanations of human sexual orientation and, logically, this seems like the most proximate cause of sexual behavior. However, he covers a vast array of research, including genetics, psychology, and anthropometrics (measures of finger length, fingerprint patterns, or inner ear clicks), so for a book that is only 188 pages, it is extremely dense. There is enough background material and it is clearly written so that biologically-oriented readers who have been following this debate will be hugely rewarded for their attention; but neophytes may well flounder.
Perhaps the most refreshing thing about this work is that Balthazart is candid about what experiments with animal models can and cannot demonstrate. They cannot model gender role (how one presents as male or female in society) or gender identity (he calls it “sexual identity”—how one psychologically identifies as male or female). He is careful not to elide these issues with those of sexual/copulative behavior (easy to identify in animals—including humans) and sexual orientation (sex selection of mates). Frequently these last two get equated—particularly by the press—in anthropomorphizing reports on “gay” fruit flies or “lesbian” seagulls. He is specifically focused on preferential or exclusive same-sex attraction, which he acknowledges is rare and difficult to demonstrate in non-human animals. To get there, however, does mean reviewing extensive research on the effects on sex hormones on the developing body and brain, and correlations between these changes and alterations in sexual behavior (the prenatal hormone hypothesis of sexual orientation).
Balthazart is careful to point out that there is no simple cross-species equivalence for these animal findings: i.e., the sexual dimorphic areas in rats are different from those in quail; and the hormones and timing for generating these differences vary significantly. Animal models for sexual orientation per se require giving test animals a choice between males and females—for example, keeping a male and a female rat restrained and available for mating in adjacent compartments. Various manipulations of hormones during the embryonic or postnatal development of rodents and ferrets are associated with dimorphic brain changes and correlated with alterations in averages of mate sex selection, but not exclusive same-sex orientation. Sheep, on the other hand, do not need any interventions to demonstrate such behavior. Almost a third of rams demonstrate bisexual mate choice, ten percent are asexual, and eight percent engage in male-exclusive sex. Experimental research in the past decade associates this sexual orientation with a sexually dimorphic area of the sheep brain and its prenatal sensitivity to testosterone, but Balthazart is cautious to note that the exact mechanism for ram sexual orientation needs further elucidation, and almost no equivalent research has been devoted to sexual orientation in females.
Taking the leap from animal models to humans is a huge one. Of course, experiments on humans would be unethical. Individuals with intersex disorders of sex development (DSD) are frequently used as surrogate “experiments of nature.” The genital anomalies in DSD are often evident at birth and are related to a variety of genetic causes. Any neurological effects are much less clear and their correlation to gendered behavior and sexual orientation are challenging to establish. However, the sexual differentiation of the body occurs earlier than that of the brain, leaving open the possibility of the neuroendocrinological hypothesis: some hormonal event happens at a critical time in embryogenesis—after genital and gonadal development—that affects critical areas of the brain influencing sexual orientation and that also causes other traits. These other traits are far more accessible than the brain and have become a convenient, if tenuous, surrogate for the neurological basis of sexual orientation. They include the biometric studies mentioned earlier and sex-differentiated psychological traits (e.g., verbal fluency, aggression, visual-spatial tasks). Balthazart is candid about how uneven these findings are, particularly between gay men and lesbians. He is even more skeptical about the genetic evidence to date.
He acknowledges that much remains to be elucidated about the prenatal hormone hypothesis and about some of the challenges to all research in the field including the complexity of homosexuality, multiple types of causality, and the potential unreliability of subjects’ self-reporting on their sexual orientation. Furthermore, the diverse biological factors may only produce a predisposition to homosexuality. After that, childhood experiences and the post-natal context of family and society would play a role in allowing it to flower. Balthazart, however, strongly favors biological over social effects, not only because of mounting scientific evidence. Unlike some biologists who would claim that science is value-neutral, Balthazart explicitly advocates for the role of biology in shaping social opinion. The biological and non-elective nature of sexual orientation, he repeatedly argues, decisively means society should end discrimination against gays and lesbians.
I certainly cannot argue with Balthazart’s activist conclusions. Whether it happens through biological persuasion or a broadly principled sense of human equality, the arc of justice appears to be bending ineluctably toward equal civil rights for GLBT people in the U.S.
Vernon A. Rosario is associate clinical professor of psychiatry at UCLA and author of Science and Homosexuality: A Guide to the Debates.
