Why are some men attracted sexually to other men, rather than to women? Since one of the most powerful forces in nature is the drive to perpetuate the species, the origin of this perverse sexual orientation is clearly of great interest to biologists. In A Separate Creation (Hyperion, 354 pages, $ 24.95), Chandler Burr provides a riveting depiction of the latest scientific investigations of the subject. Using the tools and techniques of molecular biology and guided by a theoretical framework encompassing endocrinology, genetics, and neuroanatomy, this research is rapidly advancing against a backdrop of heated debate among scientists and fierce controversy among laymen.
As presented by Burr, these are the main points that have been determined so far: Homosexual orientation is found in a small fraction of the male population (probably somewhere between 2 and 5 percent); it is probably fixed at an early stage of fetal development by some biological mechanism dependent on the flow of hormones; that mechanism is directed in some measure by a wayward gene on the single X chromosome men inherit from their mother. Burr also points out that while homosexual orientation is virtually impossible to alter, it neither compels homosexual behavior nor precludes heterosexual activity, because human beings possess free will.
Systematically reviewing the groundwork for these conclusions, Burr begins with an analogy between homosexual orientation and left-handedness. Both are found in a small minority of the population (and more frequently among males than females), both are already evident at about two years of age, both run in families, are transmitted through the mother, and are more often shared by identical twins than by other siblings. And while the external behavior connected with both traits can be suppressed, the intrinsic tendency remains. This confluence of observations suggests that homosexual orientation is fixed by nature, and quite likely by genetic inheritance. Burr tells us that this conclusion was powerful enough to persuade reputable scientists to search in a variety of directions for the underlying biological mechanisms.
Some researchers have looked for structures in the brain that might reflect differences in sexual orientation. Burr describes a controversial claim by Simon LeVay, a neuroanatomist at the Salk Institute in California, that two hypothalamic nuclei, pinhead-sized structures in part of the brain identified with the sex drive, are larger in homosexual than in heterosexual men. Other scientists question the validity of LeVay's findings. They cite, for example, doubts that the "nuclei" are anything more than artifacts of the stain used to observe them, as well as suggestions that the differences in size may have resulted from drugs taken by the deceased AIDS victims from whom the brains had been taken or from high levels of testosterone in the subjects' blood. Further, even if there is a difference in brain structure, the question remains whether it is a cause or an effect of sexual orientation.
Hormones clearly play a key role in sexual behavior, but their precise role in determining sexual orientation is unclear. Burr discusses research on a variety of bizarre sexual behavior in species including fruit flies, rats, and hyenas, both in the lab and in the field. Scientists observing these phenomena with a mixture of curiosity and prurience have connected them all to various chemical effects. However, like observations made on men and women suffering from severe hormone-related physiological and psychological disorders that involve contradictions between their genes, their anatomy, and their behavior, they shed little light on the origin of homosexual orientation in otherwise normal human males.
Taking another approach, Dean Hamer of the National Institutes of Health compared DNA samples from mothers and sons in families with both homosexual and heterosexual offspring. Using a technique called linkage analysis, he found with an extremely high level of confidence that the homosexual brothers, but not their heterosexual brothers, shared a particular variant of a gene located on the X chromosome. The gene discovered and named by Hamer is now listed in the geneticists' directory as GAY-I, locus Xq28.
Hamer's discovery by no means ends the search for a cause of homosexual orientation. If, as seems plausible, the variant gene produces a hormonal upset at some early point of fetal development, much work is needed to discover exactly what that upset is. Using analogies from genetically related diseases including Tay-Sachs disease, retinitis pigmentosa, and cystic fibrosis, Burr describes how a particular genetically related condition may really be different conditions sharing the same name. He explains how the same condition may be caused by variations in different genes, or by different variations occurring in the same gene, or by other subtly different combinations of circumstances. He also explains that the genetic variation itself may be produced by environmental factors, such as exposure to particular substances, temperatures, or light conditions at critical periods of development.
Despite all these difficulties, Burr reports, many scientists believe that in a fairly short time they will know enough to allow a prenatal forecast of sexual orientation and, possibly, to use genetic engineering techniques to alter it either then or perhaps in adulthood. In that case, sexual orientation would really become a matter of choice.
A theme Burr returns to repeatedly is the different way research is perceived by scientists and by laymen. For the scientists, the idea that homosexual orientation is not determined by individual choice or social pressures is a prerequisite for their results to have any meaning. Without that prerequisite, the link discovered by Hamer would no more indicate a genetic cause for homosexuality than finding a particular gene variant in Chinese people but not in Europeans would prove that speaking Chinese was determined genetically. Many nonscientists, however, misread the research in two fundamental ways, as Burr demonstrates by quoting media accounts of LeVay's and Hamer's findings. First, they interpret the genetic link itself as proving that homosexuality is not freely chosen, and second, they believe that if it is natural it cannot be immoral. The scientists themselves agree that the question of morality lies entirely outside the realm of scientific discourse, although it is interesting that all of those Burr quotes seem to consider homosexual behavior purely a private preference of concern only to those who engage in it, with no larger social ramifications.
Burr concludes A Separate Creation by discussing the implications of the research he has reported. "The assault of science on religion defines the modern era," he tells us, and he goes on to describe the findings about sexual orientation as the latest assault on conventional wisdom.
In this case, he says, quoting James Fallows, Washington editor of the Atlantic Monthly and former speechwriter for Jimmy Carter, the conventional wisdom that is being attacked is political liberalism. Fallows argues that scientific proof that important human traits are determined biologically rather than environmentally abolishes the liberal dogma that people only differ because of social biases or environmental factors that can be corrected by political means. He continues that conservatives can take the political advantage if they drop their traditional opposition to legitimizing homosexuality, since it is, after all, determined by nature. Neither Fallows nor Burr mentions that conservatives can have principled objections to homosexual activity as socially disruptive.
Also dismissed with a wave of the hand in all the philosophizing are " religious fundamentalists . . . [who] will probably continue to argue that homosexuality is immoral . . . because by definition religion is not subject to empirical disproof." This patronizing attitude sharply contrasts with the keen interest Burr shows in many subtle distinctions stressed by scientists. He entirely misses the fact that religion provides a picture of man and his place in the universe dramatically different from, yet essentially complementary to, the knowledge given by science. That picture is at least equally sophisticated in its acceptance of man's biological nature.
The Bible does not forbid homosexual activity because it is "unnatural," but includes it in a long list of prohibited sexual relationships. Scripture acknowledges that the instincts that encourage those relationships are quite natural, telling us "the inclinations of man's heart are evil from his youth" (explained by the rabbis as meaning from his emergence from the womb), but considers it man's fundamental responsibility to overcome those natural inclinations.
Scientific inquiry, by its very nature, regards man as part of nature. In one of his fascinating snapshots of working scientists, Burr shows us neuroanatomist William Byne, M.D., Ph.D., and his assistant Dorita Thompson dealing with human brains:
After selecting some brains she likes from the boxes, she removes them from their individual bags and smacks these cheerfully a few more times to separate them. Shards of frozen brain spray out, and the top of the drum is covered with a fine silt of grayish pinkish snow. . . . Byne, also in gloves, eagerly picks up a brain and begins pointing out its features. . . . Meanwhile, the pink snow is melting, and the top of the barrel is flecked with human brain and blood.
There are very different ways to look at man's place in nature, some of which were demonstrated in a particularly compelling way a few months ago.
First a terrorist bomb exploded in a Jerusalem bus, strewing broken bodies across the street. Then shortly thereafter, a team of religious Jews arrived on the scene and spent hours scouring the neighborhood for body parts, carefully collecting even the tiniest fragments of blood, bone, and brain for proper burial. They did not ask from whom those fragments had come, or what their sexual practices had been. They believed, however, that dead human beings must be treated with respect because live ones have the potential for holiness. Fulfillment of that potential depends on a continual struggle to overcome many perfectly natural human inclinations. By showing man how those natural inclinations work, science can help him in that struggle.
Jeffrey Marsh, trained as a physicist, writes frequently on science and public policy.