A. The Charge. Biology makes homosexual individuals fundamentally different from normals. Nothing to be proud of, that idiosyncrasy is a burden these unfortunates must bear without seeking to disguise it.
As the blogger Judson Cox observed in 2004: “Genetic traits are passed on hereditarily. All that we are is a result of our ancestors. Sex is primarily a biological function designed for procreation. Homosexuality would have to be passed on by recessive genes, like forms of blindness, dwarfism, and retardation. . . . If one claims to be "born gay," one is claiming to be a biological mistake, a freak of nature.”
B. Background. Twin and adoption studies suggest that there is in fact a biological component in sexual orientation--though it is certainly not the whole story. Identical (monozygotic) twins are more likely to share the same orientation than fraternal (dyzygotic) twins. This finding holds for both twins raised together and those raised apart, ruling out the possibility that such differences reflect upbringing alone.
Various researchers have posited that certain traits are characteristic of gay people. Statistically, for example, it is claimed that gay men and lesbians have about a 50 percent greater chance of being left-handed or ambidextrous than straight men or women. The relative lengths of gay-male fingers has also been found to be significant. The index fingers of most straight men are said to be shorter than their ring fingers, Another hypothesis suggests that the hair-whorl patterns on gay heads are more likely to go counterclockwise than clockwise. It seems, though, that there is not enough evidence to establish any of these assertions.
There are also some more carefully controlled scientific studies. A 1991 study by Simon LeVay and others published in the journal Science concluded that the hypothalamus, which controls the release of sex hormones from the pituitary gland, in gay men differs from the hypothalamus in straight men. The third interstitial nucleus of the anterior hypothalamus (INAH3) was found to be more than twice as large in heterosexual men as in homosexual men. This study elicited some criticism because it used brain tissue obtained at autopsies, and all of the homosexual subjects in the study were believed to have died from complications of HIV/AIDS.
A 2001 study showed that HIV status has no significant effect on the INAH3. This study, which also used brain tissue from autopsies, did not reveal any significant difference between the size of the INAH3 in gay men and straight men. It did, however, indicate that in gay men, neurons in the INAH3 are packed more closely together than in straight men.
It has been claimed that chromosome linkage studies of sexual orientation demonstrate the presence of multiple contributing genetic factors throughout the genome. In 1993 Dean Hamer and his colleagues published findings from a linkage analysis of a sample of 76 gay brothers and their families, Hamer et al. found that the gay men had more gay male uncles and cousins on the maternal side of the family than on the paternal side. Gay brothers who showed this maternal pedigree were then tested for X chromosome linkage, using twenty-two markers on the X chromosome to test for similar alleles. In another finding, thirty-three of the forty sibling pairs tested were found to have similar alleles in the distal region of Xq28, which was significantly higher than the expected rates of 50% for fraternal brothers. Somewhat inaccurately, this finding earned the name of the "gay gene" in the media, causing significant controversy. It is unlikely that gay genes as such will be found, but there may be, as this and other studies suggest. chromosomal variations.
Homosexual behavior has been documented among hundreds of animal species. Yet there is little scientific data to show why this should be so. Some studies of rats seemed to show that exposure to sex hormones in the womb during a critical period in brain development affects future sexual orientation. By manipulating hormone levels during this time, scientists can make rats engage in homosexual behavior later on. Many doubt that this finding can be applied to humans.
Research along these lines has encountered resistance in various quarters. Those who wish to “cure” homosexuality by religious or other intervention object to the idea that a homosexual orientation is conditioned by factors that cannot be changed. In such a perspective, homosexuality might even be regarded as “God-given,” horror of horrors. For their part, some gay-friendly observers fear that confirmation of such research might strengthen the stereotype that gay men and lesbian are oddities--what used to be termed “stepchildren of nature.” In a worse-case scenario, detection of some markers of this kind might even encourage parents to abort fetuses regarded as likely to become gay.
C. Response. Research of this kind is in its early stages, and some studies seem to be contradicted or modified by others. It is probably fair to predict that, when the research findings are all in, biological factors will be found to inform sexual orientation by providing a disposition or capacity to experience sexual attraction to one sex or the other, or to both. The outcome must be the product of particular life choices in the course of individual development. In other words, both heredity and environment will be seen to play a role.
BIBLIOGRAPHY. Simon LeVay, Gay, Straight, and the Reason Why: The Science of Sexual Orientation, New York: Oxford University Press, 2011.