Feature

Gay Genetics

Genetic links to homosexuality open up a broad range of
scientific and ethical questions.

by Martin Taylor

The announcement of recent findings by molecular biologist Dr Dean Hamer and his colleagues from the US National Cancer Institute (NCI), that homosexuality has a genetic predisposition, has detonated a political and ethical minefield.

The NCI researchers looked at the family tree of 76 gay men and found that there was a higher than expected numbers of gay brothers, gay uncles and gay cousins on the maternal, or mother's, side. The next phase of their study involved analysis of DNA from 40 pairs of gay brothers. They found that 33 pairs shared a specific region on the X-chromosome, at the location Xq28.

Although this is only a preliminary finding, which will need to be duplicated and verified by an independent group before it can be accepted as definitive, Hamer believes they have found a link between sexual orientation and a small region on the X-chromosome -- the chromosome we inherit from our mothers.

Mother is to Blame

The link to the maternal chromosome has helped to counter a common argument against a genetic link to homosexuality. The argument runs that if sexual orientation was a genetic trait, then homosexuality and lesbianism should have been eradicated by now as gay people are less likely to have children to pass on their genes.

The NCI results explain this anomaly. Because women have two X-chromosomes, the gene marker Xq28 can be masked by the second X-chromosome. If men inherit the gene from their mother, the trait will manifest itself because there is no back-up to cover the gene on the X-chromosome.

Hamer's discovery cannot account for all male homosexuality, and the finding may merely be associated with homosexuality rather than directly responsible for it. For instance, there is some scientific evidence that implicates the genetic control of hormones, and developmental exposure to variable hormonal levels, with male homosexuality. If the gene, found by Hamer, can predict the time and place of release of a particular hormone that in some way influences sexual orientation, then the gene concerned would not cause male homosexuality -- it would merely be an association. To date, Hamer's results are the strongest evidence to support a genetic link.

Conservative views paint homosexuality as a perverse state of being, a willful choice that has been perpetuated by a misguided or diseased upbringing. For a long time this view was tacitly supported by the American Psychiatric Association -- until 1973, homosexuality was listed as a mental disorder. In the 1960s, clinicians were conducting intensive therapy such as hormone therapy, electric shock treatment and even partial lobotomy and castration in attempts to "cure" homosexuality. To those involved, homosexuality is neither a choice nor a disease but an innate characteristic that has been part of them for as long as they can remember.

Hamer's results have been greeted with reticent optimism in the gay community. The discovery of the "homosexuality gene" can be likened to a double edged sword: in essence, one edge will slash the misconception that homosexuality is a choice; the other edge gives those that wish to discriminate a technological weapon to do so.

For those people that think homosexuality is a choice, and a wrong choice, this finding may convince them otherwise. A biological basis of homosexuality may strengthen the legal argument against discrimination. However, it is also possible that prenatal identification and abortion of male fetuses carrying the homosexuality gene may occur. Dr Douglas Futuyma, a gay geneticist at the State University of New York, has voiced several concerns.

Potential Discrimination

"Conservative elements in several countries have already suggested that prenatal DNA screening could be used to abort prospective gay foetuses," he says. "Society should be concerned to prevent other forms of discrimination."

Discrimination would arise if screening was used to deny health insurance or employment on the supposition that people with the Xq28 marker are gay. For example, insurers and employers could argue that gay people are more likely to be infected with the HIV virus and that the risk of insuring or employing gays is too great.

"[This action] would constitute intolerable discrimination against both gay people and some heterosexuals [that have the Xq28 locus]. Finally, I am concerned that the technology and information are easily used anywhere, including countries with poor policies on civil rights," Futuyma says.

Tony Hughes, acting director of the New Zealand AIDS Foundation, believes the most important issue that determines discrimination is probably the social attitude to the characteristic in question, not the origin of the characteristic. On matters relating to abortion of gay-identified foetuses he comments "a lot depends on whether sexual orientation is viewed as a thing like left-handedness, or as a thing like Down's syndrome".

Abuse of Hamer's work may arise, in part, by mistakenly -- or wilfully -- equating genetic analysis with genetic disorder. For instance, undertaking genetic analysis of sexual orientation might be interpreted to mean that geneticists consider homosexuality to be a "disease" and that if genes for sexual orientation exist, the "abnormalities" could be "fixed" by genetic engineering or gene therapy.

Obviously, this is a misinterpretation of the motives of geneticists; only a small fraction of the genetic variation in the human genome is associated with disease. The revelation of the extraordinary genetic diversity of normal human characteristics is one of the most fascinating of modern human genetics. To identify variation and characterize genetic influences on it is to recognise the significance and value of that variation, not to condemn it.

Hughes predicts that Hamer's findings, assuming they are replicated, have the capacity to move discussion of homosexuality into a more rational arena.

"Think, for example, of what used to be called `consumption'. Before it was discovered that an organism was responsible for tuberculosis, it was common to attribute moral fault to people who were consumptive. Biology helped rescue tuberculosis from the hands of the moralists. I think it is likely to do the same thing here."

Hamer's work is still incomplete. For instance, they have not investigated whether or not the Xq28 DNA marker is present in heterosexual men and women or in lesbians. From the work so far, it is impossible to establish the "heritability" of sexual orientation -- we cannot predict the relative contributions of genetic and environmental factors to variations in sexual orientation.

There is much work to be done and many questions to be answered, but Hughes believes Hamer's work on the genetic underpinning of sexual orientation is a very important contribution to contemporary understanding of how homosexual orientation arises.

"Like all research in the area of human genetics, it does not stand alone, however, and must first be replicated and then located within an ethical context," he notes. "At the moment many of our concepts are quite simply pre-scientific. It is past time that we came up with some rational explanations."

Martin Taylor is a freelance writer specialising in science and medical issues.