A book review by Michele O’Mara, PhD

Hammer, Dean and Peter Copeland (1994). The Science of Desire. New York, NY: Simon and Schuster.

In a surprisingly entertaining way, researcher Dean Hamer, with the help of writer Peter Copeland, describes with great detail, personality, and reader-friendly scientific explanations about the discovery of a linkage between male homosexuality and DNA markers on the X chromosome.   In the author’s own words, his goal in writing this book is “to describe what we found using the tools of modern genetics, how biological findings can broaden rather than narrow our understanding of the diversity of human sexual expression” (15).

Hamer does not assume that the process by which a male becomes gay and how a female becomes lesbian is necessarily the same, and his search for a gay gene in this study is limited to males. Initially, Hamer traced the lineages of gay men, looking for signs of homosexuality among relatives. This search revealed a disproportionate number of gays on the mother’s side of the family rather than the fathers. This, he explained, “is a pattern consistent with a special type of inheritance called sex linkage” (20).   Because of the strong correlation with the mother’s side of the family, Hamer concluded that if a gene is responsible for homosexuality, it will be found on the X chromosome.

To maximize the research, Hamer decided that while he was collecting a large sample of gay men to study, he might as well explore other issues at the same time. He added three additional areas of focus to his proposal for funding: the impact of homosexuality on AIDS, alcohol use and abuse, and mental health.   While he does touch on these outcomes briefly later in the book, they are not a key focus.

As a senior staff member at the National Institute of Health, Hamer was in a good position to attract a strong research team. With a team and funding in place, Hamer set out to attract the two separate groups of gay men he needed to serve as subjects of his research. Through a newspaper advertisement titled, “Gay Men – Do You Have a Gay Brother?” Hamer attracted one group of gay men who were known to have gay brothers. This group was used for the DNA linkage studies. The other group of gay men was selected randomly through various organizations that served gay men. There was no prior knowledge about whether or not this sample of men has gay relatives. The agencies he drew from included: the HIV Clinic of the National Institute of Allergy and Infectious Disease, the Whitman-Walker Clinic which serves gay s and lesbians, and Emergence which is an organization formed by gay and lesbian Christian Scientists.

To verify that his research subjects were indeed gay, Hammer interviewed them with a keen eye on significant variables which lend support that his subjects were currently gay. He explored their histories, looking for information about their earliest attractions to men, their first sexual contacts (86 of whom had their first sexual activity with another male, where as ironically only 73 percent of their heterosexual subjects had their first contact with females). He gathered information about when each male first acknowledged his sexual orientation to himself, and then to others, which raged from 13 to 50 years of age, with the median being 21.

After securing enough information to insure these men were verifiably gay, the next goal was to determine whether or not being gay runs in families. Chapter four offers a wonderfully accessible explanation of how genes and chromosomes work which comes in handy for those of us who may have nodded one too many times in biology class. Hammer explains genes and markers as follows:

“One way to understand linkage is to imagine that the entire genome is a city divided into twenty-three neighborhoods, representing the twenty-two pairs of regular, autosomal chromosomes plus the sex chromosomes, X and Y. The individual houses (genes) sit side by side on streets (strips of DNA). A marker is a specific block, so the marker called 700 block of Main Street would include all the houses (genes) on that block. The marker is not specific enough to pick out the individual houses, but it will always include the same houses. There are chemical procedures that allow scientists to make a probe for a particular block and pass it through the entire city, neighborhood by neighborhood, until it latches onto the block – the marker – it’s looking for” (115).

Traits that are influenced by genes tend to run in certain families because the genes are clustered in those families. When a pair of siblings expresses the same trait it is a strong indication that a family is enriched for that gene. Therefore, Hammer sought out gay brothers because they “served as signposts that their families were likely to have the gene for homosexuality, if such a gene existed” (107). If this theory is accurate, Hammer predicted that the gay brothers will have a higher than average rate of both gay maternal uncles and gay maternal cousins. This is exactly what he discovered when he added up the totals from his initial survey.

The question Hammer was trying to answer was, “is there a connection between the marker and being gay” (125)? Finding this linkage depended on three things. The first thing is to determine whether there was a gay gene near the marker. The second thing was to find out how many people were influenced by the hypothetical gene. If every gay man had the same version of the gene, then he would only have to test about 10 families to find a satisfactory linkage with statistical significance.   Lastly, he needed to determine how informative the markers were.

After testing 40 pairs of gay brothers for 22 different markers along the X chromosome, Hammer found that 33 of the 40 pairs (83 percent) were the same for a series of 5 markers in chromosome region Xq28 (138). Hammer states that there is only a one out of one hundred thousand chance that this outcome could have occurred by chance.  The second finding indicated that sexual orientation was not strongly linked to another area of the X chromosome. This outcome served to strengthen the viability of his discovery. The third finding was that gay men have more maternal than paternal male relatives who are also gay.

While Hammer’s research reveals that there is a connection between homosexuality and genes, what this study did not reveal is the precise magnitude of the role Xq28 has on sexual orientation. Hammer explains that, “to estimate the role of Xq28 in the population at large, researchers would have to isolate the gene, determine what parts of the DNA sequence were variable, and then perform a population-based survey on a large number of individuals with various sexual identifications (145).” He further describes that “the most important limitation of our research was that we didn’t’ isolate a “gay gene”; we only detected its presence through linkage. “We narrowed the search to the neighborhood, the X chromosome – and even the block, Xq28 – but we didn’t find the house” (147).

In the second half of the book Hammer turns his attention to the questions that surface as a result of his findings. He is hypothesizing here about the possible answers to the question: How might a gene at Xq28 influence the direction of attraction and behavior? Specifically he’s exploring how the gene might actually influence our DNA – the literal mechanics of what transpires; and he is also curious about what is involved or actually impacted? For example, does this gene influence that which controls the direction of our sexual fantasies? While there are no answers, per se, Hammer explores four possible theories that may offer some insight, all the while acknowledging that the “correct answer may be something we never dreamed of” (151).

One theory Hammer entertained was the role of the testosterone determining factor (TDF). This protein serves two purposes: one, it turns off the gene that would otherwise create the development of a female genital tract, and two, it turns on the genes that guide the development of the male genitalia as well as creating a masculine body.  This theory did not hold much water, however, as a quick study by Nan Hu, a researcher on his team, reveled that the “TDF sequences were present in all the men and absent in all of the women, regardless of sexual orientation”(153).

The second theory focused on the androgen receptor which serves as a middle-man between testosterone and the body. Hammer postulates that because the”androgen receptor is central to the differences between men and women, it seemed like a good candidate for something that influences sexual orientation” (156). Testing this theory, Jeremy Nathams compared the DNA samples from 197 homosexual men against DNA from 213 people from a study on vision (whom were assumed to be primarily heterosexual).   He discovered no difference between the androgen receptors of gays and non-gays which put holes in this hypothesis.

The third theory relates to the idea that there may be a connection between one’s handedness and their sexual orientation. However, research revealed the same proportion of left-handed gay men as left-handed non-gay men. Interestingly, though, Hammer discovered that among the gay brothers in his sample, 43 percent of the gay/non-gay brothers compared to 6 percent of the gay/gay brothers had opposite handedness. However, Hammer states that the sample is not large enough to be statistically significant. This raises the question for Hammer about whether some men are gay because of genes and others because of differences in brain development that correlate with handedness.

The last theory relates to the hypothalamus, and the influence of Xq28 on the brain’s structure or chemical activity. In 1992 Simon LeVay researched the brains of deceased gay and non-gay men, and measured the differences in size of their hypothalamus (more specifically a small group of cells called the third interstitial nucleus of the anterior hypothalamus, or INAH-3).   He discovered that the INAH-3 in gay men is three times smaller than it is in non-gay men. He was criticized, however, for having a disproportionately high number of gay males who died of AIDS, though research on heterosexuals that died of AIDS also had the larger INAH-3.   Hammer hypothesized that perhaps “the Xq28 makes a protein that is directly involved in the growth or death of neurons in INAH-3 ,” or alternately, he postulates “the gene could encode a protein that influences the regulation of this region by hormones( 163).” These theories provide a starting place for future research.

Chapter ten takes the reader through a variety of potential psychological influences on homosexuality, with emphasis on how a gene might influence one’s personality or psychological make-up in ways that result in homosexuality. Through a discussion of “sissy genes” which studies gender atypical behavior in childhood as a precursor to homosexuality as an adult, Hammer notes that among the Xq28-concordant gay brothers there were more similar childhood behaviors than there were among the Xq28-discordant pairs. This lends some credence to the idea that Xq28 may somehow modify or interact with the factors responsible for gender-atypical behavior (168).

The “bottoms-up gene” theory focuses on the adult behavior that is “notably and measurably gender atypical,” referring to the sex acts preferred by gay men. The most gender atypical of note is anal sex. However, upon closer examination Hammer identified little correlation between the sexual activities preferred and engaged in by the gay brothers in his study.

The “Self-Sufficiency Gene” theory suggests that Xq28 contains a gene for the personality trait called self-sufficiency which Hammer did not find any strong support for. Concluding that Xq28 influences something related to how someone adjusts to their homosexual orientation – for example if two boys have gay fantasies as a child, perhaps one child has the gene Xq28 leading him to indulge those fantasies, whereas the other may lack that gene and choose instead to suppress the gay fantasies to adapt heteronormatively. In conclusion Hammer confesses this is “purely a guess.”

In chapters eleven and twelve, Hammer explores Freudian influences on our thinking about homosexuality and then turns his focus to the role of evolution and the genes’ ultimate goal of survival. Then in a small tribute, it seems, to the ancillary research he did on alcoholism and aids Hammer includes a chapter that addresses a very limited discussion about genetics and disease. He reminds the reader that one of the main goals of his project was to identify genes that accelerate the AIDS virus, and promptly confesses that they didn’t have enough families to find a genetic link to the AIDS progression and they had too many families with alcohol and substance abuse.

Hammer conducted this research amidst a particularly charged political climate for gays and lesbians, with then president Bill Clinton introducing a Department of Defense Directive requiring that the military and gays strike an agreement of “Don’t Ask, Don’t Tell.” Consequently the press was eager to use this research as fodder for more attention to an already sensationalized issue. One of the greatest concerns by gay advocates about the location of a gay gene is the ultimate misuse of genetic research to use this information to either assess, or control, ones sexual orientation.

Hammer outlines three main reasons he does not support genetic manipulation of human sexuality. One, he states that both gay and non-gay orientations are normal. Two, he states that any discrimination that is rooted in a person’s genetic makeup is wrong. And three, the consequences of genetic engineering can be enormous for not just the individual, but for the species as a whole. He also seeks to mitigate fears that opponents of his research expressed about the misuse of a blood test that may reveal a person’s sexual orientation by assuring the reader that they did not actually isolate a gene – just a linkage.

Like many of the critics of genetic research I find myself questioning the need to search for an explanation about why some people are gay and others are not.   Because I live openly as a lesbian my fears are not rooted in the use of genetic testing to discriminate, or genetic engineering to “change” me, or to prevent the births of future gays and lesbians. I offer up this information about my sexual orientation freely and willingly without a test. My objection is that the research itself suggests there is something wrong with being gay. The search underscores the assumption that there is some aberration, something to be discovered about what goes awry in the development of a budding homosexual.

I believe homosexuality is a naturally-occurring sexual orientation that is not an aberration, rather a viable sexual orientation in and of itself. Understanding the etiology of how this path evolves rather than another is of little value to me, in as much as understanding why I am right-handed holds no interest to me. The search for understanding suggests an underlying issue with the way things are.

Hammer’s work, and his book, while well written and very educational, seems to be of most service to those in need of greater understanding or explanation for why homosexuality exists at all. Scholars, policy makers, parents of gays and lesbians, as well as individuals seeking greater clarity about their sexual orientation may turn to this work for justification. On a positive note, however, the conclusion that there is a genetic linkage among gay men may ease the conscience of a mother who fears her gay son is going to hell – giving her reasons to believe that her son is not “choosing” to be gay. And a judge may have legal grounds to side with a gay man who has been discriminated against for his homosexuality; if it is proven that his homosexuality is immutable.

While Hammer suggests that over time the discovery of a gay gene will be aided significantly by advancements in genetic research and technology, there does not appear to have been much progress toward greater understanding about the etiology of homosexuality in the last decade. A quick internet search suggests some recent exploration by Neuroscientist Yi Rao of Peking University and the National Institute of Biological Sciences in Beijing – revealing the role of serotonin when it comes to homosexuality among rats (not necessarily people though). In the end, we still seem to be a far cry from uncovering this elusive gene, and I for one, am okay with that.