:.i1l4i:OlTl"l june 2001 W Genetic Research and Homosexuality... to What degree is I sexuality the result of something innate versus the effect of environmental forces? BY LARRY RUDIGER A pair of presentations at the most recent American Psychiatric Association (APA) convention has revived a con- tentious debate: can homosex- uality be somehow forced into heterosexuality? This really points to a more basic question, though: to what degree is sexu- ality the result of something innate versus the effect of envi- - ronmental forces? Getting the Facts In earlier columns, I’ve dis- cussed some of the issues that make rigorous scientific study of this topic so difficult. Those barriers remain, including the‘ cost of such projects, the lack“ of a clear benefit (that is, com- pared to the potential pay-off of, say, effective medications for costly diseases), and the difficulties in defining the terms in question. What, exact- ly, is meant by homosexuality? Current Controversy The research presented at the APA convention touches on some of these issues. I’d rather not discuss them in detail for they’ve yet to be published. A . couple of caveats, though, are in order. First, when something. is presented at a convention, there is often a very low stan- dard for the evidence; it’s like- ly to be an initial analysis of preliminary data. Second, just because research is being pre- sented doesn’t mean it express- es the organization’s stance on a topic. ' “if I hadn't known it costs just $299-/pair when I first heard it.l would have estimated its price was at least twice that. ...t.he Aegis One is,’ an aston- ishing value. Highly recommended." john Atkinson Stereophile May 2000 sound high performance home theatre is audio 5y 0 n ‘th e we b www. so u n d e sse IS One, Competition Zero essentials In this regard, APA has not budged. They retain their opposition to “reparative thera- py” in part because there is considerable, credible evidence it causes harm. But also, APA has not retreated from their his- toric ruling that homosexuality is not related to mental disor- der. While that decision was not reached in a political vacu- um, it was and is bolstered by the evidence — which, I might add, ex-gay proponents have yet to counter in any meaning- ful fashion. Finally, and somewhat iron- ically, the author of the contro- versial interview study, Dr. Robert Spitzer, was instrumen- tal in the initial declassification of homosexuality — a highly unpopular position back in the early 1970’s. As to his recent research, I“ will be surprised to see it published in a prestigious journal because it adds practi- cally nothing to what we know: people with homosexual lean- ings who are also strongly reli- gious will go to extraordinary lengths to try and eliminate what they believe is contrary to God’s will. Stay tuned for fur- ther developments. Recent Research In my experience and opin- ion, the only research method- ology that can convincingly describe the genetic nature of a behavioral trait is a twin study. That means you define a popu- lation — typically a geographi- cal region — from which you randomly select a subset of all twins born there. They are Looking for affordable speal: (2 '7-‘P'°A9 ARCAM 'i.fai.tru.;2aas ntialsvt.com - The \/\/ing Building stems Steele.St, # I08 ' Burlington - 863.627l ~ i’iOl.ll‘S1“l"Ll£‘.S 4-8 Fri l2—8 Sat IO-8 I2-£8 hi.?e 8: as nex“ .'‘0 ti“ Mon, \/“ed, The A p p oi n'tme nt k recruited and followed over time. Because of what’s known about twins’ genetic resem- — blance (when they’re identical, it’s complete; when they’re fra- ternal — or not identical — then, on average, they’ll share half their genes in common) you can construct mathematical models to test different propo- sitions. The most interesting ones are used to estimate the relative effect of genes, the shared environment (by assuming that a twin pair’s home environ- ment is equivalent) and then the unique environment — those things that happen to each indi- vidual. It’s really just algebra on a grand scale. But it’s pow- erful because if your model doesn’t match the"data, then there’s'a vanishingly small probability that your hunch is true. For me, that’s the hall- mark of good science: if you’re wrong, then the data have a chance to tell you so. Two of these big, ongoing twin projects are run by fonner colleagues from my behavior genetic research days. One’s based in Virginia, covering the mid-Atlantic region; the other is in Australia. Both of these studies suffer inherent limita- tions of the subject. How do you measure homosexuality? Can you infer it from things that are known to be related to it — for example, childhood gender nonconformity? And what do you do about the fact it’s a touchy subject," and, when asked, even in as careful a way possible, people are likely to be evasive (or even lie)? In this regard, the mid- Atlantic study is probably more limited. They relied on a single item (how would you describe your sexual orienta- tion), and regardless of what you’re studying, that limitation alone causes problems (which ends up being expressed as imprecise estimates of genetic and environmental effects). Of about three thousand partici- pants, 2.8% reported that they were either homosexual or bisexual. Compared with fra- ternal pairs, identical twins were about twice as likely to both be gay, lesbian, or bisexu- al. Further analysis suggested that, for all the pairs studied, "the genetic part of things accounts for between 28% and 65%; the shared environmental side covers between zero and 40% — rough estimates to be sure, but there’s nothing really to be done about it. In addition, when they test- ed to see if the relatively high- er rate of non-heterosexuality in identical pairs was actually caused by their environment (known to be more similar — in part because they are identi- call), the evidence was lacking. In other words, there’s no evi- dence that identical twins are more likely to share homosex- uality because of their upbring- ing or because, being so similar in appearance, of the way peo- ple react to them. Plainly put, according to this study their parents made them gay with the genes they passed on, not with their parenting tech- niques. Meanwhile, Down Under Two papers about the much larger Australian study sample (about 9,000 twin pairs) profit- ed from that as well as more detailed, and reliable, measure- ment of sexuality. I’ll only have time to discuss one publi- cation (and will recommend the other to those most facile with math). In it, the researchers asked about both the internal sense of homosex- ual attraction as well as overt behavior — the familiar Kinsey scale. An interesting finding: bisexuality was rather less common in men while more extreme homosexuality was less common in women. Because the sample was so large, the Australian researchers were able to run separate analyses for men and women. For both genders, familial influences are strong. But it’s difficult to draw a line between genes and shared environment. Men’s homosex- uality, it seems, presented far less evidence for a shared envi- ronmental influence and may be strongly genetic. But for women, in addition to a small- er genetic effect (about 7%), about 40%.was due to the 1843-6 Papers discussed Kendler, K.S., Thornton, L.M., Gilman, S.E., & Kessler, R.C. (Nov 2000). “Sexual orientation in a US national sample of twin and nontwin sibling pairs.” American Journal of Psychiatry, 157(11), Bailey, J.M., Dunne, M.P., & Martin, N.G. ( Mar 2000). “Genetic and environmental influences on sexual orientation and its correlates in an Australian twin sample.” Journal of Personality and Social Psychology, 78(3), p 524-36. Gangestad, S.W., Bailey, J.M., & Martin, N.G. (June 2000). “Taxometric analyses of sexual orientation and gender identity.” Journal of Personality and Social Psychology, 78(6), p 1109-21. shared environment. Earlier research has found the same difference between men and women, but not with this degree of statistical power and applicability to the population as a whole. It suggests that, perhaps, lesbians are both born and made. Exactly how, this paper doesn’t say. Interestingly, though, men and women were much alike on a related variable: child- hood gender nonconfonnity, or being a tomboy (women) or sissy(men). The evidence sug- gests that it’s a bit more strong- ly genetic for men (50% versus 37%), but there’s no sign it’s caused by the environment for either gender. What of the rest, the 50% and 63% left over? It’s just that — left over. It’s some- thing of a garbage can catego- ry: everything that cannot be estimated as part of the family environment or genetic make- up, and the expected errors you get with research (people fill- ing out the form wrong, or lying, that sort of thing). Taken together, these papers are provocative. What might be present in girls’ environment that makes adult lesbian and bisexual identity more com- mon? And why does the envi- ronment seem to have so little to do with men’s sexuality, while women’s sexuality does seem related to their upbring- ing? What of the relationship between childhood gender nonconformity and adult sexu- ality? I hope future research can give us some useful answers — and questions.