There is an article today in the Chicago Sun-Times that profiles an effort by Researchers from the Evanston Northwestern Healthcare Research Institute, Northwestern University, University of Chicago, and University of Illinois at Chicago, headed by Dr. Alan Sanders, to determine whether one or more genes can be identified that may be instrumental in the development of male sexual orientation.
The project is funded by the National Institutes of Health and involves research on a 1,000 sets of gay brothers. I encourage those gay men (or ex-gay men) who read here and who have a gay brother to review the study’s website to determine whether to participate.
There was one quote in the story which I found intriguing:
Scientists have rejected earlier notions that homosexuality is a mental illness. The thinking now is that sexual orientation is determined by roughly 40 percent genetic factors and 60 percent environmental factors.
I am not particularly knowledgeable on heritability and how it is measured in terms of determining attributes. I emailed Dr. Sanders about this 40/60 allocation and he was gracious enough to respond:
I appreciate your writing in. There is not a hard and fast number, but rather, twin studies allow one to make estimates (such as that 40%, also expressed as 0.40), and I certainly provided that estimate to Jim Ritter [the reporter]. The technical term is “heritability” which means the proportion of the variance in a trait that genetics/heredity accounts for. There are a number of twin studies out there on male sexual orientation, and all of them find that similarity for sexual orientation among identical twins (who are genetically identical) is significantly higher than that for same sex fraternal twin pairs (who are as similar genetically as any other full siblings, i.e., born of the same biological mom and dad). We are passing on the estimate (remember that it is an estimate with a range of possibilities — this ~40% is just the mid-range number if you will, it could be more or it could be less genetic) from what we judge to be one of the largest and best done methodologically studies. Here is the fuller quote from our study web site’s FAQ section (https://www.gaybros.com/faq.html):
Researchers found that in a study of brothers, if one male sibling was homosexual, the chance his identical (monozygotic) twin would be homosexual was 52%; the chance that his fraternal (dizygotic) twin would be homosexual was 22%; the chance that his adopted brother would be homosexual was 11% [21].
[21] Bailey JM, Pillard RC (1991): A genetic study of male sexual orientation. Archives of General Psychiatry 48:1089-1096. PMID: 1845227There were actually several estimates of heritability even within that paper: “Heritability estimates ranged from 0.31 to 0.71. Thus, estimated heritability remained substantial under a wide variety of assumptions.”
So, if one says variation in sexual orientation is exactly 40% due to genes (and hence exactly 60% due to other contributions, i.e., the environment), this is not accurate since we are really talking about an estimate here. The main point is that genetics/heredity make very significant contributions to the trait. I hope this helps.
If you have difficulty following the above, please review the website to see if your questions are answered there.
As Dr. Sanders’ research will be the most comprehensive to date and across the largest number of gay brothers, perhaps his results will give us some sound answers as to the extent that genes contribute to a man’s orientation and which genes have an impact. I wish him the best and hope that something conclusive comes from his efforts.
Does “environmental” refer to non-genetic but still biochemical or physiological influences (prenatal hormones, etc.), or the psychodramatic scenarios you find in ex-gay literature? (Or either, I suppose.)
Liandan, my understanding is that “evironment” can refer to both prenatal and post-natal environments, including physical and psychodynamic influences. For instance, schizophrenia follows a similar heritability pattern as discussed above, but IIRC with a stronger genetic component (e.g., 75% concordance between identical twins). Interestingly, I have also seen research that schizophrenia seems to be more common among those born in winter, leading some to suggest a virus may be the cause of fundamental changes in the infant’s brain that can trigger the schizophrenia later in life – those born in winter, when humans are in closer contact and more liable to spread viruses, would be more susceptible.
Given the other research on homosexuality, particularly the finding that no specific family type tends to produce more gay and lesbian people than any other, would lead me to conclude that psychodynamic influences in homosexuality are minimal, at best.
I’m glad that so far, everything to do with the origins of homosexuality aren’t anymore variant than the origins of heterosexuality.
Certainly other genetic variables that create family resemblances, characteristics and cultural aspects are more obvious.
But looking at biological situations or genetic links to cancer or schizophrenia are unique, but also NEGATIVE physical and mental issues.
Cancer can inevitably kill, so can substance addiction and schizophrenia compromises social, emotional and mental competence.
There is far more compelling reasons for curing them or studying them for that purpose.
Homosexuality isn’t life threatening or threatening to one’s personality or social competence.
No one would presume to isolate and disqualify a cancer sufferer from marrying, bearing children or
exclusion from certain professions.
Neither would someone do that with a person with schizophrenia based on diagnosis alone, but circumstances due to difficulty in socializing and performing competently.
These studies of homosexual origin are all well and good.
But as we can see, the determindly anti gay will twist or deny the findings, however inconclusive or to what end those findings might come to.
Stigma against gay persons is still far more potent and pernicious than any other stigma, even against addicts and the mentally ill.
I think studies on stigma, and distinguishing moral, ethical and pathological behaviors against the more accepted misinformation about homosexuality would be a better course.
We shouldn’t still have to be debating on whether or not homosexuality is a moral choice.
Especially since the anti gay haven’t made up their minds about what to apply to it, except negative pathology to it because it’s exclusive to gay people.
It’s important to make distinctions, especially because of the profoundness of life or death, and equal treatment under the law.