Skip to comments.Latest Twin Study Confirms Genetic Contribution To SSA(Same Sex Attraction)Is Minor (less than 10%)
Posted on 05/26/2009 8:24:45 PM PDT by Maelstorm
Neil Whitehead, Ph.D.
Twin studies are favorites of mine because of the potential light they throw on the origins of same-sex attractions (SSA). The latest one (Santtila et al., 2008) is three times larger than any previous study - in fact, larger than all the rest put together.
Does this latest study teach us something new? Quick answer: No. It confirms the best recent studies, which tell us that genetic factors are minor; non-genetic factors are major.
The paper's title is "Potential for Homosexual Response is Prevalent and Genetic." This implies to the average reader that homosexuality is sometimes hidden, but commonly occurring, and that it is predominantly genetic. But we shall see this title is not representative of the study's actual findings.
This is the fifth systematically sampled twin study to look at SSA independently in men and women. Of the four previous studies, two were from Australia (Buhrich, Bailey & Martin, 1991; Bailey, Dunne & Martin, 2000), and two were from the USA (Hershberger, 1997; Bearman & Bruckner, 2002).
This latest study is from Finland. Using the very centralized records typical of Scandinavian states, they assembled a large, genuinely random sample of twins (6,001 female individuals and 3,152 males) for a study that was primarily on aggression. With that constraint, they were permitted only two questions about SSA: "What same-sex sexual contact have you had in the last year?" and (in essence) "If there was no prospect of anyone finding out, and you were sexually propositioned by someone of the same sex you liked, what would be your chances of accepting?"
Before we go further, let's address one small difficulty. Unfortunately, different studies use different measures for SSA. Some ask for total number of partners - this one asked only the frequency of contacts in the last year. Other surveys ask the frequency of same-sex fantasy. This one asked respondents to fantasize (perhaps for the first time) about what sexual contact with a same-sex partner might be like. The authors then say this is measuring "potential homosexuality," but you and I would probably conclude that such a measure is fairly clearly indicating something other than SSA. This measure obviously would include bisexual people, and casts the net so wide, that it also could well be testing for something like novelty, curiosity, or sensation-seeking, rather than actual sexual orientation. In this study, 32.8% of men and 65.4% of women replied "yes" to that question about fantasy, in contrast to 3.1% of men and 1.2% of women who described themselves as actually homosexually active.
The results were:
|Genetics||Shared Environment||Nonshared Environment|
|Men||27% (2.7-38)||0% (0-18)||73% (62-85)|
|Women||16% (8.3-24)||0% (0-3.6)||84% (76-91)|
|Men||37% (12-47)||0% (0-19)||63% (53-73)|
|Women||46% (32-52)||0% (0-11)||54% (48-60)|
Table 1. Relative influence of various factors for the Santtila and Sandnabba (2008) data. Error ranges in parentheses are the 95% (2 sigma) error range.
The table shows that the estimated genetic contributions are a few tens of percent, but that the error ranges (in brackets) are quite large and this could possibly mean the genetic contribution is zero. This is exactly the same as has been found previously. They also show that the non-shared environmental contribution (i.e. environmental factors particular to the individual) greatly predominate - in other words they are the largest group of causes of SSA.
Are genetic contribution results of say 27% important? No. In the twin studies world the influence would be classified as weak to modest. And any influence is indirect - it is likely to be something like an innate tendency to be very sensitive to the opinions of others. However, even this weak or modest genetic contribution is probably greatly overstated.
Twin study researchers usually involve the siblings of identical twin subjects as much as possible, because they are genetically related to the same degree as fraternal twins, hence like substitute fraternal twins. This sibling/twin comparison is very interesting because it tests for any special twin environment. For example, did the twins influence each other to be SSA? Or did the genetic similarity between the identical twins and siblings cause some lesser SSA in the siblings also? In this case, the siblings were tested along with the identical twins and fraternal twins and the results were meaningless-- i.e., they did not yield results compatible with genetic influence in SSA. Although the authors do not specify exactly what the problem was, it must have been severe ("...attempts at fitting uni-variate and bi-variate extended-family scripts for categorical data were not successful...." which is scientese for the explanation I give above). This would usually be enough to destroy a study of genetic influences, but rather incredibly, the authors simply and blithely ignore the siblings for the rest of the paper, and use the twins only, to present a calculated genetic influence. Rather, no genetic influence at all is shown when all the data are included.
This is an unusual problem for the method, so the authors with the general approval of the scientific community, including the referees of the paper, implicitly say "Well, there is an inconsistency here that will take years to sort out but in the interim here is what the results would be using the traditional methods if we ignore this." This is some use to the researchers, though laymen may shake their heads at the procedure.
As usual in these studies, family upbringing ("shared environment") was consistent with a zero percentage influence, as shown in the table, but I contend again as I have in previous talks and articles that many family factors are hidden in the non-shared environment contribution, and highly individualistic and important to the people concerned. Thus for example, the influence of a distant father may well be critical for many individuals - but might not affect an identical twin at all.
The results, by my calculations, do in fact, reinforce one conclusion drawn from previous studies. That is, if one identical twin--male or female--has SSA, the chances are only about 10% that the co-twin also has it. In other words, identical twins usually differ for SSA.
In spite of the above-cited criticisms, some useful points emerge from the study. The sample is probably the least biased so far. The authors believe prenatal hormonal theories as a cause of SSA do not hold up, because they should lead to greater similarity between identical twins, not less similarity as we see above. Also, we see a continuation of an already-established trend -- the more recent and better-conducted the study, the smaller the detected genetic influence on SSA. In the meantime, the reader should continue to assume that genetic causal effects on SSA are minor, and that other, very individualistic factors predominate.
Bailey, J.M., Dunne, M.P., & Martin, N.G. (2000). Genetic and Environmental influences on sexual orientation and its correlates in an Australian twin sample. Journal of Personality and Social Psychology, 78, 524-536.
Bearman, P.S., & Bruckner, H. (2002). Opposite-sex twins and adolescent same-sex attraction. American Journal of Sociology, 107, 1179-1205.
Buhrich, N., Bailey, J.M., & Martin, N.G. (1991). Sexual orientation, sexual identity, and sex-dimorphic behaviors in male twins. Behavior Genetics, 21, 75-96.
Hershberger, S.L. (1997). A twin registry study of male and female sexual orientation. Journal of Sex Research, 34, 212-222.
Santtila, P., Sandnabba, N.K., Harlaar, N., Varjonen, M., Alanko, K., & von der Pahlen, B. (2008). Potential for homosexual response is prevalent and genetic. Biological Psychology, 77(1), 102-105.
Homoesexuality is as natural as an other birth defect.
I think homosexuals were introduced to homosexuality at an early age, rewiring their emotional/physical response.
It spreads like a cancer among the very young.
Environmental influence = abuse by perverts.
Fifteen year ago I argued with a good friend, a twin expert, that homosexuality isn’t genetic. She is one of the totally PC PhDs in Psychology. She told me I didn’t understand research. I have worked on several research projects and her comment hurt our 30+ years friendship. I was right and she was wrong. Too bad I am not close with her anymore or I would have a terrific ‘I told you so’ moment.
So therefore, there is a genetic link to homosexuality.
Minor as it may be it does exist.
So you are accusing all the parents of gays and lesbians of being child abusers?
Unfortunately, that won't stop the pro-gay crowd from misrepresenting the data and overstating the minor factors as something of any significance. No, they'd rather hype the insignificant as, apparently, the actual data is too difficult for them to grasp.
The data continues to state homosexuals are not born with their same sex attraction and that environment is a significant factor.
I don’t understand how anyone could believe that there is not a genetic component.
It exists in other species. Mother nature does not make “mistakes” this often, sorry.
I don’t claim to know the “reason” why, by the way.
Besides, a guy like me would have to have a genetic component to be attracted to another male.
There is nothing within my control, NOTHING, that would change my preference. I simply could not be sexually attracted to a male.
This is merely introspection I know. But I just can’t see it happening any other way.
This is leaving aside the molestation/rape factor which does influence things.
At the end of the day, I don’t care who loves who and what they do consentually.
I don’t want the definition of marriage changed, however. Equal rights, fine, but the term “marriage” should not include same sex couples.
And why must something be genetic in order to be justified? Must someone be a genetic slave in order for something to be acceptable now?
Can’t someone do it because he likes it, as other people like golf?
That’s what the writer of the article concluded. Statistics is often misstated in support of homosexual activism. They can’t handle the truth.
Ultimately it would be but people are turned on by everything from rubber coats to stinky tennis shoes. The idea that sexuality is, especially fringe sexuality that has nothing to do with reproduction is primarily genetic is just not true. Most studies actually indicate that homosexuality is largely incidental with many self identified gays eventually leaving the lifestyle altogether. They just don’t have the lobby and no one dare polls to try to find the number of people who identify themselves as ex gay.
Golf doesn’t expose you to higher risks of sexual disease and shorten your lifespan. Yes they could do it just because they like it but that isn’t enough. You can’t get special civil rights and protections on the tact that I simply like to do this disgusting thing. Homosexuals have made a critical mistake with their intimidation and forcing of their behavior into the courts and into the schools and into everyone’s face.
They have unified their opposition and not just among religious conservatives. There is a growing secular opposition the numbers of young people opposed are increasing slowly but surely.
Go bait someone else.
I gave my opinion.
I’m not sorry it offended.
Then you clearly haven’t heard of extreme sports. Mountain bike? Base jumping? Superman died in a wheelchair for mere horse riding. Also see: personal responsibility & nanny government. The entire point of capitalism is that your pursue *your* happiness, not wither other people find it disgusting. Those that make this work for them, are “rich” (be it in money, pleasure or life experience), those that don’t, fail. (be it ending up poor, or dead). It’s that simple.
The question about homosexuality and marriage has absolutely nothing to do with whether someone can do it or not even though it is clearly very bad for them. Catching a disease is not an extreme sport. Forcing acceptance of a behavior that is logically and religiously incorrect on other people and abridging their freedom not to associate with it or accept it is not about capitalism. Capitalism and freedom does not flow one way and does not in our Representative Democracy flow with disregard to the validity of the claims and the will of the people.
We are not a representative anarchy. People have a protected right to make political decisions be they right, wrong, or indifferent. They could ban Mountain biking just as they have tried to ban guns. No one is trying to ban homosexuality though it once was and the laws were found at the time to be well within the confines of the first Amendment.
You can give some people all the proof in the world and they still wouldn’t want to believe the truth. It’s a shame it hurt your friendship.
I think the homosexuals are trying to get people to believe it’s genetic so people think it’s un-changeable. It’s their ‘excuse’ for their behavior. I remember back in the day when they were calling it a ‘lifestyle choice’.. whatever happened to that?