The biological determinist Left takes in on the chin again..

[_Droopy]

Latest Twin Study Confirms
Genetic Contribution To SSA Is Minor


As in previous studies, identical twins usually differ for SSA.

By N.E. 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:

Activity 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)

Potential
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.

Reference List

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.

[_SUAS]

Droopy what did it teach you..that is what we want to know..??

[_EAllusion]

For what it is worth, don't confuse "biological," "congenital," and "hereditary." They are distinct concepts. Off the top of my head, the more older brothers a male has, the more likely he is to be homosexual. The main theory behind that phenomenon is that the mother's hormonal cocktail during pregnancy changes overtime in response to male fetuses. If correct, that would be an example of the former two, but not the latter.

---------

Also, I thought that explaining a minor to moderate % of the differences in sexual orientation in genetic factors would be, like, a problem for your assertions Droopy. Is this a mea culpa or something?

[_Droopy]

Also, I thought that explaining a minor to moderate % of the differences in sexual orientation in genetic factors would be, like, a problem for your assertions Droopy. Is this a mea culpa or something?

And what would have led you to think that?

[_Droopy]

Droopy what did it teach you..that is what we want to know..??

What does it suggest to your mind?

[_EAllusion]

And what would have led you to think that?

Heh. Nothing Doopy. Absolutely nothing.

Also, hopefully you understand the difference between something being caused by a genetic factor and the differences observed in a population being explained in terms of differences in genetics. Our ability to speak English is caused by genes interacting with the environment. The incidence of English speaking is best explained in terms of environmental factors. It's a simple, but important difference people who these studies are aimed at have no problem understanding, but tends to get lost in media reporting. I suppose that's relevant when you talk about the "biological deteriminists" taking it on the chin when nothing here, you know, argues against that.

[_Tarski]

You are so goofy. What is this supposed connection between biological determinism and the left? Do you not realize that many on the far left promote the idea that gender is in large part a social construct! These folks reject biological determinism in this sense. But as usual, the left really has no uniform opinion here. "The Left" is your bogeyman

Ironically the religious Right is alway ranting about what is natural and what isn't. You see, for them, all the things they approve of re gender, sex, and marriage, are natural and one presumes, biologically determined.

Make up yer mind!

Look, it doesn't matter as far as human rights are concerned whether it is a choice or not or whether is is natural or not.

I have a right to shave my beard and put a bone in my nose and society should and does allow it.

Try to carve up the world according to what is natural and what is a choice. Then try to give me a simple formula mapping that partition of reality onto the partition right and wrong.
You won't be able to do it.

What is natural is not always right or the other way around. Adding in the variable of what is a choice and what isn't doesn't help.

In other words, one cannot determine what society should allow just based on knowing what is natural and/or what is a choice etc.


{Is a choice and is not natural}/ {Is not a choice and is natural}
....................................... ............................
{Is a choice and is natural}/ {Is not a choice and is not natural}

?????
<---->

{Society should allow}/{Society should not allow}

What is the rule here?

[_Hally McIlrath]

If homosexuality exists in the animal kingdom (and it does), then I don't really see how it can be purely a "lifestyle choice."

Do penguins watch too much of the liberal media and "go gay?" Have European giraffes caught wind of Denmark's gay marriage laws, with the result being that insidious knowledge has inevitably wrecked their previously-heterosexual giraffe marriages? What is it, if not biologically-based?

[_Gadianton]

However you want to slice it, no one "chooses" to be gay. The idea is ridiculous. The closest I could see is that if someone chooses a life of "exploration" then over time boundries might get crossed that otherwise wouldn't. I mean, for me to choose to be gay, no matter how much I despise religion, would be something like 10000 times harder than choosing to like broccoli.

[_beastie]

This wiki article has lots of interesting references.

http://en.wikipedia.org/wiki/Biology_an ... rientation

I didn't see the article reference this study, however:

http://www.cnn.com/HEALTH/9803/02/lesbian.ears/

The possibility that sexual orientation may be predisposed before birth gained new support in a research project being published this week that tested how women respond to sound.

Scientists at the University of Texas, Austin, say they have found the first strong evidence of a physical difference between lesbians and straight women -- a finding that the inner ears of gay women work more like those of men.

The study is to be published Tuesday in the Proceedings of the National Academy of Sciences.

The origin of homosexuality has long been a matter of contention. Some believe it to be a matter of choice, but others -- including many gay people -- say it is not choice but biology.

Previous research has found that two parts of the brain are different in gay and heterosexual men. Other studies have found that some genes differ between gay and straight men.

Excess exposure to male hormones before birth cited

The Texas scientists said they found the inner ears of lesbians have undergone "masculinization," probably from excess exposure to male hormones before birth.

"Their auditory centers have been masculinized and the presumption is that so have the sites in the brain that direct sexual preference," said Dennis McFadden, the lead author of the study.

It has yet to be proven, however, that there is a specific site in the brain that directs women to be lesbians, he said.

Dr. Michael Bailey of Northwestern University said the research is "compelling" and may be "consistent with the biological origin of lesbianism."

"The most likely interpretation," he said, "is that this represents some kind of effect of early hormones on the developing fetus."

Test results considered tentative

Bailey cautioned, however, that the research will not be accepted as valid until other scientists replicate the experiment.

Sandra Witelson, an expert on brain anatomy and sexual orientation at McMaster University in Ontario, Canada, said the study supports the theory that lesbianism may be "related to early factors in brain development."

Researchers stress that while science can measure trends among groups, it cannot predict sexual orientation for individuals, a caution that lesbian Laura Brown of Atlanta agrees with. The prospect that women might be tested and given hormones to control their sexuality is "frightening," says Brown. 119K / 9 sec. AIFF or WAV sound

How test was conducted

The inner ear difference between homosexual and heterosexual women was detected using a test that measures the function of the cochlea, a key sound amplifier in the inner ear, said McFadden, a professor of experimental psychology.

The cochlea amplifier in women is more sensitive than that of men, giving women an increased ability to detect very soft sounds in a very quiet room. The test measures a very slight sound the cochlea makes when responding to a soft clicking sound.

Females, with their more sensitive cochlea, respond more powerfully to this test than do men, said McFadden. This is true even among infants.
To test for differences between the sexes, the researchers recruited more than 200 adults divided into four groups: homosexual women and men, and heterosexual women and men.

Some from each of the four groups were later identified as bisexual. The sexual orientation of the subjects was determined by questionnaire. The results, McFadden said, indicated that lesbians had click-responses that were significantly weaker than those of heterosexual women.

The signal was weaker still for all males, both gay and straight. Bisexual men and women were in the middle, although McFadden said there were not enough of these to draw firm conclusions.

What is clear, he said, is that there is a dramatic difference in the development of the hearing systems of lesbians and heterosexual women. It also is known that development of the inner ear is affected before birth by androgens, a male hormone.

Androgens, said McFadden, may also "alter the brain centers that produce sexual orientation." But he said researchers have yet to find a brain structure that determines sexual orientation in women.

Why would someone "choose" to be gay, when society behaves in a discriminatory fashion against them? This is even more illogical for a member of a conservative religion like Mormonism.

Maybe the people who think others "choose" to be gay came to some sexual crossroads in their own lives, perhaps due to bisexual inclinations, and had to "choose" themselves, and hence, assume everyone has to "choose".

Besides, even if it were conclusively show that homosexuality is not a choice, people like droopy wouldn't care. They'd just pick up Card's argument that it doesn't matter, people are still supposed to overcome it because God said so.