Tag: homosexuality

Swedish twin study: Q & A with J. Michael Bailey

Recently, I posted here and here about a new study from Sweden involving twins and sexuality (Niklas Långström, Qazi Rahman, Eva Carlström, Paul Lichtenstein, (2008). Genetic and Environmental Effects on Same-sex Sexual Behaviour: A Population Study of Twins in Sweden. Archives of Sexual Behaviour, June 7, published online.) To get additional perspective on this new report, I asked prominent sexuality researcher, J. Michael Bailey from Northwestern University to comment. My thanks to Dr. Bailey for his time and expertise.

Throckmorton: How are the models used in twin studies able to separate the family influence into genetic and shared environmental effects? Clearly the environmental factors shared by twins do not look influential in this study. Many critics of this kind of work will wonder how the shared family environment cannot be influential. Hence, the question about how we can tell the family influence is genetic and not from the common parenting or social environment.
Bailey: Most studies use twins who have been reared together from birth. Shared environment is the environment shared by siblings reared together, and thus, identical twins and fraternal twins are equally similar in their shared environment (provided they were reared together, they share all of it). Nonshared environment consists of environmental factors not shared even by siblings in the same household. Nonshared environment is the kind of environment that causes differences even between identical twins reared together. The logic of the common twin study (as opposed to the rare study of identical twins reared apart) depends on their being two types of twins that vary in their genetic similarity. The assumption is that this is the only salient way that such twins differ–other differences are presumed not to have an affect on the trait of interest. If this assumption is true, then one looks to see whether identical twins are more similar than fraternal twins. If they are, this is evidence for genetic effects. To the extent that identical and fraternal twins are equally similar to each other (and more similar than random people are to each other), this suggests there are shared environmental factors. To the extent that identical twins reared together are different from each other, this supports the importance of the nonshared environment.
Throckmorton: What are the advantages of this study over your 2000 population based study (Bailey et al, 2000)? What are the limitations in contrast to your work?
Bailey: I think this study is comparable in quality to our 2000 study, although our measures of sexual orientation were more comprehensive.
Throckmorton: In the new twin study, the genetic effects are estimated at 35-39% for men and 18-19% for women. Since we are not assuming one gene codes for sexual orientation, do you have thoughts about what genetic mechanism(s) could be at work? The pedigree studies have had mixed results, have they not?
Bailey: Studies such as this one provide little if any insight into the nature of genetic mechanisms. Rather, they estimate the magnitude of genetic effects, whatever those effects are. Pedigree studies are studies that look at patterns of similarity in families, and there has been some inconsistency, with some studies finding evidence consistent with X-linkage, and others not finding such evidence. But virtually all studies have found higher rates of homosexuality among family members of gay men.
Throckmorton: The estimates of the effect of non-shared environmental factors are very high. The authors indicate that hormones in utero could be an aspect of the non-shared environment. Given that these twins shared the same womb, what kinds of non-shared effects are they referring to?
Bailey: No one knows how this can happen. First of all, nonshared environment is the kind of environment that causes identical twins reared together to be different. This nonshared environment is poorly understood but is clearly important. We know, for example, that if one identical twin has a congenital major brain anomaly such as microcephaly (being born with a very small cortex), the other twin is usually normal. Obviously, this is due to some kind of prenatal environmental factor or event. (It can’t be genetic, because they have the same genes.) We really haven’t a clue what it is.
Differences between identical twins (or fraternal twins for that matter) also reflect measurement error, and the amount of such error depends on how good the measure of sexual orientation (in this case) is. I would say the measure used in the study at hand is okay but not great.
Throckmorton: By the measure of sexual orientation, I assume you are referring to the fact that this study did not assess sexual fantasy or attraction independent of behavior. How do you think a measure of sexual fantasy would impact the results? Do you think we might get lower effects of environment on the inner world?
Bailey: I have no idea, honestly.
Throckmorton: Concerning environment, some critics of pre-natal theories might suggest that twins are not often treated alike and do not really share environments, even though they live in the same house and share the same parents. Is there an empirical answer to this concern?
Bailey: Twin researchers have typically concocted indices of how similarly twins were treated as children. Parents vary in their twin-rearing philosophies, with some favoring “treat ’em alike” and others favoring “treat ’em differently.” Typically, these indices don’t predict how similar twins become.
Throckmorton: Could the non-shared environment also include peer influences, different socialization experiences, trauma, etc.?
Bailey: Yes. Regarding sexual orientation, though, there is both anecdotal and empirical evidence that relevant twin differences arise early. For example, gender nonconformity differences in childhood are common and predict orientation differences in adulthood.

Dr. Bailey’s answer to the last question is an intriguing finding. One twin might display gender nonconformity and the other might not. These differences do arise early and cause me to question that they are often in response to parenting differences. The GNC differences however, will likely lead to very different social environments for each twin.
Going forward, research on non-shared environmental factors would shed light on how environment helps to shape the pre-natal givens.
*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.

Multiple factors involved in sexual orientation, part 2

I posted 2 weeks ago about this twin study but it is now making the media.
Here is the abstract of the article from Archives of Sexual Behavior:

There is still uncertainty about the relative importance of genes and environments on human sexual orientation. One reason is that previous studies employed selfselected, opportunistic, or small population-based samples. We used data from a truly population-based 2005–2006 survey of all adult twins (20–47 years) in Sweden to conduct the largest twin study of same-sex sexual behavior attempted so far. We performed biometric modeling with data on any and total number of lifetime same-sex sexual partners, respectively. The analyses were conducted separately by sex. Twin resemblance was moderate for the 3,826 studied monozygotic and dizygotic same-sex twin pairs. Biometric modeling revealed that, in men, genetic effects explained .34–.39 of the variance, the shared environment .00, and the individual specific environment .61–.66 of the variance. Corresponding estimates among women were .18–.19 for genetic factors, .16–.17 for shared environmental, and 64–.66 for unique environmental factors. Although wide confidence intervals suggest cautious interpretation, the results are consistent with moderate, primarily genetic, familial effects, and moderate to large effects of the nonshared environment (social and biological)
on same-sex sexual behavior.

Reactions are mixed but not really along any ideological grounds that I can see. For instance, from ScienceNOW:

J. Michael Bailey, a psychologist at Northwestern University in Evanston, Illinois, who led earlier twin studies of sexual orientation, calls the new study “good, important, and one unlikely to be bettered in the near future.” But Jonathan Beckwith, a geneticist at Harvard Medical School in Boston, says that the new work fails to overcome a number of problems faced by previous twin studies. He notes that the final sample included only 12% of the males in the Swedish registry, leaving open the possibility of recruitment bias. And Beckwith says that the failure to control for family environment could inflate estimates of genetic influence.

Co-author Qazi Rahman, was quoted by the Washington Post:

“This study puts cold water on any concerns that we are looking for a single ‘gay gene’ or a single environmental variable which could be used to ‘select out’ homosexuality — the factors which influence sexual orientation are complex. And we are not simply talking about homosexuality here — heterosexual behavior is also influenced by a mixture of genetic and environmental factors,” study co-author Dr. Qazi Rahman, a leading scientist on human sexual orientation, said in a prepared statement.

I intend to devote at least one more post to this study as I agree with Michael Bailey that it is an important study. I think along with the other 2 population based studies (Bailey’s in 2000 and Kendler’s also in 2000), it provides a picture of modest genetic effects along with a major role for non-shared enviromental factors. Many roads lead to a similar result. Nothing in this study provides a clear picture of what those environmental factors are but a simple environmental explanation (e.g., poor parenting) or genetic source (single gene, or uniform action of several genes) is not supported here.
Rahman added in the Post article:

“Overall, genetics accounted for around 35 percent of the differences between men in homosexual behavior and other individual-specific environmental factors (that is, not societal attitudes, family or parenting which are shared be twins) accounted for around 64 percent. In other words, men become gay or straight because of different developmental pathways, not just one pathway,” Rahman said.

Study examines brain differences related to sexual orientation

This post summarizes a new study by Ivanka Savic and Per Lindstrom, titled “PET and MRI show differences in cerebral asymmetry and functional connectivity between homo- and heterosexual subjects” and published in the Proceedings of the National Academy of Science. This is being reported widely in the press.
The abstract reads

Cerebral responses to putative pheromones and objects of sexual attraction were recently found to differ between homo- and heterosexual subjects. Although this observation may merely mirror perceptional differences, it raises the intriguing question as to whether certain sexually dimorphic features in the brain may differ between individuals of the same sex but different sexual orientation. We addressed this issue by studying hemispheric asymmetry and functional connectivity, two parameters that in previous publications have shown specific sex differences. Ninety subjects [25 heterosexual men (HeM) and women (HeW), and 20 homosexual men (HoM) and women (HoW)] were investigated with magnetic resonance volumetry of cerebral and cerebellar hemispheres. Fifty of them also participated in PET measurements of cerebral blood flow, used for analyses of functional connections from the right and left amygdalae. HeM and HoW showed a rightward cerebral asymmetry, whereas volumes of the cerebral hemispheres were symmetrical in HoM and HeW. No cerebellar asymmetries were found. Homosexual subjects also showed sex-atypical amygdale connections. In HoM, as in HeW, the connections were more widespread from the left amygdala; in HoW and HeM, on the other hand, from the right amygdala. Furthermore, in HoM and HeW the connections were primarily displayed with the contralateral amygdale and the anterior cingulate, in HeM and HoW with the caudate, putamen, and the prefrontal cortex. The present study shows sex-atypical cerebral asymmetry and functional connections in homosexual subjects. The results cannot be primarily ascribed to learned effects, and they suggest a linkage to neurobiological entities.

Past research has found that male and female brains are different, on average. This research finds that two brain measures differ based on sexual orientation: cerebral symmetry and how the amygdala functions. First, they confirm a previously reported sex differences in cerebral size asymmetry. In straight men, the right hemisphere is greater than the left and in women, they are the same size. Savic and Lindstrom find in contrast that gays are sex-atypical: the hemispheres are the same size in gay men and for lesbians, the right hemisphere is larger than the left. This is not unexpected given the previous differences in verbal skills (favoring gay males over straights) and visuospatial tasks (favoring straight males).
The amygdala is often researched in relation to the role it plays in emotion and anxiety. Recent research indicates that the right amygdala activates in men and the left in women during the processing of emotion. From these locations in the amygdala then connections are made to other regions in brain which again are different in men and women. In women, the connections may be more likely to activate emotion, whereas in men action may be the more likely result. Again, Savic and Lindstrom found sex atypical function for gays and lesbians. Gay men looked like straight women and lesbians looked like straight men, albeit the similarity was less for the lesbians.
What does this mean? The authors are cautious in their discussion and make some points which could support multiple theoretical perspectives. The authors examined aspects of brain functioning not known to be related to sexual behavior or attraction in order to reduce the possibility that sexual experience contributed to the development of the differences. In other words, it is unlikely that being homo or heterosexual caused these differences. The differences likely precede awareness of sexual orientation, according to the authors. I would agree that it seems unlikely that there is anything about sexual fantasy or behavior that could rewire the amygdala or change the size of the right hemisphere.
On the other hand, Savic and Lindstrom are not proposing that these differences cause the sexual orientation differences. Those familiar with Daryl Bem’s exotic becomes erotic theory will see how these brain differences could support his theory. It is plausible that these brain differences are involved in the gender atypical behavior so commonly and strongly associated with the development of adult homosexual orientation. Gender atypical behavior could be an associated feature of a same-sex orientation, a kind of sign of homosexual orientation or in the EBE account, gender atypical behavior and interest could predispose people to sexual regard the same sex as the other sex during pubescence.
Savic and Lindstrom propose three potential mechanisms for these differences. They note:

The mechanisms behind the present observations are unknown. In accordance with discussions about the sexual dimorphism of the brain, three factors have to be taken into account: environmental effects, genetics, and sex hormonal influences.

These are the usual suspects, genes, environment and hormones. Savic and Lindstrom dismiss genetic factors for reasons I cannot quite figure out. They say,

As to the genetic factors, the current view is that they may play a role in male homosexuality, but they seem to be insignificant for female homosexuality. Genetic factors, therefore, appear less probable as the major common denominator for all group differences observed here.

About environment, they observe that sex-based brain differences have been observed at birth and in children. However, cerebral maturation continues through puberty, especially in boys. Thus, social and environmental factors could play a role in how these differences or other differences not assessed here develop in individuals. They are not certain however and note:

However, to attribute such effects to the present results would require a detailed comprehension of how specific environmental factors relate to the four groups investigated, and how they affect various cerebral circuits. In the light of currently available information this can only be speculative.

In other words, we do not know what environmental factors could be influential on brain differentiation for male and female with sex typical and atypical brain structure and function. The authors are either unaware of Bem’s EBE theory or do not see it as relevant to their findings. Clearly, the researchers wanted to rule out the role of sexual behavior and preference as being the driver for the differences between gays and straight that they found in their pheromone studies. Here they believe they have found clear neurological differences which in some manner relate to the differences in sexual preferences.
The authors seem more disposed to hormonal mechanisms. They discuss hormonal factors in animals, but correctly note that the relevance to humans “remains to be clarified.” They conclude:

The present study does not allow narrowing of potential explanations, which are probably multifactorial, including interplay between pre- and postnatal testosterone and estrogen, the androgen and estrogen receptors, and the testosterone-degrading enzyme aromatase. It nevertheless contributes to the ongoing discussion about sexual orientation by showing that homosexual men and women differed from the same-sex controls and showed features of the opposite sex in two mutually independent cerebral variables, which, in contrast to those studied previously, were not related to sexual attraction. The observations cannot be easily attributed to perception or behavior. Whether they may relate to processes laid down during the fetal or postnatal development is an open question.

In a post to come, I want to bring together the Langstrom et al study of Swedish twins and the Savic & Lindstrom study. We have many coming to the conclusion that brain differences confirm innate sexual orientation. However, studies of twins seems to demonstrate a role for a variety of environmental factors which operate differently for different people.
UPDATE: In the paragraph above, where I mention “environmental factors,” I am not referring to parenting and childhood trauma. I believe the research on these topics rule those factors out as general causes of homosexual development. For some very small number of people, particular women, those factors may lead to a kind of homosexual adaptation but I do not believe they lead to same sex attraction which occurs prior to any homosexual behavior.
The studies showing brain differences are compelling and indicate a lack of choice in sexual feelings and a spontaneous emergence of those feelings.

California Supreme Court recognizes same-sex marriage right

If you get Google alerts or some similar service, you already know that the California Supreme Court has issued a ruling recognizing a right to marriage for same-sex couples. From the San Diego Union-Tribune:

The state Supreme Court struck down California’s marriage law banning same sex couples from getting married in a historic decision Thursday that declared the law unconstitutional discrimination.
The decision will surely touch off an impassioned political fight.
The 4-3 opinion is the high court’s most important civil rights decision in more than a decade, and it is an epic legal victory for same-sex marriage advocates. California is now the second state in the nation to allow gays and lesbians to be legally married.
According to the opinion, “we determine that the language of section 300 limiting the designation of marriage to a union ‘between a man and a woman’ is unconstitutional and must be stricken from the statute, and that the remaining statutory language must be understood as making the designation of marriage available both to opposite-sex and same-sex couples.”

Email alerts reactions from various groups range from “a full win” by gay groups to “a disregard of California voters” from conservative groups. The November ballot initiative will now be considered an effort to overturn this ruling.
Fallout and reactions:
Presidential candidates reactions
New York Times
Schwarzennegger
Associated Press

David Scasta talks on NPR about the APA symposium

On NPR’s Bryant Park Project, David Scasta talked about the cancelled symposium. You will need to listen to the audio to get the discussion since the article is not a transcript.
I will have some comments about this as the day goes on…