Monogamy gene focus of Karolinska Institute

The Karolinska Institute in Sweden continues to make news with genetic and sex research. Now they come forward with a study in the Proceedings of National Academy of Sciences which finds a link between relationship stability and a gene variant. Here is the KI news release:

Link between gene variant and relationship difficulties
[PRESS RELEASE, 2 September 2008] Scientists at Karolinska Institutet have found a link between a specific gene and the way men bond to their partners. The results, which are presented in the scientific journal PNAS, can lead to a better understanding of such problems as autism and social phobia.
“There are, of course, many reasons why a person might have relationship problems, but this is the first time that a specific gene variant has been associated with how men bond to their partners,” says Hasse Walum, postgraduate student at the Department of Medical Epidemiology and Biostatistics.
He stresses, however, that the effect of this genetic variation is relatively modest, and it cannot be used to predict with any real accuracy how someone will behave in a future relationship.
Hasse Walum and his colleagues made use of data from The Twin and Offspring Study in Sweden, which includes over 550 twins and their partners or spouses. The gene under study codes for one of the receptors for vasopressin, a hormone found in the brains of most mammals. The team found that men who carry one or two copies of a variant of this gene  allele 334  often behave differently in relationships than men who lack this gene variant.
The incidence of allele 334 was statistically linked to how strong a bond a man felt he had with his partner. Men who had two copies of allele 334 were also twice as likely to have had a marital or relational crisis in the past year than those who lacked the gene variant. There was also a correlation between the mens gene variant and what their respective partners thought about their relationship.
“Women married to men who carry one or two copies of allele 334 were, on average, less satisfied with their relationship than women married to men who didnt carry this allele”, says Hasse Walum.
The same gene has been previously studied in voles, where it has been linked to monogamous behaviour in males.
“The fact that the corresponding gene has proved important for similar behaviour in voles makes our findings even more interesting, and suggests that the thoroughly studied brain mechanisms that we know give rise to strong bonds between individual voles can also be relevant to humans”, Hasse Walum concludes.
The team hopes that greater knowledge of the effect of vasopressin on human relations will one day give science a better understanding of the causes of diseases characterised by problems with social interaction, such as autism.
Hasse Walum, Lars Westberg, Susanne Henningsson, Jenae M. Neiderhiser, David Reiss, Wilmar Igl, Jody M. Ganiban, Erica L. Spotts, Nancy L. Pedersen, Elias Eriksson and Paul Lichtenstein
Genetic variation in the vasopressin receptor 1a gene (AVPR1A) associates with pair-bonding behavior in humans, PNAS Early Edition, 2-5 September 2008.

Ah, the mysteries of human behavior. I think there is probably something to this. Men who look to bonding problems with their parents for the reason they do not feel connected to their mates might better look elsewhere. None of this is destiny but it makes some sense that the mechanisms underlying bonding are variable in their application due to DNA. Furthermore, none of this suggests that monogamy is not valuable or attainable — it just means some must work harder at it.

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.