Category: Research news

Multiple factors involved in sexual orientation: New study

A new study released online with Archives of Sexual Behavior and via press release today propose a relatively small role for family attitudes in the direction of sexual attraction, with more of the explanation being factors not shared by siblings.

Society’s attitudes have little impact on choice of sexual partner
[PRESS RELEASE 16 June 2008] A unique new study from the Swedish medical university Karolinska Institute (KI) suggests that the attitude of families and the public have little impact on if adults decide to have sex with persons of the same or the opposite sex. Instead, hereditary factors and the individual’s unique experiences have the strongest influence on our choice of sexual partners.
The study is the largest in the world so far and was performed in collaboration with the Queen Mary University of London. More than 7,600 Swedish twins (men and women) aged 20-47 years responded to a 2005 – 2006 survey of health, behaviour, and sexuality. Seven percent of the twins had ever had a same-sex sexual partner.
“The results show, that familial and public attitudes might be less important for our sexual behaviour than previously suggested”, says Associate Professor Niklas Långström, one of the involved researchers. “Instead, genetic factors and the individual’s unique biological and social environments play the biggest role. Studies like this are needed to improve our basic understanding of sexuality and to inform the public debate.”
The conclusions apply equally well to why people only have sex with persons of the opposite sex as to why we have sex with same-sex partners. However, the conclusions are more difficult to transfer to countries where non-heterosexual behaviour remains prohibited.
Overall, the environment shared by twins (including familial and societal attitudes) explained 0-17% of the choice of sexual partner, genetic factors 18-39% and the unique environment 61-66%. The individual’s unique environment includes, for example, circumstances during pregnancy and childbirth, physical and psychological trauma (e.g., accidents, violence, and disease), peer groups, and sexual experiences.
Publication:
Niklas Långström, Qazi Rahman, Eva Carlström, Paul Lichtenstein, “Genetic and Environmental Effects on Same-sex Sexual Behaviour: A Population Study of Twins in Sweden.” Archives of Sexual Behaviour, 7 June 2008, doi 10.1007/s10508-008-9386-1

This is more evidence that different factors operate differently for different people. In discussing sexual orientation, it may be that individual narratives have validity for the individual but cannot be generalized widely. Where have I heard that before?
Another news item is circulating today with what appears to be a mix of new and old research on brain structure and sexual orientation.
UPDATE – There is indeed new research from Ivanka Savic’s team in the Proceedings of the National Academies of Science. The study, titled “PET and MRI show differences in cerebral asymmetry
and functional connectivity between homo- and heterosexual subjects” by Ivanka Savic and Per Lindstrom is not yet published but I have a copy and am reviewing it.

Gender identity disorder research: Q & A with Kenneth Zucker

As a follow up to the recent broadcasts by NPR and several posts regarding gender identity, here is a Q & A involving J. Michael Bailey and Ken Zucker recently posted on the SEXNET email list. Dr. Zucker is the Head of the Gender Identity Service, Child, Youth, and Family Program and Psychologist-in-Chief at the Centre for Addiction and Mental Health in Toronto, Ontario, Canada. Dr. Zucker is the chair of the newly appointed Sexual and Gender Identity Disorders working group for the 5th edition of American Psychiatric Association’s Diagnostic and Statistical Manual (DSM-V). Dr. Bailey is Professor of Psychology at Northwestern University, prolific sexual orientation researcher and moderator of the SEXNET list. As the NPR article noted, Dr. Zucker has extensive clinical and research experience with persons who experience gender dysphoria. This interview was conducted by Dr. Michael Bailey via email and has been slightly edited for posting here. Both Drs. Bailey and Zucker have reviewed and approved it.

Bailey: Both NPR shows used the phrase “a girl trapped in men’s bodies.” How common is this concern over body image?
Zucker: I would say that, in general, there has not been a lot of good empirical research on body image issues in pre-pubertal children with GID. In adolescence, the Dutch group has reported clear evidence of body image dissatisfaction as one finds in adults. One of my PhD students has a dissertation that should be defended later this year in which we studied body image in boys with GID compared to clinical and community controls. We did detect significant body image differences among the three groups: body image in general and in relation to gender-specific anatomic dysphoria. The boys with GID had a poorer body image in general and, of course, with regard to gender-specific anatomic dysphoria. It is only a first pass at this issue and I will report on this down the road after the dissertation is defended.
Bailey: The case on the second NPR show is of a child (natal boy) who had extreme temper tantrums when not allowed to engage in feminine behaviors. Is this common in the kids you see, or is there something unusual about these kids?
Zucker: This is not uncommon. Some parents will report that if they try to limit cross-dressing that this can be very distressing for the boys. Some parents describe it as “he needs his fix.”
Bailey: You are more familiar than anyone else I know with the difference between the British and Dutch treatment centers that yielded the findings that only 20% of the British kids but 100% of the Dutch kids pursued sex reassignment eventually. Did the Dutch center focus on older children (who were less likely to change their minds)? To the extent that the samples were comparable, it is a shocking difference in outcome.
Zucker: I don’t think the British group has published their data yet. But, yes, the Dutch group data are on adolescents and I think that the British group is talking about clients first seen in childhood, not adolescents. The Dutch group now has a paper that is close to being “in press” on their first follow-up of GID children and then followed up later. The GID persistence rate for their boys was about 20% and the persistence rate for girls was 50%. Their persistence rate for boys appears to be similar to what I have summarized for the boys seen in my clinic (Zucker, 2005), but higher than the 12% rate for girls that we published earlier this year (Drummond et al., 2008). The Dutch group speculates that their girls were, at initial presentation, more extreme in their cross-gender behavior than the girls that we reported on, but that will require more careful analysis.
Bailey: The NPR show, and some people on it, kept implying that some of these kids are “really” transgender, and others are not. I suspect you don’t agree with this way of thinking about it, although you recognize that some kids are more likely to become transgender adolescents and adults than other kids are. Can you remind us which factors are associated with persistence of GID from childhood?
Zucker: I don’t think we know yet. Two possible candidates are age at initial evaluation (later age associated with greater persistence rates) and quantitative metrics of cross-gender behavior in childhood.

By persistence rate, Dr. Zucker is referring to the percentage of GID children who are still GID at a later assessment. In the Dutch group, as well as in Dr. Zucker’s research sample, most boys who want to be girls in childhood, end up as men who do not want to be women. For women in the Dutch sample, half remain GID. I think the assessments of low persistence of GID provide some helpful information to parents who wonder about puberty delay and behavioral interventions with their GID children.
Thanks to Drs. Bailey and Zucker for permission to post this conversation.

This is your brain. This is your brain on sex.

Something like that.
Scientific American’s Mind has an article this month giving a neural tour of the brain’s sexual response. The article supports Michael Bailey’s contention that women are more flexible in their erotic responding than men, who are more channeled into either same or opposite sex responding.
Here are the bullet points for the Mind article:

-Sexual desire and orgasm are subject to various influences on the brain and nervous system, which controls the sex glands and genitals.
-The ingredients of desire may differ for men and women, but researchers have revealed some surprising similarities. For example, visual stimuli spur sexual stirrings in women, as they do in men.
-Achieving orgasm, brain imaging studies show, involves more than heightened arousal. It requires a release of inhibitions engineered by shutdown of the brain’s center of vigilance in both sexes and a widespread neural power failure in females.

Makes for interesting weekend reading…