News, analysis and fact-checking of anti-gay rhetoric
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The FBI’s annual Hate Crime Statistics aren’t as complete as they ought to be, and their report for 2004 was no exception. In fact, their most recent report has quite a few glaring holes. Holes big enough for Daniel Fetty to fall through.A Predictive Formula for Orientation?
Timothy Kincaid
November 8th, 2007
As of yet there is no convincing study that can definitely prove that sexual orientation can be fully attributed to biology (genes, hormones, inuterine circumstances) or societal factors (parents, peers, self imaging). Twin studies suggest some genetic impact, but also seem to suggest that gene may not work alone. Studies on other mammals (rams in particular) suggest that brain structure is relevant, but we are humans not sheep and there is some argument that the brain structural differences may be a result rather than cause of sexual attraction/behavior.
However, in recent years there has been a regular stream of studies, all of which seem to support the notion that sexual orientation is heavily influenced by non-voluntary determinants, most of which appear biological in nature. Yet another has appeared in the Archives of Sexual Behavior.
Previous studies have established that left-handedness appears to a greater degree in the male homosexual population than in the male heterosexual population (it also appears among Presidents). Studies have also linked handedness with increased size of an area of the brain, the corpus callosum, particularly the isthmus.
We hypothesized that isthmal area would be greater in homosexual men, even among right handers. Twelve homosexual and ten heterosexual healthy young men, all consistently right-handed, underwent a research-designed magnetic resonance imaging scan. We found that the isthmal area was larger in the homosexual group, adding to the body of findings of structural brain differences between homosexual and heterosexual men.
This led researcher to think that right-handed gay men were less right-handed (“less marked functional asymmetry”) than their straight counterparts.
A logistic regression analysis to predict sexual orientation category correctly classified 21 of the 22 men (96% correct classification) based on area of the callosal isthmus, a left-hand performance measure, water level test score, and a measure of abstraction ability. Our findings indicate that neuroanatomical structure and cognition are associated with sexual orientation in men and support the hypothesis of a neurobiological basis in the origin of sexual orientation.
Past studies have suffered from the problems of exceptions. While “on average” an attribute might be observed to be different between the orientations, the variances were small and many individuals were observed to be on both sides of the observation window. If I am reading this correctly, however, Sandra Witelson and her team may have found a predictive test, a formula, for determining sexual orientation, using MRI and dexterity testing.
However, in Science Daily, Witelson appears to be hesitant to make such a claim:
The size of the corpus callosum is largely inherited suggesting a genetic factor in sexual orientation, said Witelson “Our results do not mean that heredity is destiny but they do indicate that environment is not the only player in the field,” she said.
While this is not a litmus test for sexual orientation, Witelson said this finding could prove to be one additional valuable piece of information for physicians and individuals who are trying to determine their sexual orientation. “Sometimes people aren’t sure of their sexual orientation.”
It will be interesting to see if her 96% correct prediction rate can be replicated in a larger population. Further, it will be interesting to see longitudinal testing to determine if sexual orientation can be predicted early in life.
In any case, this is yet one more study that supports a biological etiology for sexual orientation.
[Hat tip: GoodAsYou.org]
Patrick
November 8th, 2007 | LINK
It will never be “proven” for several reasons. First, it would be unethical to manipulate fetuses. Second, it appears there are multiple paths up the same mountain, thus no one cause will ever be demonstrated. Third, there will likely be some individuals who identify as homosexual who do so for social reasons.
However, I consider the evidence now beyond reasonable doubt that homosexuality is inborn. Furthermore, no post-natal social factor or combination of factors have been identified as determining a homosexual orientation. This is especially significant given the much longer time frame for research on post-natal causes, given the paradigms researchers have worked under over the last 50-100 years.
Spalchik
November 8th, 2007 | LINK
Although logistic regression yielded very high prediction rates, that doesn’t mean that all factors in this regression have the same weight (regression coefficients). It is important to know the regression coefficients to be able to tell which factors are most influential.
I agree with Witelson who says that people’s opinion about their own orientation cannot be relied upon with 100% certainty, and this somewhat undermines the predictive power of such a regression.
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