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Tuesday, February 21, 2006

 

Sexual orientation and genetics: X marks the spot

Here is the abstract of a new report from Human Genetics about a link between some moms and the sexual orientation of sons. This kind of stuff is interesting of course but the conclusions drawn by the researchers is speculative: "The research "confirms that there is a strong genetic basis for sexual orientation, and that for some gay men, genes on the X chromosome are involved," said study co-author Sven Bocklandt, a postdoctoral researcher at the University of California at Los Angeles." The findings I read in the abstract do not "confirm" anything. Furthermore, the study as described could not provide any pathway from a putative genetic mechanism to behavior. All they have shown is there are group differences.

As I look at it, none of this is very enlightening unless the temperament and environment of the sons is also taken into consideration. There are potential intervening variables that are not even considered by these researchers (e.g., gender atypical temperaments). GAT may be related to these changes in the X chromosome but I doubt this was taken into account.

ABSTRACT
Human Genetics
Issue: Volume 118, Number 6
Date: February 2006
Pages: 691 - 694
Extreme skewing of X chromosome inactivation in mothers of homosexual men
Sven Bocklandt, Steve Horvath, Eric Vilain and Dean H. Hamer

Abstract Human sexual preference is a sexually dimorphic trait with a substantial genetic component. Linkage of male sexual orientation to markers on the X chromosome has been reported in some families. Here, we measured X chromosome inactivation ratios in 97 mothers of homosexual men and 103 age-matched control women without gay sons. The number of women with extreme skewing of X-inactivation was significantly higher in mothers of gay men (13/97=13%) compared to controls (4/103=4%) and increased in mothers with two or more gay sons (10/44=23%). Our findings support a role for the X chromosome in regulating sexual orientation in a subgroup of gay men.

Comments:
As I look at it, none of this is very enlightening unless the temperament and environment of the sons is also taken into consideration. There are potential intervening variables that are not even considered by these researchers (e.g., gender atypical temperaments).

Urgh, Warren...

This looked at genetic markers within the mothers.

This makes a stronger case for thinking that sexuality is genetically inherited, with the actual gender behaviour/traits of the sons possibly being utterly irrelvant. Those characteristics may vary widely in the sons, but do not -- cannot -- alter the genes of the mother.
 
I understand that.

My point is what does the difference in the mothers mean? If the genetic difference in the mothers meant that the sons were more atypical in gender terms, then the relationship described by Bem and others would be supported as opposed to a direct genetic interpretation of the findings. In my opinion, it is more likely that the X difference relates to basic temperamental differences that may find expression in any number of ways. If the researchers were not asking or looking for these differences then they missed a potentially crucial and I should add empirically supported intervening variable.

If the question asked was: do the X activations relate to gender atypical sons, I suspect based on past research that the differences between gender atypical and gender typical sons would be more striking. I cannot say for certain that the researchers did not take this into account but the abstract gives no reason to think they did.
 
OK -- some of your wording confused me on that.

But the study does "confirm" a genetic basis, as Bocklandt said: regardless of whether it's direct or indirect via temperaments. (And the "" around confirm is just me delib. recognising the limits from testing only 200 women).

When I can (that is, when I have time to finish the rotten thing) I will forward some basic #s I've done around Bem's original paper. Even ignoring the fact it's based on a sample that the authors warned could not be used for the purpose, I simply cannot get pathways via temperament to add out vis Green's work etc that Bem uses to support his idea. That suggests -- as all such gaps do -- that the intervening attribute is not actually involved. Occam's Razor...

Sorry I just read that again. I'm not sure it will make any sense without the numbers. Guess I should devote a few hours this weekend :)
 
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