On the Science of Changing Sex

Fraternizing with the…

Posted in Transsexual Field Studies by Kay Brown on June 18, 2017

critical-thinking… Allies  Or, The Fraternal Birth Order Effect: Early Onset Transwomen vs. Gay Men

In a very recently published meta-study conducted by Ray Blanchard further exploring the Fraternal Birth Order Effect (FBOE), in which he had earlier noted that androphilic males tend to have more older brothers than sisters, he deals with several concerns and new research questions.  First, there had been some concerns with how best to handle the potential effects of family size.  But what really interests me is that here, for the first time, he carefully considers the effect of transgender (feminine presentation / identity) vs. non-trans androphilic men (masculine presentation / identity i.e. conventional gay men).  The results are striking!

“The pooled Older Brothers Odds Ratio for the feminine groups was 1.85, and the value for the non-feminine groups was 1.27. The corresponding risk ratios were 1.52 and 1.19.  The differences between groups were highly significant.  To sum up the results so far in common language:  Feminine homosexual males have more older brothers than non-feminine homosexual males, and non-feminine homosexual males, in turn, have more older brothers than heterosexual males.”

These results weren’t just “statistically significant”, the effect was very great with the 95% Confidence Levels not even overlapping!

But we should introduce a note of caution here.  The feminine androphilic data was very heterogeneous as can be seen in this plot of the data.  This may be caused by the differences between cultures sampled from all over the world.  Some of this data is from Samoan Fa’afafine, some from Western gender dysphoria clinics in the US, UK, and Spain, some from non-Western cultures like Brazil and Korea.  Blanchard also noted this issue and suggested exploration of this might interest some future researcher as more data becomes available.  But in any case, we are shown some very intriguing data that strongly suggests that we may be seeing a difference in etiology between feminine and masculine androphilic males.

Blanchard discusses possible conclusions regarding this,

“A … possibility is that the neurodevelopmental pathway triggered by older brothers is inherently more feminizing than path ways triggered by other etiologic factors (e.g., ‘‘gay’’ genes or prenatal hormone exposure). Thus, a group of homosexual males selected for generalized femininity is likely to contain a higher proportion of individuals who acquired their sexual orientation via the older brother pathway. Other hypotheses, equally speculative, are also possible. … Blanchard and Bogaert (1996) proposed that the FBOE reflects the progressive immunization of some mothers to male-specific (i.e., Y-linked) antigens by each succeeding male fetus and the concomitantly increasing effects of anti-male antibodies on sexual differentiation of the brain in each succeeding male fetus. According to this maternal immune hypothesis, cells (or cell fragments) from male fetuses enter the maternal circulation during childbirth or perhaps earlier in pregnancy. These cells include substances that occur only on the surfaces of male cells, primarily male brain cells. The mother’s immune system recognizes these male-specific molecules as foreign and produces antibodies to them.  When the mother later becomes pregnant with another male fetus, her antibodies cross the placental barrier and enter the fetal brain. Once in the brain, these antibodies bind to male-specific molecules on the surface of neurons.  This prevents these neurons from ‘‘wiring-up’’ in the male-typical pattern, so that the individual will later be attracted to men rather than women.”

Something not discussed, indeed I’m not sure how it can even be explored – unless the curve in the data shown for the odds of an older brother per other sibling is evidence for the effect of first born males experiencing self-induced maternal immunity creating the same etiological pathway.  I would also expect that some first born males may have this etiology due to previous maternal miscarriages and abortions of male fetuses since they too would be expected to have Y-linked antigen challenges to the maternal immune system.

Still, and all, very exciting paper well worth reading.

Reference:

Blanchard, R., “Fraternal Birth Order, Family Size, and Male Homosexuality: Meta-Analysis of Studies Spanning 25 Years”, Archives of Sexual Behavior, (2017),
https://link.springer.com/article/10.1007/s10508-017-1007-4

 


 

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