My comment to WHO on “brain sex”

I had commented that the “brain sex” evidence was conflicting and of very low quality. A pro-gender commenter challenged me to provide references showing that the evidence was conflicting. I can resist temptation but not a challenge, so I provided it. I have added emphases.

In contrast to the main “brain sex” studies on which transgenderism activists hang their hats (Zhou et al 1995; Kruijver et al 2000; Berglund et al, 2008; Garcia-Falgueras et al, 2008) — all conducted in corpses, by the way — Savic and Arver (2011) found the following in their study conducted in living male transgenderists (all erotically attracted to females):

“The present data do not support the notion that brains of MtF-TR are feminized. The observed changes in MtF-TR bring attention to the networks inferred in processing of body perception.”

Savic I, Arver S. Sex dimorphism of the brain in male-to-female transsexuals. Cereb Cortex. 2011 Nov;21(11):2525-33.

In their study in living male transgenderists (all erotically attracted to males), Zubiaurre-Elorza and colleagues (2013) later reported:

“In the present report, we studied MtF transsexuals erotically attracted to males that show a feminization of CTh but not in the putamen. Moreover, these findings on the CTh show the same tendency as those reported by Savic and Arver (2011) with respect to the cortical volume of MtFs erotically attracted to females.”

Zubiaurre-Elorza L, Junque C, Gómez-Gil E, Segovia S, Carrillo B, Rametti G, Guillamon A. Cortical thickness in untreated transsexuals. Cereb Cortex. 2013 Dec;23(12):2855-62.

Savic and Arver (2011) had noted enlarged cortical volume, but in view of their findings of deficiencies in networks involved with own-body perception, had speculated:

“[T]the enlargement of the GM volume in the insular and inferior frontal cortex and the superior temporal-angular gyrus could derive from a constant rumination about the own body. Brain tissue enlargement has been detected in response to training, and GM enlargement of the insular cortex has been reported in response to meditation, which involves mental focusing on the own body (Holzel et al. 2008; Luders, Toga, et al. 2009; Vestergaard-Poulsen et al. 2009).”

Anyway, from the perspective of assessing of evidence quality with GRADE (required in WHO guideline development), all of this “brain sex” evidence is pretty worthless, due to very serious problems of imprecision (very small numbers), often serious indirectness (e.g. postmortem studies) and possibly other kinds of bias.

Relative to imprecision, here’s another thought from Button and colleagues (2013):

“A study with low statistical power has a reduced chance of detecting a true effect, but it is less well appreciated that low power also reduces the likelihood that a statistically significant result reflects a true effect. …. The consequences of this include overestimates of effect size and low reproducibility of results. There are also ethical dimensions to this problem, as unreliable research is inefficient and wasteful.”

Button KS, Ioannidis JP, Mokrysz C, et al. Power Failure: why small sample size undermines the reliability of neuroscience. Nature Reviews Neuroscience 14: 3665-376. doi:10.1038/nrn3475


8 thoughts on “My comment to WHO on “brain sex””

  1. … so what you’re saying is that studies “conflict” because this part of a MtF transsexual’s brain may be female-typical in size due to MtF transsexuals’ constantly worrying about their bodies? And it never occurred to you that female-typical size may be a result of us similarly worrying about our own bodies? Periods, pregnancies, the “biological clock”, beauty standards, vulnerability to sexual assault and rape. In college, we would walk together to the closest car to drop each other off after night classes. Just that was a reminder to worry at least three times a week.


    1. I’m afraid you’ve misunderstood this. The Savic & Arver paper suggests that this area might be larger in male transsexual brains because of their constant self-obsession. Savic & Arver are not saying that the male tranny brains are similar to women’s brains. In fact, they explicitly say the male tranny brains are NOT like women’s brains! The enlarged area in tranny brains is different from normal men’s brains *and* from women’s brains. To account for the difference, Savic & Arver suggest that the trannies are completely self-absorbed, so maybe that’s why this portion of their brains is enlarged. The trannies do not like this study.

      Savic & Arver and Zubiaurre-Elorza et al do not conflict with each other. They conflict with the several older studies I first mention (Zhou et al 1995; Kruijver et al 2000; Berglund et al, 2008; Garcia-Falgueras et al, 2008). Trannies have bet the farm on those older studies, but they are deeply flawed and their findings don’t mean much at all.


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