On the Science of Changing Sex

Sex Chromosomes Expression Associated With Brain Sex?

Posted in Brain Sex by Kay Brown on July 27, 2020

Teenage-brainThere has been a long term assumption that sexually dimorphic brain features developed solely from hormonal difference, both organizational and activational.  Some have long suspected that at least some of the sexually dimorphic features were from differential expression of the sex chromosomes themselves.  An association between such features and differential expression has now been found in a recent study.

There is a great essay at Wired that I would recommend you read before continuing to read my essay here.  (Link)

A few comments are warranted here.

First, the hormonal hypothesis is not negated, only modified.  There remain several possibilities, first that the hormonal influence simply triggers which genes are expressed in the brain at and that it is only coincidental that some are on the sex chromosomes; second, that hormonal influence works independently from the sex chromosome expression control.  Of course, it could even be some combination of the two (and my bet is on this third possibility).  Remember, many of the genes differentially expressed are NOT on the sex chromosomes, and even those on the X chromosome, available to both sexes, are differentially expressed.

Please note:  Genes on the X chromosome are NOT all automatically expressed in women nor are they automatically repressed in men.  Further, not all of the genes found on the X chromosome relate to sexually dimorphic development (e.g. color vision receptor).

Second, we don’t know what the FUNCTIONAL differences the sex chromosomes mediate vs. the autosomal chromosomes.  We don’t know how different the behaviors would really be with such differential expression.  These difference could be related not to behaviors but to immune responses for example.  When one is confronted with ignorance, it is important to recognize it and not make conclusions that the data doesn’t support.

Third, a reminder that these differences can NOT be directly associated with important cognitive mechanisms, else females would be at an extreme disadvantage not able to express genes that lie only on the Y chromosome.  We know this because men and women have shown only tiny differences in cognitive performance of specific tasks and that general cognitive ability (IQ – g factor) do not differ between the sexes.  (Male chauvinists be damned!)

Fourth, speculating on what effect this might have on gender atypicality and the degree to which such atypical individuals may resemble the opposite sex in brain sexual dimorphism is inescapable.  Most of it will likely be found wrong later.

One can imagine certain transphobic groups using this material to show that gender atypical transsexuals (HSTS) aren’t “really” a man or a woman… cause… “biology” (essentialism based on karyotype).  But that is not the germain issue as we KNOW that other mechanisms are also involved.

Further Reading:

Essay on hormonal effects on sexually dimorphic brain development

Essay on gene control of sexually dimorphic behaviors

Further External Reading:

Wired Article

Reference:

Liu, et Al.,”Integrative structural, functional, and transcriptomic analyses of sex-biased brain organization in humans”, PNAS (2020)
https://doi.org/10.1073/pnas.1919091117

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