On the Science of Changing Sex

Etiological Conjectures, Part 3

Posted in Transsexual Theory by Kay Brown on February 14, 2013

androgynous faceAs I related in Part 1 and Part 2 of my discussion regarding etiological conjectures, there are still more questions than answers about how early onset gender atypicality and dysphoria develops.  However, there are some very intriguing clues from the biodemographics of transkids.  As I discussed in an earlier essay on how MTF transkids may be a subset population of the larger exclusively androphilic, gender atypical, but not gender dysphoric children who grow up to be conventional gay men, the biodemographics of MTF transkids seems to be very similar, if not identical, to that of at least some gay men.

Simply put, MTF transkids have more brothers than sisters, far more than one would expect comparing them to the general population.  They tend to have more older brothers than would be expected, showing that for each older brother, the likelihood that a given male would be an MTF transkid is increased by 40%.  Note that the absolute likelihood of being an MTF transkid is still very, very tiny, but the more older brothers that one’s mother had given birth to, the more likely this tiny chance is increased.  This effect is also found in conventional gay men, but only those who were feminine as children.

From this statistical anomaly, Blanchard suggested that at least some gay men and MTF transkids have an etiological cause that is effected by their mother’s prior pregnancy experiences.  His conjecture is that prior male pregnancies challenged their mother’s immune system such that they developed anti-bodies to “maleness” in some, as yet to be discovered, fashion.

I would offer a different conjecture.  It is fairly well established that placentas from each fetus a women bears releases cells that migrate to all parts of her body.  In effect, she becomes a genetic chimera, carrying the DNA of each of her children (including those who miscarried).  This means that she also carries cells in her body which are genetically “male”, that have a Y chromosome and have supposedly been epigenetically tagged as being “male” during gestastion, prior to escaping via the placenta and migrating into her own body.  I conjecture that the mother’s own epigenetic gene regulation mechanisms are invoked to bring these “male” cells in line with her female body.  If these mechanisms become especially strong, they may tag her own germ cell line prior to oogenesis with epigenetic tags that push the later born male children toward neurological femininity.

Perhaps someday, we will see which, if either, of us guessed right.

References:

Sebastian E. E. Schagen, Henriette A. Delemarre-van de Waal, Ray Blanchard, Peggy T. Cohen-Kettenis, (2012) “Sibling Sex Ratio and Birth Order in Early-Onset Gender Dysphoric Adolescents”
http://link.springer.com/article/10.1007%2Fs10508-011-9777-6

Blanchard, R., & Sheridan, P. M. (1992). Sibship size, sibling sex ratio, birth order, and parental age in homosexual and nonhomosexual gender dysphorics. Journal of Nervous and Mental Diseases, 180, 40–47.
http://www.ncbi.nlm.nih.gov/pubmed/1538206

Blanchard, Bogaert, “Homosexuality in men and number of older brothers”
http://ajp.psychiatryonline.org/cgi/content/abstract/153/1/27?ijkey=e186877631aa1c47de8fd859310668c21bcd25ef&keytype2=tf_ipsecsha

Anthony F. Bogaert, “Biological versus nonbiological older brothers and men’s sexual orientation”
http://www.pnas.org/content/103/28/10771.full

Green, R. (2000). Birth order and ratio of brothers to sisters in transsexuals. Psychological Medicine, 30, 789–795.
http://www.ncbi.nlm.nih.gov/pubmed/11037086

Blanchard, R., Zucker, K., Cohen-Kettenis, P., Gooren, L., & Bailey, J. (1996) “Birth order and sibling sex ratio in two samples of Dutch gender-dysphoric homosexual males” Archives of Sexual Behavior, 25, 495–514.
http://link.springer.com/article/10.1007%2FBF02437544?LI=true

Johannes Bohacek, Katharina Gapp, Bechara J. Saab, Isabelle M. Mansuy, “Transgenerational Epigenetic Effects on Brain Functions”
http://www.biologicalpsychiatryjournal.com/article/PIIS0006322312007299/abstract

Miranda P. Dierselhuis, Els Goulmy, “We are all born as microchimera”
https://www.landesbioscience.com/journals/chimerism/article/23348/

 


 

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