In all my posts at the beginning I will include a simple paragraph that you can cut and paste that explains why the research quoted does not demonstrate a biological basis for Transexualism. Below is the first one.
START QUOTING HERE – In 2002, research carried out by Chung, De Vries, and Swaab, showed that the differences in the BSTc area in the hypothalmus observed between males and females, did not occur until adulthood – at the earliest 22 years of age. As the majority of Transexuals report that they feel as if they are in the wrong body before the age of 22, these feelings do not appear to be connected to the size of the BSTc area in the hypothalmus. The Transexuals studied were taking feminising hormones and this is the most likely cause of similar sizes of BSTc in females and MtoF transexuals. A recent study by Hulshoff Pol et al. (2006), demonstrated that hormones taken by MtoF Transexuals as part of their transitioning, decreased both the overall volume of the brain and the volume of the hypotalmus. In otherwords, it is hormones taken by adult MtoF Transexuals that cause them to have “a female brain”. STOP QUOTING HERE.
One of the most commonly quoted pieces of research was carried out in 1995 by Zhou, Hofman, Gooren, and Swaab. http://www.ncbi.nlm.nih.gov/pubmed/19955753?dopt=Abstract
This research says that:
1. Part of the hypothalmus in the brain called the BSTc was on average 44% larger in males than females when measured in post mortem studies i.e. when the person was dead.
2. In 6 MtoF transexuals studied who had taken feminising hormones, the BSCt was a similar volume to that of biological females.
3. As the 6 Transexuals were of different sexual orientations, the authors concluded that there was “no relationship between BSTc size and the sexual orientation of transsexuals” (p. 70). Therefore, it was not sexual orientation that caused the differences in size of the BSTc.
4. Based on a small number of non transexual patents with abnormal sex hormone levels, the authors concluded that “the small size of the BSTc in male-to-female transsexuals cannot be explained by adult sex hormone levels” (p. 70).
5. In 2000, the authors published a follow up study in which they looked at the number of neurons in the BSTC. They found that the average number of neurons in the BSTC was on average 71% higher in males than females. Again the 6 Transexuals studied had a level of neurons more typical of biological females. And again sexual orientation appeared to make no difference.
These studies are quoted time and time again to demonstrate that:
a. Transexual MtoF have “feminised” brains.
b. That this feminisation happens at the foetal stage, which is what the authors of the study argued.
However in 2002 research carried out by Chung, De Vries, and Swaab, showed that the differences in size of BSTc between females and males, did not take place until adulthood – at the earliest 22 years of age. As the majority of Transexuals report feeling that they are in the wrong body before the age of 22, these feelings appear to not be influenced by the size of the BSTc.
There are different theories as to why these 6 adult MtoF transexuals should have a similar size of BSTc to adult females. These include statistical chance because of the small size of the study; adult behaviour influencing its size and the most likely explanation, adult hormones.
Ah yes, remember – these adult MtoF Transexuals had all taken feminising hormones. It has been known for years (Cooke, Tabibnia, & Breedlove, 1999), that changes in androgen levels in animals in adulthood, can change the volume of sexually dimorphic brain nuclei to correspond with the volume in female brains.
Moreover a “recent study by Hulshoff Pol et al. (2006) demonstrated the profound effect of transgender hormone therapy on brain volume in transsexuals: In eight MtF transsexuals treated for 4 months with ethinyl estradiol and CPA, total brain volume and hypothalamic volume decreased significantly with hormone therapy, based on pre- and post-treatment MRI studies.
In a control group of nine untreated nontranssexual men, total brain volume and hypothalamic volume increased slightly over a similar period. In six FtM transsexuals treated for 4 months with testosterone, total brain volume increased and hypothalamic volume remained unchanged, whereas in a control group of six untreated nontranssexual women, total brain volume remained unchanged and hypothalamic volume decreased.” http://www.annelawrence.com/twr/brain-sex_critique.html
In otherwords, “feminising” hormones routinely taken by many MtoF transexuals, appear to decrease the overall brain volume and the brain volume of the hypothalmus.
In otherwords, it appears that it is not biology causing the “feminisation” of the MtoF Transexuals brain, but hormones taken as adults as part of the transition process.