On the Science of Changing Sex

What is a Transsexual?

Posted in Science Criticism by Kay Brown on April 14, 2013

♫♫She Blinded Me with…  Science…♫♫

Science vs nonsense

Remember as you read this site;  Transsexuals and transgendered people are good people, worthy of our respect, and even of our admiration.  Nothing in this material is meant to imply otherwise.  If you are a transsexual or transgendered person:  You have value as a human being.  You have the right to be respected, valued, and even celebrated as the gender to which you identify and aspire.

In this entry, I’m going to try, real, hard, to explain the science behind what I’ve been writing about here for the past three and some years.  I’m going to try to break it down, telling the story of how it all works… and answer the various questions of the two type taxonomy doubters.

The story begins some years ago, when medical and psychology researchers tried to make sense of those individuals who were requesting ‘sex changes’.  They kept getting confused because the Male-To-Female transsexuals didn’t seem to have just one clinical presentation, one life story.  So, some of them tried to create profiles and categories, usually trying to squeeze them all into an already familiar theoretical framework.  A few people found several “types”, some found only two.  But why?  Shouldn’t there be only one?  Some decided that one of the types was a “true” transsexual, and the others a “pseudo” transsexual, or there was one “primary” and the others “secondary”.  Others found two, but called one type “early onset” and another “late onset”, almost as though there were only one type, but with two different symptomology patterns.

For more information see my essay on this early confusion.

But what was the meaning of this?  Many researchers agreed that one set was strictly “homosexual” with respect to their natal sex, transitioned very young, was feminine since childhood, and the other group was heterosexual, had “fetishistic transvestism” and transitioned much later in life.  Thus was born the hypothesis that was first fully articulated and tested by Kurt Freund, that MTF transsexuals always present with one of two unusual sexual interests, “homosexuality” or “femmiphilic fetishism”.  His concept of “femmiphilic fetishism” was that transsexuals “fetishized” both wearing female clothing and other aspects of simulating being like a woman.  He conducted a study in which he divided the MTF transwomen into two groups based on a questionnaire that statistically separated them into mostly heterosexual and mostly homosexual.  Then asked the BIG question, “Do you find wearing women’s clothing sexually arousing?”  He got a very strong statistical signal that said, yes, the mostly heterosexual group was far more likely to be sexually aroused by wearing women’s clothing than the mostly homosexual group.  This was the state of affairs in the late ’70s.

Enter a very bright and personable younger protegee of Kurt Freund’s, Ray Blanchard.  Starting with Freund’s basic hypothesis, he tested a further hypothesis using a modification to Freund’s questionnaire that placed androphilia on one axis and gynephilia on another axis, rather than as polar opposites along a single line.  This allows one to separate the asexual and bisexual individuals from the strongly heterosexual and homosexual, following up on a hunch that Freund’s method tended to lump half the asexual and bisexual individuals into each of the two other groups.  Thinking about it ahead of time, there is no reason to believe that bisexuals or asexuals would be more or less likely to be sexually aroused by wearing women’s clothing, cross-dressing.  But Blanchard had been talking to a number of candidates for surgery and noted that some who reported that they were not sexually aroused by cross-dressing were aroused by imagining themselves to be female.  So he asked about this same behavior of those who did report sexual arousal to cross-dressing and found that it was universal.  Freund was right, but it wasn’t simple fetishism… but something else… for which Blanchard coined the term “autogynephilia”.  In talking to individuals who were, using this new term, autogynephilic, he developed a new hypothesis, that if a male was gender dysphoric and not exclusively “homosexual” with respect to natal sex, then that individual would be autogynephilic.  This sounds like it is the same as Freund’s, and in a way it is, but it expands it slightly because it predicts that asexual and bisexual MTF transwomen would be autogynephilic.  Interestingly, he found that it  was true.  The data supported this hypothesis.

Having outlined the basic hypothesis, lets describe the two types of MTF transwomen.  If we take these differences between the two groups, and the similarities within each group, we can create a description of the “prototypical” member of each.  While no one individual will conform to the prototype in all respects, it still has explanatory value to describe each.
CoreyThe prototypical MTF transkid / feminine androphilic (“homosexual”) MTF transsexual (HSTS) was called a “sissy” by her peers growing up.  She avoided rough & tumble activities.  Her primary social circle consisted of one or two girls.  She actively participated in girls games and imaginary play.  Her parents were embarrassed by her femininity, and may or may not have sought professional help in trying to discourage her behavior.  As a young teen, she became interested in girls fashion and make-up, often exploring how she might look as a girl by dressing up and experimenting with make-up, with occasional trips out shopping or hanging out with her friends.  This did not, of course, involve erotic cross-dressing.  She had crushes on boys at school.  Her peers thought she might be homosexual.  She was hassled, perhaps even bullied, by homophobic boys, but otherwise was reasonably popular in her chosen circle.  She was considered very neat and well dressed in boy’s clothes.  She sought out opportunities to interact with small children and infants, taking on babysitting jobs.  As she approached adulthood, looking at her own nature, her potential future, both romantic and economic, made a rational decision to transition to living as a girl so as to grow up to be a woman socially.  Her family may or may not have disowned her in late adolescence.  As she is naturally feminine and passes quite well, she found that she was socially and romantically more successful as a woman.  She actively dated men while pre-op, but assiduously avoided direct contact with her penis, finding that emotionally uncomfortable.  Being young and lacking capital, she lived several years as a woman, taking feminizing hormones, before having SRS to improve her sex life, replacing genitalia that she didn’t use with those that she did.  She may or may not have found a husband and adopted children.

Bruce Jenner beginning transition

Caitlyn (nee Bruce) Jenner beginning transition at age 65

The prototypical autogynephilic transsexual (AGP TS = non-HSTS) was accepted as a boy as a child.  She was often a “loner”, finding her hobbies and reading to be more rewarding, but still willing and ready to participate in rough & tumble play.  She often envied girls and observed them more often than most masculine boys.  As she entered puberty, she began erotic cross-dressing in private, often masturbating while dressed, usually with lingerie.  She found this shameful and hid her cross-dressing as best she could.  She entertained thoughts of living as a woman, often in very idealized situations.  As a young adult, she dated women, often finding it necessary to imagine that she was female to “perform”.  She typically hid this fact from her dates.  In an effort to deny her autogynephilic desire for femininity, she may have chosen to pursue a stereotypically masculine, or even hyper-masculine, career such as the military.  She fell in love and found that the previously growing desire to live as a woman abated for a while.  She married and had children.  Her need to cross-dress and use autogynephilic ideation then grew, as the first blush of their romance matured into committed love.  She agonized about it obsessively, trying alternatively to push it out of her thoughts and trying to appease it by cross-dressing.  She chose to dress and groom herself in stereotypically and unmistakably masculine fashion, with perhaps even a full beard.  At one point, perhaps in her early 30s, or in her late 50s, a set-back or other significant personal change brought all of these feelings to the fore… and she made the fateful decision that she could no longer ignore her sexuality.  After having tried to ignore the cognitive dissonance between her successful social identity as a man, husband, and father, and her obligatory autogynephilic image of being female, concluded that the female image is her “true” self.  She then made steps to begin counseling with a gender therapist, obtained prescription for feminizing hormones, began electrolysis and other procedures to effect a more feminine appearance, and then began the painful steps to living full time socially as a “transsexual”, since she didn’t pass very well and had too many social connections who know of her previous status as a man to be truly stealth.  She had SRS within a short time of nominally living as a woman, as she was impatient, feeling like she had waited long enough in her previous life as a man.  Her wife may or may not have demanded a divorce.

From here on in, rather than try to keep to a linear timeline, a history of the science, it may be more instructive to ignore the actual history and imagine a group of scientists who support the theory and a group of doubters, who like the disclaimer in the movies, are all fictional and any resemblance to any person, living or dead, is purely coincidental.  These groups may interact and have a dialog, along the way to discovering and testing the hypothesis and theory so far presented, and perhaps discover more detail and corollaries.

Every new discovery should have a new theory to explain why it works that way.  So Freund and Blanchard searched for one.  The theory that resulted is that autogynephilia is part of a set of phenomena, that when grouped together, is called Erotic Target Location Error (ETLE).  This lumps autogynephilia in with autopedophilia and pedovestism, sexual arousal at the thought of being a child and dressing like a child respectively, known in the ‘scene’ as “age play”.  It also lumps autogynephilia with amputation “wannabees” and “pretenders”, people who are sexually aroused by the thought of being or becoming an amputee or of pretending to be an amputee.  The basic theory of Erotic Target Location Errors is that for every conventional erotic target, there is a subset of people who also find the thought of being or becoming a member of that class of erotic target to be sexually arousing.  Thus, an individual who is attracted to amputees, a “devotee” who also has an ETLE will also “pretend” and if it is very strong, will also be a “wannabee”.  In this theory, the ETLE is both dependent upon and in competition with the conventional erotic target.  If the ETLE is stronger at the moment, the individual will be “asexual”, uninterested in other people.  Conversely, if one falls in love with someone, the ETLE may abate, at least for a while.

For more information, see my essay on Erotic Target Location Errors.

This theory also makes another prediction, that gynephilic “pretenders” and “wannabees” will also be very likely autogynephilic, as their erotic target is female amputees, they will want to become female amputees.  This is in fact what was found; fully 50% of “wannabees” were also autogynephilic.

For more information, see my essay on Autogynephilia in Amputee “Wannabees”.

Every valid scientific hypothesis and theory should be repeatable.  An independent group of scientists should be able to repeat a given experiment or observation and find the same result.  Doubters of the two type hypothesis insisted that it couldn’t be repeated, that the data was a fluke.  Some even wondered aloud if the data was cooked up by Blanchard, saying that he was a charlatan, a fake, a liar, with an ax to grind, that he didn’t like transsexuals and was out to hurt them.  But theories were meant to be tested and repeated.  So a number of scientists, both supporters and skeptics, repeated the studies of MTF transsexuals, asking if they experienced autogynephilia.  Here are the results:

“Type”     Nuttbrock  Smith    Lawrence     Blanchard

Year                  2009     2005         2005           1985

HSTS                    23%       15%           18%             15%

Non-HSTS         73%       60%          56%             75%

Each study was not identical in their method of categorizing someone as either ” exclusively homosexual transsexual” or “non-homosexual” nor identical in the questionnaire that was used to ask about autogynephilia.  For example, Lawrence, in the data above, made the autogynephilia cut at “hundreds” of incidents of arousal to masturbation during cross-dressing.  When she counts all such incidents, 87% of her non-HSTS respondents indicated that they were autogynphilic.  But all of them had roughly the same trend in the data, most “non-homosexual” transwomen acknowledge experiencing autogynephilia while only a few self-reported “homosexual” transsexuals do.  Blanchard’s original data was repeatable.  Blanchard didn’t make up the data.  No one was in any kind of conspiracy, as some doubters have claimed.  In fact, the Nuttbrock group would have loved to have proved him wrong.

Oh, but now our doubters point to the data and show that it isn’t 0% vs. 100%.  So… this theory can’t be right!  Some suggest that there might be another type of transsexual, one that is neither “homosexual” nor autogynephilic.  Others suggest that autogynephilia occurs in both “homosexual” and “non-exclusively-homosexual”.  Those scientists who are familiar with psychological, especially sexological, studies know that not everyone answers the questionnaires accurately, for different reasons.  So they could accept these strong, repeatable, trends on face value.  But, a curious scientist digs deeper.

Anne Lawrence looked at the answers she got from her questionnaires very carefully, suspecting that not everyone answered fully honestly, especially about their sexuality and found,

“six participants classified as homosexual based on their pattern of sexual partnering before SRS reported experiencing autogynephilic arousal before SRS. Two of these participants, both of whom reported “hundreds of episodes or more” of autogynephilic arousal before SRS, had been married to women and had been biologic parents before SRS, suggesting that their reports of no female sexual partners before SRS were inaccurate. Two other homosexual participants, both of whom also reported “hundreds of episodes or more” of autogynephilic arousal, had not been married and had not been biologic parents; one, age 33 at time of SRS, reported only one male partner before SRS; the other, age 44 at time of SRS, reported multiple male partners before SRS. The remaining 2 homosexual participants, both ages 38, reported autogynephilic arousal only “once or twice” before SRS; both reported multiple male partners before SRS and one also reported MtF transgendered partners.  Seven other participants who were classified as homosexual based on their self-reported pattern of sexual attraction before SRS but not on the basis of their pattern of sexual partnering before SRS also reported autogynephilic sexual arousal before SRS. Four of these 7 participants had been married, and 2 of these 4 had been biologic parents; only 1 reported any male sexual partners before SRS. Of the remaining 3 participants, 2 reported no sexual partners before SRS, and 1 reported multiple male, female, and MtF transgendered partners before SRS.”

For this reason, Lawrence looked at the original Smith data and recategorized those who had been married to women but reported their sexuality as “homosexual” to “non-homosexual” and got a stronger statistical signal, which I reported above.

For more information see my essay on Lawrence recategorizing subjects.

Thus, respondents were not accurately reporting their true sexual orientation.  Blanchard had similar suspicions about the reported sexual orientations and about the less than 100% reported autogynephilia in his non-HSTS group, so he did a study to look at the issue of social desirability bias, the tendency for people to respond to questionnaires with answers that they personally believe will make them “look good”.  Using the Crowne-Marlow Social Desirability Scale he found that in non-HSTS subjects, there was a high correlation with wanting to “look good” and down playing autogynephilia and sexual attraction to women, while simultaneously over stating sexual attraction to men.  Knowing this, we can get an increased signal strength when we limit the non-HSTS group to only self-reported exclusively heterosexual and the HSTS group to only teenagers, which in the Nuttbrock group gives us 82% vs 14% respectively.

For more information see my essay on social desirability bias in transsexuals.

There are of course, transwomen, who clearly fit the autogynephilic profile, who deny that they ever felt autogynephilia, but most DO own up to it when questioned.  This denial of sexual arousal to cross-dressing is not limited to transsexuals, it is also found in heterosexual cross-dressers, where only 85% of them admit to arousal, the same percentage as exclusively heterosexual transsexuals.  Blanchard wondered if the ones who denied arousal might simply be mistaken, or denying it due to social desirability bias, so he did a study using a device to measure penile erectile responses.  The results clearly showed that those who denied arousal, DID in fact become aroused when listening to erotic cross-dressing narratives.

Thus, the ‘wriggle room’ for there being a “third type” of transsexual is reduced to ever diminishing possibility as one looks ever closer at the actual people. But then a new group of doubters bring up the idea that perhaps autogynephilia is not the cause of their transsexuality, but an after effect.  But not all autogynephilic males identify as women, in fact, the majority don’t.  Even in those who later transition, female self-identification usually occurs only years after intense erotic cross-dressing or other autogynephilic ideation surfaces in childhood or adolescence.  The case histories, though not necessarily their narratives, of AGP transsexuals strongly suggests that autogynephilia causes gender dysphoria and subsequent female self-identification, not the other way around.

One of the best documentations that autogynephilia is the root cause of non-homosexual transsexuality was done by Doctor and Prince, who showed that cross-gender identification was most commonly preceded by years of autogynephilic cross-dressing, that transvestism and non-homosexual transsexuality are both a continuum and a progression,

“Among our subjects, 79% did not appear in public cross dressed prior to age 20; at that time, most of the subjects had already had several years of experience with cross dressing. The average number of years of practice with cross dressing prior to owning a full feminine outfit was 15. The average number of years of practice with cross dressing prior to adoption of a feminine name was 21. Again, we have factual evidence indicative of the considerable time required for the development of the cross-gender identity.”

Further, consider that those MTF transsexuals who transition earliest, who are the most innately and spontaneously feminine, who one would expect would have the greatest gender dysphoria and strongest “female gender identity” from early childhood,  “homosexual” transsexuals, never develop autogynephilia.

For more information on how the two MTF transsexuals each have different developmental routes read my essay on the Origin of Cross-Gender Identity in Transsexuals.

Faced with ever mounting proof of the fact that autogynephila is a universal and prominent attribute of non-HSTS, a group of doubters put forth the very radical and odd notion that autogynephilia is a normal part of female sexuality.  One doubter, Charles Moser, M.D., whose other scientific and therapeutic interests include bondage, dominance/submission, sadomasachism (BD/SM), etc. did a very small study asking natal women to respond to a questionnaire that was cleverly written to obtain positive answers to ambiguous questions that only superficially resembled questions used in instruments that are only valid for gender dysphoric males.  For example, one question asked if one fantasized about having a “sexier” body?  (One would hardly expect that women would fantasize about having an uglier one!)  Another question asked about becoming aroused while preparing for a sexual encounter with a lover.  (Such arousal would arise due to anticipation, not the mere fact of getting dressed in women’s’ clothing!)  Thus, the paper is of no scientific value in exploring the nature of women’s sexuality.

On a curious side note, there is a correlation between BD/SM in which about one out of three autogynephilic males is also into BD/SM and vice versa.

For more information about this study, see my essay on the lack of validity of Moser’s paper.

While it may be comforting to autogynephilic individuals to imagine that their very unusual and intense sexuality is the same as, or at least similar to, natal women, it is not.  Most women are sexually attracted to their sexual partners.  They are aroused by sexual ideation in which their partner is the significant figure, not themselves, their own appearance, nor their mode of dress, which, if present, is of a supporting, rather than leading role.

Finally, another hypothesis is put forth by doubters, despite their obvious lack of naturally feminine behavior, that they are still neurologically “female-like”, at least in some important way, the so called, “feminine essence” or “brain sex” hypothesis.  Blanchard, in response, made the prediction that brain studies would show that BOTH populations would be different than control males, but in different ways.  He further made the prediction that HSTS brains would be shifted toward the female morphology in sexually dimorphic areas of the brain, while AGP transsexuals would not.

The first major paper that was hailed as “proof” that late transitioning, non-homosexual, transsexuals had female-like brains was Swaab’s study that showed that the BSTc was feminized in such transsexuals.  But Swaab himself later showed that the BSTc was only sexually dimorphic in adulthood.  That is to say, that this area is very plastic, responding to sex hormones, the sexually dimorphic structure being an “activation effect”, casting serious doubt on the value of the entire study, that it was very likely that years of HRT was fully responsible for the feminization of the BSTc.  The next “proof” was the hypothalamic uncinate nucleus, INAH3, that also was feminized in non-homosexual transsexuals.  However, as I personally showed, this too was caused by HRT.  Other studies, too numerous to list individually here, are beginning to show that Blanchard’s prediction is correct.

For more information, see my list of essays on Brain Sex.

There will always be doubters and outright denialists.  But to those who read the literature carefully and yes, skeptically, the growing evidence that the Freund/Blanchard two type taxonomy is correct far outweighs the doubts.

You may wish to continue reading about answering the doubters and denialists in my essay, Don’t Shoot the Messenger.


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Drum keeps pounding… ♫♫

Posted in Brain Sex, Female-to-Male by Kay Brown on April 13, 2013

♫♫…rhythm to the brain…♫♫

shrinking brainData keeps coming in regarding brain imaging studies showing differences between MTF and FtM transsexuals and control males and females.  The question still remains, what does it mean?  Two studies, by two different groups, have measured the cortical thicknesses of transwomen before beginning HRT, to ensure that they are measuring potential organizing effects of endogenous hormones, or other effects, without the confounding activational effects of HRT.  However, the two studies looked at the two different MTF populations.  One, the Zubiaurre-Elorza paper examined only androphilic transwomen (N=18). Given that this group came from Spain, which, as Lawrence demonstrated, has a very low Hofstede Individualism index which is correlated with low percentage of gynephilic transwomen, these 18 were likely to have accurately reported their sexuality as exclusively androphilic.   While the Luders study, as an earlier study reported, examined both gynephilic (N=18) and self reported androphilic (N=6) transwomen.  Given that we know from many other studies of transwomen in high Hofstede Individualism societies, and the fact that the youngest of the Luders group was 23, we would expect that not all six of those who reported that they were androphilic were exclusively so.  In fact, I doubt that more than one or two at most is exclusively androphilic, if any.  Thus arises the question, can we use these two studies to get an early test of Blanchard’s prediction that “non-homosexual” transwomen would show brain difference from controls, but not a shift towards the female typical while the “homosexual” will show just such a shift?

First, some background, since I know that not all readers will be thoroughly up to date on the hypothesis being tested, nor the relevant data supporting it.  I recommend reading the FAQ on the is blog before continuing to read this blog entry, as a starting point.  Given that there is now mountains of data supporting the hypothesis that there are two types of MTF tranwomen, one autogynephilic (AGP) and non-homosexual (with respect to natal sex) and one that is non-autogynephilic and exclusively homosexual (HSTS); and that AGP transsexuals were behaviorally masculine since early childhood, and often even after transition and SRS, while HSTS transwomen had been remarkably feminine in behavior, and often in appearance, since early childhood, Blanchard made the prediction that brain studies would show that BOTH populations would be different than control males, but in different ways.  He further made the prediction that HSTS brains would be shifted toward the female morphology in sexually dimorphic areas of the brain, while AGP transsexuals would not.

This prediction is in opposition to the so called, “feminine essence” hypothesis, which is generally popular among AGP transsexuals, in which they posit that despite their obvious lack of naturally feminine behavior, they are still neurologically “female-like”, at least in some important way.

So far, the very limited data supports Blanchard’s hypothesis and NOT the “feminine essence” hypothesis.  Also so far, no formal study has been conducted that would specifically test these two hypothesis together.

I stated earlier that I didn’t believe that the Luders study group contain many exclusively androphilic (HSTS) individuals.  The reasons I believe this are several fold.  First, they collected most of their group by soliciting via transgender organizations.  As was shown in the Veale study on transsexual sexuality, soliciting through such organizations tends to reach only AGP individuals, as HSTS youth do not tend to be members of such.  Second is the age range of the study entire group.  The youngest was 23.  This would be very unusual for a group of that had a sizable portion of HSTS individuals, given that the median age of transition is 20 years old and the top end is typically 25 years old, and even that old is very rare.  If all six HSTS individuals were 23 to 25, this would be odd.  Also given that the mean age of the entire group is 45, which is a bit higher than the typical mean transition age for a group consisting of only AGP transwomen, this would suggest that there were not many of the total group that was in their early 20’s, certainly not six out of 24 individuals.  Thirdly, as Lawrence has shown, in two different study groups, significant numbers of individuals who claim to be androphilic are inaccurately reporting their sexuality.  Added together, I don’t believe that more than one or at most two, of the Luders study group was actually exclusively androphilic.  I suspect that none of them were.

As we explore the data from these two papers, we need to keep in mind that brains, like bodies, come in different shapes and sizes, more or less.  That is to say, although there are differences between male and female brains, on average, it is difficult to point to a part of the brain and say with absolute certainty, this is a male brain vs. a female brain.  Another thing to keep in mind, if we have a mix of two populations, both may have differences unique to each population… and that when mixed, both of those differences will be detected when we average the data, blurring and blunting the differences, but we should still be able to statistically see a signal in the data, provided we have enough data.

So, lets examine the data.  First, if we look at the high level view, it would appear that there are indeed differences between the control men and women and androphilic transwomen.

Zubiaurre Brain ScansIn general, female brains have thicker cortices (CTh), at least in some areas, as the comparison between male and female controls shows.  As we had expected, MTF  transfolk are different than male controls, but FtM are not that different from female controls.  The authors described the results thus,

“We have found that control females have greater CTh compared with control males in the frontal and parietal regions; in contrast, males have a larger putamen volume than females. With respect to the transsexual groups, we observed that FtMs have greater CTh compared with control males in the parietal and temporal cortices and did not differ from control females. However, FtMs have a larger right putamen than female controls. On the other hand, MtFs did not differ from control females in CTh and had greater CTh than control males in the frontal and occipital regions. In this group, no differences were found in the putamen. All these findings suggest that FtMs have a defeminized putamen, while MtFs have a feminized CTh.

With respect to the CTh of MtFs, we found that this group did not differ from female controls but did from male controls.  These findings suggest that MtFs follow the pattern of cortical thinning typically described for females. Whether the cortical feminization of MtFs depends on a differential cortical androgen receptor distribution, a different efficiency in the androgen receptors or other causes remains to be elucidated.  But what seems clear is that in MtFs the cortical developmental process is affected and follows the direction expected for females. This points out that the developmental approach could help to understand the etiology of transsexualism.”

Let’s compare these results with that of the Luders study, which is mostly (and perhaps entirely) non-exclusively androphilic, which being autogynephilic, Blanchard had previously predicted would show differences from control males, but not in the female like direction:

Luders Brain ScansAt first blush, we see that they are indeed, as predicted, different than control males.  Some areas of the cortices are thicker, but not the same regions as control females nor androphilic transwomen.  So, it would seem unlikely that these brain difference are caused by a feminization of the brain, given that the regions are not those found in control females.  But what does cause these particular differences?  While we might be tempted to conclude that this is caused by autogynephilia, it could also be caused by another attribute that is common in this population, higher IQ.  It has been noted that higher IQ is correlated with thicker cortices.

So where to do we go from here?  This visual comparison of the two studies can only be described as tentative.  But the need for such comparisons are clearly understood by these researchers, as the Zubiaurre-Elorza paper explained,

“On the basis of chromosomal sex and behavior, Blanchard and co-workers (Blanchard et al. 1987, 1989, 1996; Blanchard 1989; see also Smith et al. 2005) have proposed the existence of 2 types of MtFs: 1) MtFs that are attracted to males (“homosexual” transsexuals in Blanchard terminology), and 2) MtFs that are attracted to women (“heterosexual” transsexuals according to Blanchard). Further, Blanchard (2008) hypothesized that homosexual MtFs would differ from heterosexual males in brain sexually dimorphic structures, while in the heterosexual MtFs, the differences might not implicate sexually dimorphic structures. More recently, Cantor (2011) has noted that our findings on the white matter microstructure of (homosexual) MtFs (Rametti, Carrillo, Gómez-Gil, Junque, Zubiarre-Elorza et al. 2011) and that of Savic and Arver (2011) on the cortical volume of (heterosexual) MtFs would support Blanchard’s hypothesis. In the present report, we studied MtF transsexuals erotically attracted to males that show a feminization of CTh but not in the putamen.  …  Consequently, to verify Blanchard’s hypothesis would require a specific design that is beyond the scope of the present study.”

For more essays on trans-brains see Brain Sex.


Eileen Luders, et al., “Increased Cortical Thickness in Male-to-Female Transsexualism”
Journal of Behavioral and Brain Science, July 2011

Leire Zubiaurre-Elorza et al, “Cortical Thickness in Untreated Transsexuals”
Cerebral Cortex, August 2012

Katherine Narr, et al., Relationships between IQ and Regional Cortical Gray Matter Thickness in Healthy Adults
Cerebral Cortex, November 2006


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