The Female Brain – Part Two

Start quoting- In 2000 Kruijver published a study into BTSc neurons in 7 transsexuals and 1 gender dysphoric man. The study does not provide any evidence of a male or female brain in transsexuals. It is clear that the changes in BTSc neurons in the brain,  measured in the study, were as a direct result of transgender hormone treatment and in the case of the gender dysphoric man, likely, a statistical anomaly. There have been non transsexual individuals who have a number of BTSc neurons in their brains consistent with members of the opposite biological sex . End of quote

In 2000, Kruijver et al. published a study in which they looked at the number of neurons in the BSTc, part of the brain. They examined tissue from the same six MtF transsexuals studied by Zhou et al; one female-to-male (FtM) transsexual and from an 84-yr-old man who “had very strong cross-gender identity feelings but was never . . . sex-reassigned”.  The research says that:

1. The average BSTc neuron number in males was 71% higher than in females.

2. The six MtF transsexuals had an average BSTc neuron number in the female range.

3. The BSTc neuron number was also in the female range in the gender dysphoric male who had not received treatment for transgenderism, and was in the male range in the FtM transsexual.

This study is posted to show that :

a. The brains of FtoM transsexuals are a male one and of MtoF a female one.

b. That the existence of the one gender dysphoric male in the study, shows that sex-change hormone treatment did not cause these changes.

However in reality the study is flawed for the following reasons:

a. In 2002, research carried out by Chung, De Vries, and Swaab, showed that the differences in the number of neurons in the 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 number of neurons in the BSTc in the brain.

b. A recent study by Hulshoff Pol in 2006 showed the major effect transgender hormone therapy has on the brains of 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. It is clear that the hormones the 6 Mto F and 1 FtoM took are the most likely explanation for the finding in relation to the number of neurons in the BTSc part of the brain.

c. The one gender dysphoric male may have an atypical number of neurons in the BTSc part of his brain either because of his advanced age (84 years) or undisclosed hormone use. In any event, a single case means very little. The same study found two non-gender-dysphoric men in their control group who had BSTc neuron numbers almost identical to that of a Transsexual MtoF individual.

d. Contrary to a popular misconception, this study did not look at any nontranssexual men who had been treated with estrogen (for example, for prostate cancer) or any nontranssexual women who had been treated with testosterone. They did examine one woman, in whom an adrenal tumor had produced increased testosterone levels and one man, in whom an adrenal tumor had produced increased estradiol levels. Neither individual had BSTc volumes or neuron numbers that were unusual for their sex, but it is probable that their cross-sex hormone levels, although increased, had not been high enough and had not lasted long enough5to be equivalent to the 5-20 years of cross-sex hormone therapy that the transsexuals had received

So in conclusion, the 7 transsexuals studied had BTSc neurons in their brain consistent with the opposite biological sex, as a direct result of hormone treatment taken as part of their transitioning process. The 1 individual who is not documented as having taken hormones may have either taken them without medical knowledge, or is simply an anomaly.


Chung, W. C., De Vries, G. J., & Swaab, D. F. (2002). Sexual differentiation of the bed nucleus of the stria terminalis in humans may extend into adulthood. Journal of Neuroscience, 22, 1027-1033.

Hofman, M. A., & Swaab, D. F. (1989). The sexually dimorphic nucleus of the preoptic area in the human brain: A comparative morphometric study. Journal of Anatomy, 164, 55-72.

Hulshoff Pol, H. E., Cohen-Kettenis, P. T., Van Haren, N. E., Peper, J. S., Brans, R. G., Cahn, W., et al. (2006). Changing your sex changes your brain: Influences of testosterone and estrogen on adult human brain structure. European Journal of Endocrinology, 155(Suppl. 1), S107-S114.

Kruijver, F. P., Zhou, J. N., Pool, C. W., Hofman, M. A., Gooren, L. J., & Swaab, D. F. (2000). Male-to-female transsexuals have female neuron numbers in a limbic nucleus. Journal of Clinical Endocrinology and Metabolism, 85, 2034-2041.

Zhou, J. N., Hofman, M. A., Gooren, L. J., & Swaab, D. F. (1995). A sex difference in the human brain and its relation to transsexuality. Nature, 378, 68-70.

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Pre Natal Exposure to High Levels of Tetesterone

Start of summary – The study is poorly designed as it assumes a certain digit ratio is clearly male or female when there is simply a correlation; it uses an unsatisfactory control group and ignores that other factors such as ethnicity have a greater impact on digit ratio than biological sex.

The study ignores research into intersex people, which demonstrates that unusual levels of androgen do not lead to an increase in Transsexualism. Schneider does not offer an adequate explanation of why exposure to androgens pre natally would lead to a different digit ratio for transitioning men; and not to different digit ration for transitioning women – end of summary. 

Schneider undertook research into the lengths of index and ring fingers in transitioningnmen and women. This research says that:

1. A greater proportion of biological men have shorter index fingers than ring fingers and vice versa in females.

2. That this is caused by the levels of androgen that foetuses are exposed to in the womb

3. That the ratio of the digit length of index and ring fingers was similar in transitioning men as biologicalwomen .

4. That the ratio of the digit length for transitioning women was similar to biological women.

This study is quoted to demonstrate that pre natal exposure to androgens causes Transsexualism.

It is true that there is extensive evidence that pre natal exposure to androgens appears to cause the difference in digit ratios. Nobody knows exactly why this is, but a common theory is that this is linked to bone growth.

However this study makes a number of assumptions that invalidates its findings. These are:

    1. That a particular digit ratio is clearly male or female. Examining both the research carried out by Schneider and other research, it is clear that there is a wide variation between individual men and women in terms of digit ratio. When Schneider refers to a male or female digit ratio he means that there is a correlation in particular digit ratios with the sex men and women, not that a particular digit ratio is clear evidence that an individual is male or female.

To explain this further consider height. In general men are taller than women. Thus if I measured the height of a number of men I could come up with a height range that I could label as typically male. But obviously men who fell outside this range would still be men and women who fell into this height range would still be women.

    2. That a group of biological females can act as a control group. A control group is a group where the factor being tested does not apply, so that it can serve as a standard for comparison. In this research a control group would be one where biological females clearly have a digit ratio that is female. Overall the females as a mass in the control group have a digit ratio consistent with females, but individually there is great variation.
    3. That variation in digit ratio is only or most pronounced between the sexes. In reality digit ratio varies considerably between different ethnicities. In his paper “Finger Length Ratios and Sexual Orientation”, Manning says “There’s more difference between a Pole and a Finn than a man and a woman.”

However, even if you discount the assumptions made and thus the very low standard to which this research has been designed, the research still does not provide any evidence that digit length ratio is linked to Transsexualism. This is because in his research Schneider ignores two key points.

  1. That intersex people whose conditions mean that they are exposed to unusual levels of androgen pre-natally do not develop Transsexualism. If Schneider’s research had any validity we would expect to see adults with certain intersex conditions exhibit a significantly higher level of Transsexualism than the general population. However, Transsexualism is extremely rare amongst this group.
  1. Schneider ignores the results of his own research that digit ratios in transitioning females are consistent with biological females. It is not adequate to claim that pre natal exposure to androgens appears to cause Transsexualism in transitioning men and ignore that there is no evidence to support a similar explanation for transitioning women.

In summary, Schenider’s study is poorly designed, makes assumptions without any evidence and ignores research, particularly into intersex conditions, that provide evidence that his conclusions are wrong.

Schneider HJ, Pickel J, Stalla GK (February 2006). “Typical female 2nd-4th finger length (2D:4D) ratios in male-to-female transsexuals-possible implications for prenatal androgen exposure”. Psychoneuroendocrinology 31 (2): 265–9. DOI:10.1016/j.psyneuen.2005.07.005. PMID 16140461

Churchchill AJG, Manning JT, Peters M (2007). “The effects of sex, ethnicity, and sexual orientation on self-measured digit ratio (2D:4D)”. Archives of Sexual Behavior 36 (2): 251–260. DOI:10.1007/s10508-006-9166-8. PMID 17394056.

Manning, John (2002). Digit ratio: a pointer to fertility, behavior, and health. New Brunswick, N.J: Rutgers University Press. ISBN 978-0-8135-3030-7. [



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Let’s be clear about intersex

This post is not a scientific explanation, but simply a response to some of the comments on my previous post about intersex. So for totally clarity:

Intersex is a physical medical condition. There are always clear physical testable signs. For example, deformed genitalia or the presence of both male and female reproductive organs.

Transsexualism is NOT an intersex condition. There are no physical signs of Transsexualism, it is a psychological condition. So someone is a Transsexual because they say they are a Transsexual. There are no physical signs for Transsexualism.

Anyone claiming Transsexualism is an intersex condition is either misguided or lying.

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Sexual Hormones and the Brain

A surprising number of “studies” that links are posted for are actually not studies at all, but proposals the author argues are worthy of research. Below is a link to such a proposal. I will post others under this category.

The author argues that “the fetal brain develops during the intrauterine period in the male direction through a direct action of testosterone on the developing nerve cells, or in the female direction through the absence of this hormone surge. In this way, our gender identity (the conviction of belonging to the male or female gender) and sexual orientation are programmed or organized into our brain structures when we are still in the womb.

However, since sexual differentiation of the genitals takes place in the first two months of pregnancy and sexual differentiation of the brain starts in the second half of pregnancy, these two processes can be influenced independently, which may result in extreme cases in trans-sexuality.”

However this is simply a theory. The author has published this paper outlining some proposed research to examine whether there is any evidence to back up this theory. So until some research actually takes place, this citation is totally meaningless.

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Intersex Conditions

It is very common for Transactivists and allies to claim that most or many Transsexual people are intersex. This simply isn’t true.

Summary – Intersex is the term used to describe a range of physically biological conditions where internal or external genitalia are indeterminate or do not match other biological sex factors. Or alternatively, where there is an over production or under production of sex hormones or the bodies ability to respond to them. Lastly intersex also encompasses abnormalities of the sex chromosomes or abnormal development of the testes or ovaries.

Disorders of sex development is another term now being used to describe intersex.

The vast majority of Transsexuals do not have an intersex condition. Claiming you have a male or female brain is not an intersex condition. Similarly the vast majority of intersex people are not Transsexuals.

There is no link between intersex people and Transsexuals.

end of summary

What is intersex?

“A variety of conditions that lead to atypical development of physical sex characteristics are collectively referred to as intersex condition. These conditions can involve abnormalities of the external genitals, internal reproductive organs, sex chromosomes, or sex-related hormones. Some examples include: 

• External genitals that cannot be easily classified as male or female 

• Incomplete or unusual development of the internal reproductive organs

• Inconsistency between the external genitals and the internal reproductive organs

• Abnormalities of the sex chromosomes

• Abnormal development of the testes or ovaries

• Over- or underproduction of sex-related hormones

• Inability of the body to respond normally to sex related hormones

Intersex was originally a medical term that was later embraced by some intersex persons. Many experts and persons with intersex conditions have recently recommended adopting the term “disorders of sex development” (DSD). They feel that this term is more accurate and less stigmatizing than the term intersex.”

Interestingly, I have noticed on the internet a few Transactivists describing their Transsexualism as a disorder of sex development. Unless they also have an intersex condition, then they are wrong. A disorder of sex development is another name for intersex and is not the same as Transsexualism or Transgenderism.

There is disagreement amongst the medical community about the boundaries of intersex. For example, how small does a boy’s penis have to be before he is considered intersex?  However, the definition of intersex is one of biology and biological differences. So an individual is not considered intersex because they have for example a male body, but “feel like a woman”.

Moreover, the majority of people who are intersex, are not Transsexuals. So for example a male baby with deformed genitalia is extremely unlikely to become Transsexual in later life. There is no medical evidence at all that there is any link between intersex conditions and Transsexualism.

Sometimes people post claims on the internet about the percentage of people in the general population who suffer from an intersex condition. This will be spurious or at the very least, posted wrongly in good faith. Nobody knows what percentage of the population suffer from an intersex condition. This is because there is no clear definition of what exactly counts as intersex and because there is no requirement for this condition to be recorded centrally.

Research was carried out by Anne Fausto-Sterling in order to estimate the frequency in which intersex conditions occur. She did this by reviewing the medical literature from 1955 to 1988. But she is clear that this is only an estimate.

Not XX and not XY one in 1,666 births
Klinefelter (XXY) one in 1,000 births
Androgen insensitivity syndrome one in 13,000 births
Partial androgen insensitivity syndrome one in 130,000 births
Classical congenital adrenal hyperplasia one in 13,000 births
Late onset adrenal hyperplasia one in 66 individuals
Vaginal agenesis one in 6,000 births
Ovotestes one in 83,000 births
Idiopathic (no discernable medical cause) one in 110,000 births
Iatrogenic (caused by medical treatment, for instance progestin administered to pregnant mother) no estimate
5 alpha reductase deficiency no estimate
Mixed gonadal dysgenesis no estimate
Complete gonadal dysgenesis one in 150,000 births
Hypospadias (urethral opening in perineum or along penile shaft) one in 2,000 births
Hypospadias (urethral opening between corona and tip of glans penis) one in 770 births
Total number of people whose bodies differ from standard male or female one in 100 births
Total number of people receiving surgery to “normalize” genital appearance one or two in 1,000 births

Occasionally Transactivists post claims that most Transsexuals are suffering from a diagnosed intersex condition such as 5alpha-reductase-2 deficiency (5alpha-RD-2) or 17beta-hydroxysteroid dehydrogenase-3 deficiency (17beta-HSD-3).

In both of these conditions, children appear to be largely one sex and then during puberty, characteristics of the other sex appear. So with 5alpha-reductase-2-deficiency, individuals can have normal male external genitalia, ambiguous genitalia, or normal female genitalia. However usually they are born with very ambigous genitalia with a phallus like clitoris, male gonads, including testicles often hidden until puberty, and Wolffian structures. They usually, but not always, have female primary sex characteristics. As a consequence, they are often raised as girls.

At puberty they develop some typically male characteristics which can include the descending of the testes, facial/body hair typically seen in males, the deepening of the voice, etc. This condition is caused by a faulty gene.

These are both very rare conditions, except in a few geographical areas such as the Dominican Republic where 5alpha-reductase-2 deficiency is more common. However, they are clearly biological conditions and are intersex conditions that are usually diagnosed close to birth or more rarely, at puberty when typically male physical characteristics start to appear.

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Sexual Hormones and the Female Brain

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.

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.”

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.

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A Biological basis for Transgenderism?

I am a radical feminist who does not agree that there is any biological basis for Transexualism or Transgenderism. In any “debate” on the internet about this issue, someone always posts links to studies that they claim backs up their idea that Transexualism/Transgenderism has a biological basis. I suspect that very few people actually follow these links. When you do it is clear that the so called research, does not provide any evidence of a biological cause.

Each post on this blog will look at one piece of research that has been used by someone on the internet to back up their claims around Transexualism and Transgender. The post will examine whether the research has any link to what is being claimed, the validity of the research and whether it proves a biological link.

Please feel free in the comments to this post, to post links to any research that you think is relevant to the argument for a biological basis for Transexualism or Transgenderism. I promise I will examine all research that you post links to.

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