The Science of Gender and Sexual Orientation

[RavenSky]

1995:

Researchers in the Netherlands have discovered that a region of the hypothalamus, located at the floor of the brain, is about 50 percent larger in men than in women, and almost 60 percent larger in men than in male-to-female transsexuals. If smallness of this brain structure is at all correlated with the feeling of being a woman, the results raise tantalizing possibilities that transsexuals may in a sense be more female than females.

The discovery is the first detection of a difference in transsexual brains and could at least partly explain why such individuals describe themselves as "women trapped in men's bodies."

Significantly, the region of the hypothalamus does not differ in size between gay and straight men, and so it cannot be said to play a role in male sexual orientation.

Dr. Dick F. Swaab of the Netherlands Institute for Brain Research in Amsterdam, who with his colleagues is reporting the work in today's issue of the journal Nature, emphasized that this section of the hypothalamus is by no means the entire source of sexual identity.

"I'm convinced this is only one structure of many that are involved in such a complex behavior," he said. "This is just the tip of the iceberg."

http://www.nytimes.com/1995/11/02/us/study-links-brain-to-transsexuality.html

 

[RavenSky]

Good article on a wide range of issues on this topic

Today we know that the various elements of what we consider “male” and “female” don’t always line up neatly, with all the XXs—complete with ovaries, vagina, estrogen, female gender identity, and feminine behavior—on one side and all the XYs—testes, penis, testosterone, male gender identity, and masculine behavior—on the other. It’s possible to be XX and mostly male in terms of anatomy, physiology, and psychology, just as it’s possible to be XY and mostly female.

Gender is an amalgamation of several elements: chromosomes (those X’s and Y’s), anatomy (internal sex organs and external genitals), hormones (relative levels of testosterone and estrogen), psychology (self-defined gender identity), and culture (socially defined gender behaviors). And sometimes people who are born with the chromosomes and genitals of one sex realize that they are transgender, meaning they have an internal gender identity that aligns with the opposite sex—or even, occasionally, with neither gender or with no gender at all.

In terms of biology, some scientists think it might be traced to the syncopated pacing of fetal development. “Sexual differentiation of the genitals takes place in the first two months of pregnancy,” wrote Dick Swaab, a researcher at the Netherlands Institute for Neuroscience in Amsterdam, “and sexual differentiation of the brain starts during the second half of pregnancy.” Genitals and brains are thus subjected to different environments of “hormones, nutrients, medication, and other chemical substances,” several weeks apart in the womb, that affect sexual differentiation.

In another study scientists from Spain conducted brain scans on transgender men and found that their white matter was neither typically male nor typically female, but somewhere in between.

At the Gender and Family Project, Jean Malpas said counselors “look for three things in children who express the wish to be a different gender”: that the wish be “persistent, consistent, and insistent.” And many children who come to his clinic meet the mark, he told me, even some five-year-olds. “They’ve been feeling this way for a long time, and they don’t look back.”

https://www.nationalgeographic.com/magazine/2017/01/how-science-helps-us-understand-gender-identity/

 

[RavenSky]

But now there's mounting evidence that gender identity is rooted in the brain. In January this year, neuroscience researchers at the University of Vienna in Austria discovered "strong differences" in the microstructure of brain connections of cisgender control subjects (men and women who identity with their biological sex) and transgender people. Using a specialized MRI technique that allows them to study brain wiring, they found "these differences in really almost all networks in the brain. It was quite a huge finding," one of the researchers, Georg Kranz, says in a phone interview. On a spectrum of neurological characteristics, whose two polarities are defined by the cisgender female brain and the cisgender male brain, the characteristics of the brains of transgender people, on average, fell somewhere in the middle.

"We show that trans sexuality is a human biological variation, and I think that is a kind of relief for transgender people," Kranz says.

Recently, a study at the University of Washington focused on prepubescent transgender children, which appears to support the notion of innate gender identity. The study sample was composed of transgender children, whose parents support their gender identity, with a control group of children who identify with their natal sex. Researchers used the children's own self-reporting about gender as well as psychological tests that assess the speed with which they associate various concepts of male and female. "We were a bit surprised," says Kristina Olson, a social psychologist and the lead researcher on the study. "We found that transgender boys respond like boys, not girls, and trans girls respond like girls and not boys. This suggests that gender identity is not something the kids are just saying or pretending or doing to be oppositional."

https://beta.theglobeandmail.com/li...25553156/?ref=http://www.theglobeandmail.com&

 

[RavenSky]

In discussions of these issues, a distinction is often made between “biological sex” and a psychological state of “gender identity” with the latter weighted as less important, less biological, or less real. Political commentator Ben Shapiro, for example, illustrates the attitude in his response to a transgender rights advocate questioning him at a recent lecture:

“I’m not going to modify basic biology because it threatens your subjective sense of what you are.” [Emphasis added.]

This sort of statement presupposes that Ben Shapiro understands the basic biology, which I’m sure he doesn’t given that biologists are still working it out.

If it is the case, as the existing science indicates, that biology operates along parallel pathways to determine and differentiate male and female phenotypes, then it is biologically feasible that genetic variation could lead to individuals with mixed sex differentiation, that is, with the gonads of one sex and a brain that leans the other way.

To put it into lay terms that policy makers and political commentators can understand, what this may mean is that your subjective sense of what you are is due to basic biology even if it disagrees with your gonads. And if this is true, the individual who Shapiro chastised might have responded, “I’m not going to modify basic biology because it threatens your subjective sense of what I am.”

https://areomagazine.com/2017/07/29/what-science-has-to-say-about-gender-identity/

 

[RavenSky]

Slightly off topic, but important to keep in mind in my opinion:

In the new study, forthcoming in the journal Sex Roles, researchers Boby Ho-Hong Ching and Jason Teng Xu presented 132 university students in Hong Kong with one of three articles to read. One article was intended to reinforce the idea that gender differences have a biological basis, one was intended to question this view, and a third was entirely unrelated to gender differences and served as a baseline comparison.

The article advocating a biological basis for gender presented a study purporting to find that "the brains of men and women are wired up differently," which "could explain some of the differences in personality and behaviour between male and female." It went on to describe the study and quote fictional experts, including "Professor Schneider," who summarized: "There is a neurological cause of sex differences, which suggests that these differences are difficult to change."

The alternative article reported the same study, but also included some cautionary remarks. For instance, the researchers noted that men and women "still have many similarities in terms of the brain architecture" and that "the relations between brain and human behavior are complex." In this version, Prof. Schneider instead warned that the studies do not "offer insights into the socio-biological developmental processes that lead to observed male/female differences...The neurological associations with sex differences are not fixed, but amenable to change by environmental factors."

After reading one of the three articles and completing an unrelated task, participants then responded to various questions designed to evaluate their stereotypes about transgender individuals, as well as their attitudes towards them. For example, they indicated how much they agreed with statements including, "transgenderism endangers the institution of the family," and "I would feel comfortable if I learned that my neighbor was a transgendered individual." A final set of questions concerned civil rights, with items such as: "Post-operative transsexuals in Hong Kong should have the right to get married in their new sex," and "Transgender people in Hong Kong should have the right to change their birth certificates."

The researchers found that those participants who had read the article endorsing a biological basis for gender differences were significantly more likely than participants who read either of the other articles to report negative stereotypes about transgender individuals, to report prejudicial attitudes, and to reject equal rights. Responses for participants who read the alternative article or the control article did not differ from each other.

The authors suggest that the article endorsing a biological basis for gender differences reinforced what psychologists call an "essentialist" view of gender — the idea that men and women belong to fundamentally different categories that have some inherent basis (some "essence"), such that the categories have sharp and immutable boundaries, and such that members of the same category share many important similarities with each other. On a view like this, it's hard to make sense of a mismatch between a person's gender identity and their assigned sex, if it's the biological basis for their assigned sex that's taken to reflect their true "essence." This, in turn, could support a more prejudicial attitude towards people who identify with a gender other than the one assigned at birth.

https://www.npr.org/sections/13.7/2...d-the-belief-in-a-biological-basis-for-gender

Sounds like some people we know.

 

[RavenSky]

First and foremost, is gender identity genetic? It seems the answer is yes – though, as with most traits involving identity, there is some environmental influence. One classic way for scientists to test whether a trait (which can be any characteristic from red hair to cancer susceptibility to love of horror movies) is influenced by genetics is twin studies. Identical twins have the exact same genetic background, and are usually raised in the same environment. Fraternal (nonidentical) twins, however, share only half their genes, but tend to also be raised in the same environment. Thus, if identical twins tend to share a trait more than fraternal twins, that trait is probably influenced by genetics. Several studies have shown that identical twins are more often both transgender than fraternal twins, indicating that there is indeed a genetic influence for this identity.

In 1995 and 2000, two independent teams of researchers decided to examine a region of the brain called the bed nucleus of the stria terminalis (BSTc) in trans- and cisgender men and women (Figure 2). The BSTc functions in anxiety, but is, on average, twice as large and twice as densely populated with cells in men compared to women. This sexual dimorphism is pretty robust, and though scientists don’t know why it exists, it appears to be a good marker of a “male” vs. “female” brain. Thus, these two studies sought to examine the brains of transgender individuals to figure out if their brains better resembled their assigned or chosen sex.

Interestingly, both teams discovered that male-to-female transgender women had a BSTc more closely resembling that of cisgender women than men in both size and cell density, and that female-to-male transgender men had BSTcs resembling cisgender men. These differences remained even after the scientists took into account the fact that many transgender men and women in their study were taking estrogen and testosterone during their transition by including cisgender men and women who were also on hormones not corresponding to their assigned biological sex (for a variety of medical reasons). These findings have since been confirmed and corroborated in other studies and other regions of the brain, including a region of the brain called the sexually dimorphic nucleus (Figure 2) that is believed to affect sexual behavior in animals.

It has been conclusively shown that hormone treatment can vastly affect the structure and composition of the brain; thus, several teams sought to characterize the brains of transgender men and women who had not yet undergone hormone treatment. Several studies confirmed previous findings, showing once more that transgender people appear to be born with brains more similar to gender with which they identify, rather than the one to which they were assigned.

http://sitn.hms.harvard.edu/flash/2016/gender-lines-science-transgender-identity/

 

[Loren Pechtel]

I don't think "more female than females" is a good description of the situation.

Instead, I think it's a reflection that "Male" and "Female" aren't binary states.

For the sake of illustration lets say that the average man is 100 and the average woman is 50 and the average M->F is 40.

But are they really those numbers? No--in reality anyone above 75 will prefer being male and anyone below will prefer being female. However, those near the middle of the range will gain little from transitioning and thus will not do so.

The elimination of this middle zone chops off the left side of the curve for M->Fs and thus you would expect the average to be lower than for those born female.

 

[Underseer]

But if we acknowledge that some people are born different, then the conservatives will feel less like special snowflakes and will cry.

 

[RavenSky]

I don't think "more female than females" is a good description of the situation.

Instead, I think it's a reflection that "Male" and "Female" aren't binary states.

For the sake of illustration lets say that the average man is 100 and the average woman is 50 and the average M->F is 40.

But are they really those numbers? No--in reality anyone above 75 will prefer being male and anyone below will prefer being female. However, those near the middle of the range will gain little from transitioning and thus will not do so.

I think the bolded was said more tongue-in-cheek, but makes an illustrative point to those who keep insisting that a penis at birth makes you a man for life.

In general, I've always agreed with your implication that gender (like sexual orientation, and even biological characteristics) seems to run along a continuum rather than a binary model. That said, some of the studies I quoted above are finding that even the continuum model does not adequately explain the complexity. They seem to be moving to a sort-of-Nolan-Chart for human gender/sexuality

 

[Malintent]

yabutt... how does one engage in a hypothalamus pissing contest to determine the leader of a group? So impractical.

 

[repoman]

Are there any MTFs that have a typically male type of this brain region? If so, are they MTF for a socialization reason instead of an inherent biological reason? Are they different from "bio MTFs"?

Ah, this looks like this actually is the case:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3180619/

 

[Angra Mainyu]

I'm reluctant to post here given what happened in the other thread, but for those interested, here's the latest science I've been able to find on the brains, which reviews the evidence from previous studies (still all very preliminary; the science on this is just beginning):

1. Gynephilic male to female transexuals (the terminology from one of the studies):

There is some evidence that there is some brain properties characteristic of their condition may have been found, but the same seems to hold of other psychological conditions. In sum, they seem to be males with somewhat abnormal brains, but not abnormal in the direction of female brains. Again, this is only preliminary evidence (in fact, there is only one study), but there is nothing suggesting a female brain.
Sources:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3180619/
https://www.ncbi.nlm.nih.gov/pubmed/21467211
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4987404/

2. Androphilic male to female transsexuals: The brain seems to be mostly male in its main structures, with some demasculinized parts (i.e., neither female-like nor male-like), and some parts changing in the female direction.

Source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4987404/

Conclusions

Overall, in vivo MRI studies indicate that the main morphological parameters of the brain (ICV, GM, WM, and CSF) are congruent with their natal sex in untreated homosexual MtFs. However, some cortical regions show feminine volume and thickness and it should be underscored that CTh presents an F > M morphological pattern. Nevertheless, with respect to CTh, this feminine cortical pattern is not the same as the one shown by control females (compare Fig. 2a and b). On the other hand, the main white matter fascicles in MtFs are demasculinized, while others are still masculine (Fig. 3a).

Of course, present-day science is just beginning to learn about the correlations between features we can observe by looking at the brain directly and mental features. It would be interesting to see whether transgender individuals are closer to their claimed gender or the gender that would correspond to their sexual organs, when it comes to psychological features that are different in females and males.


3. Gynephilic female to male transsexuals:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4987404/

Conclusions

In FtMs, the gross morphological parameters correspond to their natal sex; their cortex is generally feminine but differs from males in different regions than do control females (compare Fig. 2a and c). Furthermore, some brain bundles are masculinized (Fig. 3b). All these findings suggest that homosexual FtMs have their own phenotype with respect to cortical thickness, subcortical structures, and white matter microstructure. Moreover, these changes are mostly seen in the right hemisphere.

 

[Juma]

I'm reluctant to post here given what happened in the other thread, but for those interested, here's the latest science I've been able to find on the brains, which reviews the evidence from previous studies (still all very preliminary; the science on this is just beginning):

1. Gynephilic male to female transexuals (the terminology from one of the studies):

There is some evidence that there is some brain properties characteristic of their condition may have been found, but the same seems to hold of other psychological conditions. In sum, they seem to be males with somewhat abnormal brains, but not abnormal in the direction of female brains. Again, this is only preliminary evidence (in fact, there is only one study), but there is nothing suggesting a female brain.
Sources:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3180619/
https://www.ncbi.nlm.nih.gov/pubmed/21467211
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4987404/

2. Androphilic male to female transsexuals: The brain seems to be mostly male in its main structures, with some demasculinized parts (i.e., neither female-like nor male-like), and some parts changing in the female direction.

Source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4987404/

Conclusions

Overall, in vivo MRI studies indicate that the main morphological parameters of the brain (ICV, GM, WM, and CSF) are congruent with their natal sex in untreated homosexual MtFs. However, some cortical regions show feminine volume and thickness and it should be underscored that CTh presents an F > M morphological pattern. Nevertheless, with respect to CTh, this feminine cortical pattern is not the same as the one shown by control females (compare Fig. 2a and b). On the other hand, the main white matter fascicles in MtFs are demasculinized, while others are still masculine (Fig. 3a).

Of course, present-day science is just beginning to learn about the correlations between features we can observe by looking at the brain directly and mental features. It would be interesting to see whether transgender individuals are closer to their claimed gender or the gender that would correspond to their sexual organs, when it comes to psychological features that are different in females and males.


3. Gynephilic female to male transsexuals:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4987404/

Conclusions

In FtMs, the gross morphological parameters correspond to their natal sex; their cortex is generally feminine but differs from males in different regions than do control females (compare Fig. 2a and c). Furthermore, some brain bundles are masculinized (Fig. 3b). All these findings suggest that homosexual FtMs have their own phenotype with respect to cortical thickness, subcortical structures, and white matter microstructure. Moreover, these changes are mostly seen in the right hemisphere.

There are no ”female” or ”male” brains. The difference is widely exaggerated.

 

[Angra Mainyu]

There are no ”female” or ”male” brains. The difference is widely exaggerated.

If that's the case (it's not), then our words "man" and "woman" are surely not tracking, partly or entirely, whether a person has a male or a female brain (because, if you're correct, there is no such thing). Then, the only candidates left are not mental properties, such as having a vagina, penis, uterus, etc. So, males who claim to be women and females who claim to be men are mistaken.

In reality, there is such thing as female brains/minds and male ones, and there is plenty of evidence of that.

However, given all of the available evidence - both scientific and linguistic, assigning even some reasonably high probability to the hypothesis that a person with a female(male) mind/brain and male(female) sexual organs is a woman(man), I reckon it's very probable that gynephilic MtF transexuals are mistaken (at least, the vast majority of them), and probable that androphilic ones are.

Adding hormones complicated the analysis, because they do change the brain/mind in the direction of one sex or the other. However, the changes are either not enough to change a female brain into a (predominantly) male one (or the other way around), or if they are, then probably the words "woman" and "man" give more weigh to other features (e.g., sexual organs), and so transgender claims are mistaken - or else female bodybuilders who take hormones might be men, but that's really unlikely.

But as I mentioned, if we assume for the sake of the argument that you're correct, then all transgender claims are surely false (else, some might not be).

 

[J842P]

I'm reluctant to post here given what happened in the other thread, but for those interested, here's the latest science I've been able to find on the brains, which reviews the evidence from previous studies (still all very preliminary; the science on this is just beginning):

1. Gynephilic male to female transexuals (the terminology from one of the studies):

There is some evidence that there is some brain properties characteristic of their condition may have been found, but the same seems to hold of other psychological conditions. In sum, they seem to be males with somewhat abnormal brains, but not abnormal in the direction of female brains. Again, this is only preliminary evidence (in fact, there is only one study), but there is nothing suggesting a female brain.
Sources:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3180619/
https://www.ncbi.nlm.nih.gov/pubmed/21467211
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4987404/

2. Androphilic male to female transsexuals: The brain seems to be mostly male in its main structures, with some demasculinized parts (i.e., neither female-like nor male-like), and some parts changing in the female direction.

Source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4987404/



Of course, present-day science is just beginning to learn about the correlations between features we can observe by looking at the brain directly and mental features. It would be interesting to see whether transgender individuals are closer to their claimed gender or the gender that would correspond to their sexual organs, when it comes to psychological features that are different in females and males.


3. Gynephilic female to male transsexuals:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4987404/

Conclusions

In FtMs, the gross morphological parameters correspond to their natal sex; their cortex is generally feminine but differs from males in different regions than do control females (compare Fig. 2a and c). Furthermore, some brain bundles are masculinized (Fig. 3b). All these findings suggest that homosexual FtMs have their own phenotype with respect to cortical thickness, subcortical structures, and white matter microstructure. Moreover, these changes are mostly seen in the right hemisphere.

There are no ”female” or ”male” brains. The difference is widely exaggerated.

Well, it depends on what you mean by "widely exaggerated", if by that you mean that typical essentialist conceptions of biology do not really cohere with the reality of biology, then that is pretty much undeniable, but then, that is the case with practically all folk understandings of biological phenomenon. But bearing in mind that humans are in general not very sexually dimorphic, and indeed, humans can really be described as neotenous and feminized apes, it is true that there are population level, gross-anatomical and histological differences in brain anatomy and physiology, that could be used to predict the sex of a specimen with decent accuracy.

Whether you want to say there are "male brains and female brains" seems to me to the sort of disagreement you find between lumpers and splitters.

 

[Angra Mainyu]

Well, it depends on what you mean by "widely exaggerated", if by that you mean that typical essentialist conceptions of biology do not really cohere with the reality of biology, then that is pretty much undeniable, but then, that is the case with practically all folk understandings of biological phenomenon. But bearing in mind that humans are in general not very sexually dimorphic, and indeed, humans can really be described as neotenous and feminized apes, it is true that there are population level, gross-anatomical and histological differences in brain anatomy and physiology, that could be used to predict the sex of a specimen with decent accuracy.

Whether you want to say there are "male brains and female brains" seems to me to the sort of disagreement you find between lumpers and splitters.

I'm not sure that that is the sort of disagreement here; it might be that, but it may also be a commitment to a "tabula rasa" or "all differences are cultural" sort of stuff.

But that aside, MtF(FtM) transsexuals claim that they are women(men) even before surgery, hormones, etc. But they know perfectly well that their sexual organs, secondary sexual characteristics, and indeed any non-mental property they can observe in themselves is male (female). So, on a charitable interpretation (i.e., assuming they're not speaking nonsense, incurring contradiction, etc.), they're implying that there is indeed such thing as male and female brains, and not only so, but the difference is indeed what makes a person a man or a woman in the usual sense of the words (which are defined by ostension).
In the context of the differences being a matter of splitters vs. lumpers (i.e., if they're so small and indeed just at a population level), then it appears that having a female(male) brain/mind is not at all decisive (since there would be women with male brain/minds and men with female brain/minds if we go with the splitters, and no such thing as female brains or minds if we go with the lumpers), so the proper assessment seems to be (barring an error theory of "man" and "woman") is that MtF(FtM) transsexuals are men(women), and are mistaken. What do you think?

 

[ronburgundy]

But if we acknowledge that some people are born different, then the conservatives will feel less like special snowflakes and will cry.

Conservatives accept that people are born different, they just won't accept that the differences do not cohere perfectly with differences in genitalia. OTOH, many liberals won't accept that there are many important brain-based differences that do strongly covary with differences in genitalia. These are the folks that deny a notable role of biological sex in gender roles, claiming such roles are entirely social constructions. But if that were the case, then all the research in the OP would be invalid. If there is no biological basis for gender roles in general, then there can be no biological basis of transgenders. It is only possible to be "a woman trapped in a man's body", if there is not only biological basis for having a man's body, but for the psychology of what it is to feel and think like a woman rather than a man.

So, anti-science ideologues of all political persuasions are snowflakes who melt in the sunlight of reason.

 

[repoman]

Amen, brother.