ChemicallyEnhanced
Bluelighter
I originally intended to respond in considerably less depth and with considerably more flippancy here, but I've instead decided to treat these questions in a little more depth and with a little more charity because I understand why you might have this perspective. I hope you and others read the following (particularly as you actually asked for studies) although it will probably be long. I understand that people don't want to trudge through pages and pages of long posts, but I've actually talked a lot about stuff that people have addressed recently. As far as this question goes, however, I'm going to go into greater depth, and with better citations, than I have before. So here goes. I've also included citations in a more formal way, I hope you also check them out if only to make sure I'm not bullshitting you. The argument I will be making, in brief, is that observed brain differences which seem to be "gendered" in trans-identified persons are actually attributable to sexual orientation and general gender non-conformity and that entirely different brain structures may relate to gender dysphoria and/or trans-identification.
I can understand why this brain-sex theory is a tempting position to adopt on both assertions you make (homosexual brain differences are bullshit and transgender ones real) and I think in both cases it is traceable to misconceptions about "brain sex" to begin with. First of all, the whole concept is not without controversy (Rippon 2019, link is to a review). The term itself, what is more, is a bit of a misnomer. The purported neurological correlates of sex are both structural and, more compellingly, functional (probably the best-studied difference has to do with what is called "mental rotation tasks.") Nobody is saying that these differences are the sources of masculinity and femininity. As far as homosexuals go, and I'll speak here more often about gay men than lesbians because they are significantly better studied, nobody is saying that "feminine" brain differences in gay men means that all androphilic (male-attracted) males are effeminate, which is so demonstrably untrue as to be laughable. Anyone who knows any even remotely significant number of gay men (or lesbians) knows that, contrary to stereotypes, gender presentations are diverse. I am sure there have been multiple studies about this, although I don't have one on hand to cite, but it is obvious both that homosexuals have a diversity of gender presentation and that gender non-conformity (GNC) is much more frequently observed in homosexuals than heterosexuals.
Now onto sex-related brain differences. It has been repeatedly found that men are better at these tasks (Griksiene et al. 2019), which involve spatial perception. Evidence "suggests distinct strategies being implemented depending on the difficulty of the rotation. Men performed the task more accurately than women." It is the thesis of Dr. Rippon that these differences are not inborn but rather due to what is called in this context "gendered socialization," or rather, having grown up and been raised as male or female. The differences have actually been at least sometimes found to be influenced by hormones, which brings Dr. Rippon's thesis at least partially into question and presents an interesting question as it comes to MtF transsexuals (by which I mean natal males undergoing cross-sex hormonal treatment*) as the study I just cited states "performance accuracy in [natal] women tended to be negatively related to estradiol while the response time tended to increase with increasing progesterone. There were no associations with testosterone." This has been replicated although the association with testosterone is disputed, c.f. Hausmann et al. (2000) More on this and it's implications later.
(*I use terms in very specific ways in this and all my posts. As a lot of people probably have not been bearing with me since the beginning, I'll try to define them as we go.)
When I say the term "brain sex" is a "misnomer," I do so because it is not as if these sexed differences in brain are direct correlates with what we usually consider gendered differences in the behavior and cognition (no doubt some joker is out there is thinking that the "mental rotation of 3D objects" has to do with parallel parking, but I'm only saying that as a bit of comic relief. In general, when I talk about "gendered behavior" I'm talking in broader and larger strokes than that.) As for the question at hand, this speaks to what I would imagine is one of your stronger objections to the findings of more "feminine" brains in gay men. Some evidence also exists for more "masculine" brains in lesbians but the evidence is significantly weaker and, as is all too often the case, men are much more frequently studied than women. Good evidence also exists that gender nonconformity in homosexuals (i.e. effeminate gay men and masculine lesbians) is associated with more significant cross-sex brain differences than sexual orientation alone.
Let's have a look at what is I think is the most recent study, Folkierska-Żukowska et al. (2019), which finds:
Rahman et al. (2017) find:
I could go on for quite some time citing similar studies, but it is fair to say both that the science is convincing that there are some cross-sex differences in gay men as a whole and some groups of gay men in particular, but that the evidence is not as strong as perhaps previously thought (brain differences in homosexuals have been observed for decades, and given varying sorts of social and political interpretations. The differences were at one time widely welcomed among gay activists as they were interpreted to suggest that homosexuality was a natural variation rather than a sin or pathology.) But nonetheless evidence for them is strong and, here we start to get to the crux of the matter, the differences are more strongly observed in gender non-conforming (GNC) homosexuals (unfortunately, GNC heterosexuals, a much rarer and less-studied group, are not included as a control.)
This brings us to studies of the trans-identified brain. There have been a number of this subject, as well, and they have also been given varying interpretations. The interpretation that it sounds like you are running with is that cross-sex differences in the trans-identified male is evidence that they are in some sense ontologically female ("trans women are women.") To break this down, this is a claim that there is a "gender identity" which need not correspond with natal sex which is (a) inherent, (b) essential, and (c) stable. I have criticized this view at some length here and it is I think rather beyond the scope of the current discussion but I think worth mentioning at this point. Suffice to say, this view is, in and of itself, nonfalsifiable and is ideological if not outright theological (to wit, "natal male with a female soul") in character. It is absolutely your right to believe this but using it as a lens through which to study the science is problematic. I will not discuss this view, pro or con, in any sort of metaphysical way, but will rather discuss the very specific question of whether or not homosexuals and trans-identified individuals (of any orientation) have brains which resemble those of the opposite sex.
On to the subject at hand. The problems with this interpretation are numerous. First of all, especially up until recently, almost all of these studies were done on trans-identified males (TiMs, i.e. natal male but female-identifying) of what Blanchard would call the "homosexual-transsexual" type, i.e. androphilic and effeminate persons born as men, which is the very group, absent the trans-identification, for which the strongest evidence for cross-sex brain differences exists as set out above. As for gynephilic TiMs at worst they have been excluded from studies and most studies didn't control for sexual orientation. Also, non-androphilic TiMs were typically not given access to transition clinics ("gatekeeping") until relatively recently so studies drawing on this population inherently excluded them. There has also been an apparent rise in this population as well as a corresponding one in androphilic TiFs, so earlier studies didn't even have good access to this population if they tried (they typically didn't). What's worse, many of the individuals studied were taking hormones (e.g. Carillo et al., 2000) and/or had undergone surgery. Incidentally, the intersex genetic males with complete androgen insensitivity syndrome (CAIS) who externally present as and are typically socialized, as female although their chromosomes and internal sex organs are male, perform as females do (Hemmen et al., 2014). As mentioned above, there are suggestions that in natal females, hormonal levels are related to the measures of "brain sex" which are more frequently studied. This alone should put these studies into question. When we look at gynephilic (female-attracted) trans-identified males, the purported differences disappear. See Sevic and Arver (2011) which n.b. dealt with structural differences rather than the functional differences I've been mostly discussing above (although for the purposes of our discussion the differences on both front have basically the same results and implications.)
Burke, Manzouri and Savic (2017) builds on this. I'll quote the abstract in full:
In other words, the cross-sex brain differences noted in trans-identified people are correlates of the gender they are attracted to (i.e. with respect to their natal sex, they are correlates of the same brain differences noted in homosexuals.) Trans-identified persons attracted to the opposite of their birth sex do not demonstrate these differences. It is tempting to bring up Blanchard here as he too divided trans-identified persons primarily based on their sexual orientation. However, this is a bit too cute, as there's no evidence at least here of a neuroanatomical correlate of autogynephilia but rather one a correlate of gender dysphoria in trans-identified persons regardless of natal sex or sexual orientation. However, this is not a part of the brain which is "gendered" in persons who are not trans-identified, regardless of sexual orientation. This has been repeatedly shown elsewhere.
It is not in line with the science to put forth a hypothesis of an essential gender identity and to locate it in the brain. The strongest claim that you can make is that effeminate gay men (and to a lesser extent masculine lesbians) have a response to very specific neurological studies that appears cross-sex,more so than non-GNC ones, even other homosexual, but these still have some degree of cross-sex brain differences. Unfortunately GNC heterosexuals argen't studied, and unfortunately degree of GNC, Blanchard typology, and certain other differences between trans-identified persons hasn't been studied either but there is no evidence whatsoever for cross-sex brain differences in gynephilic TiMs or androphilic TiFs and furthermore there is no evidence that these are different from non-trans-identified homosexual and especially persons with the same sexual orientation who are both GNC and homosexual.
TL;DR - There are significant differences in the brains of trans-identified persons but they are not related to differences in "brain sex." Cross-sex differences in trans-identified persons are attributable to their sexual orientation, not their trans-identification.
I will address later on some of your other points e.g. on sports, hormone blockers, the social construction of gender, and reactionary politics (or lack thereof) as well as some other stuff said by you and others since, but I hope this response was interesting and will get read. Cheers.
A few comments I wanna make:
1) I was not being ignorant about sexuality and gender-identity; for example, I STRONGLY agree with you that to suggest all gay men are feminine or all gay women are masculine is laughable. I even have personal experience of this as my childhood best friend (from ages 5-18....sadly he moved to Australia at 18 for a gap year and decided to stay there indefinitely) is gay and there was none "stereotype" or "feminine" about him at all. First time it I knew he was gay was when we were 14 and he kissed me.
It also goes the other way sometimes: not all straight men are masculine, and not all straight women are feminine.
2) Wow, the information about the rotation differences in males and females being caused by how they are raised (as either "male" or "female") is fascination. It just shows that a lot more than we know about these differences is actually related to socially constructed gender ideas rather than actual biological sex.
3) I don't believe in notions such as having a "soul", rather that a persons gender is a part of who they are; more of the mind than of the body. While I DO believe that transwomen are women and transmen are men, I also think it would be remiss not to make the obvious distinction that while transwomen are women, they are not biologically the same as ciswomen. Even after gender-reaffirming surgery (such as breast augmentation and penile-inversion vaginoplasty) and HRT, there are differences between ciswomen and transwomen. My (trans) friend Samantha has a YouTube channel (https://www.youtube.com/user/samproductions516 ) and she has videos where she talks more in depth about these topics and from a very informed perspective (as a transwoman herself). A lot of her video's are lighter in nature ("Reacting to trans character in Big Mouth, for an example) there are certainly some that provide very interesting information/theory on what we have discussed on here.
4) Interestingly, men and woman (biologically speaking) actually have the same amount of all of the same tissues when it comes to our primary genitalia. So this is just rearranged during bottom surgery so even the basic differences of biological sex are a lot less pronounced than has traditionally been thought (obviously thus does not apply to things like testicless, vas deferens, ovaries, fallopian tubes etc).
I don't mean to toot my own horn but I do believe I have a lot of good and unbiased information and perspective to share.
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