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I need to bring up something that's been bugging me.

We talk all the time about how sex isn't just genitals, it's every piece of our being. If you look into it, even our non-sexual organs are genetically dimorphic between men and women.

The inconsistency to me though is when we say there's no such thing as a female brain. All of a sudden, all of the femaleness that is intrinsic to every other part of who we are becomes invisible. I understand that we don't want to lend credibility to the idea that TIMs can have a "female brain," but even the research that exhibits sexual dimorphism in brains doesn't show that--in fact, while "trans brains" are mildly shifted towards their "preferred gender," they are still well-within normal ranges for their sex, and still outside the average range for their "identity." It's not a gotcha, and I don't think we need to be afraid of it.

The graphic on this study (under Results) is especially good to look at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8955456/

If anything, I think admitting that female brains do exist (with some variance within the sex, of course) and that TIMs do not have them is perfectly good evidence for being gender critical. (And for those who criticize lesbians for not sleeping with TIMs because we're genital fetishists, well, no, the brain plays a part too. Suck on that, "hearts, not parts.")

Some might call it sexist to say there are differences between male and female brains, but I think the it's more that the sexist conclusions that people come to as a result of the difference existing are problematic--ie: because "female brains" exist, women must be more predisposed to doing housework, or some other nonsense.

Also, when we talk about puberty blockers being harmful because of the importance of sex hormones in adolescent brain development, I think it's a bit willfully ignorant to not assume that estrogen and testosterone might have different effects on the brain.

Prove me wrong, please, or give me another way to think about it! I just think it's something worth tackling head on, rather than brushing aside.

I need to bring up something that's been bugging me. We talk all the time about how sex isn't just genitals, it's every piece of our being. If you look into it, even our non-sexual organs are genetically dimorphic between men and women. The inconsistency to me though is when we say there's no such thing as a female brain. All of a sudden, all of the femaleness that is intrinsic to every other part of who we are becomes invisible. I understand that we don't want to lend credibility to the idea that TIMs can have a "female brain," but even the research that exhibits sexual dimorphism in brains *doesn't show that*--in fact, while "trans brains" are mildly shifted towards their "preferred gender," they are still well-within normal ranges for their sex, and still outside the average range for their "identity." It's not a gotcha, and I don't think we need to be afraid of it. The graphic on this study (under Results) is especially good to look at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8955456/ If anything, I think admitting that female brains do exist (with some variance within the sex, of course) and that TIMs do not have them is perfectly good evidence *for* being gender critical. (And for those who criticize lesbians for not sleeping with TIMs because we're genital fetishists, well, no, the brain plays a part too. Suck on that, "hearts, not parts.") Some might call it sexist to say there are differences between male and female brains, but I think the it's more that the sexist conclusions that people come to as a result of the difference existing are problematic--ie: because "female brains" exist, women must be more predisposed to doing housework, or some other nonsense. Also, when we talk about puberty blockers being harmful because of the importance of sex hormones in adolescent brain development, I think it's a bit willfully ignorant to not assume that estrogen and testosterone might have different effects on the brain. Prove me wrong, please, or give me another way to think about it! I just think it's something worth tackling head on, rather than brushing aside.

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Also, when we talk about puberty blockers being harmful because of the importance of sex hormones in adolescent brain development, I think it's a bit willfully ignorant to not assume that estrogen and testosterone might have different effects on the brain.

Yes, I am sure the different hormones have an effect. But's important to keep in mind that estrogen is only one of several sex hormones we make and that affect us females.

Moreover, research on humans and other animals considered similar show that males not only make estrogen directly in their testes and other parts of the male reproductive tract, just as females make testosterone in our ovaries - but that males also convert some of the testosterone and other androgens they make into estrogens - estradiol and estrone - in some of their body parts/tissues through the process of aromatization due to the enzyme aromatase. Aromatization is a process that only occurs one way, turning androgens into estrogens. Aromatization does not convert estrogen into androgens.

Interestingly, one of the main sites where males appear to convert quite a lof of their T into E through aromatization is the male brain.

Aromatase is the enzyme responsible for converting testosterone to estradiol. In mammals, aromatase is expressed in the testes, ovaries, brain, and other tissues. While estrogen is traditionally associated with reproduction and sexual behavior in females, our current understanding broadens this perspective to include such biological functions as metabolism and cognition. It is now well-recognized that aromatase plays a vital lifetime role in brain development and neurobehavioral function in both sexes.

https://www.frontiersin.org/articles/10.3389/fnmol.2018.00374/full

Estrogen masculinizes neural pathways and sex-specific behaviors:

Male behaviors require both testosterone and estrogen. Circulating testosterone activates the androgen receptor (AR) and is also converted into estrogen in the brain via aromatase. This conversion is the primary source of estrogen to the male brain. It is unclear whether testosterone and estrogen signaling interact to masculinize neural circuits. Using a genetic approach, we show extensive sexual dimorphism in the number and projections of aromatase expressing neurons. The masculinization of these cells is independent of AR but can be induced by either testosterone or estrogen, indicating a role for aromatase in sexual differentiation of these neurons. We provide evidence suggesting that aromatase is also important in activating male aggression and urine marking as these behaviors can be elicited by testosterone in males mutant for AR. Taken together with additional findings, our results suggest that aromatization of testosterone into estrogen is important for the development and activation of neural circuits that control male territorial behaviors.

Estrogen is also essential for male behaviors. The requirement for estrogen to masculinize behavior seems counter-intuitive as this ovarian hormone is essentially undetectable in the male circulation. All estrogenic steroids are synthesized in vivo from testosterone or related androgens in a reaction catalyzed by aromatase. Aromatase expressing cells in the brain convert circulating testosterone into estrogen, and it is this local estrogen that is thought to control dimorphic behaviors in males (Figure 1A) (MacLusky and Naftolin, 1981; Naftolin and Ryan, 1975). Consistent with a requirement for estrogen in male behaviors, aromatase activity is essential for male behaviors.

Estrogen mediates many of its effects by signaling through the estrogen receptors ERα and ERβ, which exhibit overlapping expression patterns, and regulate masculinization of the brain and behavior in a complex, redundant manner (Bodo et al., 2006; Ogawa et al., 1999; Ogawa et al., 2000; Ogawa et al., 2004; Perez et al., 2003; Rissman et al., 1997).

The role of a third estrogen receptor, GPR30, in male behaviors is presently unknown (Revankar et al., 2005).

The dual requirement for testosterone and estrogen signaling in male behaviors suggests that these two pathways may interact genetically to control these dimorphic displays. One potential site of interaction is the control of aromatase expression.

We find extensive, previously uncharacterized sexual dimorphisms in both the number and projections of neurons expressing aromatase. The masculinization of these neural pathways is independent of AR but can be induced in neonatal females by testosterone or estrogen, indicating that aromatase plays an important role in the sexual differentiation of these neurons. Moreover, testosterone activates male typical fighting and urine marking independent of AR, demonstrating that the differentiation and function of the neural circuits underlying these behaviors are governed by testosterone, at least in part, after its conversion into estrogen. Finally, our results show that adult gonadal hormones of either sex can support male territorial marking and fighting provided estrogen has neonatally masculinized the underlying neural circuitry.

Circulating testosterone and locally derived estrogen in the brain are critical for the expression of male behaviors. It has been difficult to determine the individual contributions of these two hormones to masculinization of the brain and behavior. Our gene targeting strategy has allowed us to identify at cellular resolution the small population of aromatase expressing neurons that can synthesize estrogen from testosterone. Testosterone appears to serve, at least in part, as a pro-hormone for estrogen for the male typical differentiation of aromatase positive neurons and for masculinization of territorial behaviors.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2851224/#:~:text=Male%20behaviors%20require%20both%20testosterone,estrogen%20to%20the%20male%20brain.