"Biological sex is a multidimensional variable with various components" - Discuss

[dunBle]

To save further derailment of the Sandie Peggie tribunal threads with people debating Tandora's statements on the above theme, I've started this thread to point them to instead.

@Tandora and also on this

I don't know what you mean by category 4 - well I do know what you mean in the sense that your category 4 refers to trans people.

I don't think your 'category 4' is a meaningful or accurate description of trans people, no.

In terms of your other question -

It is my position that there is a biological underpinning to transness**, which is tied to broader process of sex development. This is a position that I have come to after years of research, and is supported by the best, most up to date, evidence and theory, across multiple relevant disciplines.

**someone objected to this word earlier - it just means the state of being trans

To put it bluntly, your explanation shows a deep misunderstanding of basic developmental biology.

You mention karyotype, genes, hormone production, and hormone response, and then suggest that all of these somehow blur the boundaries of biological sex. In reality, sex is a binary developmental pathway, rooted in genetics and organised by tightly regulated embryonic processes. Humans start with bipotential gonads and both Müllerian and Wolffian duct systems. At around week 7 of gestation, the presence or absence of the SRY gene on the Y chromosome initiates either male or female development.

If SRY is present, it activates genes like SOX9, triggering testis development. The testes then produce Anti-Müllerian Hormone (AMH) to regress the Müllerian ducts and testosterone to stabilize the Wolffian ducts, forming male internal structures. If SRY is absent (in an XX embryo), the gonads develop into ovaries by default, the Müllerian ducts persist, and the Wolffian system regresses. There is no “spectrum” here. There is no third ductal path. There are two outcomes, clearly defined.

You also falsely imply that hormone balances and the body’s response to them drive gonadal development. That’s completely backwards! Gonadal development is driven by genetic signals, and the hormones come afterward. Testes or ovaries produce the hormones, not the other way around. Mutations that alter hormone receptors (like in CAIS or 5-alpha reductase deficiency) do affect the external phenotype, but they are disorders of sexual development within a binary system, not evidence of a third (or fourth/fifth/sixth) sex.

Your reference to the brain and psychosexual development is a red herring. Yes, sex hormones affect some sexually dimorphic brain regions, particularly in utero. But these effects are statistical— not categorical — and are modulated heavily by neuroplasticity and environment. Brain imaging studies don’t support the idea of a “trans brain” and certainly don’t overturn the definition of biological sex. Brain structure has no bearing on whether someone is male or female in a biological sense: which is based on gamete production, chromosomal makeup, and reproductive anatomy.
You’re using technically correct biological terms, but putting them together to imply something that human biology simply doesn’t support. This is a classic rhetorical technique in activist spaces. But biological sex isn’t determined by how someone feels, how their brain responds to hormones, or what their social role is. It is determined by a reproductive role, encoded in genes, expressed in anatomy, and observable from conception through adulthood.

So, you're blending half-understood biology with ideological framing and misusing science to bolster identity claims. Anyone who genuinely researches in a biological field would know that sex is certainly not fluid. It's a binary developmental process with rare but now well-understood deviations, all of which still fall within the binary system.

@Tandora

By category 4 I mean what I wrote. People whose bodies are completely functioning and aligned to their sex at birth but whose minds tell them they want to be trans.

Do you feel that no such people exist?

That there is a physical, medical reason for every trans person? That all trans people have DSD?

That is what I am trying to understand

If so, I can understand that it would be interesting, and perhaps beneficial for trans people to have a medical understanding.

But I am not sure how it is relevant to women's rights. How is it relevant?

And it doesn't help with the 'bad actors' who are trying to game the system. How do we deal with these?

Given that this paper was based on only 27 sets of twins it may fall into the area of low quality 'evidence'.

It needs to be replicated elsewhere and with a minimum of 100 sets. (I'm only applying what NICE and researchers were telling me about research my own area of unrelated interest as a patient).

I'd also like to see a control group of gay twins to compare any results to in all trans research (just in case we are seeing gay people being misdiagnosed as Trans).

Trans people deserve proper research. Extraordinary claims need clear evidence.

Seriously?
It's not 'bullying' and 'harassment' to seek clarity and ask for some answers about the qualifications of someone who claims expertise.

I've been piled on on MN. Aside from the personal attacks (calling me cruel, implying I was lying etc) the rest of it was precisely what is reasonable when someone sticks her head above the parapet and disagrees with a set of widely and strongly held beliefs.

That's what I see here. Nobody has been any more rude to Tandora than Tandora has been to others (unless I've missed something, which I have, I've not had the time to read every post).

*You mention karyotype, genes, hormone production, and hormone response, and then suggest that all of these somehow blur the boundaries of biological sex. In reality, sex is a binary developmental pathway, rooted in genetics and organised by tightly regulated embryonic processes. Humans start with bipotential gonads and both Müllerian and Wolffian duct systems. At around week 7 of gestation, the presence or absence of the SRY gene on the Y chromosome initiates either male or female development.

If SRY is present, it activates genes like SOX9, triggering testis development. The testes then produce Anti-Müllerian Hormone (AMH) to regress the Müllerian ducts and testosterone to stabilize the Wolffian ducts, forming male internal structures. If SRY is absent (in an XX embryo), the gonads develop into ovaries by default, the Müllerian ducts persist, and the Wolffian system regressesed.*

Sort of, but actually not quite - especially the second parag.

You also falsely imply that hormone balances and the body’s response to them drive gonadal development. That’s completely backwards! Gonadal development is driven by genetic signals, and the hormones come afterward. Testes or ovaries produce the hormones, not the other way around. Mutations that alter hormone receptors (like in CAIS or 5-alpha reductase deficiency) do affect the external phenotype, but they are disorders of sexual development within a binary system, not evidence of a third (or fourth/fifth/sixth) sex.

By gonadal development I was referring to the reproductive system at large. This development is driven by hormones. Specifically, the development of the testes and ovaries, along with the development of internal and external genitalia, is largely controlled by hormones produced by the developing gonads themselves, as well as hormones secreted by the pituitary gland.

Your reference to the brain and psychosexual development is a red herring. Yes, sex hormones affect some sexually dimorphic brain regions, particularly in utero. But these effects are statistical— not categorical — and are modulated heavily by neuroplasticity and environment.

Yes.

Brain imaging studies don’t support the idea of a “trans brain”

I'm not saying that there is anything as simple as the 'trans brain', don't be silly. But there are studies that have show differences in various measures in brains of trans people compared to cisgender controls. Obviously as with any area of science relating to understanding the complex, adaptive systems of the brain and cognition, our understanding is in its infancy.

and certainly don’t overturn the definition of biological sex.

Ideological and meaningless statement.

Got to run but can respond to the rest later.

"biological underpinning to transness"

I mean, unless you believe humans have a soul that survives death all beliefs have a biological underpinning.

I'm still not sure what the overall argument is hint hint page 27 summary 😜

I also note that one of the authors declares a few conflicts of interest.

@Tandora, I would be interested in seeing any further studies.

Probably this one

https://pmc.ncbi.nlm.nih.gov/articles/PMC12218214/

Reddit thread on it.

https://www.reddit.com/r/transgenderUK/comments/1ls677s/new_twin_study_published_in_nature_contradicts/

It's interesting that Tandora dismissed a paper analysing 30 plus years of research as "dated"

It seems from the Reddit chat the motivation is to disprove the Cass review.

Levine's paper was around about the same timing so that's obvious made it so disappointing it has to be disregarded.

And once more for those in the cheap seats. How does a "biological underpinning to transness" relate to a male-bodied doctor using female changing rooms?

Your woman hood is not defined by a single word
We know that.
But many of us have had to struggle to express ourselves because of the corruption of the meaning of the word 'woman'. 10 or 15 years it meant, as it had meant for centuries, adult human female. Now we have to say 'natal woman' or 'biological women' to clearly differentiate women from 'anyone who says they are one'

Hence all the NHS using terms like 'people with a cervix'.

It's utterly absurd. The term 'women' should not include transwomen, because we, XX women, need a word to describe ourselves, because we are not men.

And I note we're being accused of being 'silly' now.
🙄

Yes, this is where I am stuck.

Let's make the big assumption that all trans people can point to a physical, testable, medical reason for being trans.

Let's assume that maybe 2 percent if the population falls into this category, so 1 in 50 men are trans, and 1 in 50 women.

What does this mean for the other 49 women?

When do we get asked what we want?

I don't follow the relevance of 'a medical basis' at all. It's interesting, but doesn't impact the rights of women.

But I am keen to hear @Tandora 's take.

From the Reddit

Transmedicalists gatekeep and exclude members of our community. In no way do I support that. But conceiving of gender as primarily social instead ignores promising science like this, and the lived experience of other members of the community. We can push back against truscum and admit nature and nurture probably both play a part.

Until recently I was very much in the "gender is just a social construct" camp. I'd already socially transitioned - an out non-binary person who didn't see the point in starting HRT. I'm a tomboy who presents like a masc woman anyway, so why put myself through all that expense and marginalisation? Why medically transition when I'm already genderfluid? It wasn't until I read the Gender Dysphoria Bible and learned about biological dysphoria that I even found a reason to medically transition! A need to. Not because I couldn't stand my outer appearance. But because I couldn't stand living a life disassociated, depersonalised, and depressed.

I still accept non-binary people - I still am one! I still take the position that the best judge of someone's gender is the person themselves, 100%. But I don't shy away from science like this either. The closer we get to understanding ourselves on all levels - empirically, spirituality, politically - the better. Knowledge isn't dangerous unto itself, it's how we use it.

What is the Gender Dysphoria Bible?

By someone who said 'gonads' but then said they actually meant reproductive system, whilst claiming to be an expert in these matters.

Who has said trans affects the brain (but no other part of the body) and then said it's not trans brains.

Who said that males with CAIS are never male but also said they are sometimes male.

It's here.

https://genderdysphoria.fyi/en

The Gender Dysphoria Bible is a Living Document
The contents of this site will change over time as new additions and revisions are made to further expand upon the full breadth of gender dysphoria. In its current iteration it is severely lacking in dysphoria specific to non-binary, agender, & genderfluid people, as well as third gender and two-spirit narratives. The GDB is an open source and publicly funded project; contributions are extremely welcome.

Maybe this is Tandora's "research field" she works in.

The Bible. I won't say anything about the religious name.

https://genderdysphoria.fyi/en/causes

What is the Cause of Gender Incongruence?
To put it bluntly, we don’t know (at least not firmly). Science and modern psychology has proven that it is not caused by nurture; no one becomes transgender, gender identity is congenital, solidifying before we even exit the womb. It also appears to sometimes be hereditary; transgender parents have a higher likelihood of having transgender children, and many times they realize this in reverse. The child comes out to the parent, and that helps the parent realize they can come out as well.

Here is the science that is believed to influence gender identity. This does not mean that it defines gender identity, nor does it fully encapsulate one’s gender, as so many aspects of gender are cultural and social. None of this is prescriptive of a person’s identity, none of it is cast in stone.

Note how 'woman' in the illustration involves having long sweeping locks, a sort and heels.

<checks self>
Oops.
Chipped nail polish and Birkenstocks, trousers, very short and exceedingly scruffy ponytail (one up from a bun).

Not womaning right. Must get advice.

Klaxon klaxon

It's time for my favourite question again and seeing as you are stooping to answer questions at are 'beneath' you can we have a very quick yes or no to do 'nice' women deserve single sex spaces please?

It seems to me that every time @Tandora is asked about relevance to single-sex spaces, they disappear

Excellent. New to this thread but I'm quite sure Tandora is desperately researching as we speak.

P.s. It's ok to back down when someone clearly smarter enters the convo.

Everytime. I have tried to engage because I genuinely want to debate the practicalities.

It is a shame.

I genuinely want to get the whiteboard out and clarify what we agree on and where we diverge, and why.

I think we probably have a lot in common - we probably agree that we each have a right to respect, for example, and also that 'your rights end where my rights start', to paraphrase.

I can't see how we will move forward unless we understand where we differ and why.

Hoping @Tandora or @suggestionsplease1 will be back soon.