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So. Hi new people! Apparently, we're gonna talk about sex. Like physical sex! Because... there's some confusion.
First, sex defined: We're talking physical sex here, not gender. Body parts, hormones, and genetics (and more).
BLUF: BIOLOGICAL sex is a spectrum
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First, sex defined: We're talking physical sex here, not gender. Body parts, hormones, and genetics (and more).
BLUF: BIOLOGICAL sex is a spectrum
1/
Another addition, because a couple people have asked about it.
It's important to note that there are other people who traditionally haven't fallen into the "intersex" category, but also don't fall into the clearly defined peaks either.
It's important to note that there are other people who traditionally haven't fallen into the "intersex" category, but also don't fall into the clearly defined peaks either.
For example: XX people with female secondary sex characteristics, and ovaries who won't menstruate and can't carry a child without adding external (exogenous) estrogen. People like this often have difficulties finding good endocrinology care.
One more note here: This was meant to be an informational thread, based on my own data/experience as a scientist. I am not the be-all end-all of science and don't claim to be. There are rational scientists who disagree with me.
Neither, though, do I have time for a full-on scientific debate on Twitter. Maybe we can talk at an Endocrine Society meeting or something. Unfortunately, I do have a life and stuff to do. And Twitter pays no bills.
Many people have asked for reading and papers. This is an opinion piece, which I largely agree with, that references some of the more common human-based scientific papers people use to discuss this issue. Others interpret these same studies differently https://www.nature.com/news/sex-redefined-1.16943
And one more note that "spectrum" does not mean that there aren't clusters of people. Just like the spectrum of human voice range has more baritones than super-bases.
Several people have asked about the physical structures of brains that differ between sex. This work ties in neatly with what I was saying above. There's many systems and pieces of physiology that each vary, along with the sum-brain/behavior that results. https://www.sciencemag.org/news/2015/11/brains-men-and-women-aren-t-really-different-study-finds
As this is twitter, and I'm not speaking as a representative of an institution or as part of my job, I have not shared proof of my credentials. I don't want to risk labs/schools I've worked with (or family) getting harassed when they didn't volunteer that information.
I know that makes things more difficult for those trying to do their research, but it's the reality of the platform.
But I can provide some more sources for those actually interested. They include some fairly heavy duty science, but some are open access/free for all
But I can provide some more sources for those actually interested. They include some fairly heavy duty science, but some are open access/free for all
Sources:
These deal with the fact that the sexually dimorphic brain, similar to most sex differences, does not fall into a hard binary readout - but rather is on a continuum or spectrum with each cell and each brain region comprised of varying degrees of ‘male' and ‘female'
These deal with the fact that the sexually dimorphic brain, similar to most sex differences, does not fall into a hard binary readout - but rather is on a continuum or spectrum with each cell and each brain region comprised of varying degrees of ‘male' and ‘female'
Hines M (2005). Brain Gender. Oxford University Press: Oxford
Joel D, McCarthy MM (2016). Incorporating sex as a biological variable in neuropsychiatric research: where are we now and where should we be? Neuropsychopharmacology https://www.ncbi.nlm.nih.gov/pubmed/27240659
Joel D, McCarthy MM (2016). Incorporating sex as a biological variable in neuropsychiatric research: where are we now and where should we be? Neuropsychopharmacology https://www.ncbi.nlm.nih.gov/pubmed/27240659
This paper deals with the complications of epigenetics that can divert the genetic sex and gonadal hormone pathways in subtle ways to produce large trajectory changes. Epigenetics plays a large role in estrogenic apoptosis via DNA methylation.
Gregg C, Zhang J, Weissbourd B, Luo S, Schroth GP, Haig D et al (2010). High-resolution analysis of parent-of-origin allelic expression in the mouse brain. Science 329: 643–648 https://www.ncbi.nlm.nih.gov/pubmed/20616232
This one with the interactions between social experience and biology
Springer KW, Mager Stellman J, Jordan-Young RM (2012). Beyond a catalogue of differences: a theoretical frame and good practice guidelines for researching sex/gender in human health. Soc Sci Med 74: 1817–1824
Springer KW, Mager Stellman J, Jordan-Young RM (2012). Beyond a catalogue of differences: a theoretical frame and good practice guidelines for researching sex/gender in human health. Soc Sci Med 74: 1817–1824
@threadreaderapp unroll please and thank you
And one on the heterogeneity of brains:
Joel & Sterling 2016. Beyond sex differences: new approaches for thinking about variation in brain structure and function. Philos Trans R Soc Lond B Biol Sci. 2016 Feb 19; 371(1688) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4785909/
Joel & Sterling 2016. Beyond sex differences: new approaches for thinking about variation in brain structure and function. Philos Trans R Soc Lond B Biol Sci. 2016 Feb 19; 371(1688) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4785909/
Another small addition here...
I've gotten critiques saying that I'm claiming intersex people "aren't real men or women." That's NOT what the data says. What the data says is that the labels "real men" and "real women" are not accurate labels for ANYONE.
I've gotten critiques saying that I'm claiming intersex people "aren't real men or women." That's NOT what the data says. What the data says is that the labels "real men" and "real women" are not accurate labels for ANYONE.
For example, outside of the more obvious cases, I naturally have a significantly lower resting testosterone level than my brother. This means a lot of things. It means I'm likely to respond differently to hormones or mimics/disruptors.
Give us both testosterone (or estrogen, or a bisphenol) and the results would be different. It doesn't make him or me a "real" man, it means we're in different places along the response curve. It means that "real" is an arbitrary line we've drawn.
Something new on the research end, is that it looks like sex phenotype has to be MAINTAINED in adulthood. That's actually a pretty huge change in our understanding. There's a gene that's required to keep your body the way it is.
ovaries/testes have to be maintained in adulthood and can change with changes in the right genes
Sex determination and maintenance: the role of DMRT1 and FOXL2
Huang et al, 2017 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5676419/
Sex determination and maintenance: the role of DMRT1 and FOXL2
Huang et al, 2017 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5676419/
A graphic of SOME of the things that can shift sex determination around in humans. This doesn't get into some of the newer things like DMRT1 or FOXL2. But it gives you an idea of how many different paths there are even if we just look at base chromosomes/genes
Another example. We've discovered there's a larger group than thought of "late-onset congenital adrenal hyperplasia." The default for these women has been to supplement with estrogen/progesterone. For some it works, but for many it can cause suicidal depression.
i.e. trying to treat these women in the "there are two and only two" model - by trying to make their body chemistry match an idealized model - not only doesn't work, it can kill them.
This article does a decent job of encompassing a lot of the more recent discoveries. It also does a better job than most about talking about the non-obvious non-intersex parts of the continuum such as "non-classical" CAH. https://www.scientificamerican.com/article/sex-redefined-the-idea-of-2-sexes-is-overly-simplistic1/
It's important to talk about the non-obvious parts of the spectrum, as the people just a few steps out from the peaks of the curve can be hugely damaged if medicine doesn't account for the difference. And since it's easier not to, doctors often don't.
Local maxima/minima do not disprove a spectrum. I.e. if the world were mostly blue and red, it wouldn't disprove that there is a spectrum of light.
This article has a ton of good links to primary sources, and does a good job of talking about how the spectrum extends past the "obvious" points and providing examples of how it appears even in those two big peaks at the ends. https://blogs.scientificamerican.com/voices/stop-using-phony-science-to-justify-transphobia/
Someone recently brought up the issue of "phenotypes"
Blue eyed is an example of a phenotype, as is blond, or six fingered. It's basically a systems level expression of underlying biology.
A lot of people would like "male" "female" to be phenotypes.
Blue eyed is an example of a phenotype, as is blond, or six fingered. It's basically a systems level expression of underlying biology.
A lot of people would like "male" "female" to be phenotypes.
But then we're back to "what descriptive, concrete line do we draw between phenotypes to define two and exactly two?"
Genitals vary widely in shape and size, even if you don't include intersex genitals.
Genitals vary widely in shape and size, even if you don't include intersex genitals.
Ability to carry a fetus? Ask any gyno how complicated and variable that is, and how many ways a person can have or not have that ability.
Brains? As linked above, turns out we all have both "male" and "female" type structures in our brains.
Brains? As linked above, turns out we all have both "male" and "female" type structures in our brains.
Salivary constituent concentrations? Men have a huge range of salivary testosterone, that then changes as their age.
Blood hormones? Again, wildly ranging, and changing as you age.
Blood hormones? Again, wildly ranging, and changing as you age.
You can talk about genotype, and a particular hormone level, or any individual piece, but in the end the systems level result, the phenotype is... fuzzy at best. Two big fuzzy probability mountains who's foothills overlap so you can't tell where each one ends/begins.
