Our favorite "Why" questions
This is looong. Sorry.
I recently read an interesting book ("The Psychobiology of Transsexualism and Transgenderism: A New View Based on Scientific Evidence" by Thomas Bevan. Great book if you're comfortable reading scientific summaries. (A bit expensive - you'd be wise to get it from your local library.) The book is a survey of recent (book was published in 2015) research on transgender topics. I had considered writing a "book report" style post but, honestly the book covers too wide a range of information to squeeze into a single post and have it make any sense. So I just want to write about my take on a couple of "why" topics that we see come up on this forum over and over again. (1) Why do transgender people exist? (2) Why do we do what we do?
Disclaimer: I've galloped through the information and simplified a lot of things based on my (probably iffy) understanding of what I read. I know we have real genetics professionals who come to this site who can feel free to correct me where I went off track. Please do.tl;dr: The answers to 1 & 2 according to Bevan:
(1) Gender is biological. Scientific opinion is closing in on a two-factor explanation: genetics and epigenetics
(2) Biological 'gender preference' drives our choice of culturally-defined gender role.
Also note up front - this post is specifically NOT for meta-discussion about the pointlessness of knowledge or labels or kids-these-days or whatever. Do feel free to start your own thread, but please do not attempt to derail this one. (Moderators, please take note.)
In terms of nomenclature, anywhere you see me use the term "transgenderism" you can be pretty sure he used the term TSTG (transsexual/transgender.) It's apparently the norm in his field. Since people on this site get cranky about new acronyms, I just replaced it with a more common word. He also uses the term HT where we use HRT. He explains that HRT is Replacing hormones that have gone missing, while Hormone Therapy is a treatment used in transgenderism. I agree with his reasoning and may start to use it in my own life, but I'm not going to try to convert the transgender community single-handedly.
1. Why do we exist?
We see a lot of origin stories on this forum with ideas from "exposure to environmental agents" to "because my Mom dressed me in my sister's clothes when I was young," to "I think it happened as I got older and my testosterone dropped." All of which get a polite "no" from the research reported in this book.
The current thinking is that children are aware of "basic gender concepts" at 18 months and understand gender stereotypes by 2 or 3 years. If they are cisgender, they have a grip on their expected gender behavior by 3. Transgender children have the same learning milestones, but if they are not accepted as transgender, they learn to conform to the gender behavior that their parents expect of them to avoid rejection. (They become role-players.) If they understand their gender situation enough to verbalize it, they may voice it between 3 and 8 years (a common narrative of TS folks and the transgender kids we're seeing in the news these days.)
Because children's awareness of transgenderism seems to occur around 3 or 4, there are a limited number of things that could cause it. DNA, epigenetics and early childhood interaction are the factors that get the most focus.
Early Childhood Interaction
Early childhood interaction is basically dismissed as a cause of transgenderism. Scenarios that have specifically been ruled out: Emotional relationships with parents, prenatal sex preference of the mother, parental separation, parents/siblings dressing a child in wrong-gender clothing, parental abuse and violence (though it's noted that TG children do get abused more, it appears the abuse is because they're TG; they don't become TG because of the abuse.) Studies are cited for all of these situations, if your favorite explanation of why you're transgender shows up in this list, please refer to the book for details.
Genetics
There is a lengthy section summarizing results from twins studies from around the world and the upshot seems to be that transgenderism is "heritable" (i.e. can be passed along family lines,) and biological in nature with DNA as "a" (but not "the") causal factor. The correlation is considered "strong."
Finger length ratio between the index and ring finger ("2D:4D ratio,") shows a high correlation to transgenderism in both MtF and FtM individuals. This ratio was already known to have a strong basis in genetics. The ratio is higher in MtF people relative to cis-males and lower in FtM people relative to cis-females. He says this with some confidence, however, the individual studies summarized in the book seemed to have conflicting results.
Another oddity present for both MtF and FtM is tooth diameter. In a cisgender population, male tooth diameters are larger, female tooth diameters are smaller. Amongst TS people tooth diameters follow the pattern for the person's gender, not their sex. Again, tooth diameter has previously been linked to genetics.
A favorite meme of MtF transgenderism is that MtF people tend to have more male siblings. It turns out that result didn't hold up to scrutiny. Male siblings hold for sexual orientation, but not for transgenderism. What did hold up was MtF people seem to have more maternal Aunts than Uncles. No theories on why.
A search for DNA markers is ongoing and some appear to have been found. It's worth noting that most study is on transsexual (TS) individuals since they are considered the "most" transgender of all the people under the umbrella, but some/few also include folks who identify as TG, though what that means is vague (given that we can't come up with a definition among ourselves, it's not surprising.)
Bevan notes that markers have been found near the androgen receptor gene (AR) in male-to-female transgender folks and "a hormone metabolism gene" for female-to-male transgender folks. He cautions that a full genome scan has not yet been done and there probably are other genes involved. The multiple gene scenario has precedent -- eye color in humans is the result of at least five genes at work, he says (despite what you may have learned in middle-school.)
There are two very interesting things about MtF transgenderism being associated with the Androgen Receptor gene -- the first is that's where an anomaly that causes Androgen Insesitivity Syndrome is located -- AIS causes an intersex condition where female external genitals develop in people with XY (male) DNA. The author notes that if AIS only effected formation of genitals, then we'd expect the people to have a gender preference of male to match their DNA but in general they don't -- they're very happy living as female. The other interesting thing is that anomalies on that gene also are associated with "non-right-handedness" -- that is, the person is not necessarily left-handed, but tends to do some things with their left hand that a right-hander would normally do with their right. That particular trait has a strong correlation to MtF transgenderism. (There used to be an oft-retold story that there was a corelation between transgenderism and being left-handed. Now it may be that there's a stronger corelation to being non-right-handed.)
He notes that the politics of research funding skews the research to MtF transgenderism because if the anomaly is related to the anomaly that causes AIS, then researchers can get money to study AIS, classified a disease, more easily than they can find money to study transgenderism (which is no longer considered a disease. It turns out *that* battle was a double-edged sword.)
It is not known yet if the DNA anomalies are strictly inherited (germ line,) are a mutation that happens spontaneously at conception (de novo mutations,) or occur because people have multiple DNA in a single body (mosaics.) But since a number of traits that are affected cannot be affected by purely psychological issues, there is strong evidence that transgenderism has a biological/genetic component. But it seems like there is another factor in play...
Epigenetics
Epigenetics are external factors that can change DNA or may change the way DNA expresses without changing the DNA itself. Different factors have been identified for study, but none have convincing results yet.
One popular epigenetic theory (which up to now had been my favorite) about MtF transgenderism is that it might be a response to an anomolous amount of estrogen (or failure to get sufficient amount of testosterone) at week 10 of gestation when neural pathways in the brain are being formed. The idea was that if there wasn't sufficient testosterone to enable construction of the male neural pathways, female pathways would be created "by default." However, research doesn't bear this out: not only does neurological formation of sex-specific structures start before gonads are mature enough to produce sufficient testosterone, but a naturally-occurring condition, Kallman's Syndrome, results in low testosterone, which should mean males who have it should largely be transgender, but they're not. And further research on neural development has shown that the mechanism for creating the neural pathways is actually fueled by estrogen which is converted on site to testosterone as needed. So my favorite theory is on the floor.
The presence of DNA markers for transgenderism makes it less likely that epigenetics is the sole cause. However, there still might be an epigenetic factor...
Two-factor model
It could be that you need both an epigenetic event AND the specific DNA that makes you respond to it to create a transgender outcome. This is a "two-factor" model which seems to be leading the pack as an explanation at the moment. It would mean that without the DNA, the epigenetic event would not produce a transgender result. And without the epigenetic effect, DNA alone would not produce a transgender result. You'd expect a trait that requires both things to be true at the same time to be very rare, and it is.
So, no capital-A answers, but interesting advances in knowledge.
2. Why do we do what we do?
So if there's a biological reason for transgenderism, how does that work? Isn't gender a social construct? Here it gets complex. But actually it's another two-factor model: Societies define gender roles, or what Bevan describes as "gender behavior categories." We understand those categories at a very young age and in evaluating those, we are drawn to the one that best fits our biological "gender preference." The idea is, that you are most comfortable/happy when doing the activities identified with the gender behavior category most closely aligned to your gender preference. You are less happy doing the activities of a gender behavior category that is not aligned with your preference (but the activities themsevles are, in fact, genderless. Girls can play with trucks, boys can play with dolls and nothing explodes.) So when the question is "why do I feel so right when I put on women's clothes?" The answer is that doing that has nothing to do with the cloth or how it's sewn together and everything to do with your recognition that this is a thing appropriate to your gender preference.
Long ago, I asked in a post if people would rather wear jeans bought in the women's section of the store than the same jeans from the men's section. And most of the answers (as I recall) were, yes, they would prefer them from the women's section, though few knew why. Maybe now we do.
An interesting thing is that gender behavior categories are defined by cultures. In our culture, there are two (male and female.) In other cultures there are three, four or five. Cultures have created these categories throughout history and all over the planet. Asia and Africa have cultures to this day that have more than two roles. Tribes in the Pre-Columbian New World also had them. There is evidence of European cultures that once had such categories but somehow they (the categories) got lost.
Now, this is me speculating here, this is not in the book -- those cultures that recognize the need for more than two categories certainly wouldn't have developed them if there were no folks who fit into them, which I think could explain why we have the non-binary category of transgenderism in our community today. Our preferred category doesn't exist, and so, like on a standardized exam, some people (TS) see a clearly correct answer. Some (non-binary/stable) pick the one that is most-nearly-correct. And, some (non-binary/fluid) oscillate back-and-forth between answers.
Anyway -- the point is that science is marching on and we're discovering new information that may or may not be welcome news. I know many people who hope for a day when you can take a "trans test" and settle the issue unambiguously. And I know folks who dread that day. And, of course, if new, verifyable evidence comes along that shows we're just a biologically sound human variation, that has big implications in law, religion and sociology. No matter how you feel about it, it's probably good to know where things stand and where they're trending.
Again -- keep in mind -- this is my opinion of Bevan's opinion of hundreds of peer-reviewed studies. If you're interested look up the book. You might read the book and get an entirely different take-away. In which case, please come tell us about it.
