Quote from: J441 on February 02, 2015, 04:53:47 PM
I know a ton about the trans community, but I don't know much about this specific subject.
Obviously, it's not a choice. But is there something that happens in the womb that makes someone more likely to be transgender?
If you could help me out at all with this, I would really appreciate it. I'd really prefer to ask trans people who know their stuff, rather than looking up the wrong information.
Thanks so much 
As others have been saying, there's a lot of evidence suggesting that transness is a result of there being an abnormal hormonal environment during the second and/or third trimesters of a person's prenatal development. It's a not widely appreciated fact, but the sex you develop as isn't directly determined by your genes, but by what hormones are present during your prenatal development. If you look at these youtube videos:
they're all of people who are genetically male (have XY chromosomes), but nonetheless developed as female instead of male due to having a mutation to a particular gene - the gene for the androgen receptor. Because of that mutation, their androgen receptors are either completely nonfunctional or missing altogether, rendering them completely insensitive to androgenic hormones (testosterone and its derivative DHT). As a result, all their development takes place as if those hormones weren't present. In every other respect they're the same as the genetically male people who turn into men - they have internal testicles in place of ovaries, and they even have normal to above normal male levels of testosterone in their blood (however, due to the mutation, their bodies are completely unable to detect or respond to it).
People with Complete Androgen Insensitivity Syndrome (or CAIS) not only look like women, they behave like women too, and seem to be universally happy with a female gender role. What this shows it that testosterone (and DHT) play a crucial role in driving male development, and without these hormones, you'll develop as female instead, irrespective of whether you have a Y chromosome or not. It works the other way too: it's been demonstrated numerous times in the laboratory that injecting testosterone into pregnant lab animals causes their genetically female offspring to develop as male instead of female.
This free to view paper, which is reasonably readable as scientific papers go:
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3146061/talks about the history behind the discovery that it's hormones and not genes that determines which sex you develop as, and about the experiments that have been done on Rhesus monkeys demonstrating the importance of testosterone in driving male brain development.
One key thing that's emerged from the animal research is that the things determining your sex don't develop all at once: genital development occurs early on during the pregnancy, whereas the sex-specific differences between male and female brains don't appear to arise until the later stages of the pregnancy. As a result, you can produce lab animals whose genitals developed as male but with brains that developed as female (or vice versa), just by manipulating what hormones are present during various stages of the pregnancy. In some of the experiments on sheep, they even produced animals where some aspects of their behaviour were male while other aspects were female. Just as with physical development, brain development appears to occur in stages too, so exposure to external hormones can cause you to end up with a brain that's partly developed as male and partly as female.
In some of the research on sheep, they also looked at effects on the endocrine system. The hormone-exposed sheep all ended up with severely disrupted endocrine systems, and while most of them weren't completely infertile, they were significantly less fertile than the unexposed controls and had shorter reproductive lifespans.
From all of that, you can probably gather that it's not a good idea to be giving hormones to pregnant women - particularly hormones that either interfere with testosterone production, or mimic the effects of testosterone. Nonetheless, that's exactly what has been happening, and on quite a large scale too. The most infamous example of this is DES, a powerful artificial estrogen that was given to millions of pregnant women between 1940 and about 1980, as a treatment aimed at preventing miscarriages and premature births. The doses used were extremely high, far beyond that required to completely shut down testosterone production in adult men. Under the standard dosing schedule, by far the heaviest exposure to DES took place during the second half of the pregnancy - too late to have much effect on genital development, but during the critical time when the sex-specific differences between the brains of men and women are thought to develop.
The official line is that the "DES sons" who were exposed to this treatment in the womb came through their exposure virtually unscathed, however, based on what I've seen over the last 3 years, that's a load of baloney. Amongst the genetically male people I've chatted to with known or suspected DES exposure, there's a very strong correlation with transsexuality, and the one study of DES and gender that's ever been conducted found that 150 out of the 500 DES "sons" in the study identified as women rather than men.
There's a fairly lengthly thread about DES here at Susan's place:
https://www.susans.org/forums/index.php/topic,84224.0.htmlDES was phased out 40 years ago, however if one hormone can cause large numbers of people to be born trans and the whole thing pass by unnoticed, I think that makes it a lot more likely that there are other hormones still in current use that are having similar effects.
