Well … the short answer is simply that we don’t really know for sure. There’s plenty of evidence that shows the biology of gender variant people to be unique, in terms of our genetics and brain structure and stuff, but the problem is that we haven’t a clear idea yet of what causes these biological variations. There are plenty of possible causes, but nothing where scientists can say with 100% certainty “This is it.”
Of course, it’s debatable if there is even a single cause – with such a complex biology touching on brain chemistry, our endocrine system and even our genetics, there are quite possibly many factors at work that all influence a developing baby in the womb.
general research on gender variance - Overarching studies and general research looking at the causes, indications and effects of gender variance.There's a number of papers I wasn't aware of - but the list is nowhere near complete. It's not so much the contents though as the framework that is outstanding, and I think I'll be stealing it as an organising template. I hope to send some updates under those categories to Mina, and see if we can get a definitive list of useful articles.
female biology and sexuality Studies on female sexuality, gender, biology and other subjects that might be of relevance to people who are gender variant. and opportunistic mating in women (2009, biology letters)
male biology and sexuality Studies on male sexuality, gender, biology and other subjects that might be of relevance to people who are gender variant.
puberty General research on the biological and mental changes that take place before and during human puberty.
gender differentiation General research on the biological differences between human males and females and how those differences come about.
gender socialisation This research focusses on how social interaction and development, especially at an early age, influences the formation of gender roles and expectations, social ability and other characteristics. Also included are so-called “nature-vs-nurture” studies that posit purely environmental rather than biological origins for gender.
natural gender variance There is a strong argument that variation in sexual preference and gender identity is a natural phenomenon, and indeed, homosexuality and gender variance are observed in wild populations right along with intersex, and at least as far back as we’ve recorded history, transgender and homosexual people have been known to varying degrees.
biomass pollution Scientists are observing unprecedented levels of deformity and intersex conditions due to widespread pollution. Marine animals especially have been hard-hit due to high levels of estrogen-mimicking chemicals. Humankind is also not immune to this phenomena, with male sperm counts in continual decline and undermasculinesed boys being born more and more often.
diethylstilbetrol (des) Diethylstilbetrol was a medication widely prescribed from the early 1940’s until the mid 80’s as a menopause control and general hormone replacement therapy, and as an anti-miscarriage medication for pregnant women. It has since been found to be a powerful teratogen, causing widespread deformity of children born to mothers who were exposed to or used it during pregnancy. More interestingly, so-called DES-sons have a 20-fold increase of hypospadia, where the urethral tube opens on the underside rather than at the tip of the penis, and have demonstrated greatly increased incidences of gender dysphoria/transsexuality.
brain structure Some of the earliest research looking for the causes of transgenderism focussed on the brain structure, and specifically structures within the hypothalamus. This research is ongoing and has arguably given transgender individuals their loudest argument yet for acceptance and legal/medical recognition.
hormonal This research focusses on hormonal variations amongst transgendered people, and on possible influences early hormonal variation may have on brain structure and gender identity.
genetics Recent research into the etiology of transgenderism has focussed heavily on genetic indications, and late 2007 and 2008 have seen a number of interesting studies published that do indeed indicate a definite genetic component.
anthropometry Anthropometry is the measurement and statistical sampling of physical characteristics. As it relates to transgender individuals, this research looks for typically female measurements in transwomen and typically male measurements in transmen.
asperger’s and autism I’ve read in a few places now that asperger’s syndrome is up to four times as likely amongst transwomen as amongst the population at large. Unfortunately I’ve been unable to find any studies to corroberate this, but many of the same endocrine disrupting chemicals that get blamed for intersex and transsexual biological variation also feature in autism and aspergers. Interestingly, autism and related disorders have been theorised to be a form of a hyper-masculinized, structuring brain.
polycystic ovarian syndrome Polycystic ovarian syndrome is an endocrine condition that affects about 5% of cisgendered women. It causes the body to produce excessive amounts of androgens, leading to masculinisation. Up to a third of female-to-male transsexuals suffer from this condition.
the effects of HRT This research focusses on the effects that HRT have on transitioning gender variant people, both in the short term as well as long term health consequences.
body image Body image forms a major part of Gender Identity Disorder. This research studies variations in the image transgender people have of themselves and their bodies.