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.
So yeah, we’ve got a fair few bits of the puzzle, but unfortunately Sparky chewed the box top all to hell, so we don’t know what the picture we’re after is exactly.
You’ll notice that many of the linked resources discuss the same findings as others. These are included to present different perspectives on the same data, and also to target different audiences. Please also note that many of the research reports linked here are behind pay-to-view journal sites, and so only the abstract and results may be viewed freely.
Just on a last note, this is a real grab bag of stuff, from authoritative through to badly researched BS, I’m quite sure. It’s simply the stuff I’ve read and come across, so do your own reading, draw your own conclusions, and reference stuff at your own peril.
I’ll be duplicating this and future posts on causes on a single page for ease of reference. Check it out at “the causes of gender variance”, there might well be updates listed there that are not present in this post.
general research on gender variance
Overarching studies and general research looking at the causes, indications and effects of gender variance.
- [harry benjamin] the transsexual phenomenon (1966, julian press)
- [karen lovett] studies on gender identity disorder (10 feb 2008, nashua telegraph)
- [zoe brain] bigender and the brain (18 jun 2008, aebrain.blogspot.com)
female biology and sexuality
Studies on female sexuality, gender, biology and other subjects that might be of relevance to people who are gender variant.
- [uncredited] effects of estradiol on women’s infidelity (31 jan 2009, ts-si.org)
- [durante and li] oestradiol 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.
- Since I’m female I’ve not paid as much attention to male biology, but I’ve included this category for future updates.
General research on the biological and mental changes that take place before and during human puberty.
General research on the biological differences between human males and females and how those differences come about.
- [uncredited] men are red, women are green, study finds (08 dec 2008, physorg.com)
- [wizemann and pardue] exploring the biological contributions to human health, does sex matter (2001, institute of medicine)
- [committee on…] genes, behaviour and the social environment, beyond nature vs. nurture (2006, national academies)
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.
- [dinitia smith] central park zoo’s gay penguins ignite debate (feb 2004, san francisco chronicle)
- [john tidwell] the wilder side of sex [2004, smithsonian national zoological park)
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.
- [committee on…] hormonally active agents in the environment (national research council, 1999)
- [david usborne] chemicals linked to gender-bender polar bears (new zealand herald)
- [emily cook] babies in womb exposed to ‘gender-bending’ chemicals (oct 2006, daily mail)
- [gwynne lyons] male wildlife under threat (full report) (dec 2008, chemtrust)
- [gwynne lyons] male wildlife under threat (press release) (dec 2008, chemtrust)
- [jerry mosemak] bisphenol a, what you need to know (29 oct 2008, usa today)
- [katy human] effluent tipping scales on fish gender (sep 2006, denver post)
- [kent elliot] hermaphrodite fish provoke concern about pollution (sep 2006, georgetown voice)
- [lisa szabo] epa must consider effects of chemical barrage (19 dec 2008, usa today)
- [uncredited] decline of the real man is no joke (07 dec 2008, uk independant)
- [uncredited] gender-bending fish found in dc water supply (sep 2006, watertech online)
- [uncredited] hairspray is linked to common genital birth defect (24 nov 2008, sciencedaily)
- [uncredited] the male gender is in danger (07 dec 2008, uk independant)
- [uncredited] why synthetic estrogens wreak havoc on the productive system (2 apr 2008, yale university via sciencedaily)
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.
- [kerlin] gender dysphoria in males prenatally exposed to des, a 5 year study (oct 2004, e-hormone conference, new orleans)
- [seyler et al] abnormal gonadotropin secretory responses to lrh in transsexual women after des priming (jul 1978 )
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.
- [kruijver, zhou, et al] mtf transsexuals have female neuron numbers in a limbic nucleus (2000, free university hospital, amsterdam)
- [rosie mestel] brain study focusses on gender identity (oct 2003, l.a.times)
- [zhou, gooren and swaab] a sex difference in the human brain and its relation to transsexuality (1997, free university hospital, amsterdam)
- [zhou, hofman, gooren and swaab] a sex difference in the human brain (1995, nature)
This research focusses on hormonal variations amongst transgendered people, and on possible influences early hormonal variation may have on brain structure and gender identity.
- [gooren et al] estrogen positive feedback on lh secretion in transsexuality (1984, free university hospital, amsterdam)
- [wilson] the role of androgens in male gender role behaviour (1999, university of texas sw medical center, dallas)
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.
- [bentz et al] polymorphism of cyp17 gene associated with ftm transsexualism (sep 2007, medical university of vienna)
- [deborah smith] scientists find a gene for the transsexual experience (27 oct 2008, sydney morning herald)
- [emma young] mtf transsexualism gene found (oct 2008, biological psychiatry via new scientist)
- [hare et al] androgen receptor polymorphism associated with mtf transsexualism (30 oct 2008, biological psychiatry)
- [ian muchamore] discovery of genetic link to gender identity (nov 2008, biological psychiatry via medical news today)
- [linda geddes] ‘transsexuality gene’ makes women feel like men (jul 2008, new scientist)
- [molecular brain research] sexual identity hard-wired by genetics (oct 2003, reuters via common dreams)
- [uncredited] transsexual gene link identified (oct 2008, bbc news)
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.
- [schneider, pickel and stalla] typical female 2d-4d finger ratios in mtf transsexuals (apr 2005, max planck institute of psychiatry, munich)
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.
- [baron-cohen et al] the autism-spectrum quotient (aq) (2001, journal of autism and developmental disorders)
- [hoekstra] factor structure, reliability and criterion validity of aq (2008, journal of autism and developmental disorders)
- [j madeleine nash] the geek syndrome (06 may 2002, time magazine)
- [j madeleine nash] the secrets of autism (06 may 2002, time magazine)
- [steve silberman] the geek syndrome (2001, wired magazine)
- [woodbury-smith et al] screening adults for asperger syndrome (jun 2005, journal of autism and develeopmental disorders)
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.
- [futterwit et al] increased frequency of polycystic ovarian disease in ftm transsexuals (apr 2005, mount sinai school of medicine, ny)
- [futterwit et al] increased frequency of polycystic ovarian disease in ftm transsexuals, preview (apr 2005, mount sinai school of medicine, ny)
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.
- [hulshoff pol et al] influence of testosterone and estrogen on adult human brain structure (2006, vu university medical centre, amsterdam)
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.
- [kraemer, delsignore et al] body image and transsexualism (2008, university hospital, zurich)
- [lindgren and pauly] a body image scale for evaluating transsexuals (1973, symposium on gender identity)