Nature/Nurture

The debate continues in earnest, the two schools of thought butt heads at time sometimes when trans people get on the topic of why we’re trans. It sounds like the battle of Katydids: Katie Did!… Katie Didn’t but instead it sound like: Nature! Nurture! Nature! Nurture! So what really is the cause?

Well it is funny that our first lead into of it is nature is Nature.

A sex difference in the human brain and its relation to transsexuality

Jiang-Ning Zhou, Michel A. Hofman, Louis J. G. Gooren & Dick F. Swaab 

Nature volume 378, pages68–70 (1995)

Abstract

TRANSSEXUALS have the strong feeling, often from childhood onwards, of having been born the wrong sex. The possible psycho-genie or biological aetiology of transsexuality has been the subject of debate for many years. Here we show that the volume of the central subdivision of the bed nucleus of the stria terminalis (BSTc), a brain area that is essential for sexual behaviour is larger in men than in women. A female-sized BSTc was found in male-to-female transsexuals. The size of the BSTc was not influenced by sex hormones in adulthood and was independent of sexual orientation. Our study is the first to show a female brain structure in genetically male transsexuals and supports the hypothesis that gender identity develops as a result of an interaction between the developing brain and sex hormones.

Wow! That is pretty good! And in a PubMed research paper…

Brain research, gender and sexual orientation

D F Swaab 1, L J Gooren, M A Hofman

Affiliations Expand

PMID: 7560933 DOI: 10.1300/J082v28n03_07

Abstract

Recent brain research has revealed structural differences in the hypothalamus in relation to biological sex and sexual orientation. Differences in size and cell number of various nuclei in the hypothalamus for homosexual versus heterosexual men have recently been reported in two studies. We have found that a cluster of cells in the preoptic area of the human hypothalamus contains about twice as many cells in young adult men as in women. We have called this cluster the sexually dimorphic nucleus (SDN). The magnitude of the difference is the SDN depends on age. In other human research, two other hypothalamic nuclei (interstitial nuclei of the anterior hypothalamus [INAH] 2 and 3) and part of the bed nucleus of the stria terminalis (BST) have been reported to be sexually dimorphic in the human. Sexual differentiation to the human brain takes place much later than originally claimed. At birth the SDN contains only some 20% of the cells found at 2 to 4 years of age. The cell number rapidly increases in boys and girls at the same rate until 2 to 4 years of age. After that age period, a decrease in cell number takes place in girls, but not in boys. This causes the sexual differentiation of the SDN. This postnatal period of hypothalamic differentiation indicates that, in addition to genetic factors, a multitude of environmental and psychosocial factors may have profound influence on the sexual differentiation of the brain. No difference in SDN cell number was observed between homosexual and heterosexual men. This finding refutes Dörner's hypothesis that homosexual males have a "female" hypothalamus. However, in a sample of brains of homosexual men we did find that an area of the hypothalamus called the suprachiasmatic nucleus (SCN) contains twice as many cells as the SCN of a heterosexual group. A recent report by LeVay claims that another nucleus, INAH-3, is more than twice as large in heterosexual as in homosexual men, whereas Allen and Gorski found that the anterior commissure was larger in homosexual men than in heterosexual men or women. Preliminary research on male-to-female transsexuals is also discussed. The functional implications of these findings in determining adult sexual orientation are as yet far from clear.

There sure does seem to be something going on in there!

What about those who say it is nurture, but anything on that is harder to fine… however, there’s showing it isn’t. The only study that I could find was a study with twins, also from PubMed.

Genetic and Environmental Contributions To Gender Diversity: A Systematic Review of the Twin Literature

Will Conabere 1 2, Louise Bourchier 3, Sue Malta 3 4, Anja Ravine 1 2, Ken C Pang 5 6 7

Affiliations Expand

PMID: 40938572 PMCID: PMC12494644 DOI: 10.1007/s10519-025-10231-3

Abstract

Amidst growing visibility of gender diversity, the aetiology of gender identity has become a subject of increasing public interest. Prompted by the growing public debate, we review here the extant twin literature regarding the origins of gender diversity. Literature was reviewed systematically, searching Medline, Embase and PubMed databases. Studies were deemed eligible if they: (i) conducted a twin study, (ii) investigated gender identity or gendered behaviour, and (iii) provided an estimate of the magnitude of genetic or environmental contribution. After screening 290 non-duplicate titles and abstracts, 16 articles were included in the final review. Most eligible studies provided evidence of both genetic and environmental contributions to gender identity and gendered behaviour. For gendered behaviour, genetic contributions ranged from 0.10 to 0.77, non-shared environmental contributions ranged from 0.15 to 0.75, and shared environmental contributions ranged from 0.00 to 0.49. For gender identity, genetic contributions ranged from 0.00 to 0.84, non-shared environmental contributions ranged from 0.15 to 0.96 and shared environmental contributions ranged from 0.00 to 0.70. Given the variability in results and methodology between studies, the true magnitude of these contributions remains unclear. No consistent differences in contributions were identified between assigned males and assigned females. While there is also recent evidence that prenatal hormone exposure may contribute to gender identity, the overall evidence from the literature is inconsistent. Twin studies indicate both genetic and environmental contributions to gender diversity. These results are important to inform ongoing public debate in this area and highlight the complex interplay of both genetics and environment.

Okay what is the bottom line?

That no one knows what really causes gender dysphoria. But no one knows why people are left-handed. You can see the difference in the way the brain is different for left-handed people but no one knows why? But people are left-handed.

The same holds true for trans people. No one knows exactly why we’re trans, and there may be more than one way that someone becomes trans. But we can see differences in the brains of trans people, including differences that have been observed in people who had not undergone hormone treatment.

However, does it really matter what causes it, or whether there is more than one way that makes us trans?

It doesn’t matter. What matters is that it is real and how you treat us.