Sex and gender are a big part of being human, so they have an important place in the theology of many branches of Christianity. Scientific investigations into sex and gender have brought up important challenges to some traditional ideas about these things in the last century. Any theologian (any Christian) who has an honest commitment to the truth must take these scientific findings into account when developing an opinion on topics of sex and gender in humans. So let’s take a look at a few of them.
1. Sex is not the same as gender
Different words have different meanings, and those differences are important. The WHO defines the words as follows: “Gender is used to describe the characteristics of women and men that are socially constructed, while sex refers to those that are biologically determined. People are born female or male, but learn to be girls and boys who grow into women and men. This learned behavior makes up gender identity and determines gender roles”. So being male or female has to do with things like what sort of genitals one has, while gender is more about how society generally expects sexes to behave (i.e. women wearing dresses, men being aggressive, etc.).
2. Sex and gender don’t always align
Most people have the benefit of having the same gender as their sex, so it’s pretty difficult for most to understand what it must be like to experience anything different. But a difference between sex and gender is exactly what gender non-conforming people report, and science has shown some of that difference. Multiple studies have shown physical differences between gender conforming and non-conforming people in brain structures that change depending on sex . Different brains make for different experiences.
3. Gender is at least partially genetic
Research on twins has shown that in identical (monozygotic) twins, one twin experiencing gender dysphoria means the other twin is more likely to also experience gender dysphoria. The genetic factor has been statistically calculated to explain up to 62% of this increased probability .
4. Gender is partially environmentally caused
Research comparing body differences that show up early in life between male-to-female (MtF) transsexuals and control males has found that the MtF transsexuals were more feminine. Males tend to have short index fingers in comparison to their ring fingers, unlike females, and that can be detected in the womb. But MtF transsexuals tend to have a more feminine finger ratio, which could be explained by prenatal exposure to sex hormones .
5. People are human first, and male or female second
It’s easy to intuitively think of humans as only being male or female, but nobody starts out as either. While an embryo a few weeks old might have the genetic coding to develop into a male or female, it isn’t either until it manages to do that developing. It’s not as though the human soul comes in pink or blue from the outset. Sex and gender are things we become.
6. Gender differences between men and women are a spectrum
Remember that gender is about what behavior and characteristics society expects, but the reality doesn’t often match expectations. Very few men and women have characters that perfectly fit some archetype of their gender. There are general trends, but the most accurate description of gender is as a spectrum between extremely masculine and extremely feminine. In brain structure studies, it has been found that gender conforming males, Female to Male (FtM) transsexuals, MtF transsexuals, then gender conforming females are points on a spectrum from masculine to feminine brain structure [3,4]. Scientists don’t think of gender as binary because it just isn’t an accurate description.
7. Sex differences between male and female are a spectrum
Developing into a sex is a complex process, and everything can go wrong. It does occasionally happen that someone is born with one testicle, one ovary, and ambiguous everything else . Chromosomes aren’t always a helpful measurement of sex either, because it’s possible to be an XY female, XX male, or have a jumble of too many sex chromosomes altogether . There are all sorts of disorders of normal sex development, so in reality, even sex is most accurately described as something like a spectrum between obviously male and obviously female.
8. Sex differences can be physically altered
If a human doesn’t have a sex until they physically develop one, then it is only physical differences between one sex and the other. People born with ambiguous genitalia are often given surgery and hormone therapy to become clearly male or female . But if sex can be truly altered at one stage of life, then it’s important to note that sex can be truly altered at other stages of life.
9. Gender non-conforming people trying to conform isn’t the healthiest goal
What’s healthiest for one gender dysphoric person isn’t necessarily what’s best for another. With psychotherapy, some gender dysphoric people can come to peace with their gender identity being dissonant from their sex at birth . Others will only ever continue to experience distress unless they receive hormone therapy and/or surgery .
10. Gender affirming therapy can be helpful
Longitudinal studies of people who have underwent gender-confirming medical interventions (GCMI) like surgery or hormone therapy to alter their sex have shown that this is an effective treatment. GCMI decreases mental illness in gender dysphoric people .
11. A low percentage of gender dysphoric children remain gender dysphoric as adults
Only about 6-23% of children who experience gender dysphoria continue to experience gender dysphoria as adults . So most kids just grow into their assigned gender. The data for adolescents isn’t as good, but it seems that gender dysphoria in the teenage years is more likely to persist into adulthood .
11. We don’t know how common transsexualism is, but sex abnormalities can be fairly common
Estimates of how common transsexualism is has been estimated to be between 0.45 to 23.6 individuals per 100,000. Reported numbers have been increasing in the past few decades, which suggests that transsexualism may be under-reported, and actual prevalence might not be very well understood . From a strictly neonatal perspective, ambiguous genitals at birth occurs in about 1 in 5000 births, and genital abnormality at birth has been estimated to be as high as 1 in 300 births .
12. Gender non-conformity is an urgent issue to address
Statistics have shown that gender non-conformity puts individuals at a higher risk of abuse and bullying . More abuse means more mental health and suicide risk . It’s a real ugly scene, and Christians have a responsibility to do something about it. Part of doing something about it means developing theology that understands the issue, including both the scriptural and scientific facts.
 Arcelus J, Bouman WP, Noortgate WVD, Claes L, Witcomb G, Fernandez-Aranda F. 2015. Systematic review and meta-analysis of prevalence studies in transsexualism. European Psychiatry 30: 807-815.
 Dhejne C, Vlerken RV, Heylens G, Arcelus J. 2016. Mental health and gender dysphoria: a review of the literature. International Review of Psychiatry 28(1): 44-577.
 Krantz GS, Hahn A, Kaufmann U, Küblböck M, Hummer A, Granger S, Seiger R, Winkler D, Swaab DF, Windischberger C, Kasper S, Lanzenberger R. 2014. White matter microstructure in transsexuals and controls investigated by diffusion tensor imaging. Journal of Neuroscience 34(46): 15466-15475.
 Rametti G, Carrillo B, Gómez-Gil E, Junque C, Segovia S, Gomez Á, Guillamon A. 2011. White matter microstructure in female to male transsexuals before cross-sex hormonal treatment. A diffusion tensor imaging study. Journal of Psychiatric Research 45: 199-204.
 Roberts AL, Rosario M, Slopen N, Calzo JP, Austin SB. 2013. Childhood gender nonconformity, bullying victimization, and depressive symptoms across adolescence and early adulthood: an 11-year longitudinal study. Journal of the American Academy of Child and Adolescent Psychiatry 52(2): 143-152.
 Rothkopf AC, John RM. 2014. Understanding disorders of sexual development. Journal of Pediatric Nursing 29: e23-e34.
 Smith ES, Junger J, Derntl B, Habel U. 2015. The transsexual brain – a review of findings on the neural basis of transsexualism. Neuroscience and Biobehavioural Reviews 59: 251-266.
 [WHO] World Health Organization. [date unknown]. Geneva (CH): World Health Organization. Gender: definitions; [date unknown; accessed 2016 Jul 10]. http://www.euro.who.int/en/health-topics/health-determinants/gender/gender-definitions
 [WPATH] World Professional Association for Transgender Health. 2011. Standards of care for the health of transsexual, transgender, and gender-nonconforming people. International Journal of Transgenderism 13(4): 165-232.