Boy Or Girl? What’s The Science Behind Transgender?

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Germaine Greer had her say on transgender people, now it's Science's turn.

Please be advised that the following article is about a controversial subject and goes into detail about sexual identity and references sexual organs.

Outspoken second-wave feminist Germaine Greer recently caused controversy by claiming that transgender women “can’t be women” and “just because you lop off your penis…it doesn’t make you a woman”.

Of course in a sense she is absolutely right. Genitals alone do not define your gender. Cancer or severe injury can result in the necessary removal of testes or penises for example. Yet the men that undergo these procedures are no less men afterwards. Medical vaginectomies, or the removal of part or all of the vagina, does not mean that a woman stops being a woman. Obviously surgery alone does not define your sex. But that’s not what Greer meant.

So what does define your gender? The simplest and most common sense answer is the genitals that we are born with. Boys have penises, girls have vaginas. Nature determines your sex.

Except when it doesn’t.

The Problem With Genitals

You may have heard recently about something unusual that happens in a small village in the Dominican Republic. One in 90 children there that are born girls are not destined to stay girls.  Once these children start puberty, they grow penises and testicles. They are known locally as guevedoces, literally “penises at age twelve”. Scientists call them pseudohermaphrodites and Dr. Julianne Imperato, one of the first to study the guevedoces, discovered that the startling transformation was due to an enzyme deficiency.

We all start out as female in the womb. At the risk of over-simplifying, boys then get a shot of testosterone that changes the clitoris into a penis and changes the vagina into testicles. Guevedoces don’t have as much of an enzyme called 5-alpha-reductase. It’s this enzyme that converts the testosterone into the male genital building hormone dihydro-testosterone. At puberty, the “girls” undergo another surge of testosterone that belatedly causes the outward change into boys and ultimately men. The phenomenon is not confined to the Dominican Republic and further cases have been reported in Papua New Guinea.

The condition that results in the guevedoces’ late transformation is one of a variety of conditions that come under the umbrella term Intersex. Simply put, an Intersex condition occurs where a person’s sexual anatomy doesn’t fit the typical definition of male or female. It can mean that a person’s genitals look different to the norm for their sex, or that the genitals look like the norm on the outside but the internal anatomy may more closely resemble the opposite gender.

So children are not necessarily defined by the genitals they are born with. Can we find a better definition for gender?

The problem with genitals!Click To Tweet

The most fundamentally basic of all is to define gender from our chromosomes. Males have XY chromosomes and females have XX chromosomes. So, even though prepubescent guevedoces don’t have male genitalia they would probably have XY chromosomes. Chromosomes define gender.

Except when they don’t.

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The Problem With Chromosomes

The world-renowned biologist and atheist Richard Dawkins weighed into the Greer controversy on twitter, saying “Is trans woman a woman? Purely semantic. If you define by chromosomes, no. If by self-identification, yes. I call her ‘she’ out of courtesy.”

So Dawkins obviously defines gender by chromosomes. However, other scientists think that that’s too simple. For example, some women may have an Intersex condition known as Androgen Insensitivity Syndrome (AIS) where genetically they have XY chromosomes. Symptoms of the condition vary but a woman may go through her whole life never knowing that she has AIS, identifying as female and undergoing changes at puberty consistent with being female. Similarly, men with an Intersex condition called de la Chapelle Syndrome have XX chromosomes, yet may be ignorant of the fact.

People with AIS and de la Chapelle syndromes are infertile, but infertility can be caused by many things.

“In light of this, sex should be considered not a product of our chromosomes, but rather, a product of our total genetic makeup, and of the functions of these genes during development.” – Dr. Charmian Quigley, Medical Advisory Board member for the Intersex Society for North America.

So becoming male or female is a complicated process that relies on many things happening together. Chromosomal makeup, what genes express and when, the cocktail of hormones and enzymes being released and reacted to. It’s a complicated business.

The Problem With Identity

People with Intersex conditions differ from people who are Transgender. Transgender people generally have hormones, genitals and chromosomes that seem consistent to one sex but they believe themselves to be of the opposite sex. Intersex conditions manifest as some sort of physical mismatch between the genders that shows up in chromosomes, internal sexual anatomy or genitals that may differ from the norm. There is crossover between the groups but they are also distinct.

So, a transgender person may look male, have XY chromosomes, have the same male sex hormones levels and undergo male changes during puberty. Yet all the while the person feels like a girl trapped inside a boy’s body. Similarly, a female may identify as male. Why? Is it all in the head? Possibly, but that doesn’t mean that it’s not real and the head is a great place to start searching for answers.

 “Medical care of transgender patients, including surgical and hormonal treatment, has largely been met with resistance by physicians in favor of psychiatric treatment, owing to misconceptions that gender identity can be changed.” – Boston University School of Medicine

Surprisingly, there are not a lot of studies on transgender issues. But those that have been carried point towards actual differences between transgender people and their cisgender peers. Wait, before we get into the science, we need to define a couple of terms. Transgender, or transsexual, can refer to someone who may feel like they’re a member of one sex trapped in the body of another or that their birth gender is just wrong somehow or may refer to someone who has an intense desire to be a member of the opposite sex. Cisgender refers to someone who identifies with the gender that they are assigned by birth.


A study led by psychologist Kristina Olson looked into gender identification of children using implicit and explicit measures. In other words, the study used self reporting questions as well as techniques designed to test how deeply a thought, feeling or belief is held. Were transgender children lying to themselves and others or did they truly believe that their gender was misaligned? The study consisted of two groups, one had 32 transgender children ranging in age from 5 to 12 years old. The other group had the same number of cisgender children of the same ages.

The study used different measures including the Implicit Association Test (IAT) to explore gender identification. IATs are standard tests that judge the speed in which subjects respond to questions and prompts. The children had to identify themselves with one or other facet of gender, the time taken to answer was noted. How “automatic” the answers are shows how deep the conviction is. Many questions were asked but essentially they were all variants of one over-riding question; “Are you a boy or a girl?”

The results from both groups were indistinguishable. Girls identified as girls and boys identified as boys, it was impossible to discern from the data alone which group was which. The physical gender did not impact at all on the data.

“While future studies are always needed, our results support the notion that transgender children are not confused, delayed, showing gender-atypical responding, pretending, or oppositional — they instead show responses entirely typical and expected for children with their gender identity,” – University of Washington study lead by Kristina Olson.

Of course, the size of the study was small and the transgender children were in supportive families. This may or may not have influence on the study. Olson is planning to repeat the study using larger number of children.

Neuroscience has also studied the brains of transgenders with interesting results. There are physical differences between the brains of males and females, which brains do transgenders align more closely with? A Spanish team of neuroscientists at the National University of Distance Education in Madrid used MRI scans to examine the white matter in four key regions of male, female and transgender brains.

One study involved 18 female-to-male (FTM) transgender people who had had no treatment. They compared them to scans of 24 male and 19 female cisgender people. The brains of the FTM transgender people resembled the male more than the female brains.

In a second study they compared 18 male-to-female (MTF) transgender brains to 19 male and 19 female cisgender brains. The results were surprising in that the transgender people’s brains were halfway between the male and female brains.

transgender quote by Laverne Cox

So there is conclusive proof that something different is happening in the brains of people with transgender. An Australian study in 2008 found that male-to-female transgender people have a different receptor gene for testosterone or androgen than cisgender males. Testosterone and androgen are hormones which determine maleness. The researchers conclude that this difference in the receptor gene can result in a “more feminised brain”.

A review of the existing studies performed by the Boston University School of Medicine determined that the evidence was strong enough to recommend that medical professionals should no longer regard transgenderism as a psychological condition. Rather the review concluded that “there is increasing evidence of a biological basis for gender identity.”

The Problem With Society

Nearly 80% of Irish transgender people have considered suicide and 40% have attempted suicide at least once. That figure is mirrored in the US where 41% of American transgender people have attempted suicide. One in fifty transgender Americans have been violently assaulted in a doctor’s office.

Germaine Greer accused Caitlyn Jenner of transitioning to a female because “he/she wanted the limelight that the other, female, members of the family were enjoying and has conquered it, just like that.” Caitlyn Jenner claims that she knew from a young age that she felt female. Who should we believe?

The simple fact of gender is that it’s complex. There are straight, gay, bi- and asexual men who range in attitude and/or appearance from camp to macho. There are straight, gay, bi- and asexual women who range in attitude and/or appearance from butch to princess. There are girls that turn into boys. There are men and women that differ anatomically from the norm. There are people who do not identify with the gender that they are born into.

Surely our society is strong enough to incorporate everyone without forcing people to conform to a simple stereotype? The science is clear, transgender people do not arbitrarily choose one day to switch sex. There is more to it than that. Isn’t it better to have more happy, adjusted people than to stick to over-simplified concepts of gender?

What do you think? I acknowledge that this is a controversial subject and I am open to listening to alternate views. However, as the issue concerns real people with real feelings please refrain from hurtful or derogatory remarks. Thanks!


    • The Intersex Society of North America
    • NCBI – A Case of XX Male Syndrome, Lisker et al. 1970
    • Daily Telegraph -The astonishing village where little girls turn into boys aged 12
    • ABC News – Cardiff University rejects petition to ban Germaine Greer from lecture over views on transgender people
    • Independent, UK – If Germaine Greer’s views were radical, this transgender woman wouldn’t have been sent to a men’s prison
    • Boston University – Review article provides evidence on the biological nature of gender identity
    • APA – Transgender Kids Show Consistent Gender Identity Across Measures
    • Neuroscience News – Sex Hormone Levels Consistent With Birth Gender in Transgender Teens
    • – Science Just Proved That Being Transgender Is Not a Phase
    • ABC Science – Transsexual study reveals genetic link
    • Irish Times – Study finds almost 80% of transgender people have considered suicide
    • Live Science – High Suicide Risk, Prejudice Plague Transgender People
    • Vanity Fair – Caitlyn Jenner: The Full Story

This post has been edited to reflect opinions expressed in the comments.

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Boy Or Girl? What's The Science Behind Transgender?
Article Name
Boy Or Girl? What's The Science Behind Transgender?
Are transgender people just choosy or can people be born into the wrong gender? It's time to check out what science has to say.
Dermot Barry
What does science say about transgender people? Is gender fixed at birth?
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