Sex is not binary

As a trained scientist, I am often told that I am very logical in my thought processes. That may or may not be true, but what I am sure of is that I love hard facts. Facts that have solid research behind them. I therefore get very agitated when I hear people say things or I read things that have little evidence, or at best, misconstrue what evidence there is.

Let’s take something like your sex; we have male and female, right? Everyone knows that. But is that really true? Is the world that simplistic? Well, let us deconstruct the problem of what sex is, and what we mean by male and female.

To do this I want to start by taking you through what was called in my youth, a “gedankenexperiment” or thought experiment. The first part of this is to think about yourself and what makes you, you! The way to do this is to imagine that you can replace any single part of your body with a robotic part. Take your left leg, for example, and imagine replacing it with a robotic one. Are you still you? I would hope so. Exchanging your left leg will not affect who you are.

Now let us try other body parts. Which part would you have to change to not feel yourself anymore? I think it’s not too much a leap of your imagination to realise that the vital part of your body is your brain. Everything else is pretty much replaceable, but your brain and its function make you who you are.

So now repeat the experiment but replace the robotic part with a part from the opposite sex to which you were ascribed at birth. So, for example, I was assigned male at birth, so if I simply replace each part of my body with a female part, at which point do I stop being my assigned birth sex and become the other sex? The Frankenstein-like thought experiment is a bit weird and the hybrid person may feel strange, but the brain still controls who you are. If I replace everything but my brain which sex am I? I would, in my core, feel I was the same person even when I look at myself in the mirror and see a different body.

The result is not rocket science. We know who we are because of the brain and not because of other parts of the body. Our brain is what makes us who we are. As the neurobiologist Dick Swaab said “Everything we think, do, and refrain from doing is determined by the brain. The construction of the fantastic machine determines our potential, our limitations, and our characters; we are our brains”

Let us park that part of our experiment and come back to it later. Now consider how we assign sex. At the moment of birth someone looks at our genitals and most of the time says, “it’s a boy” or “it’s a girl”. Of course, for around 1.7% of births, a decision cannot be made and so we have intersex people. It’s been pointed out before that this is roughly the same percentage as redheads in the world. It is worth noting that we don’t force redheads into being blonde or brunette, yet society tries to force intersex people into the binary.

So, our present identification of male and female is based almost exclusively on the design of our external genitals. However, what if we have a person with male genitals on the outside but some female parts on the inside? Why are the visible genitals more important than the non-visible parts?

A good example of such a person was a man who, although having had a normal “male” sex life, at 37 years old found he had a working womb and was having periods — with blood passing out of his penis. A 70-year-old man with 4 children was found to have a womb. Neither of these were identified as intersex at birth.

So, we can see that just looking at the outside genitals can’t tell us everything about a person and it’s obvious that our view of intersex people is far from complete. Let us look deeper inside.

What about other sex markers, for example, chromosomes? Well, it’s not as simple as saying two X chromosomes gives a female and XY gives a male. There are many syndromes which cause genital and other structural differences, to the normal binary expectations. There are cases of women who had the internal and external genitalia of a woman who even had babies but were found to have XY chromosomes. Again we see that the picture of what makes a person male or female is much more complex than simply looking at external genitals.

Doctors now believe that individual cells can differ in their chromosomes — so at a cellular level we are all a mix of XX and XY chromosomes. We know that as a foetus develops, whether it is male or female is not under the control of a single gene but of opposing gene networks. At each stage, the tension between these causes differentiation to male or female, yet during each stage it is possible for the balance to be different and have male and female combinations. As Professor Anne Fausto-Sterling says, “What matters, then, is not the presence or absence of a particular gene but the balance of power among gene networks, acting together or in a particular sequence. This undermines the possibility of using a simple genetic test to determine “true” sex”.

The implication here is that simple genetic tests cannot necessarily determine your “true” sex (the quotes are Dr. Fausto-Sterling’s), so are we being at all realistic to say that a quick look at some external features of the body really tells us about this person? It seems like whenever we look in detail at sex markers, things become less black and white. I could go on talking about sex hormones, but you get the idea.

At this point in the narrative, most self-respecting scientists would be thinking at the very least that our view of binary sex is incomplete and at worse, wrong. Our bodies are just so complex and diverse that the more science delves into the details, the more we see the complexity unfold.

Now let us return to our first experiment where we saw that it was the brain that controls who we are. What if we could show that the brain function of an individual is different from their assigned sex, derived from their external genitals? In other words, if, for example, a person had a brain like a female and a body like a male, this person would by our first thought-experiment be female even though identified at birth as male.

Even though much of the brain is indistinguishable between males and females there is increasing evidence to suggest that, people who identify as the opposite gender to their assigned birth sex, actually have some brain structures and functionality more associated to their chosen gender.

Evidence from research published in 2012 shows that identical twins are more likely to both be transgender than non-fraternal twins, suggesting that there is a biological component to being transgender. Results from the 1990’s show that brain structures such as some types of neurones and areas of the hypothalamus differed in men and women regardless of whether the woman was a cis or a trans woman.

Research from the Netherlands shows that exercise “lights-up” distinct parts of the brain depending on whether the person is male or female. In this study trans men were shown to have the same areas excited by exercise as cis men. Other research on a brain property known as mean diffusivity, showed that trans people have a level somewhere between cis men and cis women.

It needs to be emphasised that much of this research is new and science is only just starting to understand the brain and it’s male/female character. It is probably best summarised by neuroscientist Professor Margaret McCarthy. She writes:

“…it is quite literally impossible for the brain to take on a uniform “maleness” or “femaleness”. Instead, the brain is a mix of relative degrees of masculinisation in some areas and feminisation in others. On average, there are likely to be some areas that are more strongly feminised in a female and others that are more strongly masculinised in a male, but averages are never predictive of an individual’s profile”.

So, let me try to summarise where we are. Many scientists and researchers believe that there is a biological underpinning to gender identity. Take, as one example, the Endocrine Society, the world’s largest organisation of endocrine clinicians or scientists. Their position is that “There is a durable biological underpinning to gender identity that should be considered in policy determinations”. The latest science also shows that some people’s brains, both structurally and functionally, are not congruent with their assigned sex at birth.

So, what are the implications? If, as the latest research shows, the brain structure and function of some people is incongruent from their assigned birth sex and more in-line with their gender identity, what does that say about how we should identify “birth sex”? We seem to believe that a person’s genitalia are more important than their brains and minds. Yet it is the brain that determines who a person is!

So clearly, the person is not the problem, but the simple method we use to define sex: external genitals. Now, one must ask, why do we still use such a definition from long ago, based on one simple criterion? It’s because the idea was cemented by stories such as “Adam and Eve”, at a time when the world was thought to be flat, the Earth was the centre of the universe and evolution was unknown to humans. Isn’t it about time we update our view of biological sex to the 21st century and leave ignorance from the past behind?

Sadly, like the Catholic church who fought Galileo in the 17th century, there are many people who profit from supporting this outdated view of biological sex. But just as Galileo was vindicated, science will win — perhaps not this year or even this decade, but one day it will.

I would like to finish with a quote from neuroscientist Gorge Kranz: “All available evidence points towards a biologically determined identity”. Kranz says, “In [transgender] people you would say there was a mismatch in the testosterone milieu during the development of the body and then during development of the brain, so that the body was masculinized and the brain was feminized, or the other way around.”

Perhaps we should all take a step back and look carefully at the facts when it comes to biological sex — after all, the science of a few thousand years ago is pretty outdated these days.