Let's Talk About Sex: The Science

One of the reasons discussions around trans people have become so challenging is because over the past century we've become used to looking to science to tell us what the answer is. The rise of popular science reducing very complex scientific processes to easily digestible simplifications for public understanding has given people the impression that science can provide answers to almost everything and it's only a matter of time before it answers everything else.

Any scientist worth their salt though will tell you that certainty in science is rare and the more you know about something the more your realise there is still to know. Would it surprise you to learn that Einstein's Theory of General Relativity

and Quantum Theory are actual incompatible with each other? Most people think that's settled science but physicists have been searching for a unification theory for decades. They both can't be right but they are also both right as they're able to explain the world as we see it. Most likely they're both partially right and one day we'll discover the missing part of the puzzle.

Richard Feynman and Alber Einstein

the fathers of modern physics

My point is science is complex and incomplete and messy. Full of wonder and bafflement as well as clairty and understanding. That's its beauty but also in failing to express that complexity and trying to help people comprehend difficult concepts it's failing.

Biology is no exception to this complexity. As scientists we like to classify things to make it easier to look at trends and groupings which can help our overall understanding. Sex is one of of those groupings that looks at different properties between different members of the same species. How does that classification work? Well it's really complex. Scientific America tried to visualise that complexity with this diagram.

Asleep yet? Probably. I'll be honest, I'm a doctor with an extra degree in biomedical sciences and it hurts my head trying to fully understand that diagram. So the human response to that complexity, because no one likes feeling as though they don't or can't understand something is to react to it with something along the lines of

"Oh for goodness sake. It's not hard, men are men and women are women, that's just common sense, stop it with this nonsense"

And so here we are with a common sense position that's total scientific nonsense but easily digestible to the public.

So what does the science say? I'm going to miss out some of the very deep complexity in the hope of giving you some idea or what's going on but not completely losing you!

I'm also not going to labour points about people who don't neatly fit into these categories, i.e. intersex people, who have their own story to tell about how a binary world makes their life difficult.

Lets start simple:

The body produces everything from DNA. Think of that as the alphabet and genes as sentences. Those sentences then need some grammar and that changes how we express those genes. Like in acting you can take the same sentences and change where the full stops and emphasis is and you completely change how it sounds. That's called epigenetics. All of those sentences are then put together in collections of genes called chromosomes. Think of those as the books. All of your chromosomes together form a library. You can already see that small changes at any one of these levels is going to make a significant difference. How all of these things come together to produce you as a human is called your phenotype.

When we try to classify sex we usually start with the phenotype. What we can see and observe. The differences between males and females is called sexual dimorphism. Which in humans is actually quite small compared to some species.

Primary Sex Characteristics: These are the things we're born with. Your external genetalia, your reproductive organs. Females are generally born with a vagina, a uterus and ovaries containing ova. Males are generally born with a penis and testes and will have the capacity to produce sperm. These are the things that when you pop out of your mother a healthcare professional looks at and exclaims. "it's a Boy!" etc.

Secondary Sex Characteristics: These develop as we get older and enter puberty. For Females that includes breast development, periods, hyper extensive elbows (I know!) and some body hair growth. Males however start producing sperm, grow beards and extensive body hair, more muscle mass, deeper voice.

Physiological Sex: There are differences in how bodies function in humans. They're relatively small differences but important. Females have lower red blood cell counts (which carry oxygen) and have different kidney function mainly due to their lower muscle mass. Males and females have completely different sex hormone profiles, although everyone has oestrogen, progesterone and testosterone, the amounts of each is completely different between the sexes. There are significant and important immune system differences too.

Chromosomal and Genetic Sex: Humans in general have two pairs of each chromosome, 46 in total or 23 pairs. The 23rd pair are called the sex chromosomes and under a microscope they look like an X or a Y. Females generally have 2 copies of the X chromosomes and Males Generally have one X and one Y chromosome.

These chromosomes carry certain genes that either continue development in the womb as a female or express genes (SRY) that shift that path onto the male path of development. It is worth noting though that around 1 in every 1000 births will have chromosomes or genes that don't match the appearance of someone on the outside

I could go on but that is hopefully enough to show you the complexity of biology. You will always find examples in every category where someone who you think obviously fits in the 'Male' or 'Female' box, who on further examination or testing doesn't.

So how does this relate to trans people? That also depends on whether they've medically transitioned or not. As we transition our, secondary sex characeritics change. Trans women grow breast tissue body hair reduces, muscle mass decreases and body fat distribution changes. Trans men grow beards, get a deeper voice gain muscle mass etc. Physiologically trans women become more like cisgender women and trans men more like cisgender men. Of course somethings don't change like primary sex characteristics, although many do surgically alter those. Most of us never have and never will have our chromosomes tested.

So what is my sex? if you base it purely on 1 or 2 of these criteria you'll continue to call me male. However if you take all of these factors together in their entirety then you'll see that my phenotypic sex is much closer to that of a female than a male now. To only take 1 or 2 factors in consideration is to look at the world on a black and white television. Why would you do that when you can see the world in full technicolour glory?

Am I the same? Absolutely not, I don't claim to be. Scientifically I'm a kind of third sex but in a world where only two options are available to me, I know where I should fit.