
If you’ve come here from the title to argue with me, welcome. Sit down, and I’ll make you a cuppa. While you’re waiting, check off the number of conditions you meet from my recent rhyming-couplet subscriber call, so you have a good idea of where I’m coming from.
Here you go. A good British brew, and do help yourself to a biscuit.
Okay, let’s have a chat. Well, I’ll chat, you munch. We don’t want you spraying biscuity tea everywhere. Though you might do that anyway when you hear what I’m about to tell you.
It’s a couple of years ago. One of my offspring mentions, in a stream of conversation,
“We are all female at conception, anyway.”
“What?”
“We’re all female at the start. Then some of us become male.”
“No, that’s rubbish. Where did you get that?”
“The internet. There’s a scientific paper.”
“What? No, no, no. It’s basic genetics. You know I did genetics at university, right?
“Yeah, Mum, you never stop telling us. You nearly got kicked out for non-attendance, and then you got a first.”
“I’ve maybe only mentioned it a couple of times, surely?”
“Whatevs.”
“Can you really not be bothered with that last syllable?”
“Whatever, Mum, come on, what did you want to tell me?”
“Okay. So we all have 46 chromosomes: 23 from our mum, 23 from our dad; 23 pairs. The pair that determine biological sex are a bit different from all the rest, in that they are completely different shapes. Our mums can only give us the one shaped like an X, because that’s what she’s got, two ‘X’s, one from her mum and one from her dad. It’s the two Xs that made her female.”
“There’s more to it than that. I’ve been reading—-”
“You mean when it goes wrong. Let’s get the basics sorted first. In the normal run of things, our mums can only give us an X, but from our dad, we can either get an X-shaped sex chromosome or a Y chromosome, which isn’t shaped like a Y, more like a blob.”
“A blob?”

“Yes, a blob. It hasn’t got much on it. This is why men are actually, genetically, more fragile. The male chromosome pair is XY, so the dad has one of each in every cell in his body. When sperm —”
“Don’t say ‘dad’ when you’re talking about sperm.”
“Sorry. Okay. So when sperm are created in the testes by a process called spermatogenesis, one of the guy’s cells, with its full 46 chromosomes, splits into its pairs, two sets of 23, and each of those sets will either have the X chromosome he got from his mum or the Y chromosome he got from his dad.”
“Okaaaayyy…”
“So the egg has 23 chromosomes, and the sex chromosome is always an X. And the sperm has 23 chromosomes too, and the sex chromosome is either an X or a Y. So whatever sperm reaches the egg and burrows through to the nucleus first, that’s what determines if you’re male or female. If you get a Y in that mix, you’re male. From conception. We don’t ‘all start female.’”
“Okay, but people are saying we do.”
“Well, people are wrong.”
“You want to watch Traitors now?”
“Sure.”
A year passes. Then one of my favourite feminist Instagrammers says the same thing. FFS! What is going on?
I ask in the comments where she’s getting her information. She links me to this chapter in Exploring the Biological Contributions to Human Health: Does Sex Matter? (answer, yes it does):
All human individuals—whether they have an XX, an XY, or an atypical sex chromosome combination—begin development from the same starting point. During early development the gonads of the fetus remain undifferentiated; that is, all fetal genitalia are the same and are phenotypically female. After approximately 6 to 7 weeks of gestation, however, the expression of a gene on the Y chromosome induces changes that result in the development of the testes.
Ah. She has misunderstood it. She doesn’t know what phenotypically means. I explain what this paragraph is really saying; it means it looks female. It doesn’t mean is female. She argues with me as vociferously as if I were standing outside her house with a can of petrol in one hand and a lighter in the other.
I stay polite and rational. She stops responding. Ah well, I think. Instagram. Hardly an intellectual’s paradise. But I thought she was fairly savvy. What the fuck is going on? Why is she so invested in this completely fake fact?
One answer to that can be found in one of my favourite books about the real-world results of confirmation bias: Mistakes Were Made But Not By Me. If you commit wholeheartedly to one side of an argument, it can very quickly become impossible to change your mind.
Roll on a couple more years, and here I am on Substack, which truly is an intellectual’s paradise. People here read deeply, think critically, understand nuance, and are able to debate with civility. So I am a little shocked last week when one of my favourite science-friendly writers (I’ll spare him the blushes) restacks a Note saying words to the effect that Trump’s recent Executive Order has made all men trans because it wants to define everyone’s gender as their “sex at conception” and “we all start female”. Oh no, not you, Mike!
I respond to his Note with a comment explaining why it isn’t factual, and to my (intellectual) relief, he says he’ll remove it until he has done his own research.
But the next day, another writer I respect and subscribe to,
, posts ‘Trump’s Definition of Gender Accidentally Makes All Men Trans (Congrats!)’ (subtitle: If we’re being scientific). Oh no, not another one! Liz has nearly 30,000 subscribers. This post currently has over 250+ likes. So again, this fundamental untruth gets a boost. And it gets worse. I now see that The Guardian, a paper I used to subscribe to, and have written for, has gone for the same counter-factual take, quoting the same misunderstood source.As we know, a lie will fly around the world while the truth is getting its boots on,1 and this one has apparently huge appeal among people who would, I imagine, position themselves — like me — as people who want a kinder, more tolerant, more harmonious world.
Liz’s article is paid comments only; the comment I read were all wholly in agreement, and in my experience, comments aren’t the right medium for proper counter-arguments, especially when people are super-invested. So this article is my response to her post, the Guardian article, and every other person who currently believes “we are all female at conception”. And if you care about making this world a better place — which can’t be done on false foundations — I hope you’ll take it seriously, and share it widely. Let me lay it out.
Genotype, phenotype and karyotype
“Genotype” means what genes you have for a particular characteristic. With eye colour for example, a person might have the genotype Bb where ‘B’ is the dominant brown eyes and ‘b’ the recessive blue eye gene. With eye colour, because the brown gene is dominant, BB and Bb individuals will be brown-eyed adults. Only bb individuals will be blue-eyed. When first born, Bb will have (as all babies have) blue eyes: temporarily, that is her phenotype. Within a few weeks and for the rest of her life, her phenotype is brown-eyed. But she can get pregnant by another brown-eyed person, and so long as his genotype is Bb (and not BB), they have a one in four chance of having a blue-eyed baby (bb).
Phenotype is purely about physical appearance. So saying that until they are 6-7 weeks gestation, male and female embryos are phenotypically female means they look the same. The external genitalia have not formed yet, so they are not obviously male.
But they are not obviously female either. Here is a 6-7 week human embryo. This one is 1.6 cm long, just over half an inch. The size of your middle fingernail. The legs haven’t even developed yet. Nor have the fingers, the nose, the mouth. Phenotypically, it’s not that different from the early embryo of any other mammal. Yes, there’s no penis or scrotal sac, but nor are there external female genitalia. How developed are the labia, the clitoris?

The more I think about it, the more I think the author describing a 6-7 week embryo as “phenotypically female” is as sexist as dividing the human population into “men” and “non-men”. They seem to be saying that Penis+Balls = phenotypically male and No Penis+Balls = phenotypically female. As if female genitalia are equivalent to nothing.
But let’s be clear. Phenotype is irrelevant. What an embryo looks like at this stage does not reveal its biological sex. You can’t judge whether it is genetically male or female by its looks. But you can tell its biological sex (if you don’t mind destroying its viability), by taking a DNA sample. In other words, by checking its karyotype.
Yes, there is a tiny proportion of the population who has a DSD (Disorder of Sexual Development), which leads to some people having karyotypes different from XX or XY. Or they might have an XX or XY karyotype but lack a particular gene needed for normal sexual development. DSDs affect 0.018% of the population, according to this source; some estimates are higher because they include additional syndromes. Phenotypes change in some of these cases: there is a DSD where a child will appear female at birth but, with the onset of puberty, under male levels of testosterone released by internal testes, will become the male they have been, genetically, since conception. In other words, though they looked female, their genotype was always male, and with puberty, their phenotype changes to match their genotype.

Although it looks like DSDs complicate the matter, in one very straightforward way, they do not. DSDs are not relevant to the argument I am making here, which is that it is simply not true that “we are all female from conception.” Approximately half the population does not have a DSD, and is a very clear XY from conception in every cell of their body. Their XY karyotype triggers the development of a body whose reproductive system, in the vast majority of cases, will eventually create sperm. These individuals were not “female at conception”, and it is really important that we stop spreading this untruth.
Why?
Because we want to live in a better, saner, less chaotic, more tolerant world.
We can’t build a better world by spreading misinformation and misunderstanding. If we’re infuriated by the “fake facts” generated by those whose actions and amorality we abhor, the answer is not to generate and spread fake facts of our own.
This isn’t about politics. This is about staying grounded, at a time of chaos, in what is real and what is not. What is true and what is not. Things that are fundamentally untrue are not good ammo.
You might as well go around saying all dogs start out as cats. I bet dog embryos and cat embryos look very similar in the early stages, and that is what is being said here. When they are barely more than a cluster of cells, male embryos and female embryos don’t look different.2 Until we put them under a microscope and look at their DNA. And then they do.
We have to do better than this. Please, good people, do better than this.
Post-it Notes
This week I have:
Lost 2.5 days to a headache
Taught a workshop at UCL
Completed my tax return
Attended a (wonderful) woman’s (wonderful) wake
Taught the first of my last three workshops for The Poetry School
Posted this 48 hours later than scheduled due to all of the above
Over to You
As you know, I like to keep this a politics-free space because we are focused on post-asteroid thriving rather than the dinosaurs. Let’s see if that’s possible this week when the untruth I’m critiquing is being used as political ammo!
Have you been exposed to the falsehood “we all start female”?
If the answer to 1 is YES, did you believe it?
If the answer to 2 is YES, have I managed to persuade you otherwise?
What’s your favourite biscuit?
What’s your longest-ever headache?
What’s the best wake you attended?
What’s an untrue thing that people say that really gets your goat?
Should we all start keeping our goats in the backyard where people can’t get them?
Many versions of this proverb are delightfully explored here, starting with Jonathan Swift’s early version, “Falsehood flies, and the Truth comes limping after it; so that when Men come to be undeceiv’d, it is too late; the Jest is over, and the Tale has had its Effect…”
I shall never forget the weatherman who confessed on Would I Lie to You that until he was in his thirties, he thought lambs were different animals than sheep.
You explain this very well. Your calm, educated review of the subject will be accepted by most, but those with a misinformed view will persist in bad science. That said, our kindness to one another will strengthen our connections to each other, and respect for all by all should always be our goal. You have done that in your writing by stressing the science.
In my opinion, the expression of gender traits is very complex and could be compared to a sliding scale. We are what we are because of genetics, environment, or chemical makeup. Our challenge is to love and accept the other, not because we are forced to but because of our basic humanness—just love.
My daughter and I had this conversation, but as I never was a geneticist, I didn’t have the ability to explain why I thought she was wrong. I know enough to understand X and Y and what makes a baby male or female. And then I saw funny memes of it being used to make fun of Trump. I think especially women are fairly scared of the things/laws Trump might create around women. He has threatened all sorts which look like undoing all the good women’s movements over the last hundred years or so have done. But truth is truth and that’s always the side I want to be on. So I will put my daughter right - in a non confrontational way :)
One day I aim to have a garden large enough for a goat or three ;)