I don't know who needs to hear this, but please do not fall for teleological biology

I would like to apologise if this is too long or not suited for this community. Feel free to remove it/correct me on anything that is wrong or offensive.

TLDR: Sex is not determined by which type of gametes your body is "organised around" making. This is teleological biology, which isn't empiric. If you're going to argue with someone over this, do not try to argue around the argument by saying something along these lines:

1. Sex is biological, but gender isn't.
2. Sex is binary, but gender isn't.
3. Yes, but trans people should be able to get care regardless.

While these arguments are in good faith, they do not address the core issue with the argument and can give way to bigoted arguments against trans and other groups of people.

Don't fall for the "Sex is defined by whether your body is organised to produce large gametes (female) or small gametes (male)" argument. I've heard this talking point being used in a lot of spaces online, even by other trans people, and this is simply false. I'm not even sure if writing this is a good idea, or will even amount to anything. However, I've seen this argument be entertained in far too many spaces, without little to no refutation of the actual point. I don't feel comfortable not saying anything about it.

For those that are a bit more philosophical, you might have already figured it out, but didn't know what this type of argument was named (or maybe you did. I didn't). This is written more for those that might not realised why this argument is wrong and harmful.

I'll start with why this argument (and some replies that tried to sidestep it) is harmful for trans people. If you already understand that, you can skip to the next section, where I go through my arguments against it.

How is it harmful to trans people (and other intersectional groups)

This of course reinforces the idea that there are only two sexes. It ascribes a model, some sort of essence, that a person must follow, either willingly or unwillingly. Either way, it is supposed that the person would "feel right" following said norm. This is true, whether or not the person arguing this point intended to or not. It sells this sort of "supposed" body that is to be the norm.

Like I mentioned, the person arguing for this might not see the harm this causes. This doesn't stop it from being harmful. Even if they say that's not what they intended, this is what giving credit to this argument implies.

One might be tempted to argue against it with the following counterpoints, which are done in good faith, but still have harmful implications:

1. Sex is biological, but gender isn't

   This is wrong, not because the sentence alone doesn't hold truth, but because it implies that there is some truth in the argument that we're supposed to make gametes. Sex is somewhat based on biology (there are certain social factors that are to be considered), but the teleological argument isn't arguing for biology anyways. This is just saying: "Yeah, you're right about sex, but not gender", but that's not true. Implying this also ascribes a fixed sex to trans people, (saying that trans women are necessarily male, or trans men are necessarily female, which isn't true)

2. Sex is binary, but gender isn't

   I consider sex to be, at worst bimodal, at best, a combination of various sexual traits (which might not point towards male/female). There are points to be argued against bimodality (for example, how can someone be "more male" or "more female" than others? I still haven't figured that out). Nevertheless, sex is not binary. Any way in which people have tried to define it to a binary fails, because there are countless counterexamples. Saying this could not only de-legitimise the identity of those that do not want binary sexual characteristics, but also push the rhetoric that encourages correctional surgeries done to intersex people without their input.

3. Yes, but trans people should be able to get care regardless

   Of course, yes. But only the last part. This argument again only reinforces the argument that "trans women are women, but male", or vice versa for trans men. This is not true. Sex (biologicaly) is a combination of attributes, primary or secondary. Hormones and surgery do change these secondary characteristics. I admit I feel a bit unqualified to continue this train of thought, but this leads to two possible conclusions. Either you consider trans people to be the sex they say they are at birth, or you acknowledge that trans people can change sex, or even both. This is, of course, considering that not every trans person wants to go through medical transition, and that not all trans people necessarily identify with a sex even if they transition or not. Again, there is a social aspect to sex that is often left out of the conversation. I still make this argument for those that try to ascribe a sex to someone in order to invalidate their identity.

Why is this argument wrong

This argument relies on teleological biology. It is a premise that all beings are configured/made for a certain goal or purpose. This goal can go from something as incredible as "spiritual enlightenment" or "to fulfil god's will", to something a bit more complex to address, like "survival" or "reproduction". More information about here on this Wikipedia article: https://en.wikipedia.org/wiki/Teleology_in_biology.

In short, this is completely wrong (if you believe in the theory of evolution. If you don't idk why you're even reading this). The human body isn't "organised around (place anything here)". Saying that implies purpose and will. That the human body is "supposed to produce gametes" is not only a bigoted concept that leads to the equation humanity to one's ability to reproduce, but is ascribing a purpose to something that has none.

I wrote two examples in another comment (one analogy and one more close to the topic), but I'm just gonna put it here:

Take a meteorologist providing forecast for tomorrow’s weather. With whatever means they collected data, they assert: “it will rain tomorrow”. Tomorrow comes, and it is sunnier than ever. Scientifically speaking, the meteorologist cannot say “the atmosphere failed to make it rain, even though it tried to”. If this seems absurd, it’s because it is. In that case, the meteorologist is supposed to adapt their model into something that more accurately reflects the data given.

The problem is even more visible once you take the example of an intersex person, born with XY chromosomes, but with a uterus (Swyer’s Syndrome). One person could base themselves on the XY chromosomes to say that the person was “supposed to produce small gametes”, as you put it. Another person could base themselves on the fact that (with medical intervention) the person can produce large gametes, therefore, that the person was “supposed to produce large gametes”. Either answer is wrong, since the body isn’t actually “supposed” to do something. It just does what it does, regardless of what you think it is supposed to do. The correct thing to do would be to say: “They aren’t supposed to do something. If our model is to be empirical, it should reflect what is actually going on with their body, not ascribe a will to it. We should rethink how we see the definition of sex”

Again, sorry if this feels long winded, but I feel like this is something important to mention. But as always, don't argue with someone that is of bad faith!

edit: After thinking a little, this should be marked with a content warning. Sorry to anyone that stumbled upon this.