I've just been called "unscientific" for saying that you cannot change sex

Erm... Babies? Anyone ever heard of any male animal suddenly growing ovaries and uterus?

I'm in a Facebook group of people who love nature and it's got a specific scientific slant / interest.
Scrolling through posts from a couple of years ago I noticed someone had posted something about how some lionesses grew manes in the absence of a male, and someone followed this by saying their hamster had been female but had spontaneously grown testicles and fathered some baby hamsters! As in produced sperm and mated with the other female.

Noone in the group questioned this.

A group of self proclaimed scientific people.

If the posts weren't years old I'd have challenged them, but I felt bigoted for thinking about trying after the event.

There are some creatures that actually do change sex naturally. They move from egg production to speed production, from one reproductive role to another. We can’t do that. The best we can do is surgeries and exogenous hormones to mimic becoming the opposite sex. But these do not actually change ones sex.

That it actually can change- because apparently also eye colour can change throughout life.

Well obviously, we potentially could change sex, if anyone could figure out how to do it. Some animals do it.

We obviously don't naturally, and no-one has figured out a way to make us do it. Whether a human is male or female is determined at conception, and does not change. We're not clownfish.

If we did have a way to do it, you can bet there would be a huge split between the people who actually had changed sex and those who were merely identifying.

The only reason there can be so much nonsense about how you define "trans" is because no-one is actually changing sex. Everyone is pretending, and all trans people are the same sex as they've always been.

(Do they think there are trans clownfish who are male but only identify as having changed sex, when they actually haven't? And you can't tell the difference between those and the fish who actually have?)

lols. Cause it is not clear cut. That's what trans and scientific people find funny:

Science is messy and complicated, so it’s best to steer clear of it and stick to a few slogans, such as “Sex is real.” (This one has the advantage of implying that trans people deny that sex is real, which makes them seem unreasonable.) Don’t, whatever you do, talk to actual biologists or psychologists currently working on the subjects of sex or gender. They are obviously interested in maintaining the trans-friendly status quo, and their testimony can be ignored. (Side note: you may have wondered whether people with intersex conditions complicate the issue. My advice? Acknowledge they exist, but in the next breath make sure to dismiss them as a negligible minority.)

There are animals (mostly fish) that change their sex. The difficulty with trans folk is there is observed sex, and then other things going on that make them who they are.... which means sex is not that clear cut.

Also chromosomes. Yes they cant change, but there are more than just XX and XY combinations, and other stuff in there as well.

Trouble with science - it ain't black and white. Which is kinda cool really.

Because the chromosomes don't change? Can you ask for hard evidence of a person who has changed sex?

Ask them how babies are born?