The delusion! Biology is not a work in progress, nothing has changed since we were neanderthals.
Well no, material reality is what it is, but the framework of our understanding changes.... that's kind of the deal with science isn't it?
Science is surely the means of describing and studying our material reality - what we know currently doesn't dictate our material reality - we don't understand things to be one way and then if we observe them to be another say "nope, can't be happening, science says no".
As far as I can see we study that thing that appears to be anomalous to see whether or not we can come to understand it as some sort of anomaly, or if indeed we need to reconsider the whole framework of our understanding.
Worth remembering that homosexuality was once considered a psychological condition - for a long time in fact - because obviously at the time the framework of our understanding was such that there was only one "sexuality", and anything else must be an anomaly - a "condition".
Not so these days; these days we recognise that human beings have the capacity to experience and exhibit alternative sexualities to mere heterosexuality. The framework of our understanding has been updated.
So we observe that people report "being in the wrong body", or whatever else. It seems to me that currently science is rather open to the possibility - it may be sceptical, I don't know, but it certainly seems open - open to the possibility that this may not be an anomalous psychological disorder, and may actually be a naturally occurring biological phenomenon. In which case it wouldn't be appropriate to call it an illness, and it would be appropriate to update the framework of our understanding.
Society seems to think that's the way we're going... but obviously on a person by person level the jury's still out. And between scientists as well, no doubt.