No; 99.9% of the time, people present themselves according to their biology.
Except how they do that varies, and has always varied.
Also, it's probably more like 99/98%.
Also, as we have already established, you cannot assess their biology - you can only assess their appearance or what they tell you.
There is nothing to stop them from lying to you, and there is no way for you to know; as it has always been.
Right, so restricting classifications to biology is useless. Why not simply accept that we don't classify people by biology, and that we use social definitions?
And how does this manifest itself in mammals that are not human?
The same. Some mammals are also born with a mix of feminine or masculine traits, or both or neither set of genitalia.
Not that it would matter. We can still distinguish ourselves through social definitions and language - things that no other mammals can do (or, if they do, they keep it really quiet).