You get born with a snake or a vagina, there's no alternative there mate.
It doesn't even matter if you act like a female 100% - you are still a male, and vice-versa.
biologically, yes.. socially? not necessarily.
society won't call you a male if you genuinely look/act like a female, let's be real.
if you were in public and you saw a female acting like a female and doing female things, (regardless of whether it was actually a female or not) chances are you'd still refer to them as female.
transgender people already know that they're biologically male or female. that's exactly their problem. They don't want to conform to the social expectations of their corresponding love. Maybe wearing dresses appeals to a biological male rather than a t-shirt and some jeans. Or maybe a biological female doesn't like all the typical girly things and is more appealed by masculine things. Why should they be forced to conform to societies' "rules" and expectations of the two genders?
While I believe there are only 2 genders and 2 corresponding lovees, I do believe there's a gender spectrum with male and female as opposite ends, with the spectrum in between just being differing levels of masculinity/femininity.