[Ed. – An excellent survey of the relevant points.]
Modern science shows that our sexual organization begins with our DNA and development in the womb, and that sex differences manifest themselves in many bodily systems and organs, all the way down to the molecular level. In other words, our physical organization for one of two functions in reproduction shapes us organically, from the beginning of life, at every level of our being.
Cosmetic surgery and cross-sex hormones can’t change us into the opposite sex. They can affect appearances. They can stunt or damage some outward expressions of our reproductive organization. But they can’t transform it. They can’t turn us from one sex into the other.
“Scientifically speaking, transgender men are not biological men and transgender women are not biological women. The claims to the contrary are not supported by a scintilla of scientific evidence,” explains [Dr. Lawrence] Mayer.
Or, as Princeton philosopher Robert P. George put it, “Changing sexes is a metaphysical impossibility because it is a biological impossibility.”