In order to transition from one gender to another, there must BE two genders, since you can't transition unless the genders are discrete (separate) AND distinct from one another. Which means what? That a basic, rigid, standard, foundational definition or demarcation must be in place for each of the two sexes. (The word "sexes" is from a Latinate term signifying "cut into two".) In other words, you cannot identify as ANY sex unless there are standard criteria, qualities, characteristics, or traits which differentiate the sexes. My suggestion? The hip bone is the only one in the human body which is gender specific; if you have the one developed from XX chromosomes, then you're a female, and if you have the one developed from XY chromosomes, then you're a male. A thing must be defined by the most basic, unalterable aspect of it, thus the hip bone should be the defining trait for gender. And since people do not change their hip bones, no such thing as transgenders or transsexuals, only transvestites and mentally ill people with body dysmorphism.