Some of the confusion may be caused by the definition of the words. Gender identity resides in the brain of a person, it's who YOU think you are inside your own head, and we have no way to detect that scientifically yet. This may be a software issue in the brain, we don't know. We have yet to find a hardware cause in the brain, but the important thing is to realize that who YOU are inside your own head is the most important parameter because that is what makes YOU the YOU that you are. All the physical stuff is just hardware and we can retool that as necessary, whereas the brain cannot be changed by any technology we have.
In a repressive sexual binary culture the incidence of "non-normal" is no measure of real numbers of "non-normal" people. When science admits that they cannot predict nor define "normal" anymore, then we need to stop persecuting or discriminating against what we see as "non-normal" people who are doing no harm.
People need to stretch their definitions a little and realize that we don't know enough about sex/gender to deny rights to anyone who is not harming others.
If you really want to read something that will expand your view of sex/gender I would suggest BIOLOGICAL EXUBERANCE: Animal Homosexuality and Natural Diversity by Bruce Bagemihl, Ph.D. A huge, scientific work (over 700 pages) detailing the sexual activities of just 450 of the more than 1500 species of animals that exhibit homosexual sex and pair-bonding. Bagemihl has thousands of sources, notes, and papers by researchers as the base for this work. Gay, straight, bi, group, oral, anal, transgender, tribadism, mutual masturbation, and recreational sex are all common in the animal kingdom. This is a book about scientific research that questions our paradigm about "just reproductive" sex. Is it possible that stricly reproductive sex is on the periphery of sexual activity and that social or recreational sexual contact is not only far more common than we thought, but in fact makes up the bulk of all sexual activity? Maybe.
