There are several ways to answer this question. Most often the focus is on the PHYSICAL gender.
If you have chromosome analysis done, one of the 23 pairs of chromosomes in each cell determines whether you are “supposed” to be a boy or a girl. If the pair are both “X” chromosomes (written “XX”), your development was supposed to be as a girl. If you have an X and a Y chromosome (“XY”) your development was supposed to be as a boy. The “Y” chromosome is dominant; even if a person has extra X chromosomes in the “pair” (it would actually then be a “trisomy” or “polysomy”) of chromosomes, a Y chromosome “forces” development as a boy. The only exception is if the “SRY” (Sex-determining Region Y), a gene on the Y chromosome, is missing or defective. This is the master switch which directs development as a boy. Without it, the development is directed to be as a girl, even though the Y chromosome is present. If the SRY appears on an X chromosome, a rare occurrence, the development is directed to be as a boy even if no Y chromosome is present.
That the XX or XY chromosome pair completely determines the gender of the person is the way it is SUPPOSED to work, but as with many things biologic, errors can creep in, including the aforementioned missing, dysfunctional or misplaced SRY. In addition, a fetus may not react “correctly” to the direction imposed by the chromosomes, and is born with a mixture of gender-specific characteristics, or be missing some, or have some which are inconclusive or misleading in appearance. This can lead to a person who is “intersex” (possessing a variation in sex characteristics including chromosomes, gonads and/or genitals that do not allow an individual to be distinctly identified as male or female). Such a person may actually be one gender but were incorrectly identified at birth, or they may have characteristics of both genders.
It has been common practice to recommend surgically “fixing” intersex babies with both or indeterminate genitalia, to give them the “appearance” of normalcy and “the best choice of having a ‘normal’ life”. This has come under fire lately based on cases where the gender chosen turned out to be at odds with the child’s gender identification, or the surgery resulted in serious problems as the child grows and matures. On the other hand, some of these children who were NOT “fixed” suffered severe harassment at school, to the point where their families had to move and start over somewhere else. So the solution is not clear cut, but it is obvious that the current methodology “needs work”.
An unfortunate way some people use to determine gender is that a person is whatever gender God made them. This method is fairly useless to humans; if a person CHANGES their sex characteristics and thus their apparent gender, this method becomes absurd. If God objects, it is up to Him to deal with this person, not the rest of mankind. Besides, refer to the cases above, where God made some people who were incorrectly identified or unable to be identified as a particular gender.
Perhaps the least impractical method of (informally) determining gender is via the sex characteristics present, particularly the external reproductive equipment. A normal male will have a penis and scrotum; a normal female will have a vagina. This is by no means a guaranteed method of determining gender, but is simple enough and should serve in the majority of cases. The resulting gender choices would usually be male, female or “in transition”, although due to the variability of biology, we need to have available a neuter (neither male or female), a dual (both male and female) and an “unknown” (unable to determine) gender on the list.
As mentioned, a person who is not satisfied with the physical gender they are, can change it through sex reassignment therapy. This is not a trivial or quick process, which includes hormone therapy and surgery and can take two years or more. Before the process starts, they are one gender and after it is complete, they are the other. At each of these points in time, such a person should have all the rights, privileges and responsibilities of the current gender; that they often do not is a pretty damning indictment of humankind. We have a label for such a person, transsexual, which makes it easier for us to treat them inappropriately during and even after the process. If we were better creatures, there would be no concept of difference after the process was complete. Collectively, we are not…
But back to that multi-year period of transition; what is the gender of that person during that period? Until actual surgery occurs, the “reproductive equipment” methodology would at first glance seem to apply, but this has a severe problem. Before the surgery, there will be hormone therapy, which can cause behavioral, emotional and physical changes inconsistent with the original gender. Plus, generally there will be a period of time (often six months) where the person must live, in all possible aspects, as the new gender. It is unfair (and not loving) of us to make a hard process even harder by not treating the person as the new gender during this time frame. But even people who are theoretically comfortable with the process can be “freaked out” when they unexpectedly find out that the equipment is not consistent with the perceived gender.
The most likely place for this to happen would be a rest room or other gender specific location where clothing tends to be removed. A transsexual generally cannot (and should not have to) avoid all gender specific locations during the time when they are “pre-living” their new gender, yet the others in that location have the risk of not knowing whether such a person is “harmless” (a transsexual going through the gender transition, or a transvestite who likes or even needs to on occasion dress and act like the opposite gender but has no intention of changing gender) or “dangerous” (a sexual pervert or other predator pretending to be the other gender as a means to some nefarious goal).
To make things even more complicated, there is the MENTAL gender aspect, referred to as “gender identity”. This is the gender that a person THINKS they are. I understand that this is formed at a young age (often by three years old and almost always by seven years old), is based on other things besides the actual gender of the person, and once formed is difficult to change. There are indeed valid cases where a person thinks they are a different gender than what they physically are, particularly if they were deliberately or accidentally brought up as the “wrong” gender, or had no valid gender guidance when growing up. But it is my opinion that it is not fair for these people to insist that the rest of the world bow to their opinion. If a person is not “certain” enough that their physical gender is “wrong” to undergo sex reassignment therapy, then why should they be given any of the “benefits” of the gender they do not have the equipment for?
In most cases, this should not be a problem for the world (but often is). If a job or activity can be done by either gender, then anyone who can competitively do the job or activity, should be allowed to. The problem occurs in situations where mixing people of differing gender has significant chance of causing problems. In some cases, such as a person who is physically a girl but is convinced they are a boy playing on a boys sports team, it may be able to contain the “locker room” problem because schools tend to have boys and girls locker rooms and as long as the segregation is observed and the person can accept this, the chances for problems are minimized.
There is, however, a disturbing trend to allow people to utilize the segregated locker room or rest room they claim is appropriate for them. This seems to be inviting problems. Perhaps the person with a physical/mental gender contradiction really would be more comfortable in the rest room or locker room of the perceived gender. But what about everyone else? In the case above, let us say that “Sam” comes into the locker room after a game, strips down and enters the showers with the boys. “She” may be confident enough of her masculinity to not mind the boys around her, but the boys are likely to have problems either with shyness or lust. Or both.
Many people tend to consider the segregated rest room a “safe” zone where they can remove/adjust some of their clothing and perform bodily functions without worrying about attention from the opposite sex. In some locations, they no longer have this option, as a boy can use the girls restroom if he “feels” he is really a girl. Or says he feels that. I’d be willing to bet that there will be at least a few scummy types who will claim that they feel they are a girl in order to ogle girls in various stages of undress.
So what is the answer to access to gender specific locations? I don’t know, but I suspect a middle ground needs to be found, which takes into account the safety and “comfort” of those who do not have problems with their gender as well as the real and reasonable needs of those engaged in the gender transformation process. And to the degree practical, keeping the comfort of those who have gender “confusion” in mind as well.
This does not have a simplistic solution as is popping up around the country. To say “you can use whatever restroom you want to” is just begging for problems. How many parents will react to this potential risk to their daughter’s safety by counseling them to “if you see a boy in the girls restroom, kick him in the nuts”? How many assaults, “justified” and not justified might result? Conversely, how many rapes or other sexual assaults? How much damage will be done to the psyches of a generation?
Oh, and let’s not penalize the poor facilities owners by making them have 18 different restrooms for every possible type of person out there.
Individual restrooms are not really a problem; these should be encouraged to be mostly “universal sex”. In places where “multiple occupant” facilities are appropriate, the stalls should be designed for maximum privacy. A third, gender neutral facility should be encouraged, particularly in new construction, but not required in existing structures. This gives us the greatest potential to cater to all.
As to who can use which facility, that is more difficult. Certainly anyone can use a gender neutral facility, by design. It might not be unreasonable to say that in buildings which have a gender neutral facility, only men can use the men’s room and only women can use the women’s room. But there are many buildings which do not and likely will not have a gender neutral facility. In those cases, those undergoing gender transition and those otherwise “provably” with a mental gender at odds with their physical gender should be able to use the room of their choice. The trick is that “provably”. Someone saying they “feel like a woman” should not, based solely on that claimed feeling, have access to the woman’s room. They need to show that their condition is real. How this could be done without significant fraud or misuse, I don’t know. Whatever the method, their behavior and dress should be consistent with the gender of the facilities appropriate for them to use.
Easy? No. Comfortable? Probably not. But again, God wants us to love everyone, and if we love someone, we do what we can for them. And as His children, we should do everything we can. As Humans, we should at least do what is practical for for us to do.