Oriphiel

Why does it have to be either nature or nurture? Why can't both have an effect on people and their identities?

In my opinion, gender is partly a social construct, and partly something inherent. After all, there was a pre-societal time before we had such constructs as the idea of the modern man and woman, and yet almost every culture in the world developed to have men and women in roughly the same roles (though it isn't absolute, since there were/are a few matriarchies, even though they're few and far between). And this is taking into account the fact that these similar customs came from ancient nations that had very little to no communication with each other. The average man and the average woman have differences, both physically and mentally; different averages of physical strength, different ways of interpreting and solving problems, etc. So yes, in a way, each gender is born different, with skill sets that lend themselves to fulfill certain roles.

Many of society's ideas of what is "correct" for those gender roles are created to accentuate those natural inclinations. They're like those old fancy dresses that had wire frames, and accentuated a woman's hips (a sign of her femininity/fertility) to a ridiculous degree; they are not necessarily naturally inherent in the gender, just as the dress is not apart of the woman, but they play off of what is usually there. These can have obvious correlations; some of the more obvious are that men, being born on average with more physical strength and testosterone, are expected to take part in a variety of physical activities, and women, being burdened and vulnerable while developing (and, after birth, caring for and breastfeeding) a child, and usually having higher amounts of estrogen, are expected to be "protected", and to find value in emotive and social roles. But there are also gender roles that are more specific for each culture, and show how fleeting our ideas of what comes naturally in a man and woman can sometimes be; in ancient China, it was considered a strong sign of male bonding when two men held hands, a sign of togetherness and brotherhood, and it was also considered very moving when a man was brought to tears, showing their passion for something. In various Native American tribes, homosexuals were accepted in the community, and were considered to simply be men who were born with a female's spirit inside them. Another example is how not so very long ago, in america, pink was considered a "boy's color", while blue was considered "feminine". Also, in ancient Rome, there were many female gladiators, although evidence of their existence is only recently starting to be found and accepted. Anyway, in many modern cultures, these are now considered "unmanly"/"unwomanly".

My point is, a lot of what we consider to be a "man" or a "woman" is inherent, but society takes those natural differences and comes up with a few culture-specific ways of expressing those genders that is not inherent. And remember, you can't forget that these gender roles work off of averages, but not everyone is average. Everyone is different. Is it really so strange when a man born with a certain factors, like a higher then usual amount of estrogen, ends up identifying with the opposite gender? Their desire to switch comes as naturally to them as someone else's desire to stay. But that's not to say that they are immune to societal constructs; homosexuals have plenty of activities that they are expected to enjoy, and an image that they are supposed to project.

Just my two cents. Feel free to TL;DR.