- There are two and only two genders.
- Okay, then there are two and only two biological genders.
- Gender is determined solely by biology.
- Okay, it’s mostly determined by biology, right?
- Please tell me it’s determined by DNA.
- Gender can be reliably determined through visual means. After all, no man would ever wear a burka.
- Once gender is set, it never changes.
- Even if the gender can change, it will only change from the one value to the other value.
- Only one gender can be “active” at the same time.
- We’re tracking gender now, so we’ve always tracked it.
- I only need to be concerned with human gender.
Source: http://www.cscyphers.com/blog/2012/06/28/falsehoods-programmers-believe-about-gender/
That goes in topic with: Genders do not actually exist, since there are several factors, as enumerated. If genders exist, an allegedly exhaustive list would be a potential source of discrimination against new and personal expressions. Said this, the currently known list of 112 gender variations (which can be applied to male/female, except those that are in the exact middle) has a lot of funny examples of these expressions that remind us of Sakura Card Captor or something like. Say I want a new gender because I don't fit even inside "helio-" variants (!!!), the list would not be exhaustive.
Gender is a personal manifestation sourced in a mix of factors and, said this, there is a quite wide range as one per person (at least, who asks themselves about). This is because our society is quite diverse.
So, when you have that kind of explosion principle, solely depending on your business model you fall back to average user expectations:
Gender Ideology (which IT IS - despite the fact I totally support it) is a self-collapsing system that only serves to bring the individual into the social scene on its own. It is totally useless as a category system, but then you fall back to the other two attributes, and let the users in your community do the rest of the job.