- 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/
@BU-AWolfe
As I noted in my earlier comment (and as others have too), even from a strictly legal standpoint, that's not actually the case. There isn't a single, coherent legal gender for all people. For example, in the US your birth certificate, your passport, your driver's license could each say different things and the procedures to change each are different. All states allow changing gender on your driver's license, but many don't allow changing the birth certificate. Some states allow non-binary option (X instead of M or F) for driver's license. The federal government allows changing the gender on the passport and the procedures is easier than some conservative states have for changing driver's license but doesn't allow third option (like some other countries do, including Malta and Bangladesh). Transgender children will sometimes be in the public school system as their gender but won't have changed their legal gender anywhere else as they are minors and can't do so. So even from a government perspective, it's not clear cut and actually generally not a simple matter of birth assignment. Even your birth certificate could say something different if you had it changed.
So this isn't just an ideological thing like some people try to make it - if you as a programmer assume that a record from two different databases must not be referring to the same individual simply because the two databases have different gender markers, you are making a bad assumption.