At my company, a few years ago, we were redefining our data model.
In the definition of a 'Person' gender was an included attribute. Almost everyone assumed it was a two-valued attribute (M/F). I caused great muttering and fulminating when I pointed out (we are a medical corporation), that even in my limited experience it is far more complicated than that. I forget the exact numbers, but I believe the ISO (International Standards Organization) recognizes nine genders, and one Medical Standards organization in the US recognizes fourteen.
To give some illustrations:
Simple Male and Female, everybody recognizes.
Hermaphrodite (Male and Female simultaneously) is a surprisingly common medical fact.
Some of our facilities are involved with Transgender Surgery. We need to be able to characterize those patients.
Homosexual and Bisexual Male and Female may have Privacy issues in 'mixed' gender rooms.
Genetic gender may not be the same as Social Gender for everyone...
And coding for Gender raises huge privacy issues. One would not normally consider that disclosing whether someone is male or female is a big deal, but think about some of the above situations...
In some cases Gender is extremely sensitive medical information.
Laughing in the rain.
Dancing in the desert sand,
Somersaults through life.