[Retric]

A population the size of China is going to have plenty of people that don't fit the M/F choice. For an extreme example a fully functional hermaphrodite could be both or self identify as one or the other. Some people are XXY genotype or even XXXY so even genetic testing can be ambiguous.

http://en.wikipedia.org/wiki/Intersex

[thaumasiotes]

You do realize XXY and XXXY are genetically male...?

[Retric]

There mostly male, but often with significant female secondary sexual characteristics and sterility. This is of-course ignoring Mosaic people which have two set's of DNA so you can be XXY and XX at the same time... http://en.wikipedia.org/wiki/Mosaic_(genetics)