For example, the teacher profession is generally female dominated at 80%, but gender segregation becomes even worse when a teacher finish studying and chooses a specialization. Language teachers are above 90% female, while music is 80% male. There is no innate reason why the language of music and the language of text has this difference, but over time it just have been that more women choses languages and more men choosing music when picking a subject to teach. This trend that people has a tendency pick places (especially within a profession) where ones own gender is majority was given as one of the primary theories in a government report on the subject a few years ago here in Sweden.
I see it as the best theory available to explain the data and general trend for gender segregation.
Given that populations of humans will naturally self-organize themselves into groups (whether based on race, culture, music choices, geographic birth, language, etc), the expected outcome is almost never going to be perfect representation. I don't think black people are genetically predisposed for basketball, just like latinos are not genetically predisposed for baseball, and yet the respective demographics are over-represented in NBA and MLB respectively.