Firefly: Character Names

I'm re-watching Firefly. I really love all nine of the main characters on that show.

I've noticed there is a pattern to the names:

Three real-world names: Mal, Zoe, Simon

Three made-up names: Inara, Kaylee, Jayne

Three words-for-names: Wash, River, Book

And there is at least one male and one female character in each category.