In nature, have you ever heard of those frogs that are essentially both? They take on the role of whatever gender is needed for the survival of their species. I see Quina as a creature like that. They don't have a specific gender really, but they can take on the role of a gender when necessary. (Reproductively I mean.)

Qu's live in swamps generally, so I assume they evolved from a lifeform that lived there prehistorically. So, I guess you could say I see Qu's as a highly evolved tribe of amphibians, who are neither, yet both sexes. (Hence the 'he/she' but also the 'it' that is used to refer to Quina. If Quina had no gender, the words 'he/she' would not be used, they would just use 'it'. That's why I figure, somehow, Qu's are both, yet neither.)

(Mind you, this entire theory could be debunked if the translation in the English version changed what Quina was originally refered to as in Japanese.)

It's kind of hard for me to explain. The best thing I can think of is those frogs from real life that have no defined gender role until it becomes necessary. (Like when it is mating season... or whatever.)