Wow, that's a pretty solid model.

> Most of the time the answer to such more general questions is because it works and isn't a deadly disadvantage.

I didn't really think about this but yeah, it makes a lot of sense.

> Also male and female isn't answered with a simple XX or XY chromosome pair. There are species of frogs where in the north XX are female and XY are male, but in the south XX are male and XY are female and in the middle 50-50 chance. Sex isn't determined by only one chromosome. It's far more complicated and can differ between species.

Learning something new everyday it is!