[DouglasKC]

Did you know the Earth is about 4.5 billion years old, not 6000? Makes a difference

Yup. And no it doesn't make a difference...at least as far as fruitflies turning into something other than fruitflies.

[VadeRetro]

Is there a mechanism that stops populations genetically and/or physically isolated from each other from getting more and more different at some level? If so, what is that mechanism and what is that level?