the bb population just got there and had not had time to breed with the aa population -- "for awhile" does not readily apply if they weren't there long enough to breed
I'll definitely ask that one, thanx.
the bb population is a migratory variation to a non-migratory aa population -- they pass through every year on their migratory route, but never interbreed because they aren't there during breeding season
It's a bit of a stretch, but I'll try.
there have behavior barriers to mating that prevent interbreeding even if it is possible
This is a hypothetical question in ecology, this kind of assumption is a bit irrelevant.
BTW: I have been watching the videos Modulous posted ("Beyond Belief"),
highly recommended!!!