And let's have a peek at those mice: Mus musculus domesticus, the house mouse, and Mus spretus, the Algerian mouse, make sterile hybrids if they're bred. But, as far as their genes indicate, they are more closely related than humans and chimps are. Does that raise any problems for the ante-Flood hyperspeciation? If these two aren't interfertile, how do we get beavers from mice in a couple thousand generations?