[Stultis]

But, can they mate and crossbreed??

Uh, yeah. They're all one species. One subspecies even.

  GENUS    SPECIES    SUBSPECIES
  -----    -------    ----------
  Mus      musculus   domesticus

Although there were found to be varying degrees of reduced fertility among the various races. The article linked in my original message to (refusesto)connectthedots has all the details.

[Elsie]

Uh, yeah. They're all one species. One subspecies even.

Then quit using this to back up some claim of Evolution!