Well, first evolution occurs on the level of a population, so you'd need a group of anything's great-great-a bunch more greats-grandchildren to be different for any evolution to occur. So one bison can't evolve from one cow. A bit more importantly, evolution involves descent from modification. read more
Bison were around before the current cattle breeds. Most of the domesticated cattle breeds were developed in the last 700 years (Not including the Bod Indicus breeds of the Far East and Mediterranean regions. Bison evolved before our cattle. You can devolve and animal, but it would take a very long time. read more