Physical changes can be reversed while chemical changes cannot be reversed because you cannot undo a chemical reaction
The Alberts and Kaibab squirrels differed from their respected paths by
geologic isolation. The two species of squirrels were separated and then
eventually adapted to their respected environments.
NOT EXACT DEFINITION: Diseases that can be passed from one living organism to the other. Two examples are flu and several STIs (such as herpes). Sorry I couldn’t think of any more :)