Many dog breeds came from breeding different classes of dog.
No **** :P
No, what I meant by unnatural is not fur colour or things like that, it's more breeds like the chihuahua that could break legs by jumping down too high steps, or anything that is not viable at all out of the attention of their owner. Or, more extreme, breeds (don't know if this exists or not) that suffer from side effects like anatomical difformities that give pain or things like that.
