It just happens that some of the secondary results of the selected traits alter what the animal look like. There was an experiment done by a Russian researcher. He selected captive foxes for traits that we favor in pets: nonaggression, pleasant disposition, and so on. An unintended secondary effect was that these foxes started to look like dogs. read more
However, “pig” usually refers to the barnyard variety, a wild boar is the kind that lives out in nature and is the ancestor of domestic pigs, and “hog” is used to describe larger pigs and boars. read more