In 1980 Vietnamese Pot Bellies were imported into the United States, these pigs typically ranged from 50-250 pounds. Just like any other species on earth, there is a size range, people too, just think about it. Some people are short and 100 pounds, some are tall and 220 pounds. Their individual size is largely determined by their genetics.
Before the Pot Bellies, many smaller feral lines roamed the country. Typically wild pigs/Feral pigs do not get the size of our farm hogs, which were bred to produce meat and lots of it. Some of the smaller lines of ferals are known to be on the East coast in Florida areas and some on the West Coast like the Catalina Island Ferals.
Some native species in other regions are naturally smaller, like the Yucatan Hairless pig that roams Central America. So many want to claim that mini pigs, teacup pigs, micro pigs are just underfed pot bellies, when in fact they are not. In fact if you took the DNA of these pigs and sent it to UC Davis, for $400 they could tell us exactly what breeds are in our precious tiny pet pigs.
I'm not saying that some breeders don't underfeed their pigs to keep them small, because they most certainly do. A pig can be small and still be healthy with nice rounded bodies, no bones showing or felt. Take my Catalina for instance, at a mere 11.75" shes a healthy 45 pound round piggy.
Over the years breeders tend to breed smaller and smaller because like I said previously, genetics plays a huge role in sizes.
Many labs around the country have bred smaller pigs for scientific research. I will show some examples on the left. Most of these sizes are bred to be comparable to a human so that heart valves and such can be made into people. The Gottingen University in Germany typically tries to breed for 125 pounds, I cringe when I see breeders say they have Gottingen pigs, these pigs are never released for breeders and are always a whitish pink pig.
The Mayo Clinic has created a small pig, again for their purposes as well as the Clawn institute in Japan. All this information is available through Google, with contact information!
So over time the mini pig was created, there is NO specific breed, but just a description of a miniature pig, now becoming widely known as THE AMERICAN MINIATURE PIG, its not a potbelly, its not a large pig, its not an underfed pig. Teacup, micro, micro mini, pixie and dandie pigs.....all the same thing, not magic, not special breeds, no special imports. Therefore nobody is going to have the miraculous 10-15 pound adult mini pignd what got them to where they are.