In NC, SC and TN they have the sanctuaries of the National Parks in very rugged mountains. After Jimmy Carter hoodooed the people into confiscating the Biedler timber farm as a "virgin uncut forest", it hunting ended, which had been controlling the hogs which migrated down the Saluda from the mountains.
The Congaree National Forest, later Monument, now Park, is bordered on one side by a farm which grows hybrid seed corn. The hogs went after that and flourished. The only controlling force is flooding which traps and drowns them.
There are also some pure stock European wild boar in Ontario, for those of you you like hunting in snow and really cold weather.
Yes, domestic hogs gone wild will look more and more wild with each generation, even without breeding with wild pigs. Dogs will do the same. I have shot wild dogs that were killing my cattle which looked like they were from Africa.
