Well that makes sense. Dogs and cats domesticated themselves and moved right into our homes. Pigs still live outdoors, at least they all did until the "Vietnamese potbellied pig" craze of the past couple of decades. As I mentioned before, dogs are not as good hunters as their wolf ancestors. Their teeth, metabolism and instincts have spent 15,000 years adapting to the life of a scavenger. Except for the largest, toughest ones, the farthest most "feral" dogs go is the nearest garbage pile. Cats have only been with us for five or six thousand years, so they have not had the time to evolve into a new subspecies. Many domestic cats are encouraged to kill rodents, and lost or abandoned cats still know how to hunt. Yet their favorite prey is still rodents and other small "vermin," and that's what attracted them to our habitations in the first place. So "feral" cats are just as likely as dogs to hang out on the fringe of civilization, keeping the rats in check, rather than migrating back into the woods. In fact, at least here in the USA, many communities have a population of undomesticated cats that they feed and encourage to hang around, just like they did five thousand years ago. Pigs are scavengers too, and it's not unlikely that they invited themselves into our settlements to clean up the garbage. I don't know how many lost or abandoned pigs there actually are in the world, because someone is likely to come along and help themselves to the free pork chops. But if there are any, I wouldn't be surprised to see them rummaging through the garbage near our homes, with the dogs.