I have another possible explanation for why the wild-type genes keep showing up: maybe they work better for feral chickens. If white chickens, or black chickens, or bigger chickens (etc) get eaten by predators, the only ones left to breed are the wild-type ones.My sense is that the hybridization has been going on for a long time in all feral populations in the U.S. The ancestrial genes must be really strong because they keep showing up despite all the pressure. Modern geneticists tend to discount the concept of throw-backs and atavism. But, it's difficult to ignore what you see with your own eyes.