My step brother (who's not the brightest lightbulb I may add) breeds pitbulls. He routinely drowns puppies that try to bite him before they have eyes open and teeth. To me that does speak about genetics. I've never heard of any other breed that will try to lock on before they can even walk. And if you have geniuses like my step-brother providing the genetics of your dog, beware. And I'm thinking there are plenty of other breeders like him out there... Yes, I think how they're raised makes them who they are. But, the genetic predisposition to draw blood may be there. Depending on the breeder, of course. Personally, I'd be so wary of lawsuits and possible negative outcomes, I'd never own one.