This is untrue.
More important than a dog's past is a dog's present. Dogs raised from puppyhood, lovingly socialized and cared for, may still be dog selective or develop a behavioral issue. Dogs are individuals, influenced by biology as well as environment as well as unknown factors and interactions; dog owners generally can only control for environment. What really matters is how the dog is managed, which must be based on how each dog actually responds, interacts, and behaves, regardless of that dog's known or unknown upbringing.
Dog bite incidents (involving any breed) do not occur because the dog had a bad first owner. They occur because their present owner failed to contain the dog, or watch a child properly, or recognize the limits of their own pet. I'm not saying a dog's history is totally irrelevant, but I am saying it can be neutralized by a good owner.
Although many news reports of dog attacks include phrases like "the dog bite was unprovoked" or "the dog has never shown signs of aggression until..." Proper investigation (or even overlooked comments in the news reports themselves) indicate that these phrases rarely are accurate. With nearly negligible exceptions, dogs do not seriously injure human beings without having a history of behavioral signals. Whether or not these signals are noticed and/or covered up by an owner who clearly has reasons to lie (the laws favor folks with no prior knowledge of a dog's aggressive propensities) is indicative of the dog-owner relationship.
Most of the dogs in our program came into shelters as strays. We very often are asked: What do you know about his past? Truthfully, we rarely know anything. We do not know where they were born. We do not know if they were hit. We do not know if they were exposed to other dogs, cats, or kids. What we do know is what we can observe, and it is not difficult to make adjustments to a dog's routine, care, socialization, or training based on what we see. We've been placing dogs with unknown histories in loving family environments for years without a single incident arising therefrom.
Dogs live in the present. So should we. Please adopt a rescued "pit bull" today!
