When a dog bites someone, we seem to want to vilify the dog that makes an “unprovoked” bite, and save the dog that we perceive as “good” if he bit when someone rolled over his toe with a bicycle.
Any dog that bites has a reason, whether humans can identify it or not, so in my opinion there are no unprovoked bites. As a professional trainer, however, the thing that most concerns me about any dog is not necessarily whether it actually snaps at something, but its level of acquired bite inhibition (ABI) if it does. Acquired bite inhibition is the ability of a dog to use his mouth effectively as a warning, without doing damage, much like brandishing a sword at someone without stabbing them.
In the wild, if members of canine species settled every argument they had with a serious bite, their hunting companions would soon be useless to them — it’s hard to help bring down a deer if your hunting partner wounds you and you can’t help in the chase. Thus, properly socialized canines learn to hold “ritualistic” fights, or use menacing body language, to tell other dogs (and us) to back off.
Virtually all of the activity that helps dogs acquire bite inhibition happens before they are 5 months old, and most happens between ages 8 to 16 weeks. They learn by playing with many puppies of different breeds and sizes, with a few tolerant adult dogs mixed in, hopefully under the supervision of a competent trainer who can monitor the interactions so that no puppy is bullied or overwhelmed, or removed from normal play too soon. Current thinking, according to the American Veterinary Society of Animal Behavior, is that pups can join a group class in a facility that uses proper sanitation right after their first set of shots. A properly socialized dog is less fearful, and fear is responsible for 80 percent, or more, of all aggressive behavior by dogs, whether it’s directed at humans or other dogs (dogs that are aggressive toward other dogs are not necessarily aggressive toward humans, and vice versa).