Most of our dog breeds have some
form of aggression in them, since they needed different
forms of aggression to do their work: terriers are often
aggressive towards other dogs and animals — they were and are fighters, the man working dogs imprint humans as being of their same species so they show the same kind of aggression that they show towards other dogs, the sight hounds were bred to be killers of game and
sometimes other canines, the mastiffs were bred to take down large game and guard property, the flock guards were bred to be
aggressive towards canines, the hounds were bred to be
aggressive towards furred animals, some of the pointers were bred to be able to guard the hunter's game, etc., etc..