My Border Collie is extremely aggressive. She has never been beaten or abused in her life and yet she has turned into this barking and snapping nightmare.
Dogs do both.
The basic way of canine life is hierarchy. Most move about frequently and don't stay long enough to maintain fixed territories. Circumstances change a bit when dogs begin to establish a fixed home base with cooperative hunting. They become territorial, usually as a group. Physical Features of Aggression Dogs must gear up, as all animals do, for aggressive encounters.