Fear aggression can be caused by a number of things such as the dog’s genetic makeup, the environment the dog was raised in as a puppy (before 8 weeks), and the nurture and guidance we provide once we get said dog. Often times I find aggression stemming from the latter and falling on us and our lack of guidance in helping the dog reach its full potential. It’s actually quite rare to have a genetically aggressive dog but it is possible. I always suggest when dealing with aggression to have your dog evaluated by a trainer and come up with a training plan from there.