Aggressive behaviors can range anywhere from growling and barking to biting and attacking. The most important thing is to figure out the reason a dog becomes aggressive. Violence indeed can be instilled. Many dogs are aggressive because they were treated with violence.
Many dogs have never experienced love and once they do their first reaction is to retract. It's hard for them to trust again. But after repeated demonstrations of affection they finally give in and learn to be loved. Take a look at this dog's amazing transformation.