IS MY DOG AGGRESSIVE?
Dog aggression is almost always a normal behavior. Abnormal canine behavior is often over-diagnosed.  All dogs have the potentially to behave aggressively or show aggressive signalling such as growling, etc. and often do in contexts where aggressive behavior would be consider appropriate. We shouldn’t look at aggressive behavior as being nasty or wrong.
Perceiving threats where there aren’t any
But when aggression starts to interfere with the relationship between the pet and the owner, other people, or other animals, it becomes a problem. When dogs perceive a threat when there clearly is none, or the dog is clearly over-reacting, this dog is not behaving normally.
Often when this happens, most dogs with behavior problems are not just misbehaving: they are not normal. To treat them as normal, but misbehaving and to expect a normal response to corrections can be dangerous. Read more on the right treatment methods.
Will my dog outgrow it?
Unfortunately in most cases, true dog aggression often escalates as the dog ages. While it may be natural to feel guilty, make excuses and procrastinate around doing anything about it, all dogs are capable of causing serious harm. The sooner you get help with your dog’s aggression the easier it will be to help your dog live a more harmonious life with you.
Canine Aggression: Neurobiology, Behavior and Management, Ilana R. Reisner, DVM, Phd, DACVB, Orginally appeared on : http://www.vetshow.com/friskies/cani.htm
Dtsch Tierarztl Wochenschr 1991 Jan;98:15-9 [Behavior disorders on Dogs -- study of their classification] [Article in German] Feddersen-Petersen D. Institut fur Haustierkunde, Universität Kiel
 Clinical Behavioral Medicine for Small Animals, Karen L. Overall, M.A., V.M.D., Ph.D. Diplomate, American College of Veterinary Behavior, Department of Clinical Studies, School of Veterinary Medicine, University of Pennsylvania, Philadelphia. Pennsylvania, Mosby, Inc. 1997