Agression or normal puppy behavior

Question
Dear Dawn,
  My wife and I have a five-month old German Shepherd male who we absolutely adore.  He represents all of the wonderful qualities you hear about GSD--loyal, obediant and extremely intelligent.
  My question relates to his recent tendency to "nip" at people when they come to our house.  For the initial 15-20 minutes when our friends/family come over, he's extremely protective, ie, barking ferociously, and in some cases, nipping at their hands and jumping onto them.  After that initial 20 or so minutes, he calms down, but remains watchful and wary of them--which we can deal with.  We socialize him regulary with trips to the park, Pet Smart and other areas where there are people.  In these settings, he's still wary of strangers but doesn't show the same level of territorial behavior.  
Thus, my question is, is this behavior at our house aggression, normal puppy "nipping" and jumping, typical of the breed or a combination of all.  Our concern is is that these behavior are the early signs of an aggressive dog.  

Answer
Hi John,  yes you should be concerned about your puppy's wariness at such a young age.  A puppy should not show any sort of protective ability until at least a year of age as they are not mentally mature enough to understand what they are doing.  Your 5 month old puppy has the mental equavilancy to that of a 6 year old human child, so think of a 6 year old child being protective and wary of people.  That is considered abnormal behavior, and normally is genetic in nature, especially in GSD's.  A lot of breeders breed for prey drive which tends to breed a lot of over-aggressive dogs.  When they do this, you start to see puppies that are showing aggressive tendencies at too young of an age.  Basically you are handing that 6 year old child a gun, and saying ok, protect us.  They don't have the mental maturity to do that, so they don't know what to do and that is how you get dogs who bite people at a young age.  They basically can't be trusted and end up being a liability in the long run.  If this is what is going on with your puppy, there is nothing you can do as it is genetics that is controlling it, not environment.  You are doing the right thing by socializing him, and if he is still showing aggression/wariness of strangers, then it has to be coming from genetics.  Did you meet the parents?  

Jumping up is common for puppies as well as play biting, but nipping and barking ferociously is not.  I would really watch his behavior, and get him started in obedience training as soon as possible so that you at least have an upper hand when it comes to controlling him.  If his aggressive tendencies start to escalate before he reaches 10 months, then I would seriously worry about him.  Remember, by nature, he shouldn't show any protective abilities until at least a year of age.  GSD's are one of the most overbred prey drive breeds there are, and that is why they are at the top of the list for biters in the nation because of the breeding to produce the strong prey drive.  Hope this helps, and good luck,

Dawn