I adopted a white GSD mix. Comments from others have made us suspect that he may be a low content hybrid. Should I be overly cautious?

I have read with interest your discussions on hybrids. I adopted a 6 month old male pup from our local SPCA in December. He was described as a ?White German Shepherd mix,? but looked pure bred to me at the time. I currently own a female GSD which I obtained from a breeder at 9 weeks of age. As Diablo (the male) has grown and developed the last 3 months, his body shape, fur, facial structure, some behaviors, and comments from other ?dog people? have led us to suspect he may be a low content hybrid. I contacted the SPCA to ask if they knew where the litter came from, but they have not replied. He is very sweet and playful, but timid toward strangers. His eyes are yellow. His body is thick, and his fur is much more dense and fluffy than any other GSD I have ever had, although his tail is like a GSDs, not husky-like at all. His muzzle is more elongated than a traditional GSD and most telling (to me, anyway) is that Diablo does not bark ? he has NEVER barked ? he whines or yips. A herding dog that does not bark seems very strange. He either lays down or paces when in the house.

That being said, we love him ? we are socializing him, he attends obedience classes, he is a wonderful pup. Since I really cannot positively determine parentage, should I be overly cautious, or am I just scaring myself into thinking he may become some kind of monster? Thank you so much!

Sue