Although your puppy's health is vulnerable at a young age, more dogs die from lack of early socialization than from disease. (wonder-puppy.com)
# 2 Lack of early socialization with mother or litter mates Kittens taken away from their mother or litter mates at any time during the sensitive period between two and seven weeks (and even before 12 weeks) miss learning many important elements in how to play appropriately, including inhibiting bite pressure, using paws instead of unsheathing claws, and reading social cues and respecting boundaries. (thenoseprint.com)
The root of a dog's biting may be in lack of early socialization, fear, dominance, confusion over his role in the pack, a health problem requiring a trip to the vet or a dietary imbalance. (paw-rescue.org)