Development of Puppies and Genetics
It is possible that two puppies from the same litter with the same genotype can sometimes have different phenotypes because they were exposed to different experiences after birth and were subsequently raised in different environments.
The traditional development stages of puppies overlap. They are not black and white and there will be variety in each individual dog.
It is essential to see the puppy in front of you and use the development stages as a guide, rather than expecting every puppy to conform to the stages.
The effect of early socialisation on the later behaviour of a dog is very relevant to canine behaviour problems. It has been demonstrated that if a dog is isolated from 3 days of age to 20 weeks of age he will most likely be disturbed (Agrawal et al 1967).